6l,tlr v

lUE }TAI{AGET'IE¡I1 OF SPOTTED ÄLFALFA APEID,

TEEM2A?HIS lWE1LIr GTONETL) E. MACALATA,

IN I'RYT.AI{D LUCERNE PASTT'RE IN SOI'1I AT'STR.AIIA

A theeis presented in fuLfiLment of the nequirements fon the Degree of Doetor of P?tiLosophy, EaeuLty of AgricuLturaL Seience, llnioereity of AdeLaide.

by

P.G. ALLEN I'l.Ag.Sc.

Department of Agrlculture, SouÈh Australia

March, L984 To

I',II]RRAY V. SMITH

( r 942-r 980)

A friend and colleague whose research contributed to the knowledge on gxazl-r.g managemenÈ of dryland lucerne pastures grovtn on siliceous sands in the Upper- south-East of South AustralLa. INDEX

Page No.

SI]MMARY (1) STATB"lENT (v)

ACKNO!,ILEDGEMENTS (vi ) SECTION 1: IMRODUCTION I 1.1 Value of Lucerne Pastures in the Upper-South-East of South Australia 2 I.2 Control of SAA 1n the U,S.A. 3 f.2.1 The early use of chemical insecticides 3 L.2.2 Conservation of native predators 5 I.2.3 Introduced parasites 5 L.2.4 Pathogens 6 1.2.5 Resistant cultivars of lucerne 7 1.3 FuÈure Control of SAA in Sout,h Australia I 1.4 References 9 SECTION 2: TITE STITDY AREA . TTIE UPPER-SOUTTI-EAST OF SOUTH AUSTRALIA t2 2.I CllmaÈe T2 2.2 Soil L2 2.3 I'fanagernent of Lucerne-based Pasture L4 2.4 References 16 SECTION 3: TIIE SEASONAL ABUNDANCE AND ESTABLISH},ÍENT OF SAA IN DRYI.,AND LUCERNE IN TIIE UPPER-SOUTII-EAST OF SOUTI{ AUSTRALIA L7 Sumroary L7 3.1 Introduction 18 3.1.f Seasonal abundance of SAA overseas 18 3.I.2 Expected seasonal abundance of SAA in South Australia 19 3.1.3 Design of an experirnent for a 3-year study of SAA abundance in dryland lucerne pasture r9 3.1.4 The spread of SAA in South Australia 20 3.2 l"laterlals and Methods 20 3.2.L The abundance of SAA in Èhe UPper-South-East 20 3.2.2 Initíal migration of SAA inÈo the experimental site 24 Page No.

3.3 Results and Discussion 24 3.3.f The abundance of SAA ln the UPper-South-East 24 3.3.2 Initial migratlon of SAA into Ehe experirnental site 30 3.3.3 Abundance of SAA alates in dryland lucerne pasture 32 3.4 References 33 SECTION 4: INFLUENCE OF SAA ON PERSISTENCE AND PRODUCTION OF DRYLAND LUCERNE IN flIE UPPER-SOUTII-EAST OF SOUTH AUSTRALIA 36 Summary 36 4.1 Introductlon 37 4.2 SAA Danage to Lucerne Plants 38 4.3 Background to the Experiments 40 4.3. f Experlmental site 40 4.3.2 Climate 4T 4.4 Influence of Different Threshold Densitíes of SAA on the ProducÈion and Persístence of Gtazed Dryland Lucerne Pasture 42 4.4.L I'faterials and nethods 43 4,4,2 Results and discussion 47 4,5 Influence of SAA on the Growth and DM of Individual Plants of Lucerne in the field 66 4.5.1 MaÈerials and methods 66 4.5.2 ResulÈs and discusslon 68 4.6 Economic Threshold for SAA in Dryland Lucerne Pasture 72 4.7 References 73 Appendices 77 SECTION 5: INTLUENCE OF CHEMICAI INSECTICIDE, GRAZING AND CULTIVARS OF LUCERNE ON TIIE DENSITY OF SAA IN DRYLAND LUCERNE IN THE UPPER-SOUTII-EAST OF SOUTII AUSTRALIA 85 Suumary 85 5.1 InEroduction 86 P"e:__Ig.

5.2 l"faÈerials and MeÈhods 87 5.2.1 Influence of chemical insectícide and grazing 87 5.2.2 Influence of resisEant cultivars of lucerne 89 5.3 Results and Discussion 90 5.3.1 Influence of chemical lnsectlcide 90 5.3.2 Influence of graztng 93 5.3.3 Influence of resistant cultivars of lucerne 97 5.4 References 100 SECTION 6: INFLUENCE OF PREDATORS A}ID PARASITES ON THE DENSITY OF SAA IN DRYI,AND LUCERNE IN THE UPPER-SOUTH-EAST OF

SOUTIT AUSTRALIA 103 Summ¡¡Y 103 6.1 Introduction 104 6.2 ldentification and Abundance of Potential Predators of SAA r05 6.2.1 I'faÈerials and methods r05 6.2.2 Results r06 6.2.3 Discussion r07 6.3 Augmentation of C. r'epand.a' During Summer 108 6.3. I I'faterials and meÈhods 108 6.3.2 Results 110 6.3.3 Discussion r15 6.4 Influence of Predators of SAA ln Spring and Summer rL7 6.4.I MaËerials and roethods r18 6.4.2 ResulEs L22 6.4.3 Dlscussion L27 6.5 Abundance of. Tnioæye conplann'tus ín Dryland Lucerne Pasture L29 6.5. I l"faterlals and methods 129 6.5 .2 Re sult,s 130 6.5.3 Discussion r32 6.6 The Role of Natlve Predators and Introduced ParaslÈes in the Control of SAA 1n Dryland Lucerne Pasture r35 6.6.1 Predators 13s Page No.

6.6.2 Tactics for management of SAA r37J 6.7 References 139 Appendices r46 SECTION 7: LETHAL INFLUENCE OF IIIGH TEI"ÍPERATI]RE ON SAA IN DRYI"AND LUCERNE IN TIIE UPPER-SOUTIT-EAST OF SOUTII AUSTRALIA 149 Sumrnary r49 7.I InÈroduction 150 7.2 Influence of Daily Maxlmum Temperature on Ëhe Density of Field SAA 151 7.2.L Materials and nethods t5l 7 .2.2 Results r52 7.2.3 Discussion 157 7.3 Lethal Effect of ltigh Temperature of SAA in Fíeld Crops r58 7.4 lllgh Teroperature and the Low Numbers of SAA in the Upper-South-East in I980/81, and l98L/82 159 7.5 References 162 Appendices 164 SECTION 8: INFLUENCE OF FOOD QUALITY ON TIIE ABUNDANCE OF SAA DURING SPRING IN DRYI"AND LUCERNE IN TTIE UPPER-SOUTII-EAST OF SOIJTII AUSTRALIA 168 Sumnary 168 8. I Introductíon r69 8.2 Materials and Methods L7L 8.3 Results 173 8.3.1 Rate of increase of SAA 173 8.3.2 Propertles of the plants 175 8.4 Discussion 177 8.5 References 179 Appendices 181 SECTION 9: LIFE TABLES AND RATES OF INCREASE OF SAA ON DRYLAND LUCERNE IN TIIE UPPER-SOUTII-EAST OF SOUTH AUSTRALIA 183 Sunmary 183 9.1 Introduction 185 9.2 l"faterials and Methods 186 Page No.

9.2.L Types of cages 187 9.2.2 SAA for cage treatments 19r 9.2.3 Age of lucerne regrowÈh 19l 9.2.4 TemperaÈure r9r 9.2.5 Tine of nowing Ehe pastures and start of each experiment 192 9.2.6 Tf¡ne and methods of sampling aphids 192 9.3 Results 194 9.3.1 Fecundity and survlval of SAA in leaf cages 194 9.3.2 Growth sÈatistics for SAA at Culburra 199 9.4 DLscussLon 209 9.4.1 Relatlonship between rates of increase of SAA and some envíronmental factors at Culburra 209 9.4.2 Comparison of growth staÈisÈics of SAA at Culburra and Ín other studies 213 9.4.3 RaÈes of increase and the population dynanies of. SAA in dryland lucerne pasture 216 9.5 References 2t7 Appendices 22r

SECTION IO: TIIE LOI^IER TEI"ÍPERATURE TITRESIIOLD FOR DEVELOPI"IENT AND RATES OF DEVELOP}4ENT OF NT"IPITAL SAA IN SOUTH AUSTRALIA 225 Summary 225 10.1 Introduction 226 10.2 The Rate of Development and the Threshold for Developnent of Nymphs of SAA at Low Temperatures 227 10.2.1 Materlals and methods 227 10.2.2 Results 230 f0.2.3 Discussion 232 10.3 Rate of Developnent and Survlval of Nyrnphs of SAA in the Field 236 10.3.1 Materials and methods 236 10.3.2 Results and discusslon 240 Page No.

10.4 References 246 Appendices 249 SECTION 1I: A CONTROL PROGRA}.{ FOR SAA IN DRYLAI.ID LUCERNE AND ITS II'ÍPLEMENTATION IN TIIE UPPER-SOUTII-EAST OF SOUTII AUSTRAIIA 250 Summary 250 I l. I Introduction 25r 11.1.1 Pest control 251 ll.2 Data on the Ecology and Control of SAA in Dryland Lucerne Pasture 252 LI.2.I The management of lucerne pasture 253 LL.2.2 Seasonal abundance and fmpact of SAA on lucerne Pasture 254 1L.2.3 Tactics for the control of SAA in lucerne Pasture 255 11.3 A Control Progran for SAA ln l¡¡cerne Pasture 256 11.3.1 Problems with the conÈrol program 259 11.4 Inplemtation of the Control Program in the Upper- SouÈh-EasË 260 11.5 References 263 (i)

ST]MMARY

I The spotted alfalfa aphid (SAA), Theríoaphis trifoLii (Monell) f. rnøeuLata, qras accldentally introduced inËo Australia and first recorded in South Aust,ralia in ì4ay L977. The known destructive capacity of SAA in s.usceptible lucerne crops in North America stimulated the need for research on the feasibility of the shorÈ-tern control of SAA in highly suscept,ible, low-productívity lucerne (cv. Ilunter River) pastures grordn under dryland (rain-fed) conditions on infertlle, silíceous sands in the Upper-South-East of South Aust,ralia. This research is the subject of this thesis.

2 The profitability of production from the lucerne-based pastures is low and Che cost,s of any control program_for SArl\ need to be ninimal for acceptance of the program by landowners. Experiments were conducted in the field to determine an economíc threshold for SAA in dryland lucerne pastures, Èo test the feasibility of a number of control tactics for inclusion in a control strategy and to study certain aspects of the ecology of SAA which were consldered useful to explain the populatÍon dynanícs of SAA in lucerne pastures.

3 The optinum herbage product,ion from lucerne pastures is achieved with rotationaL grazíng by livestock. Standard rotationaL grazing for dryland lucerne was used in a damage assessmeriÈ experiment conducÈed for three years in dryland llunÈer Rlver pastures in the Upper-South-East. The ímpact of SAA on the persístence and production of lucerne plants in the pastures grazed wit.h sheep \.{as neasured, and the dace showed that Ehe ¡oean densit,y of SAA had to be kept below 40 to 60 SAA per stem of lucerne for the persistence of viable pastures. After two years, the number of plants in unprotected pasture \ras reduced by 857.; this loss in plants was attributed to reduced levels of total non-structural carbohydrate in the Eap-roots of damaged plants. Ttre above threshold denslty of SAA vras usually the economic threshold for herbage production as well.

4 In Èhe Upper-South-East, SAA is usually most abundanÈ during summer' less abundant in autumn and scarce during winter and spring. The low nunbers of SAA durLng spring were unexpected and data from predator- (ir ¡

exclusion experiments and pitfall traps in sprlng demonstrated that predators, roainly various species of spiders and a brown lacewing. Mienotwe tasnaniae (Walker), were responsible for the lor¿ numbers at thaE time. In some years, SAA does noE fncrease to pest densitíes for part or whole of the summer, apparently due to the occurrence of many days with lethal daily maximum temperaÈures (>38oC).

5 The efflcacies of chemical insecticide and gtazíng as conÈrol tactics for SAA were rrpasured in the abovementioned grazlrtg experiment. Low raÈes of applieation'of deneton-s-methyl provided high mortalities (95i¿) of SAA in the flrst year, but the mean mortality was gradually reduced to about 707" Ln the Èhlrd year; thls reductfon in mortality was attributed to insecticlde-induced resi.stance ¡,rhlch initially emerged in populaEions of SAA 1n nearby irrLgated lucerne ,atrr¿" where the use of cheulcal insectÍcides was far more lntensive than in dryland lucerne pastures. Severe grazJ-r^g rùith sheep, which removed virtually all the lucerne herbage, reduced the numbers of SAA by more than 957" and was a useful control Èactic; by contrast, light gtazlng was an unrellable tactic because after it, SAA somet.imes increased in numbers and sometines decreased in numbers by up to 95%, and the level of reduction and fts occurrence could not be predicted.

6. Native predators, mainly the transverse ladybird , CoeeineLLa repanda Thunberg, were present ln lucerne pastures during summer hrt they did not effecÈively reduce the numbers of SAA at that tirne. Attempts to augnent the influence of this species of ladybird by nodifyíng the graztng mânagement to provide a less-dlsruptive environnenÈ for it were not successful. The introduced parasite, Tniorye eotnpLanatzs Quitis, was released at the experinental site and becane established, but densiÈies of the parasite were not sufficient Èo control SAA aÈ any tine, possibly because of hlgh ambienÈ temperatures during summer.

7 The fecundity and survival of female aphids 1n leaf ceges on different ages of lucerne regrowth in the field were determined in winter, spring and summer, respectively. The fnnaÈe capacities for Íncrease, Ím, of SAA calculated from these daÈa showed that the age of regrowth of lucerne (r1r.,

within the five-week regrowth period used to manage lucerne pastures did not influence the value of rm, and that tenperaÈure and food quality s/ere favourable for increases in the densiÈy of SAA at each of the above times of the year. The highest capaciEy for increase of SAA occurred in summer. The values of r, were noË always realised by SAA either in stem cages in the field or in field populations. In ¡he stem cages, actual rates of increase of SAA decreased as the denslty of SAA increased and the quality of che lucerne deteriorated due to SAA-induced stress on the lucerne plants. ltith f ield populations, the actual rates of increase r,tere virtually zero in spring, urainly due to the influence of predat.ors, and negat,íve ln winter, mainly due to a low rate of survival of nynphs.

8. The raÈes of developmenÈ of nymphal.SAA at low temperetures and subsequently Èhe developmental threshold were determined in constant tenperature rooms by exposing cohorts of newly-born nyuphs on lucerne plants Eo short periods of various low Èeuperatures, respectively, and then allowing Èhem to complete their developnent at a higher, favourable temperature. The developmental threshold was estimated as 3.loc and is considerably lower than the thresholds estimated for SAA 1n prevl-ous studies where relationships between developmental rate and temperaEure r¡7ere assuued línear for the whole renge of favourable temperatures. In the field, the rate of development of nymphs increased with roean temperature and thei.r survival rate T,¡as high during spring and summer and low during autumn and winLer. Data on the rates of increase of populations of SAA, and on the survival and rates of development of nynphal SAA supported empirical observatlons on the population dynamics of SAA in dryland lucerne pastures

9. The study demonstrated that SAil\ eould be controlled in susceptible lucerne pastures with rotational, severe grazir'g and the strategic use of low rates of chemical insectlcide when mean densities of SAA exceeded the threshold of 40 to 60 SAA per stem of lucerne. A control progran, based on this infornation, was actively prornoted to landor¿ners but was not widely ímplemented; reasons for the non-acceptance of the program are discussed. (rv)

10. Regular sampling for SAA on llunt,er River and on SAA-resistant cultlvars of lucerne that were grovJn on lnfertile, siliceous sand and r¿ere rotationally grazed clearly denonstrated the advantages of using reslstatt cultlvars of lucerne as a long-term tactic in the conÈrol of SAA in dryland lucerne fot graztng ln the Upper-SouÈh-East. (v)

SÎATEMBNT

This thesls does not contain any fnformaElon whlch has been accepted for Ehe qward of any other degree or dLploma 1n any Universlty and, to the best of my knowledge and belief, this thesls does not eonEaln any lnfornation previously publlshed or wrltten by any oEher person, except when due reference 1s made in the text of the thesis.

Consent is given for thls thesís to be nade available for photoeopying and loan. (vi)

ACKNOIILEDGEI'IENTS

The study required for this thesis was undertaken while I was employed as a research entomologist wlth the Department of Agriculture, South Australia. I wlsh to thank Professor T.O. Browning, formerly Professor, Department of Entomology, Waite Agricultural Research Institute (WARI), for allowing ne to conduct this study ln the Department of Entomology. I ¡¿1sh to sincerely thank Dr. D.A. l"faelzer, my prlncipal supervisor, for his valuable guídance on the aius of the study, hls encouragenent during the experiments and his constructive couments on the m¡nuscript.

Sinllar to m¡ny other research projects, this project has relied on Èhe assistance of nuuerous people. Ilithin the Department of Agriculture, Mr. P.R. Birks and Dr. P.E. Madge, successive Leaders of the EnEomology Unit, supported and encouraged the study withln the Unit; Mr. K.R. Henry, Technical

0fficer, Entomology, provided invaluable technical assistance and interest 1n all aspects of the study; Messrs. D. Reeve, G. Lucas and M. Fewings assisted with the collection of field data; the late lfr. M.V. Smith, Senior

Research Officer, Lucerne Management, rdas involved in the measurement of carbohydrate levels in lucerne t,ap-roots; other members of the Entonology Unit assisted in the field at various times; District Offlcers ln the Upper-South-

East provided useful inforuatlon on lucerne pastures in t,he region; and

Mr. E.D. Iliggs, Princlpal Pasture Agronomlst, arranged the finance and maintained an interest in this project. I wish to acknowledge and thank all of these people for thelr support.

MosE of the experiments in Ehis project were conducted on the property of

Messrs. J.T. ârrd I.M. Filmer, near Culburra. Their enthusiastic assistance and loan of equlpment, land and llvestock was appreclated, and I sincerely thank them and their farnllies for their support. (vir )

I wish to acknowledge the loan of meËeorological recordfng equipment from Èhe Bureau of I'feEeorology.

The spiders trapped in the study were identified by Dr. V.E. Davies and

Dr. R.J. McKay, Queensland l'luseum; their identification enhanced Ehe Sectlon on predators of SAA.

I wlsh to thank ìßss S. White, fornerly at I,IARI , for her assístance with certain aspect,s of the statistlcs, and Messrs. G. Taylor and B. Palk, WARI, for their help wtth Ehe photograph of the dlfferent instars of SAA.

During this project, a close associatLon was maintained with numerous landowners in the Upper-South-East and I wish t,o thank thern for their time and constructive comnents on the management of lucerne pastures. I wish to Èhank l,fiss S. Thomas and lufrs. I'f. Siggers for Èheir involvement in Ehe typing of this thesis.

I am most grateful to y wife, J111, and ehildren, Scott. and Bíndi, for their patience and encouragement during the preparation of this thesis. ' I I to¡.'tt ii'l .l; I i: ; F r rulr¡ ,,'i i !*... -._ . i -1-

SECTION 1: INTRODUCTION

The spotted alf a1f a aphld (sAA) , Therioaphí.s trLfoLii (M,oneLr) f . rnaeuLata, was accidentally lntroduced into Australia and flrst record.ed in

Queensland in March 1977. llithin Ewo months, iE was also recorded from New south l.Iales, Vlctoria and south Australía (wilson et aL. 19gl). Tn south

Australla, SAA became abundant ín all districts growing lucerne, Medieago satiùa L., withín a year of its first discovery (wilson et aL. lggl). In the nid-1950s, SAA rapidly spread through south-western U.S.A. (Dickson et aL.1955) and became a serlous pest of lucerne, ê.g. in California, SAA rapldly gaíned the reputatlon of belng th^e "most destructive and spectacular pest of alfalfa (lucerne) to ever enter that state" (Smith 1959). Estímates of the economic value of SAA damage to t.he lucerne industry in the U.S.Ao â[€ often quoted in the literature and lnclude a $9m. loss in Calffornia in 1955, despite

$4m. invested in control Eeasures (Harper I956), and $2.4m. and. $8.5n.losses during 1955 and 1956, respectively, ln Kansas (Burkhardr 1959).

The uany references to Ehe destructive capaclty of SAA in susceptible lucerne crops 1n north America clearly demonstrated the need for control of SAA and stimulate

(cv. Hunter River) pastures gronn under dryland (rain-fed) condítíons on siliceous sands 1n the Upper-South-East regfon of South Australla. The short- term control of SAA was expected to uainly rely on the judicfous comblnat.l-on of insecticidal use and grazíng management. This research ís the subject of thls t,hesls. -2- l.I Value of Lucerne Pastures in the Upper-South-East of South AustralLa f-rt L977, there were about 600 000 ha of Hunter River lucerne-based pastures in the Upper-South-East (Section 2) which were used for direct grazirrg of. llvestock. Lucerne was the key species and the general belief was that it provlded herbage for at least 501l of. the annual livestock production from the pastures (Smith 1977). It yielded hlgh-qualíty, green feed during summer and autumn to fatten lambs and yearling beef for premium, out-of-season narkets in early \rinter; thís management practice gave an obvious economic advantage for production from these pastures, especíally as they had relatively 1o¡¿ annual productLon, as díscussed later. If the lucerne in these pastures was kllled by SAA, or its production lras greatly reduceF, there rdere no known alternative pasture species which could be sown on the infertile soils of much of the region to replace lucerne satisfactorily. In particular, the deep síllceous sands on whích lucerne pastures qrere grovrn are riot suitable for intensive cropping,

Èhough recent studies suggest that lupins, Lupinus anguetifoLius.t., may be a possible short-tern alternative for limited areas to improve the cash flow of propertles (I,I. Ilawthorne, pers . comm. ) .

In late 1978, r,rhen SAA first invaded the Upper-South-East, the annual gross nargins from grazing livestock on lucerne-based pastures was estimated at about

$40 ha-i (Smictr l97S); this low uargin was due ro a combinarion of rhe low productlon (an average of about five dry sheep equlvalents - DSE - per hectare) of the pastures and, more significanEly, the very low market value of sheep and cattle at that time. The region had just experienced two years with ralnfall below average and many properties also had a restricted cash f1ow. For these reasons, the naintenance of lucerne pastures on the siliceous sands in the Upper-South-East was considered to be essential, initially to allow int.roduced parasltes for SAA to be effectlve and, ín the longer Eerm, to allow gradual resowing of the regfon with suitable aphld-resistant cultivars of lucerne. -3-

Because of the very low annual gross nargins from these pastures, the cost of any program for control of SAA needed to be very low for acceptance by landowners.

L.2 Control of SAA in the U.S.A.

There is considerable literature on the control of SAA in the U.S.A. (Davis et aL. 1974) and the following dlscussion is based rnainly on experí-ences from south-western U.S.A. because of the sfunilariÈies tn the climate of part of that, region wíth South Australla (Kf¡nball and Brooks 1959). Ilowever, experiences in Ehe U.S.A. were nainly confined to the control of SAA in irrigaÈed lucerne for hay þroduction, not dryland lucerne pastures for grazíng.

The conÈrol of SAA appearei to pass.through Ehree broad phases since SAA became established in the U.S.A. Firstly, Èhere was the intensíve use of broad- spectrum, chemlcal insecticides (Reynolds et aL. 1956), then an íntegrated control approach which relied on the strategic use of selective lnsecticides to adequately control SAA but al1ow the survival of naËive predators and recent.ly-

íntroduced parasftes of SAA (Stern et aL. f958), followed by the sowing of SAA-resistant culËivars of lucerne (ilagen et aL. L976). Generally, t,he value attributed to each control nethod appeared to be st,rongly influenced by the discípline of the particular authors; this bias was a reflection of the initial research into the control of SAA whlch was based on lndividual disciplines, rather than being mrlti-disclpllnary, or studying the system as a who1e. I.2.1 Ttre early use of cbemical ÍnsectLcLdee Inttially, chemical lnsecticides were consldered essential for successful production of lucerne ln the presence of SAA (ReynoLds et aL.1956).

Insecticfdes were nalnly applied as sprays, though there was some promotlon of granular formulaÈions to reduce the problems of spray drift and toxlcity of sprays Èo bees (Dobson 1958). -4-

The insecticides l¡Iere organic phosphates and only provided Cemporary relÍef from SAA. The nain reasons for this tenporary relief were the rapíd increase in nuubers of SAA during warm weather, uneven application of sprays ¡¿hich left islands of SAA as a source of reinfestation and the rapid recolonisation by alates from nearby, heavily lnfested, untreated fields (Reynolds et aL. f956).

Rapid reinfestation necessitated the need for at leasË one and, sometimes, t\.ro applications of chemical insecticide per cut of lucerne during the rnain periods of activity of SAA.

I,Iithin a short time, by 1956. resistance by SAA to the most commonly used

ínsectlcides, parathion and malathlon, began to emerge (Stern and Reynolds L957,

1958). In the Antelope Val1ey, resístanc.e to parat,hion, based on LD50s, increased fron 4-fold in 1956 to 113-fo1d ín 196l (Stern 1962). The development of resistance in SAA and a paucity of natural enemJ es in lucerne stands, because of the inEensive use of broad-spectrum chenical ínsecticídes, led to the need to flnd a chemical insect,icide which would provlde adequate control of SAA but allo¡v the survival of native predaÈors and introduced parasites (Stern et aL.

1958). Numerous chemical insecti-cides r¡rere tested and demeÈon was Èhe most promising selectfve lnsecticide (Bartlet 1958, Hagen and Snith 1958, Stern et aL.1958). SÈern et aL. (1958) also concluded that deueton should lower the long-term cost of chemical control because of Èhe low rates of application and fewer applicaEions requfred whÍch, in turn, could reduce the incidence of insect,icide-induced resisÈance ín SAA.

The reliance on chemical insectlcides was short-lived and. after L957, thelr use markedly decreased (Stern 1962). Stern (1962) aÈtributed the decreased use Eo the wldespread utllisation of integrated control, relyÍng nainly on.predators and parasites, and the planting of SAA-resistant cultivars of lucerne. -5-

L.2.2 ConservaÈl-on of nat,ive predators The numerous references Èo native predators in lucerne in the U.S.A. infer that a nuuber of different speeies r,rere iuportant in the control of SAA but most references have noÈ lncluded quantitative data to support their claius.

Conclusions about the inportance of predators in cont,rolll-ng SAA were roainly made from correlatlons of predator and SAA densities obtained from Èenporal field sampling, voracity studies in the laboraÈory or slmply observing whet,her known predators lrere present in lucerne crops (e.g. Neuenschwander et aL. 1975, Simpson and Burkhardt 1960). Simpson and Burkhardt (1960) and rn¡ny others considered that Coccinellidae, especially Hippodø¡tria eonuergens Guerin, .rsere the most important, followed by Chrysopidae, Anthocoridae, Nabidae and Syrphidae, in thaÈ order. The lower efficlency of the laÈter fanilies l¡as attrlbuted to their lower abundance. Snlth and llagen (1956), Dickson et aL. (1955) and others stated Ehar predators did not prevent economic outbreaks of SAA but could be important in controlling low densitíes in t.he spring and autumn, or in preventing reÍnfestat,ion after chenical control. Goodarzy an.d Davis (1958) claímed that cocclnellids \ùere most effectlve predat,ors, especially by preventing lncreases in numbers of SAA in sprlng until chenical insecticldes were applled for the control of lygus bugs, Lygus spp.. L.2.3 Introduced parasltes

During 1955 and 1956, three parasites of SAA were introduced into California and, by the end of 1957, they were establlshed over large areas of Írrlgated lucerne and were playlng an increasingly important role in the blological control of SAA (van den Bosch et aL. 1959). Ttre three parasites

'were Trioxge eontpLarultus Quills, Praon eæsoLetum (Nees) and ApheLinus aeyehís I'talker; these species varied in thelr clirnat.lc preferences and -6- different species were domlnant ín different districts. Generally, T. eolrlpLa,Tløtzg r¡ras more abundant than Ehe other two, and was most active duríng

sprlng, autumn and r¿inter (Hagen et aL. 1976).

In some districts, the influence of parasites was considered to be

secondary to predaÈors and pathogens; however, they had a subtle influence on

SAJ\ abundance by parasitízing Èhose aphlds ¡¿hich escaped the predators and pathogens (van den Bosch et aL. 1959). In other districts, the leve1 of

parasitism approached I00% at certain times and was hlghly signifleant in

controlllng SAA (van den Bosch et aL. 1959). The three species of parasites

were released and became established in other staEes of che U.S.A. where they

were also considered to be a substantial factor in the conÈrol of SAA (Angalet

1970, Barnes 1960, Ilagen et aL. 1976).

An advant.age of the parasites for control of SAA compared Eo predaEors and pathogens was the frequenÈ, heavy attacks of parasites, ê.g. T. eonrpLanatue, on low densities of SAA, on which predators and pathogens' by eontrast, do not usually function effectively (van den Bosch et aL' 1959)' Ilowever, as with studies on predators, Ehere is a pauctty of data which objecEively tests the efficiency of the three introduced parasltes in controlling SAA.

L.2.4 Pathogens A survey for pathogens of SAA in California shortly after SAA had been dlscovered revealed that there were five differenÈ species of ent.omopthorous

fungi infecting SAA (ltall and Dunn I957a). Initlally, fungl r,rere not considered to be very effective because of a low percentage lnfectlon 1n the flrst sprlng

(I1all and Dletrick 1955) but, subsequently, Ilall and Dunn (1957b) recognised that the spread of fungi, whether naturally or by the artlflcial means lvhich

were beLng practised, was spectacular and resulted in widespread control of SAA

in a number of counties. Fungi also becarne distributed throughout flelds quite

rapidly and reappeared when SAA increased in numbers after a period apparently -7- free of SAA. They clained that fungi should be acknowledged as an important part of the predator-parasite-pathogen complex in the biological control of

SAA. t. 2.5 ResistanÈ culÈlvars of luce¡te

Stanford (1956) predícted that SAA-resisÈant cultivars of lucerne would be a sure and i-nexpensive meËhod to control SAA; this prediction was parÈly supported by Hanson (1961) when he compared the low cost of developíng the first resisÈanÈ cultivar, Moapa, Ì¡rith its high value to Èhe lucerne industry in south- rârestern U.S.A. I'fore broadly, Hagen et aL. (1976) staEed that, sÍnce the replacement of suscepÈible cultivars with resistanÈ eultivars of lucerne, SAA was rarely a pest ln lucerne fields for hay in western U.S.A. Although resistant cultivars are now generally acknowledged as the biggest single influence on t,he control of SAA ln lucerne stands in the U.S.A. (Swincer L979), they have not necessarlly eradicaÈed the problem. Since the use of resistant cultivars and other control methods, seven new biotypes of SAA have been recognised in south-western U.S.A. (Nielson et aL. f970, Nielson and Don

I974). Of these new biotypes, five developed resistance Èo resistant cultivars of lucerne; one of these was widespread and the others had eíther a linit,ed or unknown distribution. The nechanisn of development of blotypes was not fully understood but it lras apparent that biotypes of SAA do continue to develop and change (Nielson et aL. 1970), thus suggest,ing the need for a collectlon of varled pools of resistant gern plasm Eo counÈeract any future biotypes. Data on biological activity of biotypes indicate that damage or vlrulence of a biotype was related to aphid feeding and physiological mechanisms rather than fecundity of SAA, i.e. as a biotype became more virulent, the number of susceptible clones in a resistanÈ cultivar increased. This trend suggested that resistant culËfvars should be bred from a broad base of unrelated, híghly-resistant germ plasm Èo decelerate the development of virulent biotypes (Nielson et aL. 1970). -8-

The value of resistant cultivars in E.he cootrol of SAA, together with Ehe energence of blotypes to resistant culËivars, led to the release of a large number of cultivars for com¡nercial produet.ion in the U.S.A. (Nielson et aL.

I97 1) .

1.3 Future Control of SAA in South Australia The long-term control of SAA in South Australia will nainly rely on the replacement of susceptible ltunter River lucerne with SAA-resístant cultivars of

lucerne. I,Jhen SAA initlally infested lucerne pastures in t.he Upper-South-East,

there rdas considerable concern that the resistant cultivars of lucerne commercially avallable in the U.S.A. would not be a suitable replacement for Ilunter River, especlally for long-Eerm grazing under dryland conditions in the harsh environment of Èhe Upper-South-East. The cultivars in U.S.A. were

developed for short-lived sÈands producing high yiel-ds of hay and seed under irrigation. Aecept,able persistence undex grazíng was also doubted because American cultivars had more upright and exposed crowns compared to the more prostraE.e croltns of llunter River. Re-establlshment of lucerne pastures on siliceous sands can be difficult'

mainly because of sand-blasting of seedllngs, burial of seedlings with sand and

r^rater repellancy of the sands. Competition for moisture with cover crops and

weeds, and a number of specles of insects other than SAA can also adversely effect re-establishment. In some regions, the success rat.e of establishing viable new lucerne pastures is 50% or less (P.M. King, pêrso coum.). The time requlred t,o produce sultable resistanE cultivars of lucerne and the problems wíth their establlshnenÈ in slliceous sands 1n the Upper-South-East necessitated the development of a short-term strategy to control SAA in exlsting suscep¡ible lucerne pastures. Such a strateg-y 1s the topic of this chesls and could include the judiclous use of chenical insectlcides and grazíng and, perhaps, conservation of native predators and introduced pêEasites. -9-

1.4 References

Angalet, G.l^1. 1970. Population, parasltes and damage of the spotted

alfalfa aphid 1n New Jersey, Delaware and the eastern shore of Maryland.

J . eeon. E\-Lt. 63 : 313-315 .

Barnes, 0.L. 1960. Establishrnent of imported parasites of Ehe spotted alfalfa aphid in Arizona. J. eeon. Ent. 53: 1094-1096. Bartlett, B.R. 1958. Laboratory studies on selective aphlcldes favouring

natural enemies of the spoEted alfalfa aphid. J. êcort. 874t. 51:

37 4-378.

Burkhardt, C.C. 1959. Effects of heavy fall infestaÈioûs of spotEed

aLfalfa aphlds on subsequent spring.growth of. aLf.alfa in Kansas. J. eeon. Ent. 522 642-643.

Davis, D.l{., Nichols, }1.P. and Armbrust, E.J. 1974. 1. A blblíography of the spotted alfalfa aphid, TherLoaphis macuLata (Brckton) - (Itonoptera: Aphidae). I11. NaE. Ilist. Survey Bío1. Notes No. 87. 14 pp. Dickson, R.C., Lalrd, E.F. ând Pesho, G.R. 1955. The spotted alfalfa

aphid . HíLgandía 24: 93-t 17. Dobson, R.C. 1958. Granulated systemíc insecÈicides on establlshed stands of alfalfa for control of the spotted aLfalfa aphid. J. eeon.

Ent. 5I: L22-125.

Goodarzy, K. and Davis, tr'I. 1958. Natural enemies of the spotted alf a1f a aphid 1n Utah. J. eeon. Ent. 51: 6L2-6L6. I{agen, K.S. and Smlth, R.F. 1958. Chenical and biologlcal methods of pest control . AgrLc. Cttem. 13: 30-32, 89-92. llagen, K.S., Viktorov, G.4., Yasamatsu, K. and Schuster, 14.F . 1976. Biological control of pests of range, forage and graln crops. fn,

Theory and Practice of Bfological ConÈrol. Ed. C.B. Iluffaker and P.S. lfessenger. Academic Press Inc. 788 pp. : 397-442. -10-

Ilall, I.M. and Dietríck, E.J. 1955. Fungl on spotted alfalfa aphid.

CaLif. Agrie. 9: 5, 16. Ilall, I.M. and Dunn, P.I{. 1957a. Entomopthorous fungi parasitic on the spotted alfalfa aphid. HiLgardia 272 f59-181.

Hall, I.M. and Dunn, P.II . 1957b. Fungi on spotted alfalfa aphid. CaLif. Agnie. 11: 5, 14.

Ilanson, C.II. 1961 . l"loapa aLf.aLf a pays of f . Crope SoiLe l3: I l-12.

Harper, R.I,l. 1956. Spotted alfalfa aphíd. Agrie. Cttem. I 1: 44-45, 133 .

Kimba1l, M.I{. and Brooks, F.A. 1959 . Plant climates of California. CaLif. Agríe. 13: 7-12.

Nlelson, lrf .üI. and Don, Il . 1974. Interaction between biotypes of the spotted alfaLfa aphid and resistance in alfalfa. J. eeon. Ent.

67 z 368-370.

Nielson, l"f .I{., Don, I1 ., Schonhorst, M.H., Lehman, [rl.F. and ],Iarble, V.L. L970. Biotypes of the spotted alfalfa aphíd in the western United

St ates . J . eeon. 87,t. 63 : 1822-1825 .

Nielson, 11.W., Schonhorst, M.l{., Don, II ., Lehrnan, l,l.F. and ltlarble, V.L. 1971. Resistance in alfalfa co four biotypes of the spotted alfalfa aphld. J. eeon. Ent. 642 506-510.

Neuenschwander, P. , Ilagen, K.S . and Smit.h, R.F. 197 5. Predation on aphids in California's alfalfa flelds. HiLgandía 432 53-78. Reynolds, ll.T., Smith, R.F. and Swift, J.E. I956. InsecÈicides for alfalfa aphid. CaLif. Agn'ic. 10: 11-12. Simpson, R.G. and Burkhardt, C.C. 1960. Biology and evaluation of certain

predators of Theríoaphis tnaeuLata (nuckton). J. eeon. Ent. 53:

89-94 .

Smlth, M.V. 1977. Grazlng unnagement of dryland lucerne pastures on sandy soils. Dep. Agric. Fish. S. Aust. Fact Sh. No.78177. -11-

Smíth, M.V. L978. Existing llunter River dryland lucerne stands - should they be protected? Lucerne Aphid I,Iorkshop, Tamworth. Dep. Agric. N.S.W. 273 pp. : 253-255, Smith, R.F. 1959. The spread of the spotted alfalfa aphid, lhterioaphie nø.euLata (Buckton), in California. HíLgandia 28: 647-683. Smith, R.F. and llagen, K.S. 1956. Enemies of spotted alf alf a aphid. CaLif. Agrie. l0: 8-10. Stanford, E.I{. 1956. Aphid resistanE al-fa1-fa plants. CaLíf. Agric. 10: 3.

Stern, V.l*f . 1962. Increased resistance Ë,o organophosphorus insectícldes in the parthenogenetlc spotted alf alfa aphid, Thel-Loaphie tra.euLata, in

Calífornia. J. eeon. Ent. 55: 900-904.

Stern, V.l'f . and Reynolds, II .T. 1957. Aphid resistance to parathlon.

CaLí,f. Agnic. 11: 4, 14.

Stern, V.M. and Reynolds, H.T. 1958. ResisÈance of the spotted alfalfa aphid

Eo certain organophosphorus lnsecticides in southern California.

J . eeon. Evtt. 51 : 312-316. Stern, V.lf., van den Bosch, R. and Born, D. 1958. New control for alfalfa aphid. CaLif. Agrie. l2z 4-5, 13. Swlncer, D. 1979. A study tour. The legurne aphids. Agron. Brch. Rep. Dep. Agric. S. Aust. No. 104 : 2I pp. van den Bosch, R., Schlínger, E.I. , Díetrick, E.J. and l{al1 , I.M. 1959. The role of Ímported parasites in the biological control of the spotted alfalfa aphid in southern Callfornia in 1957. J. Eeon. ETtt. 52: 142-154. l{ilson, C.G., Swlncer, D.E. and trIalden, K.J. 1981. The origins, distribution, and host range of the spotted alfalfa aphld, Therioaphis trLfoLi.i (Monell) f . maeuLata, wttt. a description of its spread in South Australia. J. ent. Soe. Sth. Afr. 442 331-341. -r2-

SECTION 2: luE STIIDY AREA - lTE ITPPER-SOUTE-EAST OF SOUTE AUSTRALIA

The nain regions ín the Upper-South-East which rely on lucerne-based pestures include Counties Cardwe11, Buckinghan and ì,lacDonne1l, and southern reglons of Countles Russell, Buccleuch and Chandos (Figure 2.1). 2.L Cllnate

The clinate ls Mediterranean, or winter ralnfall, with an average annual rainfall varying beÈween about 400 urn and 550 mm. The monthly average ralnfall and the average daily mean teoperature for each month recorded at Keith (45 ku

SE of Culburra) are shown in_Figure 2.2.

2.2 So11

Lucerne-based pastures are mainly grorrn on deep, siliceous sands (pII=6 co

7) which Russell (1960) defined as soils where the depth of sand exceeded 900 mn and frequent,ly extended six meEres or more below t,he surface. Russell Ï1960) considered that these soils were the problem soils of South Australia because they were always deficient in a number of major and mfnor nutrients necessary for plant growth, and they had a very 1ow lrater holdtng capacity. They were also susceptible to wind erosion. Srnith (I972) attrlbuted the success of lucerne on these infertile soí1s to the deep-rootÍng perennial habit of lucerne and, in particular, Eo the successful adapt.atlon of Ehe main cultivar, Ilunter Ríver. This cultivar has been shown to have the abllity Èo: explolE a great depth and volume of soil for water and nineral nutrients.

supply lts own nlÈrogen frorn syrnbiosis \rtlt. Rhizobiwn spp.

overcome problens experienced by annual pasture speeies due to \üater repellancy which occurs vrith these sands (Bond 1964).

respond rapidly to sunmer rainfall, possibly as little as 5 mm. -13-

OADELAIDE

\ Toilem r n no roo

. Norocoorte 0 100 Kilometres

FIGIIRE 2.I: The nain regions in the Upper-SouÈh-EasE of South Australfa with dryland, lucerne-based pastures, and Èhe 400 m and 550 nrm lsohyet's. -L4-

(J o

ct 0 E E o e c o o FIGI]RE 2 .2: Monthly average rain- o E .g 2 falls (-) and average (to à'õ daily mean temperatures I E' qlo (---) , KeiEh. o 10 t, o

JFMAMJJASOND

2.3 l{anagement of Lucerne-baeed Pastures

In Ehe context of world agriculture, che culture and grazing managemenE of lucerne pastures on these solls is unique to Australia. The density of the lucerne planÈs is low (Plate 2.1), as few as six plants per square meEre is considered viable (M.V. Smithr. pêESo comm.)r and the age of lucerne pastures often exceeds 20 years. Optfmum production and persistence of Èhe lucerne plants are obEained with strategie rotationel grazlng, especially during late- spring, summer and autumn (Leach 1978). During winter and early-spring, most of the dry maE,ter is produced by other pasture species, such as annual legumes, e.g. subterranean clover, TnifoLíum subtenaneum L., and annual medics, Medieago LittoraLis Rhode, M. truneatuLa Gaertn., perennial grasses¡ ê.go perennial veldt grass, Ehnharta caLgeirla, Sm,, and volunteer annual grasses, e.g. Br.omus and VuLpia sppro AlÈhough the average stocking raEe is only about five DSE, the poEential stocking rat'e varies considerably from year Eo year depending on the weather, especlally rainfall. Thls variation in stocking - l5-

PLATE 2.I A viable, dryland lucerne-based pasture in the Upper-SouÈh-EasÈ durlng summer showing the low density of lucerne plants. -1 6- rate tends to lead Èo under-utilisation of lucerne herbage in years with high ralnfall and a rlsk of ovet-grazing wiEh concommit.ant long-term damage in years with low rainfall (Snith 1977). 2.4 References

Bond, R.D. 1964. The influence of È,he mlcroflora on the physical propertles of

so1ls. II. Field sLudies on \.rater repellent sands . A1t6t. J. SoiL Ree. ?z 123-31. Leach, G.J. 1978. The ecology of lucerne pasÈures. ïn, Plant Relations ln

Pastures. Ed. J.R. trlilson, CSIRO Aust: Melbourne: 290-308. Russell, J.S. 1960. Soíls of South Australia - the deep sands. J. Dep.

Agrie. S. Auet. 63: 298-307. .

Smlth, l'1 .V. 1972. The ecology and utilizatlon of dryland lucerne pastures on

deep sands ln the Upper South East of South Australia. l.l .Ag.Sc. Thesis. University of Adelai-de. 247 pp.

Smith, I'l .V. 1977. Gtazlng Ítanagement of dryland lucerrie pastures on sandy soils. Dep. Agric. Flsh. S. Aust. Fact Sh. No. 78/77. -r7 -

SECTION 3: TEE SEASONAL ABUIIDAI{CE AND ESTABLISEI,IEI{Î OF SAA IN DRÏLA}ID

LUCERNE IN THE I]PPER.SOUTH.EAST OF SOUTE AITSTRALIA

Sunnary

Three years of saupling dryland, lucerne (cv. I{unter River)-based pastures, rótatlonaLIy grazed by sheep, demonstrateà that peaks of actívíty of SAA occurred in summer and autumn, with a minor peak in early-winter 1n one year. The tíming and density of peaks appeared to be ínfluenced by a combinatíon of mean temperatures and time of grazírrg; generally, the higher the mean Èemperature the hlgher the density, though maximum temperatures hlgher t.han 38oC had a deleterious effect on SAA. SAA could not be detected in dryland lucerne pastures during winter, though reasons are prclvided to suggest that SAA does survive ln these pastures during winÈer in very low numbers. Expected peaks of activity of SAA in spring did not occuro

The mlgratlon and establishuent of SAA ínto a dryland lucerne-based pasture in the Upper-South-East was monitored with yellow vrater traps and regular saropling of lucerne. The results suggest that the number of yellow traps used werà not an efflcient method of detectlng the first Lmmigrants of SAA in an area wlth abundant lucerne; they only trapped SAA aft,er SAA was established and lncreasing in density. -l 8-

3.1 Introductlon

3.1.1 Seasonal abundance of SAA overseas The rnain periods of abundance of SAA in lucerne stands overseas are in spring, summer and autumn, as suggested by experience 1n both Israel (Harpaz

1955) and Arl-zona (Nletson and Barnes 1961). I¡Ihen SAA was first recorded in the U.S.A. and Mexico, high densities of SAA were found in sprlng and they danaged lucerne plants extensively (licksoû et aL. 1955, Nielson and Barnes

1957, Young and Padilla 1957). In the following years, lower densities of SAA were found in susceptible lucerne stands ln spring and these lower densities erere attributed to the widespread use of chemical lnsecticides and the increased abundance of predators with a new host (Dickson et aL. 1955). The highest denslEies of SAA occur in summer, and the densitles decrease during autumn; in years with warm autunns, t.here may be a secondary peak in densities of SAA

(Conrad and Medlet 1965, Dickson et aL. 1955).

Since the íntroduction of SAA into California, SAA has settled into annual patterns of abundance, and periods of hlgh densitles can be predicted with some accuracy (Reynolds et aL. 1956), ê.8. SAA lras most destructive during sprlng and autumn in the Iruperial Valley, during early-summer to nid-autumn in Èhe more inland San Joaquín Valley, and in late-summer, or not at all unless there was a period of hot, dry weather, ln coastal areas. .

The overwíntering behaviour of SAA overseas varies wit.h winter temperatures; l-n warmer, southern regíons of the U.S.A. and around the Mediterranean, very low numbers of nymphs and parthenogenetic adults are found in the field during winter (llanglitz et aL. 1966, Simpson and Burkhardt 1960, Harpaz 1955) whlle ln cold reglons north of latitude 40otl a holocyelic sÈrain produces viable, overwintering eggs (ùlanglitz et aL. 1962). -19-

3.L.2 Expected seasonal abundance of saA 1n South AuetÌalia

The main periods of abundance of SAA in grazed lucerne pastures in the

Upper-South-East of South lurstralia qrere expected to be in spring, summer and autunn, based on the above experlences overseas. The highest densities of SAA srere expected 1n the Upper-South-EasÈ durÍng suürmer because mean temperaÈures aÈ that tlme are near the optimum mean tenperatures (2O-25oC) for the rate of development of juveniles of SAA and for the fecundity of SAA (Graharn f959. IÃarpaz 1955) i and in most years there would be abundanÈ food for SAA. Ilowever, maximum daíIy temperatures in excess of 38-40oC can narkedly suppress numbers of SAA (Dickson et aL. 1955, llarpaz 1955). Such temperatures occur in rnosË sumners in the Upper-South-East, t,helr fnequency lncreasing from 0 to 2 days per sunmer in coastal areas up to 0 to 9 days per summer in inland ereas (Bureau of

ì4eteorology), so the numbers of SAA could sometines be reduced in summer. The

Upper-South-East is centred on latitude 30oS and, for this reason, a holocyclic strain is unllkely to occur there.

3.1.3 Deelg¡ of an experiment for a 3-year study of SAA abundance 1n drylaod lucerne peature

Followlng the establishment of SAA in the Upper-South-East, landowners wanted to know 1n r.rhich periods of the year SAA could be expected to cause economi c damage to lucerne pastures. This informaEion was required to help select Èhe besE streteg'y for the short-term control of SAA, especially for evaluaÈing the number of appllcations of cherni-cal insecticide whlch roay be requÍred on the low-producÈion pastures

A fleld experiment was conducÈed in lucerne pastures 1n the region for a period of Èhree years, malnly to evaluate the lnpact of SAA on dryland, Ilunter

River lucerne pastures. The experlmenÈ compared the productlon and persistence of lucerne plants in rotationally gtazed pasÈures which r,rere Ereated with

ähenical lnsecticfde for the control of SAA at different threshold denslties of -20-

SAA, wlth pastures which were not treated with chemical insecticide. The regular monitoring of SAA in the untreated lucerne pastures also provided data which could be used Èo predict seasonal patterns of abundance of SAA in the region.

3.1.4 The spread of SAA Ín South Australfa

SAA was first recorded in SouEh Australla near Adelaide ln I'fay, L977 . trI1lson et aL. (1981) descrlbed the rate of spread of SAA in South Australia based on data from regular sweep-net sauplíng of lucerne and other hosts of SAA, samples collected by District Agronomists and insecÈ specimens forwarded by landowners for identificaElon. They used the Eeru "spread" in the same mânner as Snith (1959), viz. 'a movenenE by some portion of a species which results in a major nodification of its geographical range'. Thls definition of spread is also meaningful for this section because lt ímplies both immigration and establishment. The spread of SAA across South Australia vras also monitored by a grld of I'foericke-style, yellow water traps as part of a natíon-wíde program (R. Laughlln, pêrse coum.).

Some of these \^tater traps were set up 1n the untreated lucerne pastures in the field experiment discussed in Section 3.1.3 prior to the establishment of

SAJ\ 1n the region because landowners \üere partieularly coneerned to know when

SAA flrst migrated into the Upper-South-East and became established. These traps also provided an opportunity to Eest theír efficiency ín deÈecting the first immigrant aphids in an area compared to sanpling the host plant 1n the field. 3.2 ì,faterlals aad Ìlethods

3.2,L The abundance of SAA tu the Upper-South-Eaet (i) Tlte eite

Changes in aphid numbers were estimated in a ten-year-old, Ilunter River lucerne-based pasture near Culburra, 160 kn SE of Adelaíde (tr'igure 2.1). The mean annual rainfall at Culburra ls 480 mm wiEh predominantly Iùinter rainfall. -2r-

The soil type ls a slllceous sand (üc2.2L, Northcote L979), pH = 6-7 and about one to two netres deep over clay. The lucerne-based pastures r{ere rain-fed and pasture specles, other than lucerne, mainly included the annual grasses,

VuLpia sp. anð. Bnormts sp. , and subterranean clover, TnifoLi,un subte?raneutn L..

The site at Culburre $ras selected because the pastures had a good densíty of víable Hunter River lucerne (6 to 15 plants r-2), was situated approximately nid-way between the coastal and nost inland regions growing dryland lucerne in the Upper-South-East (Figure 2. I) and was free of SAA at, Ehe beginning of sanpling. The site was completely surrounded by large areas of sinllar pastures.

(¿í,) The tneatment¡ The treatmerits in the experlmenË are described in more detail in Section 4.2. Data in this section are obtained from Ehose areas not. treated with chemical insecÈlcide for the control of SAA (TN) in the experimental fÍelds. There r¡ere four separate fields, deslgnated Fields L,2,3 and 4, respectively, each of 7.2 ha. The fields were rotationaLLy grazed with sheep in sequence, Fields I to 4, using a slx-paddock system, i.e. one week grazed, five weeks ungrazed, and a sÈocking rate of fíve DSE per hectare throughout the period of sanpling. The six-paddock, rotationaL gtazl'ng sysËem was used because it was recognised as a system which naintains adequate production and persistence of lucerne on slliceous sands (Srnfth 1970), and five DSE per hectare vrere considered to be an average stocking rate for lucerne-based pastures ln the region. The first gtazi'ng of Field I commenced on 11 October L977. I.Iithin each fleld, a quarter of the fie1d, 90 m x 2OO m, rras selected at, random and not treated r.tl-th any insectl-cíde to control SAA, though parathion, 140 g a.c. ha-l ^, was applied to all fields on 31 January 1978 to control the wingless grasshopper, PhauLaeridiwn o¿ttatwn (SjosÈ.). ths ¡sm¡inder of each field was used for other Ereatmerits on damage essessment and control of SAA (Section 4). -22-

(ii¿) SanpLing Luee.ne for SAA The saupling of lucerne for SAA commenced on 18 November 1977 using standard s\reep nets, 375 rnm di.ameter and made wlth calico; ten lots of.20 sr,veeps per treaEment area (a total of 800 srreeps per field) were taken each week using stratified ran

* In this Thesis, a sample which is used to determine the mean value of a parameter for a populatíon of plants or animals consists of a number of sanpllng units (Cochran 1963). -23- aphids, r{as carefully bent over an opened bag to minimise losses of aphids from the stems caused by their abillty Eo jurnp when disturbed (Díckson et aL. 1955). Each bag was sealed and taken to a laboratory for counting the numbers of SAA pêË stêrtro In 1979 and 1980, sampling \.¡as confined to one untreaEed area whlch was divided into two equal replLcates, and 20 stems per replicat,e were sarnpled at random each time. In the laboratory, stems and bags were washed in hot water (ca.70oC) to remove SAA and the r¡ashings were then filtered through fine g,avze mesh. The aphids were washed from Èhe inverted gauze mesh r¡ith 80% ethanol onto white fllter paper in a Buchner funnel under pressure. Each filter peper was stamped wíth parallel lines to facilitate the counting of all of the SAA under a low- porüer, binocular microscope. After the numbers of SAA on each stem had been counÈed, SAA fron stems from each untreated area (1978) or replicate (L979, 1980) were bulked to determine the age-structure of each population. The age- structure was obtained by deEermining the lnstar of each SAA in the sample, and the rnorph of adults, except when samples exceeded 200 SAA. In the latter cases'

Ehe sarnples were sub-sampled by shaking Ehe aphids in a vial with 802 ethanol and then decanting approximately 200 to 300 aphlds onto the filter paper. These sub-samples \{ere used Eo determine the age-structures of the populations. At some times, the relatlve smallness of Èhe sub-sanples compared to the samples may have reduced the rellability of the estímates of age-structure (Catter et aL.1978), but sub-sampling was necessary because of the large numbers of aphids sampled at t.hose times.

( ít: ) l,Ieather reeords Daíly raÍnfall and Eemperature \rere recorded EhroughouÈ Èhe Ehree years of sanpling with a standard rainfall gauge anil a thernohygrograph in a sÈandard Stevenson screen, respectively. Continuous r¿ind speed and direction were measured with a I'loefle@ anemograph for the firsÈ year of sampllng. -24-

3.2.2 Inttlal nlgratLon of SAA Ínto the experfmental site (i) IeLLou uater traps

One yellow waË,er Erap r,tas placed in the centre of each of the four untreated areas in the experimental site at Culburra on 30 Novernbet 1977. The traps were yellow plastic basins, 305 mm in dlameter and 125 nm in depth; they were fixed a metre above the ground on steel posts. The yellow colour was that. used for all water traps in a project monitoring the dispersal of SAA Èhroughout

Australia (R. Laughlín, perso comrno)¡ lloles were drilled near the top of each basín to act as overflorüs and they were covered wiÈh fine gavze to prevent any trapped SAA fron also being washed out by rain. The basins srere filled with wacer and liquid detergent to the level of the holes. A piece of fine nylon gauze lined the inside of each basin to facilltate the collection of the sample; iÈ was held in place with a plastic insert at Èhe top of the basin. AÈ each sampling time, the gauze was carefully lifted from the trap, thus collecting any trapped insects, and placed in a labelled plastic bag with a small quantity of

80% ethanol to preserve any ínsects. The sealed bags were Èhen taken to a lâboratory for sorting and counting of the numbers of SAA per trap. The Eraps

\rere sampled each week from 7 December L977 to 7 July 1978. 3.3 Reeulte and DlecussÍon

3.3.1 The abundance of SAA ln the Upper-South-Eaet

SAA was firsE detected ín Ehe experimental site in the south-western corner

(Fleld 4) on 13 December L977 in sweep net samples. By Èhe next week, SAA was detected in all flelds at the slte. Estlmates of the numbers of SAA per sr^teep and per plant from 18 October 1977 to 6 January 1978 are shown in Table 3.1; these are only crude estimates and would under-estimaEe Ehe E,rue densiEy of SAA, but they do suggest an increasing trend ln denslties of SAA after 13 Decenber

1977. The first sanpling of stems on 9 January 1978 showed that nean aphid densities had reached 23 to 27 SAA per stem of lucerne in Fields 2, 3 and 4, which had not been grazed since the detection of SAA in the site (table 3.1). -25-

TABLE 3. I The total number of SAA per lvater trap per week(A) and nean number of SAA(B) on lucerne plants durlng the inltial colonisaÈion of SAA aE Culburra, L977/78.

Date Field I Field 2 Field 3 Fleld 4 AB AB AB AB

18.10.77 - 6.L2.77,r 0 0 0 0 00 0 0 13. 12.77Ï 0 0 0 0 00 0 0.4 20. 12.77Ï 0 0.1 0 0.4 0 0. r 0 0.8 4.1.78t 0 8.7 0 8.7 0 6.r 0 17 .6 6.r.781 4 8 5- 3 9. I . 78** 9 5.4 23 23.4 30 26.6 23 25.0

* Values of B on 18.10.77 to 6.12.77 : roean number of SAA per slreep. 1 V.lrr"" of B on L3.I2.77 to 4.L.78 = mean number of SAA per A4 sheet of paper. ** Values of B on 9.1.78 = nean number of SAA per sÈem of lucerne. - Not sanpled.

In 1978, peak densities of SAA occurred in sunmer (December to February) and in autumn (l"larch to l4ay) as expected - especlally tn Fields 3 and 4 (Figures

3.1 and 3.2); SAA was not estabtished in the site sufficlently early to detect any peaks of density ln spring (September to Novenber) 1977. The minor peaks of density in early-winÈer (June) in 1978 were unexpected but were attrlbuted to the unusually warrn weather in late-May; occasionally, ninor peaks of SAA also have been recorded tn early-winter in Arizona in years with a simllar vreather pattern to that at Culburra in 1978 (Nielson and Barnes 1961). The tining of peak densitles of SAA in the fields during 1978 was nainly lnfluenced by a combinaÈfon of the application of paraÈhion at the end of January, which reduced densities to one t,o tno SAA per stem of lucerne in all fields, and the subsequenÈ times of, grazÍ-r'g pastures ln the different fields. The effect that

gtazLng wiÈh sheep had on densities of SAA varied, but in most instances, caused _26_ a marked reduction in densities; the influence of gxazLag on the abundance of

SAA is discussed in more deEaíl in Sect,ion 5. The combined deleEerious effects of parathion and grazÍ:ng withln two to Èhree weeks afÈer the application of paraÈhion caused Ehe initíal peak densiEies in Flelds I and 2 to occur later than in Fields 3 and 4 (Figures 3.1 and 3.2). In conÈrast to Fields 3 and 4, the populatíons of SAA in Flelds I and 2 dLd not have sufficient time to markedly increase in numbers following the applicatlon of parathion and prior to grazLng. The timing of further peak densities in the differenÈ fields was dÍrectly related to the tines that each field was grazed with sheep.

Ttre rnagnitude of the peak densities of SAA in each grazing cycle varied with the È1me of the year and was considered to be directly related to temperature - t,he higher the nean temperaiure, the higher the densiÈy. An exception to this direcÈ relationshíp was in the second week in March when there were three consecutive days with naxi-mum temperatures exceeding 38oC. These high tenperatures apparently caused the reduction in numbers of SAA fn Field I and reduced the expecÈed raÈes of lncrease of SAA ln Fields 2 and 3 durfng Ehat week; this deleterlous effecÈ of high temperatures agrees with observations of Harpaz (1955) and w'ill be discussed further l-n Section 7. At tiues, the nagnitude of peak densities also varied between fields during corresponding grazltg cycles; this variation was atÈributed to different t,emperatures during the grazfng eycle in each field whlch !Ías an artefact of the different times of grazlng. The peak denslty during grazlng cycle III was higher in Field I than in the other Fields (Figures 3.1 and 3.2) and thís higher density reflected a higher nean temperature tn Field l. The nean temperatures 1n Fields I to 4 durlng thl-s grazing cycle were 15.3oC, 13.8oC, I3.4oC and 12.8oC, respectively. The nagnitude of densities of SAA also depended on the quality of the host lucerne plants. In February and March, when SAA was mosÈ abundant, reductions ln numbers of SAA were due Èo reduced food quality caused by SAA -27 -

FIELD 1 o c 700 oL o 2 60 1 n -fr lv o 50 E o a 3 L o o-

tJ) 100

L (u o 3

o FIELD 2 cL q, o ) 1 11 11 E o E o 400 VI L 3 o o- 20

Ø 100 p

oL 300 oì 1 50 o- o a L r5o s o o Jon Feb. Mor. Apr. Moy June

commence ment of grozing cycle

P_ porothion

FIGIJRE 3.1: The mean number of SAA per sÈem, number of SAA per waÈer trap and Etre 7" alates in Ehe fteld population of SAA ln untreaÈed lueerne pasture in Fields I and 2 from January Ëo June L978, Culburra. -28-

FIELD 3

60 T n 1T II o E o o L æ 9osc L

oL o 3

o 50 o\ ct E

FIELD I,

m o 1 ! tr E o a L o(uo-c <9L ln¿

o'L ìo

(l, sË o J on l-eÞ. Mor Apn Moy June I I commencement of grozrng cycle I - P - porothion

FIGI]RE 3.2: The mean number of SAA per stem, number of SAA Per !üaÈer trap and Ëhe % alates ln the fteld populatfon of SAA 1n untreaËed lucerne pasture in Fields 3 and 4 frorn January to June L978, Culburra. -29-

Èhe summers and autumns of l97g and 1980 were similar to those in 1978; peak rlensities occurred during grazío,g cycles with E,he highesE mean temperat.ures' Ehe timing of the peaks was influenced by the time of grazlng and Ehere were reductlons 1n the highest densittes of SAA during February or March due to re{uced food quality caused by SAA damage to the lucerne plants (Figure 3.3). In late-autumn (April-May), the densiEies of SAA decreased in 1979 and remained low in 1980 when the mean temperat.ures \¡rere less than about lOoC (Figure

3.3 ) .

19 79

60 T 11 111 1V t

o C o o J 20 o I E o o L o 1 980 o- n T Í 11J ry_ tn

o ot- .o E z 1 I

Jon. Feb. Mo r, Apr. Moy June

commencefnent of grozing cycle

FIGIIRE 3.3: The mean number of SAA per stem in untreated lucerne pastures from January to June, 1979 and 1980, Culburra. -30-

SAA was not detected in any stem samples from any of Ehe fields from early- July to the end of Septeuber ln the t,hree years of sampllng. Intensíve visual sampllng of lucerne pastures in the fields also falled to detect overwinÈering

SAA. However, I suggest that SAA does overwinter ln dryland lucerne pasture, but in denslties too low to be detected by the methods of sampling used, because the first SAA detected following each winter r^rere nyuphs and apterae in low numbers, not alates. Also, densities of SAA in lucerne crops in other reglons of the State at the end of winter are very low and thls ninimlses the likelihood of the production and migration of alates lnto dryland lucerne past.ures in the Upper-South-East at that time.

The most unexpected result from studying the seasonal abundance of SAA in dryland lucerne pastures was that SAA was scarce during sprlng in both years following the initlal estalishment of SAA fn the siÈe. SAA did not start to increase in numbers until late-January in 1979 and rnid-December 1n the 1979/80 summer, even though mean Eemperatures r¿ere favourable during both springs and there was abundant food of apparently suitable qua1lty. Predators appear to be the nain reason for E.he low abundance of SAA in spring and Èheír influence on

SAA at thls tíne of the year is discussed 1n Section 6.

This study on the abundance of SAA in dryland lugerne pasÈures over a perlod of three years suggests that, in most years, SAA ls a potential pest of lucerne pastures 1n the Upper-South-East in summer and autumn, but not in spring and wLnter.

3.3.2 Initlal mlgratfon of SAA lnto the experinental site

The f irst alates of SAA rrere not eaught in yellow rìrater traps until 6 January 1978 (table 3.1), approximately 3.5 weeks after alates and apterae were flrst detecÈed in the lucerne using srdeep nets and the shaking of plants.

This lag suggests that the use of one yellow trap per 7.2 hectares r{as not a rellable nethod for detecting the flrst imnlgrants of SAA into a new region with -31- extensive areas of its host plant, and Èhat alates were only trapped once SAA had become establíshed in an area and was íncreasing in density. The lnadequacy of the yellow traps for the early detection of aphids may have been due to Èhe snal1 Èotal surface area of Èhe t,raps compared to Ehe overall area of lucerne ín the síte; or perhaps the aphids were more strongly attracted to their host plant than to yel1ow Èraps. Costa and LewLs (1967) shov¡ed that, wíth a number of different species of aphids, the larger the trap the more aphids were caught, but numbers per unit area of trap decreased wlch increased trap size. They concluded that r¿hen few aphids were flylng, many small traps would catch more than a few large traps of equivalent area. I^Iith regard to the attraction of SAA to yellow traps, Eastop (1955) showed that a number of species of aphids do differ in thelr aÈtraction to yellor arrnì but he did noÈ discuss the behaviour of SAÀ, and neither did any other reference reviewed. Sanpling at Culburra only tested yellow water traps in an area with abundant food, 1t did not Èest thelr efficacy in monlÈoríng the spread of SAA across areas of host scarcity. In this latter situaÈion, yel1ow rtater traps may be useful, especÍally as they do trap SAA (Table 3.1, Figures 3.1 and 3.2) and are a simple and cheap method of trapplng aphlds, as Eastop (1955) showed for oEher species of aphlds.

The spread of SAA to the site and the increase in its dlstribution and abundance rdithln the slte were probably due nainly to natural migration of alates from nearby, heavily-lnfested regions, as happened in the U.S.A. (Dickson

1959, Nielson and Barnes 1961, Smlth 1959). Initial rnlgracion lnto the site may have occurred durlng the period , 25 to 27 November 1977, when northerly wLnds were recorded on these days aÈ the slte. These wlnds had an average speed varying frorn 15 to 18 kn hr-l and lasted for up to 7.5 hours per day. Alates of SAA fly wlth the wind and the probability of incoming flights of SAA in any fleld is dependent on the dfrectfon of Èhe wind and the location of Ehe mLgrant -32- source (Tanakl and Snith L972>. There were heavÍly-infested, irrigated lucerne crops w-lthin f00 kn north of Culburra prlor to SAA being detected at Ehe slte

(i.lílson et aL. 1981), and SAA alates are known to migrate such distances and stíll reproduce (Dlckson 1959). Generally, surface winds are from Ehe south and wesÈ durlng sprlng 1n South Australfa, but these winds were probably not responsible for the lnftial inrnlgrant SAA because SAA was noÈ recorded 1n lucerne pastures or crops to the south or west of the site at that time.

3.3.3 Abundance of SAA alatee tn dryland lucerne pesture

The percentage of alates ín field populations was usually less than about I5it. An exception was in all fields for two weeks following the application of parathi.on on 31 January 1978; the high peJcentages (up to 37.5%) at Ehose Eimes Iüere atÈribuÈed to the relatfvely low denslty of aphlds afÈer the application of the parat,hlon and nrigration of alates into t,he site as demonstrated by the relatlvely high nunbers of alates caught in the yellow traps then. C,enerally, higher percentages of alates occurred at the same Èime of the year as Ehe higher densities of SAA, as would be expected from studl-es of Toba et aL. (1967) which showed that production of alat,es of SAA was primarily lnduced by crowdíng of first instars. There rùere some exceptlons which could not be explained, in partieular the low percenÈage of alates in late-l'fay when densitles of SAA were relaÈÍvely high, e.g. in Field 2 (Figure 3.1).

The number of alates caught tn yellow Èraps varied conslderably from week to week (Ffgures 3.1 and 3.2) and Lt was of interest to deternine whether the number of alates Èrapped could be related Ëo any factors in Èhe aphid/crop system. The number of aphLds l-n flight wLthin a field ls governed by the number of alates available for flight and is only weakly correlaÈed with weather

(Johnson 1954), though there are thresholds of light and temperature below whtch species of aphids so far tested cannot take off (Taylor 1963). Factors oÈher than weather which nay influence the number of alates available for fllght are -33- denslty of SAA, and food quality and quantlty. The numbers of SAA caught each

¡seek in yellow traps in the four fields at Èhe experlmental síLe could noE be correlated with any of the factors mentioned abover ê.8. for each week, the poor correlation beEween mean densities of SAA per stem of lucerne and numbers of SAA per water trap is evident in Flgures 3.1 and 3.2. The inabilíty to correlate Èrap catches with oËher factors 1n the environment paralleled the experience of

Johnson (1954) where he regarded that regressíons of trap data of the bean aphid, Aphis fabae Scop., on Eemperature and windspeed alone did noÈ, appear to be profitable - the number of alates available for flight depends on a cornbination of many factors. At Culburra, most alates lrere trapped during

February and ì4arch when SAA was most abundant in the fields. During this perlod, the highesÈ numbers of SAA trappeà each week tended to be in those weeks when either the densities of SAA in the fields fell due to reduced food qualíty caused by SAA damage, or when pestures \rete grazed with sheep. Alat,es ceased to be trapped after Èhe first week ín June (Figures 3.1 and 3.2). 3.4 References Carter, N., Alkman, D.P. and Dixon, A.F.G. 1978. An appraisal of llughesr tlme-

specific life table analysis for determinlng aphid reproductive and xcortality rates. J. Anin. EeoL. 47: 677-687. Cochran, I,l.G. 1963. Sampling Technlques. John l{iley & Sons, Inc. 4I3 pp.

Conrad, M.S. âûd Medler, J.T. 1965. The spotted alfalfa aphid in l^Iisconsin.

J. eeon. Ent. 582 180-181.

Costa, C.L. and Lewis, T. 1967. The relatlonship between the size of yellow water traps and catches of aphids . Ent. eûp. & appL. I0z 485-487. Dlckson, R.C. 1959. Aphid dispersal over Southern Californla deserts. Ann. ent. Soe. Am. 52: 368-372.

Dickson, R.C., Laird, E.F. âûd Pesho, G.R. 1955. The spoEted alfalfa aphld. HiLgardia 242 93-1I7. -34-

Eastop, V.F.1955. Selection of aphid specÍes by different kinds of inseet traps, Natune 176z 936. Gilbert, N., Gutlerrez,4.P., Frazer, B.D. and Jones, R.E.1976. Ecological

Relatíonships. trl.H. Freeman and Company. 156 pp. Graham, II.M. 1959. Effects of Eemperature and hunldity on the biology of L'herioaphis naeuLata (Buckton). lJnits. CaLif . PubLe. Ent. 16: 47-80. Ilarpaz, I. 1955. Bionomics of TherLoaphis tm,euLata (Buckton) in Israel. J. eeon. Ent. 48: 668-67I.

Johnson, C.G. L954. Aphid nigration 1n relatlon to weather. BioL. Reü.

29-. g7-tlg.

MangliEz, G.R., Bergmen, P.W., Ilowe, I{.L." and Calkins, C.0. L962.

Overwinterlng in Èhe egg stage by the spocted alfalfa aphid l-n Nebraska. J. eeon. E?tt. 55: 292-294.

Manglitz¡ G.R., Calkins, C.0., trlalstrom, R.J., IIÍntz, S.D., Kindler, S.D. and Peters, L.L. 1966. Ilolocycllc strain of the spotted alfalfa aphid in Nebraska and adjacent states. J. êcorl. Eht. 592 636-639.

Nielson, M.I,rI. and Barnes,0.L.1957. Life hlstory and abundance of the spotted alfalfa aphid in Arizona. J. eeon. Ent. 50: 805-807.

Nielson, l"f .trrl. and Barnes, O.L. 1961. Population studies of Ehe spotted a1-fal-f a aphld in Arizona ln relation to temperature and raínfall. Ann. ent. Soe. Am. 542 44L-448.

Northcote, K.H . 1979. A Factual Key for the Recognition of Australian Soils. 4th Ed., C.S.I.R.O. Rell1n Technical Publications, S. Aust., L24 pp.

Reynolds, lI .T., Snith, R.F. âûd Sr¡if t, J.E. 1956. Insect,icides for alf alfa aphid. CaLíf. Agrie. 10: 11-12.

Simpson, R.G. and Burkhardt, C.C. 1960. A three-year overwintering study of the spotted alfalfa aphid. J. eeon. Ent. 53: 220'222. -35-

Smith, M.V. 1970. Effects of stocking rates and grazTng management on the persistence and productíon of dryland lucerne on deep sands. Proe. Xï

Int. GnaseL. Congn. Univ. Queensland Pressz 624-628, Smíth, R.F. 1959. The spread of the spotted alfalfa aphid, Th,eríoaphis trweuLata (Buckton), in California. HíLgandia 28: 647-683.

Tanaki, G. and Snith, R.F. L972. Influence of wind and uigrant aphid source on

the flight and infestation patterns of the spotted alfalfa aphid. Ann.

ent. Soe. Am. 65 : I I3l-1143. Taylor, L.R.1963. Analysis of the effect of temperaEure on insect,s in fllght. J. Anim. EeoL. 322 99-117. Toba, II.H., Paschke, J.D¡ ând Friedman, S. L967. Crowdfng as the prinary factor

fn the production of the agamic af"t" form of therioaphis tnøeuLata (Itonoptera:Aphididae). J. Ineect PhysíoL. 13: 381-396. hlalden, K.J.¡ Swlncer, D.E. ând trlilson, C.G. 1978. Sanpling techniques for the

spoEted alfalfa aphtd. Lucerne Aphid lbrkshop, Tamworth. Dep. Agríc. N.S.tr{. 273 pp.z 63-65. f,I11son, C.G. , Swincer, D.E . âfld llalden, K.J . f 981 . The orígins, distribution and host range of the spoÈted aLfalfa aphid, llterioaphí,s trifoLií (Monell) f. maeuLata, wLtt. a deseription of its spread in South Australia. J. ent. Soe. Sth. Afr. 442 331-34I.

Young, Iù.R. and Padilla, R.A. 1957. The spotted alfalfa aphld, Therioaphis

(PteroeaLLídíum) t¡tøcuLata (Buckton) in Mexico . BuLL. ent. Soe. Am. 3: 31-32. -36-

SECTION 4: INFLI'ENCE OF SAA ON PERSISTENCE Æ{D PRODUCTIOtr OF DRYT"AND

LUCERNE IN lEE TIPPER-SOUTH.EAST OF SOU1U AUSTRAIIA

Suunary

Fleld experlments in rot,atlonaLLy-grazed, IlunEer River lucerne-based pasture in the Upper-South-East denonstrated that mean densities of SAA needed to be maintaLned below about 40 to 60 SAA'per stem of lucerne for acceptable persistence and production of lucerne. Untreated lucerne suffered reduced herbage productíon, even in the absence of SAA, following heavy lnfestations gf SAA, and au 85% loss of plants after trùo years. These losses may be partly attributed to reduced levels of tocal non-structural carbohydrate in Eaproots of untreated lucerne. ExperimenÈs \^rith indlvidual plants falled to clearly define how SAA affected the different components of yield, such as number of buds and number and length of stems per plant.

For the most part, 40-60 SAA per stem of lucerne was noÈ accepted as an economic threshold by landowners in the reglon, mainly because of lnherenE practical dlfflculÈies and cost regulred to rnaíntain SAA aE such low densities over large areas of low-productivity pasture. Consequently, SM was not widely controlled in dryland lucerne and, after three years, t,here was an estimated 90 to 951l reductlon of commercial dryland lucerne pastures in the reglon whlch could be mainly attributed to SAA. -37 -

4.L IntroducÈfon

The accidental lntroduct,lon of SAA lnto the Upper-South-East of South Australia ln late-1977 seriously threatened the econonic vlabillEy of about

600 000 ha of dryland lucerne-based pastures used for grazíng livestock. The lucerne, cv. Hunter River, was hlghly susceptible to SAA, and experíence in south-western U.S.A. 1n the l950rs clearly demonstrated that SAA had the potentlal to severely danage susceptible lucerne plants (Parker et aL. 1956,

Snith 1959). Lucerne plants were responsible for at least 50% of. È,he llvestock producÈion fron lucerne-based pastures in the Upper-SouÈh-East (Smith L977) and had the added advantage of provldíng high quality green feed during summer and autumfi to fatten young livestock for prem{um, out-of-season markets Ln early winter. Also, most of the pastures lrere grolrn on infertlle, siliceous sands

(Russell 1960), and Èhere lrere no alternat,lve pasture species which could be sown in most of the areas rrith lucerne to compensate for any losses in the production of lucerne caused by SAA.

- In Èhe U.S.A., SAA reduced Ehe quanÈity and quallty of production and the persistence of unprotected lucerne plants (Parker et aL. 1956); and lucerne could not be successfully grown wlthout che¡nical insecticides (Reynolds et aL. 1956). Because of the continuous need for chemical lnsecticides, a number of threshold densÍties of SAA were suggesÈed as crlteria for t.he econom{ c appllcation of insectÍcides. These densiÈ1es varied for established lucerne and lncluded oean denslÈies of 5 SAA per trifoliate leaf of lucerne (Nielson and

Barnes 1961, Hanson 1961), 20 to 40 SAA per sÈen of lucerne (Reynolds et aL.

1956) and 75 SAA per stem of lucerne (Parker et aL. 1956). Dickson et aL.

(1955) stated thaÈ 40 SAA per sten of lucêrne on stems 45 cn long caused sticklness and inferred Èhat densitles should be nalntained below that number.

A more general criteríon for treatnent was the appearance of 1or,r quantities of honey-dew excreted by SAA together with increasing densities of SAA (Reynotds and Dickson 1955). -38-

All of the above Ehresholds applied to highly productive, irrigated lucerne for hay and could not be extrapolated confidently to the low-productlve, gtazlr.g pastures 1n the Upper-South-East of South A¡stralia. So informatíon r¡ras urgently needed on denslties of SAA which could be sustalned by the lucerne plants without apprecíable losses ln production and persistence. Low gross narglns per hectare from lucerne-based pastures in the Upper-South-East at that tine dictaÈed the need for thresholds Eo be as high as possible, thus lncreasing the lÍkelihood that SAA could be controlled economically wiÈh chemícal insecticldes in the shorÈ-term. This sect,ion descrlbes field experiments which quantified the effect of

SAA on the productlon and perslstence of grazed, dryland lucerne pasture and tested whether predetermined, arbitrary threshold densitles of SAA could be used as econom{c thresholds, as described by Stern (1973), to determine the need for chemical insecticides. Experirnents were also conducted wiÈh índividual lucerne plants ln Èhe field Èo elucidate damage caused by SAA fn terms of shorter stems and internodes and fewer vegeEat,ive buds, stems and Ínternodes per plant.

4.2 SAA Danage to l¡¡cerae Plants

In established lucerne pastures, initial infestatlons of SAA occur on Èhe

1or¿er leaves and as the aphlds íncrease in abundance and the plants are damaged, the synptoms of damage in the plants progresslvely change from yellow vein banding of leaves to local chlorotic areas on infested leaves, then to leaf drop

(initially Èhe basal leaves) acconpanied by stunting, wilÈing and general necrosis of Èhe whole plant (Paschke and Sylvester 1957). SA*A, produce an excesslve anount of honey-dew and hLgh densfties of the aphid cause plants to become very sticky; the honey-dew may support the grorúth of black, sooty moulds

(Reynolds and Anderson 1955).

Ilowe and Snlth (1957) and rnany others suggested that planÈ injury caused by SAA may be due to a toxin thaÈ becomes systemic when inJected into Èhe plant -3 9- wlth saliva durLng feedíng. Experiments by Paschke and SylvesÈer (1957) indicated that the induced dísease was a toxaemia, noÈ viral, though considerable variabillty in their experiments preverited then from being more conclusive. Nickel and Sylvester (1959) dernonstraËed Lhat "toxin injection, as measured by dlsease incidence, was a constanË and somewhaË addítlve functlon of feeding time", however, they could not isolate the toxic principal. They hypotheslsed that the toxin was solely of lnsecÈ orfgin, but warned that the spptoms may result from a toxin formed partially by plant derivatives r¿hose productíon, llberat.íon and stabllity was dependent upon the environment of intact plant Eissue, as suggested by Nuorteva (1956). If the latter r.ras true, lsolatlon of the toxin r¡ould be even more. difficult. Mittler and Sylvester

(1961) also suggested that Ehe injury may be due to a toxin but their studies lndicated that the considerable drain of fluid and nutrlents imposed by SAA on lucerne may be largely responsible for thê severe ínjury caused by SAA. Evidence was not found ln the literature to suggest that any toxic effects of

SAA on Èhe plant carried over from one regrowth perl-od to the next, in the absence of SAA.

The commercial irnplications of these effects of SAA on dryland lucerne for grazlng were best extrapolated from American experience with damage ln estab- líshed lucerne for hay production. Parker et aL. (1956) summarised these effects whlch included:

- reduced yields of dry matter, well in excess of 507"; - redueed quallty of hay, e.g.lower proteln and carotene contents, or lncreased levels of coumestrol (Loper I96B); - reduced palatability of severely danaged lucerne to lfvestock; - weakened stands of lucerne whlch allowed t.he invasíon of grassy weeds;

delayed regrowth of lucerne after grazírg or mowing; -40-

- death of plants, eventually resulting in Ehe complete loss of a stand.

The death of lucerne ruay be aggravated by plant pathogens¡ êrgo crowrt rot,s and root rots, which nornally do not debllitate healthy plants. 4.3 Background Èo the Experlnents 4.3.1 Experimental slte

The siEe at Culburra r{as selected for damage assessment experiments because there were four adjacent fieldsr êâch fenced and 7.2 ha in area, which contained reasonably slmilar and unl-form stands of economically viable, ten-year-old Hunter River lucerne. The pastures \{ere non-írrigated and pasture species other than lucerne were mainly the annual grass, B?om)B sp., and subterranean clover, TnifoLítnn eubterraneum, cv. Þft. Barker. The topography of the site was slightly undulating. The soll was r ,rtr""ous sand (tJc 2.2L, Northcote 1979) with a depth of one to t\úo metres over clay.

AlI fietds were EreaEed with parathlon, L4O g a.c. ha-l, on 3I January 1978, to control the wingless grasshopper, PhauLaeridiwn üittatm (Sjost.), and were Eop-dressed with superphosphate, 90 kg h.-1, on 8 March 1978. The four fields were desígnated Flelds I, 2r 3 and 4, respectively.

Throughout the t.hree seasons of damage assessmenE studles, t,he fields were rotationalLy grazed with Merino sheep in the sequence Fteld 1 Eo 4 within a six- paddock system, i.ê. êach field was gtazed for one week, then not grazed for five weeks (regrowth period). The six-paddock rotational grazítg system was used because 1t rüas recognised as a system which maintained adequate productlon and persístence of lucerne on siliceous sands (Srnith 1970). The pastures r^rere grazed at a stocking rate of flve dry sheep equlvalents (DSE) per hectare during the experíments; thts stocking rate was considered to be an average stocking rate for lucerne-based pasÈures ln t,he reglon and. at uosÈ times, this stocking rate resulted in virtually the eonplete consumption of lucerne herbage by the end of each week of graztng during each of the three years of experiments. -4L-

4.3.2 ClLnate

The mean annual rainfall at Culburra is about 480 m with predorninantly r¡ínter rainfall. The nean monEhly rainfall (3O-year mean) and monthly rainfalls during L976 and L977 f.or Tintlnara, situaÈed about 19 k¡n east of Ehe experimental site, are shown ln Flgure 4.1. The most lmportant feature of raÍnfall was the below average rainfall in t.he trio years prior to the experiments; this dry perlod r¿ould have severely restrLcted the amount of subsoll moisture and its abllity t,o sEimulate grovrth of lucerne during Èhe first

sunrrpr of the experinenÈs.

100 Tintinorq 30 y': meon Culburro 1978.

50

100 Tintinoro 1976 Culburro 19 79

? E 50

o .c o É. 100 ïntinoro 1977 Culburro 1980

s0 lll JFMAMJJASOND JFMAMJJASOND

FIGURE 4.1: I'lean monthly ratnfall (30 years) for Tintinara; monthly rainfall 1n 1976 and 1977, Tlntlnara; and rnonÈhly rainfall measured at Èhê experlmental sit,e ln 1978 to 1980, Culburra. -42-

4.4 Influence of Dl-fferenÈ ltreehold DensLties of sAA on the ProductÍon and

Persfstence of Grazed. Dryland Lucerue Pasture

Most field studles on Èhe assessment of damage by Lnsects reported in Èhe literature tend to rely nainly on quantÍfying effects of a range of densitíes of the pest on yield or quality of a particular crop, such densitles eiÈher occurrJ.ng naturally or being rnodified with nethods including ehenlcal lnsecticldes' artiflcial removal or additLon of pests, and natural enemles of pests (Snith L967).

In the following serles of experiments, the densitles of SAA in differenÈ areas of dryland lucerne pasture were either maintained below different predetermi ned threshold densities using chemical insecticlde or were allowed to lncrease in the absence of chenical lnsecticide. Couparisons rùere then made between Èhe persistence (p1ant density) and production (herbage dry natter) of lucerne plants exposed to the differenÈ densltles of SAA, respectively.

Conparlsons were also made between Èhe total non-structural carbohydrate (TNC) of the tap-roots of lucerne In different areas; the amount of TNC in Èhe tap- roots was used as an index of plant vigour.

The Èhresholds tested l¡ere based on (a) Amerl-can experience with SAA in frrigated lucerne, (b) a higher threshold than used in irrigated lucerne to reduce Èhe number of applications of Lnsecticide which nay be requlred, and (c) visual evaluatlon of the flrst leaf drop caused by SAA. The last threshold was lncluded ln an effort Èo obviate the need to estÍnate actual densiËies of SAA ln commerefal pastures; aÈ the tine of these experiments, pracÈieal techniques were not avallable for reliable estimates of denslÈ1es of SAA in lucerne pesture over large areas with ninluum efforÈ - tndlvidual flelds of lucerne-based pasture 1n the Upper-SouÈh-East can be as large as 200 ha.

Tle Ëhree thresholds lüere consldered Eo be within Ëhe potential range of densltles of SAA rshich may dauage lucerne plants and were sel.ected as a DatÈer -43- of expediency to rapidly establlsh thresholds which could be used as critería to ald decisíons on the application of chemical insecticides for immediate control of SAA in the Upper-South-East. 4.4.I MaterÍals and nethods

The series of experi.ments on damage assessment !¡ere lnitiated rüith the commencement of grazíng of Field I on ll October 1977. The three experinents can be convenfently referred to as experiments ín L977/78, L978/79 and 1979/80. la 1977/78, the following four treatmerit.s were allocated at random Èo equal areas, 90 u x 200 m, within each of t,he four f ields: TN - nil chemical insectlcide. T¿O-OO - chemical insecticide appl.ied when nean density of SAA was

greater than 40 to 60 SAA per stem of lucerne.

TfgO_ZOO - chemlcal lnsecticide applied when roean density of SAA was

greater than 180 to 200 SAA per stem of lucerne. TV - ehemical insecticide applied with inltial leaf drop from

lucerne plants caused by SAA (visual darnage). The chemical insecticide was demeton-s-methyl (l'fetasystox@), 75 g a.e. ha-l to the end of March Ig78, then 37.5 g a.c. ha-l to the end of the experfment, applied with a boon sprayer using 130 L ha-l of water.

Í¡ L978/79, treatments T¡ and T¿*O-OO only were continued ín Field 2 only, because resources were also allocated Eo other studies on SAA at the slt,e and the data in 1977 /78 demonstrated that Èhe required threshold for SAA was less than the thresholds TtAO-ZOO and TU.

Sinilarly Ln 1979/80, only treatments T* and T¿O-OO !,Iere continued in Fi.eld 4 only. The treatments were Eransferred frou Field 2 to Fteld 4 ln rgTg/80 because there rüere severe losses of plants ln T¡ in Field 2 by the end of the L978/ 79 experiment. Each treatment area in Fields 2 and 4 was the same slze as Èhe orlglnal treatment areas used in L977/78. fn L978/79 and L97918O, there rÍere tlto replicates per treatment. -44-

(i) Eet¿nating numbers of SAA

The density of SAA was estlmated as the mean number of SAA per stem of lucerne using the stem sarnpling mechod descrlbed in Section 3.2.1. In L977/78, 30 stems of lucerne \rere selected from each treatment replicate at each time of sanpling and, In 1978/79 and 1979/80, 20 stems qrere sampled from each replicate.

Estfmates of density of SAA were made each week during t,hose periods of the year when SAA were deEected by Èhe method of sarnplíng. (í.ì,,) Estinating ntonbeps of Lueente pLants

To measure the persist,ence of lucerne plants, denslties of plants ín each replicate were estimated at the beglnning of the experiment (OcÈober L977) by counting t.he number of plants in 20 quadrats, I n x 1 m, in each replicate. Th; sanpling was based on random stratifiea by area with one quadrat "'.rpff.rg sampled per stratum. SirnÍlar samples of plants r¿ere taken again 1n May 1978 and in January L979. In latter years, densities of plants were estímated 1n each of

10 quadrats per replicate in treatments TN and T49_66 in Field 2 in May 1979 and in December L979, and in Field 4 in Decernber 1979 and in June 1980.

The data for October 1977 and January 1979 were analysed wlth 2-way ANOVÀs to determine if there srere any dlfferences tn planE density beEween treaÈments and/or beÈween flelds (replicates) at the start of the experl-ment and after the first year with damage by SA4, respectively. The data 1n January 1979 were expressed as percentages of the initial densities (October 1977), then transformed to arcsine æ-f and analysed by a 2-way ANOVA to test for dlfferences ln plant losses between treatments from OcÈober L977 to January

1979. The densities of plants 1n T* and T49-66 in both Fields 2 and. 4 after January 1979 were conpared rlíth StudenÈ's t-Èests.

(iii) Eetimatíng drg ¡¡atter of Lueerne

The dry natter (O¡t) of lucerne herbage in each replicate was estiuated by cutting all the lucerne herbage from random quadrats in the replicates; all herbage cut from each quadrat was placed in a labelled plastfc bag whLch was -45- then sealed and taken to the laboratory where the herbage lüas dried in an oven at gOoC for 15 hours. The dried herbage from each quadrat was weighed while warm and its weight recorded. Prelininary weighings demonstrated that the amount of lucerne herbage fn each quadrat was dried t,o a consÈant dry weight

I,¡tth this nethod. Initially, 10 quadrats, each 1m x I m, Iüere taken from each replicate; after September 1978, 20 quadrats, each O.7l rn x 0.71 n (0.5 m2), Iùere sampled per replicate. All sanpling was based on stratified randou sanpling by area with one quadrat sampled per stratum.

Tn 1977/78, the mean IM of lucerne herbage in each replicate was estfmated at the end of each flve-week regrowth (ungrazed) period just prior to gEazing Èo provide estlmaÈes of the total IM avallable for grazLng 1n each replicaÈe. The first estimates of Ill were made on 10 February 1978 in Field l. Tn L978/ 79 and 1979/80, the IM of lucerne was estlmated each week durlng those regrowth periods when SAA was detected Êo quantify the influence of different densities of SAA on Ilf production during each regrowth period.

The data for the 1977 /78 experlmenË were analysed with separate comparlsons between the IM of treatments 1n each field at each sampling tine uslng l-way

ANOVAs. A square root transformaÈion was used to provlde homogeneous variances Ln each analysÍs (P<0.05, BartleÈtts test for honogeneity). These separate analyses for each field were necessary because the four fields were sequentially grazed. tlith sequential grazttg, the regrowth periods for the differenÈ flelds dld not colncide in time and, hence, the fields nere sampled at different times and Èhe weather, especLally temperature and rainfall, dlffered during the regrowÈh perlods for each fleld; the difference fn weather rnay have dlfferentlally fnfluenced the regronth of lucerne and the effects of SAA on the lucerne plants. Ttre dffferences in reans of IDI between T* and T40_60 at each tLrne of sampling in 1978/79 and L979/80 were tested with SÈudentrs t-tests using square-root transformed data. -46-

(it:) Estimating earbohydr.ate resetuea in Lucerne tap-noots

The following met,hod was used to estimate Ehe amount of TNC (SníÈh L969) in lucerne tap-roots in T¡ and T49-69. Sampling lucerne plants in the field: At each time of sarnpling, 25 plants per replicate of the above treatments were selected at random. With each plant, all the herbage rras removed then the remalnder of the plant was dug up to glve at least 15 cm of tap-root. The tap-root was then cut in a manner to give 15 cm of tap-root starting from immediately beneath the crown. Prominent lateral rooÈs were removed from this section of tap-root and the tap-root was then qulckly placed in a labelled plastic bag in dry ice. The tap-roots $rere Eaken to the laboratory where they were stored at about -20oC until there was time ' for them to be analysed for TNC.

Preparation of tap-roots in the laboratory: The 25 t.ap-roots from each replicate were dlvided into flve lots of five tap-roots per lot and then the tap-roots, still frozen, rrere cut into lengths ca. 5 'n long. The sma1l lengÈhs of tap-roots in each lot were thoroughly mixed and a sub-sample, 20 to 30 g, was taken from each lot for analysís of TNC.

Determination of TNC: The levels of TNC in the t,ap-roots were determined by the South Australian Department of Services and Supply, Chenistry Dívísíon, using a method descrlbed by Anon (1973). Each sub-sample of tap-root was dried at 70oC for 48 hours and then nilled to pass through a sleve with I mn round. apertures; 0.2 g of the ground tap-root from each sub-sample was used for Èhe determinatlon of TNC. The starch and oÈher non-structural polysaccharides 1n each ground sanple of tap-root rras extracted and hydrolysed to glucose in a perchloric acid medium (the nethod in Anon (1973) used water to extract the sLarch and ot,her polysaccharides); the extract was Èhen mtxed with ant,hrone in a sulphurlc acld solution and the absorbarrce of the resultant blue-green complex

\ùas measured with a spectrophoÈometer. The level of glucose in each ext.ract. was calculated by conparing the absorbance value of the extract wlth those of -47 - standard glucose solutions. The % TNC r¡ras calculated as the proportion of glucose in each tap-rooE.

Tine of sanpllng for TNC: The levels of TNC in tap-roots of lucerne rvere estimated each five weeks fron 2l March 1978 to 14 February L979 in T¡ and

T+O-OO ln each field. Sampling in each field on the same day every flve weeks enabled the determLnation of levels of TNC in tep-roots of protected (Ta6-6g) and unprotected (T*) plants at different stages of regrowth of the plants after grazírg because the fields rrere sequentiaLly grazed. Sampllng from ì,larch

1978 to February 1979 provided estimates of TNC in tap-roots, first during periods of high abundance of SAA and then 1n periods when SAA was scarce (Sectton 3.3.1).

4.4.2 Results and díscuseLon

(i) SAA d.atnage to dnyLand Lueemte pLantg

The visual danage caused by SAA to dryland lucerne plants was simílar to that described by Paschke and Sylvester (L957 ) (Seccion 4.2); t,here was initial wilting of stems Ehen shedding of the lower leaves (Plate 4.1) followed by necrosls of the whole plant with high densities of SAA (Plate 4.2) . SAA also produced excessive amounts of honey-dew and the plants did become very sticky with high densit,ies of the aphld. In contrast to irrigated lucerne crops, the honey-dew did not support the growth of sooty moulds in dryland pasÈures, probably because of the mrch lower levels of humidity in dryland pastures compared to irrigated crops. In late-summet 1979, severely danaged lucerne plants 1n the experimental site appeared t,o support sooty moulds; however, the black appearance of the plants was due to infections by the fungl,

Stagonoepo?a neL¿Loti (Leaves), Leptoephaeria p?atenlis (sterns) and Pseudopeziza medicaginie (leaves and stems). Infectlons by these fungi have been recorded ín dryland lucerne planEs príor to Ehe introduction of SAA inÈo the region and \úere considered to be independent of the lnfluence of SAA. -48-

PLATE 4. I Lower leaves shed from lucerne plants infesEed with SAA.

PLATE 4.2 : A necrotic lucerne plant resulting from severe damage caused by a high density of SAA' -49-

(i¿) Deneity of SAA

fn L977/78, the peak densities of SAA 1n TU were simílar Eo Ehose in

TN, and densitles in T¿O-OO and T196-200 were usually maintained below the respective Ehreshold densities for È,he tvro creatment.s with chemical insectlcide

(Appendices 4.3 to 4.6). SAA r¿as most abundanÈ 1n the period laEe-February to nid-April, and Èhe peak denslties of SAA in T* at this tine were usually nuch greater than the threshold densities in T49-56 and Tlgg-2gg. ln 1978/79 and

1979/80, densities of SAA in T¿O-60 ¡¿ere also usually maintained below the treaÈment threshold (Appendix 4.7) and Èhe peak densíties in T¡ exceeded this threshold in March and April, 1978179, and in the period January to March,

L979/80 (Figure 4.2). SAA r¿as not detected in any of the experimental fields frorn July to December each year (Section 3.3.1).

(i¿i) Numben of appLieations of ehemical inseetieide The numbers of applications of chemical insecticide for those treatments involving chemlcal insecticide are given ín Table 4.1 (1977/78) and Fígures 4.3 (L978/79) and 4.4 (1979/80). In 1977/78, two applications per regrowth period r¡Iere requlred to maintaln T+O-OO durlng the February-l{arch period when Ehe densitles of SAA were hfghest. Exceptions were perlods ending on 24 February

1978 ln Field 3 and 7l'larch 1978 in Ffeld 4 r¡hen only one spray per period was applied for control of SAA; however, parathion sras applfed for the control of wingless grasshopper in the early stages of these regrowth periods which negated the need for an extra appllcatlon of chemlcal insectieíde for SAA. There was only one regrowth period (31 March 1978 in Ffeld 2) when two applicatLons were necessary to maintain T1g0-200. By contrast, in February-March 1979, trüo applications rrere necessary to meintaln T46_56 in the fírst regrowth períod only, and from then on in both 1978/79 and 1979/80 only one spray or none \{as requlred (Figures 4.5 and 4.6). Timing of the application of chemical insecticide with the Èhreshold, Ty, was difficult to determlne and al1 -50-

TABLE 4.I Peak densities of SAA in Tç and number of appltcations of insecticides for SAA, determined by the threshold densities for each treatment, ln different regrowth periods of lucerne, Culburra, 1978.

Fíeld Regrowth Peak+ Number of applications of lnsecticide perlod denslty for treatment: endfng: of SAA in Tnn T¿o-oo Trgo-zoo Tv

I 10.0 2 .78 60 0 0 0

23.03.78 240 2 I t 5 .05.78 270 I 0 0 16 .06 .78 r10 I 0 0

2 17 .02.7I 150 0 0 0

31 .03 .78 380 2 2 I 12.05.78 40 0 0 0 23.06.78 r70 I 0 I

3 24 .02.7I 610 I I 0

7 .04.79 580 2 I I 19.05.78 30 I 0 0 30.06.79 70 0 0 0

4 7.03.79 700 I I 0

14.04.78 430 2 I 0 26 .05 .7 8 30 I I 0 7 .07 .79 20 0 0 0

+ I'fean number of SAA per stem of lucerne. From 24-7-78 to 18-12-78, denslty of SAA < 1.0 SM/stem of lucerne in all treatment âfê€rs ¡ -51- chemícal insecticide in thls treatmenÈ was applied late 1n the regrowth period, usually after damage and stickiness of follage due to SAA !¡ere mosË obvious. Often the effect of this treatment was simllar Ëo T¡; 1f the chemical insecticide had been applied earlier, TU would have approached TtgO-ZOO.

At some times, aphid densities were difflculc to maintaln below or at different thresholds due to rapid lncreases in densities, especially durlng rüarmer periods of the year. Thus in the regrolùth period ending 17 February 1978 in Field 2, peak densities were about 150 SAA per stem in all Èreatment areas, yet T40-69 lras not treated (Table 4.1); ín thls regro\,rth period, densiEles of

SAA increased from less than 30 to about, I50 per stem in the last week of regrohrth. Another example of this problem was the rapid lncrease in numbers of

SAA after Ehe third week during the regrowth period ending 5 ì,larch 1979 (Flgure 4.sb). The t,otal nr¡nber of appllcatlons in each treatmerit Ln 1977/78 decreased fron T4O_60 to T''O_ZOO to Tu (Table 4.1), a trend which rüas expected wlth t,he design of the experiment. (it:) Density of Lueerne pLants Table 4.2 shows the denslty of lucerne plants 1n Fields I, 2,3 and 4 at the beginning of the experinent (October L977), after the first mafn perlod of abundance of SAA (May 1978) and after the first year wiÈh SAA (January L979). There rùere no significant differences (F3,9 = O.47, P>0.05) in plant density between treatnents 1n October 1977 , though there r,Ias a díf ference between fíelds (F3,9 = 8.94, P(0.001) (Appendtx 4.1). Sinilarly, Èhere were no significant differences (F3,9 = 1.18, P>0.05) in plant densiEy betr¡een treatEents ln January L979 (Appendix 4.1). In addition, the percentage ehanges in density of plants for each treatuenÈ from October L977 to January 1979 were not signiflcantly different (F3,9 = 0.86, P>0.05) (Appendix 4.2). The above similaritíes in planÈ density demonstrate that SAA did not reduce plant density -52- after the first, year of damage in any of the treatments, even though mean densit,ies reached 700 SAA per stem of lucerne in T¡ (Table 4. t). This absence of mortality of plants after one year of heavy infestations with SAA agrees with

Klndler et aL. (1971) who Èest,ed the effects of SAA on stands of susceptible and resistant cultivars of lucerne in fíeld ceges.

TABLE 4.2 Mean density of lucerne plants for each treatment fn each field during Ëhe first year with SAA at Culburra,1978.

l"fean density of lucerne plants (n-2 ) Fleld Dat,e in treatment: TN T+o-oo T Ttgo-zoo V

I 0ct 1977 7.5 6.1 6.8 7.6 lfay r978 L2.6 7.2 8.7 8.8 Jan L979 6.5 4.0 6.2 7.0

2 0ct 1977 8.1 6.8 5.4 7 2

May r978 8.1 7.2 7.2 7 2 Jan 197 9 5.4 6.6 3.6 6.7

3 Oct 1977 8.5 9.0 8.2 l1 .8 May 1978 12.5 11.0 10.8 11 .4 Jan 1979 9.1 10.2 9.2 11. 4

4 0ct 1977 9.9 1r.8 11.8 9.7 May 1978 15.0 13.4 15.3 15. 6 Jan 197 9 9.9 13.7 12.6 13.5

In the second year of SAA infestation, treatments T* and TOO_UO were conÈinued in Fleld 2; a slgnificant, decrease 1n plant numbers in T* (compared to T40-60) occurred after the second main period of abundance of SAA (l"fay L979) with a further decrease following the next wlnter and spring (December L979) (Table 4.3). The loss in plant nuubers ln T" from October 1977 to -5 3-

December 1979 was abouÈ 85% compared to 28% ln T+O-OO. The loss of plants in

TaO_OO was significanÈ (t3g = 2.04, P<0.05) and was probably attributable previous three years nainly to the adverse effects of the low rainfall of the ' especially during tlne L977/78 summer, rather t,han to SAA', per se. Such reductions in denslty of lucerne plants durl-ng dry perlods had earlier been demonstrated in pastures in the Upper-South-East prior to establishment of SAA

ín the reglon (Snith 1972>.

The pattern of negligible losses of plants during the first year of SAA followed by severe losses in unprotected lucerne in the second year vras consistent with subjective assessments trade by landowners and district agronomlsts in the region. Severe losses. of lucerne plants in commerclal fields following the second year of SAA were attributed by farrners and agronoml st,s to a number of causes, e.g. the dry seasons, oversËocking - which resulted from low prices for llvestock t,ogether wlth poor growEh of lucerne due to dry condítlons

- and damage by ínsects other than SAA, especially wingless grasshopper, as well as SAA. However, the considerably lower number of plants in T¡ compared to

T¿O-OO in Deceuber 1979 denonsÈrates that SAA rùas a najor factor i-n the decline in plant density since 1977 (Table 4.3). After L979, the Ereatment, T¡, was noÈ continued for a further year in

Field 2 because of'the severe losses of plants already sustained. If the treatmen! had been continued for a thlrd year, there would probably have been further plant losses because, coÍtmercfally, an estimate of only about 5 to Ili¿ of the origfnal 600 000 ha of dryland lucerne pastures ln the Upper-South-East survived the third year wiÈh SAA. This dranaÈic loss in stands of lucerne rÍas due to the relucÈance of rnost landowners to protect dryland lucerne pasture ¡¿ith chernLcal insecticides, as dlscussed later, so the experience in the Upper-Sout.h- East clearly paralleled Smlthrs ( 1959) finding that SAA was "the most destructive and spectacular pest of alfalfa ever to enLer that staEe (California)". -s4-

TABLE 4.3 Mean denslty of lucerne plants in treatments with nil insecticide and lnsecticide at 40-60 SAA/sten of lueerne, Field 2, Culburra, f978- 1979.

Date I'fean density of lucerne Value Probability plants (r-2) in treatment: of E3g

TN T 40-60

0ct r977 8.1 6.8 1.42 NS, P < 0.05

May 19 78 8.1 7.2 0. 68 NS, P < 0.05 Jan L979 5.4 6.6 0. 95 NS, P < 0.05 I(av r979 2.4 5.5 3.44 P < 0.01 Dec 1979 l.l 4.9 8. 78 P < 0.01

NS - not significant

(u) AoaiLabLe tuI of Lueømp The weight of available Ill of lucerne herbage at the end of each regrowth period for the dlfferent treatments in each field for the first year with SAA are given in Table 4.4. In Field 1, the Il{ ín T46_69 was significantly less (P<0.05) than that in one or more of the oEher treatments each time the DMs differed between t,reatments. The lower ll'fs ln T+O-OO could not be attributed logically to the effects of different densÍÈles of SAA in Ëhe treatments because SAA was always less abundanÈ in T+O-OO due t,o the applicatl-ons of chenical insecÈiclde

(Appendix 4,2); but the lower DMs nay be explained by the uneven topography fn Field l. Field I was the nost undulaÈing field and, by chance, T40-60 tt" allocated an area wiÈh the deepest sand 1n the experlmental site, such sand being less productive for lucerne plants Ehan shallower sand in the site, especially in dry years. For this reason, daÈa on Èhe avallable IM of lucerne frorn Field I w'ill not be lncluded 1n further discussion. -55-

TABLE 4.4 Mean available IM of lucerne (kg ha-t) at the end end of regrowth periods for each treaEment in each field, and the peak densiLy of SAA in T" for each regrowth period, Culburra, t978.

Fleld Regrowth Peak densiÈy l'lean D'f* in treatment: perlod of SAA in TN I T40-60 Tt8o-zoo Tv TN ending: I 10.02.78 60 140 140 170 2r0 23.03.7 I 240 56 58 60 38

5 .05 .78 270 68b 130 a 180 a 180 a 16.06. 78 110 25 20 20 L7 28.07.78 25c 52b 9la 34 bc 8. 09. 78 57 7L r00 74 20.10.78 120 c 200 ab 260 a 140 bc L.12.78 0.5 370 690 980 760

2 17.02.78 r50 r60 140 190 190 31.03.78 380 60a 34b 18b 7c I 2.05. 78 40 r50 100 r30 92 23.06.78 170 55a 23b 22b 25b 4.08.78 89 36 7Z 63 r5. 09. 78 160 76 150 92 27.r0.78 230 165 180 180 8. 12. 78 0.5 990 b 600 b 1700 a 840 b

3 24 .02 .7 I ó10 150 170 r80 160 7.04"78 580 60a 19b 17b l0b r9.05 .78 30 170 120 220 160 30.06.78 70 120 a 43b 44b 52b I I .08. 78 r60 94 130 rl0 22.09.78 340 a 67c 260 a 150 b 3.1r.78 52Q a 180 c 370 b 220 c L5.L2.78 0.5 420 a 170 c 310 b 220 bc

4 7.03.78 700 170 ab 210 a lI0 c 130 b 14.04.78 430 59b 29c L2Q a 97a 26.05.7I 30 r90 r70 r80 r80

7 .07 .78 20 94 130 120 94 r8.08.78 200 260 r80 170 29.09.78 630 430 490 360 10. I 1.78 52O a 400 b 500 ab 240 c 2r.12.78 0.5 460 440 370 440

t l,fean number of SAA per stem of lucerne. * Mean Ilfs followed by the sone letter at the end of each regrowth perlod are not slgnlflcantly differenÈ at P ( 0.05 (Appendlx 4.8). -56-

In Fields 2, 3 and 4, the DMs ir T4O-60 r{ere consistently more than those in the other treatments whenever the D{s were significanÈly different (P<0.05) bet\reen treatments (the predominance of the syubol "a" - used Eo indicate the highesÈ IMs at each t,íme of sampling - under T4O-OO 1n Table 4.4 clearly demonstrates the occurrence of more IM in T+O-OO). The dífferences in Dt'l occurred in t:t,¡o periods of the year, initially from March to June (summer Eo early-winÈer) when SAA was most abundant, and then from September to December

(spring) when SAA r¡tas scarce. In Ehe first period, the higher IMs in T+O-OO only occurred when the peak denslty of SAA in T* exceeded 40 per stem (Table

4.4); these higher XMs were attributed to less damage by the lower densities of

SAA in T¿O-OO than in other treetmenÈs (Appendices 4.3, 4.4 arrd 4.5). tr'Ihen peak densitíes of SAA in T* were 40 per stem or less during summer and early- winter, the Dl"fs for each treatment were similar (Table 4.4).

The higher production of IM in T¿O-OO in Fields 3 and 4 in spring

compared to oÈher treaËments (Table 4.4) was noÈ expected and will be dlscussed in the following sub-section on carbohydrate reserves in lucerne rooEs.

At some times in both the summer to early-winter and spring periods, D4s in

some treatûents r{ere eiEher more or similar to those it T40-60, ê.9. on 8

December 1978 in Field 2 arrd a number of tines in Field 4 (Table 4,4). The

similar or higher Ilfs in Ty compared to T+O-OO in Field 4 were difficult Èo explain, especially as densities of SAA in TU were considerably higher than those ir T40_60 (Appendix 4.5). Much of TU was on some of the more shallow,

hlgher productive sand in Èhe experimental site, but the prevalence of this soil

type ln TU was not considered to fully explain the dlscrepancy.

T* TOO-ag end each regrowth period The levels of Ilf 1n and at the of ' together with the peak density of SAA tn Tt for each regrowth period' for the experiments in L978/79 and L979/80 can be eompared in Figure 4.2. The peak

densities of SAA ín T* exeeeded the upper threshold density of T40-60 (i.e. -57 -

60 SAA per stem - represented by the upper broken line for each year in Fígure 4.2) ín tero regrowth periods in 1978/79 and in three It L979/80. In four of

these five regrowth periods, T+O_OO yielded sígnlficanÈly nore I}f than TN; the hlgher IMs ir T40-60 vrere attributed to the lower densíties of SAA in

T¿O-OO due to the application of chemlcal insecticide (Appendíx 4.7). In the other regrowth period (ending 31 }farch 1980) , the Ilfs in T* and TOO-Ug r.rere

simllar, even though the density of SAA in T* well exceeded Ehe threshold density (Appendix 4.7); in Èhis inst,ance, the similar Xl"ls were contrary Èo the postulated trend. In both 1978/79 and L979/8O, the DMs in T* and T4O-UO were simílar whenever the peak denslty of SAA in T* was less than 60 aphids per sten (Figure 4.2).

The differences in IM beÈween T¿O_OO and T" measured at the end of each regrowth period in both 1978/79 a¡d 1979/80 were similar to Ëhose ít L977/78,

i.e. T¿O-OO usually yietded significantly nore IM Èhan T¡ when densities of

SAA in T" exceeded 60 SAA per sten of lucerne.

The relationships betrüeen IM and denslty of SAA each week duríng three regrowth periods in 1979 are shonn in Figure 4.3. In the first regrowth period,

the density of SAA was similar in T* and TOO-UO for the first two weeks

after grazing, then SAA rlas rnore abundant ln T* than ln T+O-OO because aphids were controlled ír T40_60 with two appllcations of chemical Ínsecticide

(Ftgure 4.3a'). The influence of the higher density of SAA fn T* on IM was

not apparent until after the third week; SAA suppressed the production of IM during the fourth week then caused a narked loss ín IM during the flfth week (Figure 4.3a). At the end of both Èhese latter weeks, the IDI in T* was sfgnlficanÈly less than that 1. T40-60 (P<0.05, t7g=2.75 and t7g=4.00,

respectively). The large decrease in t,he numbers of SAA 1n T* in the fifth week was due to severe deterioration in the quality and quantiÈy of lucerne

herbage caused by SAA. The densíty of SAA in T+O-OO rapidly j-ncreased above -58-

1978t 79

3 NS It 600 t* *,1

400 ! .o oL o-

NS _c. 3 -c 10 NS 200 o E L o E t_ t_ ooì 60 L lr0 0 coì E L o 8112 22t1 5ß 17tt 28t5 o ) ì E' 1979 / 80 ro II.DO Ð0 NS E a ol_ ilr* o 1200 b o.

'l o E 1000 < ol U1 -J

o o I00 oL o -o c e L J o C o 300 60 0 J J J o ùo 400 NS

,***

1 N 200

NS 60 lr0 0 26t11 7 t1 18t2 31t3 12t5 23t6 NS not signif icont rrl p < 0 01 *r*- p ( O.OO1

FIGURE 4.2: Mean available lucerne Df in treaEment," T40-60 (left hand column) and T¡ (right hand column) after 5 r¡eeks regrowth at dif f erent, tl-mes of the year, Èoget,her wl-th corresponding peak mean number of SAA fn T¡(x-x), Culburra, L978/79, I979/80. -59- the treatment Ëhreshold ln the fourth week (Figure 4.3a). This increase in density caused a decrease (P(0.10) in IM ir T4O-60 durlng the fifth week, even though the aphlds rüere treated with chenical insecticide aÈ the end of the fourth week. The loss 1n Ilf w'IËh Lhe rapid i-ncrease in the numbers of SAA in

T¿O_OO supported the hypothesLs thaË low threshold densitles of SAA had to be naintalned to naxlnise production of dryland lucerne plants. It also emphasised the problem of malnÈaining SAA aÈ such a low threshold during favourable periods of the year for SAA, especlally in commercial lucerne pastures whlch are usually grown 1n large fields on large propertl-es.

In the second regrowth period, the density of SAA in T* was greaÈer than h T40_60 during the last two r¡eeks due to the use of chemical Lnsectlcide ln

T+O-OO (Figure 4.3b'); the hlgher densities of SAA 1n T* reduced Ehe overall rate of lncrease of Ilf but did not cause rapid decreases in ll'f, as in the first regrowth perlod (FÍgure 4.3b). One reason for the different patterns ln the loss of ll'f 1n T* between the first and second regrowth perlods was possibly the lower numbers of SAA in T* in the second regrowth period. The lower denslty of SAA was nalnly due Èo lower ambienÈ temperatures in the second regrowth perlod conpared to the first. The higher llf in T¿O-OO Èhan in T* after only two weeks (P<0.001, t7g=3.47) mey have been due to an error in sampling IÌ1 because the densities of SAA durlng the Ewo weeks were sírnilar in both treatments and were less than the densíty of SAA expected to cause a loss of IM. The rapld lncrease in the number of SAA ir T40-60 in the thl-rd week did not cause the marked reducÈl-on fn Ilf experÍenced rü1th a similar increase in

SAA in T¿O_OO in the ffrst regrowth period.

In the third regrowth period, the rates of lncrease of both IM and SAA were consLderably lower than the t$to previous perlods, nainly due Eo decreasing ambient, temperatures from February Èo June (Figures 4.3c and 4.3c'). T¿O-OO had significantly more I!1 than T¡ after four weeks (P(0.05, t7g=2.45), -60-

(o) zg1.z9 - s3.29 (o') 29.i.79 5.3.29 6

5

I I a 30 3 + t c

200

o 1 0 C 3- (u (J J

To o E E t, ol (bl 12 .3 .79 - 17 . t, .79 o (b') 12. 3 . 79 - 17 . .79 j I o o o- i o t o c tJ) o )o o1

o ø ã oC : E o o lcl 21. t, .79 - 28 .5 .79 (u (c') 2t, . t' .79 28. 5 .79

æ0 o

1

123/.5 123 /.5 Weeks ofter grozing Weeks ofter g rozi ng

x-x T¿o-oo ' T lnsecticÍde: ï¿o-oo '-' N I-

o-P< 0.05 b-P<0.01 c-P< 0.00'l

FIGTIRX 4.3: The available mean lucerne DM and the correspondlng rnean density of SAA l-n treatmenÈs T* and T46-69 each week during the four regrowth perl-ods f rom 29 .L.79 to 28.5.79, Culburra. -6 r- though this dlfference may have been a sampling artefact for two reasons. The first reason was that, if there lras to be more D'f in one treatment, Èhan the other, more would be expected in T* because the density of SAA was lower in

Too than ir T40-60; the second was that Ehe density of SAA in T+O-OO in Èhe fifth week dld not seem Èo be sufflciently high to cause the apparent reducÈion in IM io T40_60 durLng the flfÈh week.

The relationships beEween I!1 and densiÈy of SAA during four regrowth periods in 1980 are presented Ín Flgure 4.4. The lower yields of ll"l in both treaEments during the regrowth periods in 1980 conpared to IMs in the corresponding periods in 1979 were naínly due to low rainfall from December L979 to I'farch 1980 (Flgure 4.1). The only dlfferences in.Ilf between T* and

T¿O_OO in 1980 occurred Ln the first regrowth period when TOO_6,9 yielded more IM Ehan T* after both four and five weeks after gtazi-ng (P<0.001, t7g=3.48 and E7g=4.44, respectively) (Figure 4.4a). These differences in Dl'f could be aÈtributed to the higher numbers of SAA in T¡, following the application of chenical insecticide Èo T¿O_OO at the end of Èhe second week

(Flgure 4.4at ) . The marked decrease in the numbers of aphids in T* in the fifÈh week was due to a reduction in the qualiÈy and quantity of lucerne herbage caused by SAA - a phenomenom similar to that in Èhe first period in L979 (Flgure 4.3a'). In Èhe second regrowth perÍod in 1980, T* and T+O-OO produced similar yields of IM (Figure 4.4b), even Ehough the density of SAA in TN did exceed the threshold of 60 SAA per stem (Figure 4.4br). The poor growËh of lucerne ln this regrowth perlod nay partly explain why the Ills in T* and

T+O-OO were simílar. The densíties of SAA renained low ln both T* and

T¿O-OO in the third and fourth regrowÈh perlods (Figures 4.4et and 4.4d') and, consequently, Èhe Dl{s did not differ slgniflcantly between the treatments in either perlod (Figures 4.4c and 4.4d). -62- (o) 14,1 , 80. - 18.2.80. (o') 14.1. 80. - 18.2 .80 s00 50

400

30 I 20 t c 1 \.

o C L o (b) - o (u) 2s. 2.80, 3.3 80. 2 2s 2.80. -31.3 80 f' trt c, o ol I J E t o 1 o 100

o ot- o- o c o Ø o (c 7 .4 80 12. s.80. 7. t, 12.5 .80 ) ) - 300 el 80 - o o o 'õ I o c o t õ 1 !

C o o

(d) 19. s. 80 - 23. 6.80. (d') 19. 5 . 80 23. 6.80 3 300 -

2

1 1

1 2 trs 3t, Weeks o Weeks grozing fter .groz ing ofter I-X T¿o-oo .- TN I - insecticide: T¿O_OO c- p<0.001

FIGT]RE 4.4: The avallable mean lucerne DM and Èhe correspondlng uean denslty of SAA ln treatment,s T¡ and T4O-US each week during the four regrowth perfods fron 14.1.80 Eo 23.6.80, Culburra. -63-

The above relaÈLonshlps between IM and densitíes of SAA denonst,rate the need to naintain SAA below about 60 SAA per stem throughout the regrowth perlod and also the need to inspect lucerne pastures no laÈer Èhan two weeks after severe grazLng to deternlne wtrether control of SAA is necessary. (oí) Canbohydrate neserÐee in Lucerme noots

An lnteresting feature of the production of lucerne E["f in 1978 was the higher Dì,fs tn 1¿O-OO compared to other treatments l-n sone fields durLng the perlod, October Eo Deeember, in the absence of SAA - as dlscussed 1n lul above and shown in Table 4.4. Reasons for this feature are not known but uay be due to a reduction 1n the vigour of lucerne plants in T* from approxlmately March to November, as suggested by Èhe signlficantly (P<0.05) lower percentages of TNC ln lucerne tap-roots l-n Tl{ conpared to T¿O_OO durlng that period (Figure

4.5). Levels of TNC three days after grazlng represented the TNC available to pronote early regrowth and is probably the most realistlc comparison between treatments; levels at 24 days after grazlng probably represented the lowest levels of TNC in lucerne during the regrowth periods and provided the smallest, dlfferences between treatments.

The use of percentage TNC to explaln the above differences in apparent vfgour of lucerne should be used wlËh caut,Lon. Graber et aL. (L927) suggested that accumulated root reserves (carbohydrate and nitrogen) lintÈed the amount of top and root regrowth of lucerne and other perennlal, herbaceous plants followlng harvesElng. SubsequenÈly, conslderable work was based on Èhe premlse that the percentage carbohydrate in roots at the tine of cutÈfng foliage was the sfgnificant determlnant of the ability of plants to resune grorüth (Mitchell and

Denne L967). Davldson and I'filthorpe (1965) considered thet this ernphasls on percentage TNC over-simpllfied the relationshlp and that t,here tsas llttle evidence Èo support 1È. They studied carbohydrate reserves in Èhe regrovtth of cocksfoot, Daety'Líe glomerata L., and hypothesised from thelr data that -64-

3 doys ofter grozing T 40 t I 2. SE

30

(Jz l- o 20 s o o T¿o-oo Ix TN 10 T

30 21, doys ofter grozing t 2.SE

20 u z t- s TN 10 r¿o-oo

MAMJJ ASONDJF 1978 1979 o - P<0.05

FIGIIRE 4.5: Z TNC 1n the cop 15 cm of lucerne tap-roots in treatmenEs T¡ and T40-60, 3 and 24 days afÈer eaet:. grazing cycle from March 1978 to February L979, Culburra. -65-

"reserve carbohydrates form part of a lablle pool and are used for the synthesis of new compounds and respiration when photosynthesis is resËricted" and that

"thls lab1le pool contributes significantly Èo nerü grohrth only during the first few days followlng defoliation and the extent of its contribuÈion depends on the severiEy of defoliatlon and on the level of the envlronmental facÈors influencing growt,h and of those influenclng phoÈosynÈhesis". At Culburra, lucerne Isas severely defolLated at each tine of grazing and, perhaps, TNC togeEher w-1Ëh oÈher root reserves were importafiE to promote vlgorous, early regrowth whlch then maxlntsed any beneflÈs from the plantrs environment, Ehus ensuring a greater production of herbage wfthin the five-week regrorrth period. If the regrowth perfod was longer, the vigour of l-nitlal regrowth nay not have been as lmportanÈ and final Ilf uay noÈ have differed; in such a case, there mey not have been posltÍve relationships between percentage TNC and Dþf. The apparent beneficial effecÈ in late-winter and spring from protecÈing lucerne ¡vith chemical insectlcide durlng sunmer and autumr Iüas contrary to Burkhardtrs (1959) experlence ln Anerica; he found that treatmenÈ of SAA in lrrlgated lucerne stands in autumr did not increase yields in spring, though it dtd slíghtly increase the quallty of lucerne herbage. However, the results aÈ Culburra dld agree wiÈh Kain et aL. (1979) and Fick and Lui (L976) who studled the effects of dífferenÈ specles of insects on lucerne in New Zealand and

Amerlca, respectl-vely. Y,al-r' et aL. (1979) showed that damage by bluegreen aphid, Aeyrthoeiphon l

Sirnilarly, Flek and Luf (1976) demonstrated that alfalfa weevil, Hypera poetiea (Gyllenhal), can reduce levels of TNC in lucerne roots and Èhat hlgher levels of TNC were followed by hlgher yields of forage. -66-

The levels of TNC in lucerne rooEs at Culburra in 1978 were mrch lower than expected for lucerne plants grown on siliceous sands fn the Upper-South-East;

SniÈh (L972> studied the grazing üBnagemenÈ of dryland lucerne pasture in the

Upper-South-East and estimated Ëhat there was 43% TNC 1n lucerne ÈaP-roots three days after gtaz1-rrg in March 1969, in a treeÈment \ülÈh the s¿rme rotation and stocklng raÈe as at Culburra. IIe also suggested that plant deaÈhs occurred with

TNC T* and T40-60 levels below about 16Z TNC. The levels of in both "t Culburra in 1978 were lower than 43z^ and, at t,1mes, lower Et.ar' L6% (Ffgure 4.5) which nay reflect the stress on planÈs caused by the previous tlro years of dry weather, and may partly explain Èhe loss of plants it T40-60 durlng the second year afÈer establlshment of SAA ln Èhe region, even though they were protected wlth chenical insecticlde.

4.5 Influence of SAA on the Growth aad llf of Indlvidual Plante of Lucerne Ln rhe Fleld The experiments ln Sectiot 4.4 quanÈified the gross effect,s of different densities of SAA on the lt"f production of lucerne herbage in lucerne-based pasÈures. The following series of experiments attempÈed Eo deËeml-ne the components of herbage yield which were mainly affeeted by SAA. In Èhese experlments, the number of basal br¡ds and number and length of stems per plant nere compared beÈween lnsecticldally treated and untreated lucerne plants in the experimental s1Èe at. Culburra. 4.5.f Materlals and æthods At the beglnning of the regrorùth perlod, 12 March to 16 þril 1979, 20 paírs of lucerne plants were selected in both t,reatmenÈs T* and T49-69 1n Field 2 so Èhat the plants in each pair were near Eo each other and norphologlcally simllar. One plant of each paÍr was selected at random and kept free of SAA with four applications of 0.15% derneEon-s-Dethyl applied w'ith a hand applicator; the other ¡sas allowed to become naturally lnfested wíth SAA. The -67- number of basal buds per crorün was estlmated just after severe grazl-rrg by sheep and then the number and length of stems for each plant r¡ere estimated at 14, 2I and 28 days after grazing. Each plant was harvested at ground leve1 after 35 days; total Ilf per plant ¡sas estimated by drying Èhe cut herbage from each plant separately in an oven aÈ 90oC for 15 hours and then weighlng 1t. Ttre aphíds on each plant \úere not counted because the counting of aphÍds requlred desÈructl-ve sanpling of the plants; so the mean densiËy of SAA on untreated plants in T* and T40-UO !¡as consldered to be similar to that estlnated for the populatlon of SAA in T* and T4O-OO at, corresponding times

1n Èhe experiment in Sectlon 4.4. An exceptlon was in T49_60 after 2l days after gtazing; at this tlme, the rshole of T4O_6O lras sprayed wfth chenlcal insectlcide for the experiment Ln Sectfon 4.4. Because T¿O-OO needed t,o be sprayed, Èhose infested plants being used 1n the lndividual plant experiment plus 20 extra plants, selected aÈ random 1n T+O-OO area, were covered w'1th plastfc buckets Èo protect them from chemlcal insectlclde. The extra plants were used to estinate nean densities of SAA which could be expected on Èhe naturally-infested, experinental plants at those sanpllng ÈÍmes after 2I days after grazlng,

In 1980, this experiment rúas repeated three t.lmes usl-ng the same 20 palrs of plants tt T40-60 in Field 2 durlng regrowth periods l1 February to 19 I'farch, 24 March to 24 þrt1, and 5 May to 5 June, respectively. The nethods were sl-milar to L979, excepË that denslties of SAA on l-nfested plants were esÈimated by sanpllng a single sten from each of three plants around each pair of experimental plants at each tLrne of sanpllng; both the planEs and the stens were selected at random às fn Section 3.2.L. The numbers of SAA per st'em r,rere evaluated using the same washlng method as in SecÈIon 3.2.L. In the lasÈ trùo regrowth periods, rean length of sten lnternode for each plant was estlmated by selecting flve stems per plant at random and m-easurlng the length and number of internodes for each stem fron the basal node to the last. fully-developed node. -68-

DaÈa were analysed using Studentrs t-test to separately compare different componeriÈs of growÈh for lnfested and unínfested plants at each sanpling time. 4.5.2 Results and dlscusslon

The only component r¿hích was significantly affected (P<0.05) by SAA was the number of sterns per plant after 31 days on lucerne plants whLch lüere protect,ed ín 1978 (Figure 4.6b). Ttre lower numbers of stems on the infested plants were attríbuted to high densitles of SAA, though the true denslty could not be esÈinatedr apparently due to disturbance of aphids when the Plants were covered with buckets to avoid them from belng sprayed wlth chenlcal insecticide, as dlscussed in Materials and rnethods. Ilowever, visual assessment of these infested plants and infested plants which Iüere unproÈected in 1978 and noË covered w1th buckets, suggested Ehat densítles of SAA were not narkedly dÍfferent between the two samples of plants aÈ the same tlmes. The naln differences between uninfested and lnfesEed plants which eould be attrLbuted to SAA were the higher total stem lengths per plant (Figures 4.6d and

4.7d) and Il"1 per plant (Table 4.5) in the uninfested plants. These final parameters of yield are obvlously related and rely on a comblnation of the above components.

TABLE 4.5 Mean Ilf of individual lucerne plants, infested or unÍnfested rrith SAA, five weeks after grazing, Culburra, I979, 1980.

Date Lucerne -SAA +SAA Significance

17 .4.79 Protected 1978 r0.2 5.4 ) LSD (0.05) = 2.6 Unprotected 1978 10.8 6.8 )

19. 3. 80 5.1 3.3 t1g = 2.43 P<0. 05 24.4.78 2.5 r.7 t19 = 1.90 P<0 .05 -69-

Lucerne ptonts -protected 1928. Lucerne plonts - unprotected lgz8 (o) 400 r-o OC O-L o

tJ', Þ o n o .(uE zoO+

(b) 6 Ø E o 6C o \ x äõ_ oo L z. o-

(c)

EEOc Á Eol oc

d) b c E oì oEf-- E L @= oo õ- E 100 +Loo F- o_

10 20 30 10 20 30 Doys ofter grozing Doys ofter grozing

o- P < 0.05. b- P< 0.01. c- P < 0.001.

FIGI]RE 4 .6: Mean densiËy of SAA on unprotected plants (a), and nean number of basal buds and stems (b), rnean sEen length (c) and total stem length per plant (d) for lndividual plants ¡slth SAA ('-.) and wlthouÈ SAA (x-x) at dlfferent tlmes after grazJ-ng was completed from 12.3.79 Eo L6.4.79 for lucerne plants that were either proEecÈed or unprotected fron SAA in 1978, Culburra. -7 0-

This seríes of experlments did not clearly demonstrate whether one component of yield was more affected by SAA Ehan others. However, damage by SAA appeared to occur in the latter half of the regro\ùÈh perfod and rüas a resulÈ of increasing numbers of SAA removing excessive quantlÈl-es of sap from plants which caused stems to shed leaves and becone dry; this damage was similar Èo that described by MftÈler and Sylvester (1961) and was mainly responslble for Èhe dlfferences in DM.

SAA was expected Èo reduce the yleld of I!1 by reducing the number of stems early Ln the regrowth period; the yield of regrowth of llunter River lucerne depends primarlly on the number of shoots and the Èinne when each resumes growth after cutting (grazíng) (Leach 1969). Dffferences in llf between Ereated and untreated plants could noÈ be aEtrlbuÈed to fewer stens 1n the untreated plants early 1n the regrowth perl-od because the number of stems !Íere noÈ reduced by SAA aL Èhat time, probably because the experlments tested the influence of SAA on the growth of lucerne plants 1n a rotatlonaLLy grazed system where initial numbers of SAA present on basal buds and young shoots lnnediately after grazLng Itere generally very low. If the lucerne was not as heavily gtazed and high numbers of SAA survived grazlng to lnfest young shoots, the aphlds may have caused sf.gnlficant losses in the numbers of stems per planÈ early 1n the regrowth perlod. Then protectlon of shoots ln the first, week rnay be necessary to prevent losses in the number of stens and Dt'í. The experiments in Sectiort 4.4 also showed Èhat, when SAA danaged lucerne in the grazLng system used at Culburra, the flrst signlficant losses occurred late in the regrosrth cycle.

Data from the experiment conducted from 5 May to 5 June, 1980, could not be lncluded in the dlscusslon because experlnental plants became heavily fnfested

¡,¡'tth redlegged earthrnlte , HaLotydeus d.estmteton (Tseker) , rvhich could not be controlled independently of SAA; so the amourit, of damage caused by each pest could not be separated. -7L-

11.2.80 - 19-3 80 2t,3 80- 2Lt,80 (o) lr0

LO OC 3 O-r

(b) 60 U' E (u 40 o aco Ëã. õb 2 ¿,d

(c) 1 E^oç oE

l-+_7 ogl OC =o

(d 4000 s ol 30 Oc -L E Cv c LÞoc fio o- ú 1000 Ê3. 10 20 30 10 20 30 Doys ofter grozing Doys ofter grozing o:P<0.05 b- P<0.01 c-P<0.001

FIGURE 4.7: Mean denslËy of SAA on unproÈected planÈs (a) ' and mean number of basal buds and stems (b), mean stem length (c) and total sEem lengÈh per plant (d) for lndividual plants wi¡h SAA (.-.) and wlthout SAA (x-x) at different Èimes after grazLng was completed from 11.2.80 to 19.3.80 and from 24.3.80 Eo 24.4.80, Culburra. -72-

4.6 Economic lAreshold for SAA ln Dryland l¡¡cerne Paeture

Kain and Atkinson ( 1975) concluded EhaÈ the accurate determination of economí c thresholds for insect pests of pastures was not feasible and thaÈ a saÈlsfacËory compromlse would be reached when densities of pasÈure pests can be predlcted Eogether vrlth Ehelr damage; this lnfornat,lon could then be used by landowners to make a decision on whether control measures should be lnplemented. TheLr prudence on economlc thresholds for pasture pests ls partly based on problerns of lnfË1ally converting losses l-n pasture quality and quantity lnÈo anirual production and then into monetary equivalenÈs, especially as value of livestock can vary rnarkedly within relaÈlvely short perLods.

Data from Èhe experimenÈ at Culburra. did províde information for the predictlon of densltles of SAA (Seetlon 3.3.1) and damage caused by SAA, but, slnilar to Kain and Atkinson (L975), a deflnite economlc threshold or range of thresholds was dlfficult to esÈablish. The nain graztng experiment demonstrated that severe losses of lucerne plants, 1n excess of 85i[, could be expected within tlso to three years 1f mean densLÈ1es of SAA rùere not rnafntained belo¡s about 60 SAA per stem of lucerne; such losses would halve Èhe potential livestock production of lucerne-based, dryland pastures. Ttre experiment also demonstrated that production of IM of lucerne herbage was slgniftcantly reduced lf densitles of SAA exceeded the above

Èhreshold. However, the actual quantiÈy of Ill saved by controlllng SAA wlth chemical insectlclde varied considerably, depending on the season, e.g. the snall quantlties saved in the dry surnmers of 1978 and 1980 cornpared Eo 1979 were probably not JustffLed econornically, especLally conpared to the cost of regular lnspectlon of pastures Èo determine ¡vhen to treat and Èhe need for at least three appllcaÈions of chenical lnsectlcfde per year. For these reasons, the need to nalnÈain vfable densl-tles of lfunÈer Rlver lucerne plants in pastures on a particular propercy lras the maln crl-ÈerLon for -7 3- accePting 40 to 60 SAA per stem of lucerne as an economig threshold, and this need varied considerably between properties. Ilowever, siuilar to Kain and Atkínson (1975), landowners'decÍsions to treaÈ SAA 1n dryland lucerne pastures in the Upper-South-East were based on "lntuiÈion, alternative courses of actlon and socio-economis factors". For the mosÈ part, thls low threshold, which was necessary to naintain lfunter Rlver lucerne pasture, elas not accePted 1n the reglon because of (a) the Ínherent difffcultles, as well as cost' in maintalnfng low nuubers of SAA on propertles with large areas of pasÈure, (b) the bellef that native predators and introduced parasiEes would effectively control SAA'

(c) the avallabl-llty of SAA-resisEant culËlvars of lucerne, and (d) in some areas, the use of alternative crops, e.g. cereals and lupins, for Lmproving short-term cash flow, at least. 4.7 References

Anon. L973. Determination of soluble carbohydrates in herbage. fn Tt:.e

Analysis of AgrfculÈural Materlals. Min. Ag. Flsh. Food. Tech. 8u11. 27

(Lond. ) . Burkhardt, C.C. 1959. Effects of heavy fall ínfesEatíons of spotted alfalfa aphids on subsequent sprlng growth of alfalfa in Kansas. J. eeon. Ent. 52| 642-643.

Davidson, J.L. and ltilthorpe, F.L. 1965. CarbohydraÈe reserves in Èhe regrowth of cocksfoot (DaetALie gLomerata L.). J. Br. Gnaseld. Soe. 20: 115-

I r8.

Dickson, R.C., Laird, E.F. and Pesho, G.R. f955. The spotted alfalfa aphid.

HíLgardia 24 93-Lt7.

Fiek, G.I,f. and Lul, B.I{.Y. 1976. Alfalfa weevll effects on rooÈ reserves'

development rate and canopy sÈructure of alfalfa. Agron. J. 68: 595-

599. -7 4-

Graber, L.F., Nelson, N.T., Leukel, W.A. and Albert, I^I.B. L927. Organic food reserves in relatlon to t,he growth of alfalfa and other perennial herbaceous plants. Unlv. tr{is. Agric. Exp. Sta. 8u11. No. 80: 3-128. Hanson, C.H. f961. Moapa alfalfa pays off. Crope SoiLe 13: LI-L2. Ilowe, I{.L. and Snlth, O.F. L957. Reslstance to the spotted alfalfa aphid in Lahontan alf alfa. J. eeon. ht. 50: 320-324.

I(aln, I,l.M. and Atkl-nson, D.S. L975. Problens of insect pest assessment 1n pastures. N.Z. Eltt. 6z 9-13.

Kain, W.M., Atkinson, D.S., Oliver, M.J. ârd Stiefel, tr'l. 1979. Pest assessment sÈudles of blue green lucerne and pea aphids ln the southern North Island

of New Zealand. Pnoc. 32nd N.Z. hlee! and. PeBt Contr. Conf. : L7L-L79.

Kindler, S.D., Kehr, I.I.R. and Ogden, R.L. L97L. Influence of pea aphíds and

spotted alfalfa aphlds on È,he stand, yield and dry xoaEter, and chenical

composftion of reslstant and susceptible varleties of alfalfa. J. eeon. Ent. 642 653-657. Leach, G.J. f969. Shoot numbers, shoot size, and yield of regrowth in three lucerne cultÍvars. Auet. J. agnie. Res. 202 425-434. Loper, G.M. 1968. Effect of aphld infestatlon on coumestrol conEent of alfalfa varietíes differtng in aphid reslsÈance. Crop Scí. 8: 104-106. I'flÈchell, K.J. and Denne, M.P. 1967. Defoliation and root development of

lucerne. fn The Lucerne Crop. Ed. R.II.M. Langer. A.H. and A.l,l. Reed. 314 pp. z 2L-27. lllttler, T.E. and Sylvester, E.S. 1961. A comparison of the lnjury Lo alfalfa

by the aphids , llten'Loaphís rrueuLata artd Maeroeiphwn píei. J. eeon. Ent. 542 6L5-622. Nickel, J.L. and Sylvester, E.S. 1959. Influence of feeding time, stylet penetratfon and developmental lnstar on the toxlc effecÈ of the spotted alfalfa aphid. J. eeon. Enþ. 522 249-254. -7 5-

Nielson, M.trI. and Barnes, O.L. 1961. Population studies of the spoeted alfalfa

aphid in Arizona in relaÈ1on to temperature and rainfall. Ann. ent. Soe. Am. 542 44L-448. Northcote, K.H. 1979. A Factual Key for the Recognition of Ar¡stralian So1ls. 4th Ed., C.S.I.R.O. Rellin Technícal PublfcaÈlons, S. Aust. I24 pp.

Nuorteva, P. f956. Studles on Ehe effect of the salfvary secretlons of some

Heteroptera and Ilonoptera on plant growth. Suom. Hgont. Aikak. 222

r08-1 r7 .

Parker, R.V., Burton, V.E. and Smith, R.F. 1956. Aphid darnage to alfalfa hay. CaLif. Agrie. l0: 5, L2. Paschke, J.D. and Sylvester, E.S. 1957. Laboratory studies on Èoxic . the effects of Thenioaphíe ma.culata (Buckton). J. econ. Ent. 50: 742-

7 48. Reynolds, H.T. and Anderson, L.D. f955. Control of the spott,ed alfalfa aphid on alfalfa in souÈhern CalLfornla. J. eeon. Ent. 48: 67L'675. Reynolds, E.T. and Dickson, R.C. 1955. Yellow clover aphid on alfalfa - chemícal control. CaLif. Agrie. 9: 5, 15. Reynolds, Il.T., Snith, R.F. and Swift, J.E. 1956. Insectlcides for alfalfa aphfd. CaLif. Agrie. I0: It-12.

Russell, J.S. 1960. Soils of SouÈh Australla - the deep sands. J. Dep. Agrie. S. Auet. 63: 298-307. SBith, D. f969. Renoving and analysing total non-sÈructural carbohydrates fron plant tl-gsue. Unfv. I{Ls. Agrlc. Exp. Sta.8u11. No.4L.

Snith, I'l .V. 1970. Effects of stocking raËes and grazLng nanagement on the perslstence and productf-on of dryland lucerrre on deep sands. Pnoe. XI

Int. GnaseL. Cong?. Univ. Qqeensland Press : 624-628. -7 6-

Smlth, I'f.V. L972. The ecology and utílization of dryland lucerne pastures on deep sands ln the Upper SouÈh East of South ^A¡rstralia. M.Ag.Sc. Thesis. University of Adelafde. 247 pp. Sri.th, M.V. L977. Graztag mrnagement of dryland lucerne pastures on sandy so1ls. Dep. Agrlc. Flsh. S. AusÈ. Fact Sh. No. 78/77. Snith, R.F. 1959. The spread of the spotted alfalfa aphfd, Therioaphie

rw,euLata (Buckton), 1n Callfornla. HiLgardia 282 647-683. Snith, R.F. L967. Princlples of neasurement of crop losses caused by lnsects.

Proe. EA) Sgnrpoeiwn qn Crop Losses z 205-224.

Stern, V.l"f . L973. Economic thresholds. A. ReÐ. Ent. 18: 259-280. -77-

Appendíx 4.1 Analyses of variances for testing differences in mean numbers of plants between Ereatnents aË the beginning of dauage assessuent experiments (OcÈober L977) and aft,er the first year wlth SAA (January L979), Cu1burra.

Source of D. F. Sum of Mean F-ratio Varlatlon Squares Square

October 1977

Ftelds 3 879 .97 s 293.325 8.943 P < 0.001 Treatments 3 46.775 L5.592 0.475 NS Residual 9 295.200 32.800 I^llEhin 304 2534. 000 8. 336 Total 3r9 3755.950 tL.77 4

January 1979

Flelds 3 2383.7 62 794.588 21.070 P < 0.001 Treatnents 3 L34.Ltz 44.704 t. 185 NS Residual 9 339.4t2 37.712 tr{ithin 304 497 4 . rO0 16.362 Total 319 7831 .386 24.550

NS - not, significant at P<0.05 -78-

Appendlx 4.2 z Analysls of variance for Èesting differences in percentage changes ln plant denslty (arcsine ,-1) b"ateen treatments from October 1977 to January L979, Culburra.

Source of D.F. Sum of I'fean F-rat1o Varlatlon Squares Square

Fields 3 1365.739 455.246 5.494 P < 0.01 lreatnents 3 2L3.796 7 L.265 0. 860 NS ReslduaL 9 7 45.732 82.8s9 Total 15 2325.268 r55.018

NS - not slgniflcant at P<0.05 LEGE¡ID FOR APPENDICES 4.3 TO 4.7

TN nll chenLcal lnsecticide T¿o-oo chenLcal lnsectlclde, 40-60 SAA per stem Ttao-zoo chernlcal lnsectfclde, f80-200 SAA per sten tv chenical lnsectlclde, visual danage

start of gtaztrl:g for one r¡eek

p parathlon

d demeton-s-methyl , 75 g a.c. ha-l dr deueton-s-methyl, 37.5 g a.c. ha-l -79-

Appendix 4.3: Field I - mean number of SAA per sEem ln each treaE,menE of the grazLag experiment from January t,o June 1978, Culburra.

Ttrt

p

t o-uo

I 30 b d o 2 d 2 p d o E o ï',ro-zoo o oL o-

.n d

2 o p 1 L 4o )E z. T V

1 P

Jon Feb Mor Apr. Moy June -80-

Appendix 4.4: Field 2 - mean number of sAl\ Per stem in each t.reatmenE of the gtazLng experimenE frorn January Eo June 1978' Culburra.

700 T N 600 500 l.

1 p

700 T 600 40-60 500

40 (u C L d (u o^ d a¿ d

10 p o

E o Tr ñ eo - zoo 600 oL o- <40 Ø30 d d o

1 P L o -o E TV z.=

5 d

300 200 d p 1

Jon Feb Mor Apr. Moy June -8 1-

Appendix 4.5: Field 3 - mean number of sAA per stem in each treatment of the gtazLrtg experiment from January to June L978' Culburra.

T N

p 1 -¡-a-o1a a

T 40 -60

o I cL o I : o f I d d d I d o p I E o T o 180-200 oL o.

d UI d o a p o /\ .-/\, -o E a z TV d

d' 1 p

Jon Feb Mor Ap r Moy Ju ne -82-

Appendix 4.6: Field 4 - mean number of SAA Per sEem 1n each treetmenf of the gtazlrtg experimenË from January to June 1978' Culburra.

7 T N 600

100 P

T 6 40-60

d

o c oL () 2 d d d d 1 p o

E T 180- 200 o 6 th 500 Lo o-

3 d d tf) d

o l0 p t- o -o E 700 z) TV 600 500

400 30

10 p

Jon Feh Mor: APr Moy June -8 3-

Appendix 4.7: 1979 and 1980 - mean number of SAA per stem in T* and T+O-OO in the grazLtg experiment from January to June each year, Culburra.

1979

rc0 TN

1

-.-a-a-a-'-

T¿o -oo

o d d' ct- o U dl =

o

E 1 980 o Tt¡ UI (- o o-

Ø

o 2

L o 1 -o F zf tao-uo 60

1 dt d d'

-t-.-.-.¿ J on Feb Mor Apr. Moy June -84-

periods Appendix 4.8 Transformed ræans of l¡,l of lucerne at the end of regrowth for each treatment ín each field, and the least significant difference between uteans for each sampling time, culburra, L978'

-2) Variance LSD¿tJr Field Regrowth MeanDþl*(sm i' Ereatment: TN rac io pe riod 14o-60 rt8o-zoo Tv endlng: F¡,36

l NS r0. 02. 78 3.67 3.61 4.0s 4. 48 .4I 23.03.78 2.40 2.4r 2.34 r.94 0. 78 NS 0. 89 5.05.78 2.49 b 3.58 a 4.L7 a 4.L4 a 4.42 NS 16.06.78 r .68 r.53 t.52 r .45 0.65 0.53 28.O7.78 1.70 c 2.33 b 2.94 a 1.87 bc 6.37 8.09.78 2.45 2.54 3,23 2.69, l .84 NS 4.77 o.62 20. r0 . 78 2.27 c 2.93 ab 3.55 a 2.50 bc 1.12.78 I .40 I .83 2.04 I .83 I .71 NS

4.42 t.97 NS 2 17.02.78 4.02 3.58 4.25 12.75 0.41 3r .03.78 2.47 a 1.87 b r.47 b I.02 c t2.05 .78 3.85 3.05 3.54 3.03 l.7r NS 0.28 23.06.78 2.4O a 1.64 b r.6l b 1.69 b 9.99 4.08.78 2.87 r.86 2.6r 2.38 r.75 NS NS 15.09.78 3. 86 2.47 3. 69 2.95 2,42 2.85 2.7 2 2.98 o.7 4 NS 27 "1O.78 3.24 0.57 8. r2.78 2.13 b r.63 b 2.70 a r.93 b 3. 60

4.05 0.32 NS 3 24.02.78 3.79 3.97 4.22 0.4 r 7.O4.78 2.47 a 1.49 b r.4l b 1.14 b r 1.64 2.20 NS 19.05. 78 3. 99 3.55 4.67 3.82 0. 49 30.06.78 3.54 a 2.15 b 2.12 b 2.33 b 10.7 6 I NS I 1.08.78 3.95 3.01 3. 59 3.27 .58 L9 .47 0. 86 22 .09 .7 I 5.84 a 2.28 c 5.ll a 3.67 b o.7 3 3.r1.78 4.96 a 2.88 c 4.09 b 3.10 c 9.79 0.7r t5.12.78 4.56 a 2.75 c 3.61 b 3.17 bc 6.78

3.62 b 4.s7 0.60 4 7 .03.78 4.06 ab 4.55 a 3.31 c 0.45 14.04.78 2.48 b l.8l c 3.46 a 3.09 a 14.59 0.21 NS 26 .05 .7 I 4.39 4. L2 4.24 4. 19 1.52 NS 7 .07 .78 3. t0 3.6r 3.46 3.05 r.69 NS 18 .08 . 78 4.4r s .06 4.16 4. r0 2.73 NS 29 .O9 .7 I 7.73 6.52 6.84 5.83 0.4 3 10.r1.78 5.08 a 4.44 b 4.91 ab 3.48 c t5.76 0.34 NS 21 .12 .7 8 4.64 4.59 4.26 4.52

* Mean Ilts follo¡¡ed by rhe se¡ûe letter et Èhe end of each regrowth period are not slgnificantly dlfferenE at P(0.05. *'t LSD - Ieest sÍgnifícant dffference beElteen IIEans' P=0'05' NS - ûean6 not s{gnlficantly different aE P < 0'05' -85-

SECTION 5: IIIFLIIENCE OF CEE!'ÍICAL INSECTICIDE. GRAZII{G AI{D CITLTIVARS OF

LUCERNE OI{ lEE DENSITY OF SAA IN DRYI,A}ID LUCERNE IIT lEE

IIPPER-SOUTE-EAST OF SOI]TE ATISTRALIA

Sunnary

The efficacies of two readily available tactics for the control of SAA ln dryland lucerne pasture, ví2. chemical insecticide and grazíng' were quantified using data from a rotatiotaL grazing experiment in lfunter River lucerne-based pasture infested with SAA. Low rates of àpplication of demeton-s-nethyl provided high levels of conÈrol (957() in the first year buE the level of control was gradually reduced to about 707. Ln the third year. This reduction was attributed to insectíclde-induced resistance \,thich mey have pertly resulted from the innlgration of resisÈant alates of SAA from nearby irrlgated lucerne stands; chemlcal insecticides were used more lntensíveLy f.ot Ehe conËrol of SAA in irrigated lucerne stands than in dryland lucerne Pastures.

herbage Severe graz1¡¡;g wit,h sheep, whlch reuoved virtually all lueerne ' caused reductions in numbers of SAA ln excess of. 95"/" and, more gommonly, in excess of. 987". The effect of less-severe grazing varied and ranged from an increase in numbers t.o reductlons up Èo 95%. The level of control wtth less- severe grazlrtg could noÈ be predicted and this type of gtaziîg rlas not a rellable tactÍc for the management of SAA.

Regular sanpling for SAA on llunter River and on three SM-reslstant cultivars of lucerne that lrere gïorrn on infertlle, siliceous sand and were rotationaLLy gtazed, clearly demonstrated the advantages of using resistant cultivars of lucerne as a long-tern tactic in the nanagement of SAA in dryland lucerne fot grazlng in the Upper-South-EasÈ. -86-

5.1 IntroducÈ1on

Sect,ion 4 demonstrated that SAA lras a severe pest of dryland, Ilunter River lucerne pasture used for grazlng in the Upper-South-East, and that uean denslties of SAA needed to be nainÈained belorl about 60 SAA per stem of lucerne for acceptable persistence and production of lucerne pastures.

The two uain tacÈ1cs for short-term control of SAA which were immediately available to landowners in the Upper-South-East were chemical insectlcide and grazíng management. Longer-Eerm tactics included Ehe introduction of parasltes of SAA (I,I1lson et aL. L982) and resowing susceptible lucerne !ûíth resisÈant cultivars of lucerne (I. Kaehne, pers. conm.). l,Ihen SAA was accidentally introduced lnto south-wesÈern U.S.A., there \ùas an iniÈ1al dependence on chemlcal lnsecticides for the productfon of lucerne (Reynolds et aL. 1956) and wlthin two to three years there $ras a change from broad-speetrum lnsecÈicides, including parathion and naldison (malathion), to more speclfic aphicides because of insectlcide-induced resistance in SAA (Stern and Reynolds 1958) and a greater appreciatlon of the need Èo protect predators of SAA (Stert et aL. 1958).

This change led to the effective use of lciw rates of chemical insecticides such as demeEon, demeËon-s-meÈhyl and plrínicarb (BarÈlett 1958, Ilelgesen and Tauber L974, Reynolds and Anderson 1955).

0n the oLher hand, the effect of grazing on t,he numbers of SAA ln the U.S.A. and elsewhere nas not clearly quantified in the llterature and the availabie evldence was inconsistent. Hacpaz (I955) claimed that, in Israel, grazltg cattle reduced numbers of SAA, partly through Lngestion of aphids by the cattle, but Nielson and Barnes (196f) observed that grazl-ng sheep did not appreciably effect denslties of SAA in Arizona. In the latter system, any effects of gtazLng Day have been obscured because gtazLr^g occurred durlng winter when densitles of SAA were low. Despit,e the linlÈed informaÈion avallable' grazing was considered to be a potential tactlc for the control of SAA in the Upper-South-EasÈ, mainly because optimum production of lucerne herbage relied on -87- regular, severe defoliation over a short period of time r.rhich lüas expected to provide a hostile envlronment for SAA. Optimunn producËion of lucerne pastures occurred wiEh severe defollation because severe defoliatl-on stimulated regrowth frou basal buds rather than from the less-producÈive axillary buds of plants (Langer and Keoghan 1970, Leach 1978). Replaeement of susceptible culÈivars wit,h SAA-resistanE culti.vars of lucerne r,{as a major factor in the control of SAA in the U.S.A. (Ilagen et aL. I976). Painter (1954) had suggested earlier that ecological factors could nodify the expression of plant resLsÈance to insects. Thls lnfluence r,ras confirmed by Mcl"furtry (1962) and others who showed that resistarice to SAA in lucerne was reduced at mean temperatures belor.r about 15oC and that it was also reduced when lucerne rùas grown in potassium-deficlent soils. A slmilar influence of nutrlents may effect the level of resistance of resistant cultivars in the Upper-South-East where lucerne is grown on sands which are infertile, lncludíng low levels of available potassíum (Russell 1960' SniEh L972). Ttris section describes the influence of chemlcal insecticide, grazlng with

sheep and the resistance of three resistant culÈivars of lucerne on Ehe denslty of SAA. Such data vrere necessary to evaluate Ehe potential of each tactic for

the management of SAA in grazed, dryland lucerne Pastures 1n the Upper-South- East.

5.2 ùfateriala aod l{ethode

5.2.L Influeoce of chenLcal lnsectLclde anid' ErazLnlg Chenrical insecticlde and grazLtg were frequently used in the naín grazí-rrg experiment in Hunter River lucerne-based pasÈure at Culburra fron 1977 to 1980. The experimenÈal site and methods of the experiment are descrlbed in Sectlon 4. In Èhis experLment, cheml-cal insecticlde was part of Èhose treatments in ¡¡hich

fnsecticlde ¡.ras applled when the densl-Èy of SAA exceeded pre-determined thresholds; and gtazírg occurred ín all treatments for one week ln every slx

weeks. -88-

The influences of chemical insecticide ard grazing llere calculaÈed as percent,age differences in densiEies of SAA before and after spraying or gtazÍ-ng, respect.lvely. I'he effects of these tr,ro tâcÈics were considered Eo be independent of other experimental treatmenÈs, and appropriate daÈa were used to calculate then whenever the opportunity arose in any field.

Densft,ies of SAA were esÈimated once a week in the m¡in experiment but when the influence of grazirr.g r{as to be evaluated, estimates of SAA numbers were within a day of the sheep eiËher belng puÈ in or t,aken out, of the fleld. To

measure the effect of a chemical insectlclde, estinates of numbers of SAA were usually nade eiEher one or tr¡Io days prior to Èhe applicaËlon of the lnsecÈicide

and again fíve to six days after it. The. chenical insecticide was demeton-s- nerhyl which was applied at 75 g a.c. ha-l prior to 24 þril 1978 and then at

37.5 g a.c. ha-1 for the remainder of the experiment. During the course of

Èhe nain experíment, 21 estirnates $rere obtained of the effect ot 75 g a.c. ha-l dereton-s-methyl 1n !g78, and six, nine and Èwo estimates of the effect of.37.5 g a.c. ha-l ln 1978, 1979 and 1980, respectively. The number of estimates on the effecEs of severe grazing were 14 in 1978, Èhree in 1979 and j-rr two in 1980; 58 estímaÈes were obtained of the effect of less-severe gxazLng 1978, si-x 1n L979 ar.d eight in 1980.

The mean percenEage mortalities of SAA with 37.5 g a.c. ha-l detetôn-s-

nethyl in 1978 and 1979, respectively, rüere conpared wiÈh a Mann-I'Ihftney U-test;

and the apparent decrease in the efficacy of this rate of demeton-s-methyl fron 1978 to 1980 was tested with a linear regression of percentage Bortality on time of application of the chenical insecticlde. The number of estlmates of percentage mortaliÈy ln 1980 were too few to compare' sÈaÈisttcalLy, the mean

percentage mortallty in that year wfth those in previous years.

T'he residual effectiveness of the tr¡o tactics rvere evaluated from

subsequent weekly densities of SAA. At each time of sampllng, the age structure

of SAA was also deÈermined, as described in Section 4' -89-

5.2.2 Influence of resistant cultlvars of lucerne In 1980, densities of SAA on three resistant cultivars of lucerne r^7ere eompared w-ith those on Hunter Rlver lucerne in a dryland, lucerne varieÈy trial cornparing agronomi c. features of a number of different cultivars of lucerne resistant to SAA. The trial was conducted by the South EasE Region, Department of Agrlculture, South Australia, on siliceous sands at logan Rocks, 13 krn SE from Èhe experimenÈal siÈe at Culburra. The trial l¡Ias sor{n in nid-June 1979 with a seeding rate of 3 kg ha-l of lucerne and 190 kg ha-l of super- phosphaÈe, includíng coPper, zíne and rnolybdenum; the size of each plot was 50 m x 4.2 m. The trial conslsted of 22 cultivars of lucerne by three grazLng systems by four replicates. The three gr¿zíng systems were those systeEs recommended for grazLng winÈer dormant, winÈer semi-dormant and winter active cultivars of lucerne, respectively. The systems varled in the time for the regrowth period and were correspondingly one week graztrtg, six weeks regrowth; one week grazitg, five ¡,reeks regrowth; and one week grazing, four weeks regrowth. Densities of SAA were estimated on three reslstant cultivars , vlz.

CUF l0I, WL 318 and I']L 5f4, and Hunter River in the system recommended for winÈer semi-dormanÈ lucernes; this grazíng system was the same as that used in the main experiment at Culburra. The same three repllcates $Iere sampled per cultivar, and 15 stens of lucerne per replicaÈe vrere sampled for SAÀ at each time of sanpling. The numbers of SAA per stem were estimaÈed by the nethod descrlbed in Section 3.2.1. Samples were taken each week from 22 Octobet L979 to 17 June 1980. During that tine, all the replicates $Iere grazed with sheep for one week in the weeks beginnlng 17 Novenber 1979 and 10 January, 15 I'farch a¡d 24 M.ay 1980, respecÈivelY' Daity temperatures at Iogan Rocks were considered to be Èhe same as those measured at Èhe nain experínental siÈe at Culburra' -90-

5.3 Results and DlscuesÍon The field data used to Eeasure the influences of chemical insecticlde and sheep gxazLng on the density of SAA are presented graphieally in SecEion 4 in Appendices 4.3 to 4.7, inclusive. 5.3. I Influence of chentcal lnsectlclde Demeton-s-nethyl was used in the experinent at Culburra because it was the main chemical insecticlde recommended for the control of SAA when SAA was first recorded fn south AusÈralia. Mean percentage mortality of sAA aÈtributed to different rates of demeton-s-methyl for the three years are given in Table 5.1.

TABLE 5. I : Mean Percentage mortallty of SAA caused by demeton-sroethyl, Culburra, L978, I979, 1980'

Rate of demeÈon-s-nethYl l,tean % mortalityl (n^r,e") (n*) (g a.c. ha-t¡ 197 I 1979 1980

75 9 5.0 (87 .3-9e .7 ) (n= 2l )

37 .5 96.0 86.0 7 1.0 ( 8e . 6-99. 6) (72.5-99.3) (69 .0-7 3.7 ) (n=6) (n=8) (n=2)

* n = number of occasions on which a sample was taken. t % nortality with 37.5 g a.c. ha-l: 1978 vs Lg7g, means significantly dlfferent at P(0.05 (U=8, Mann-Whitney U-Èest).

These means nay slíghtly under-estimaÈe the actual nortallty caused by the chemical insecticide because estimates of posÈ-treatment densities *.¡s net mâde for at least fl-ve days after the application of demeÈon-s-methyl - a delay caused by the experimenE belng conducted about 200 lan from Adelaide. However, the high norÉälities obtained in 1978 suggest that any under-estimate \úas -91- mlni¡nal and ¡,rould not detract from the daËa in determining the effectiveness of chenical lnsectícide as a control tactic. Reductions 1n numbers of SAA after applying demeton-s-nethyl hrere attributed to Èhe chemical insecticide entirely because, a! each tine, there were increases ln numbers of SAA in conparable areas where deneton-s-nethyl !Ías not applled (Appendiees 4.3 to 4.7)'

l.Jhen SAJ\ was f irst recorded in South .\¡stralia, the recommended rate of demeEon-s-nethyl to control SAA was 150 g a.c. ha-I (Swtncet 1977), but this rate r,ras later reduced to the range 37.5 to 75 g a.e. h"-1, the lorser raÈe applicable to less-dense stands of lucernê¡ ê.g. dryland lucerne pastures and recently-motrn or grazed, irrigated lucerne stands (Anon. i981). Data in Table 5.I confirm that 35.7 g a.c. ha-l was as effecÈive as 75 g a.c. ha-l in dryland lucerne past,ures in 1978. The .fii"".y of the chemical insecÈiclde

appeared Èo be independenÈ of age of re-growth of lucerne and of Èhe initlal density of SAA. Sarnpling in subsequenÈ weeks after the application of demeton-s- rnethyl suggested that neither rate of applfcaÈion was sufficiently residual

for the conÈrol of SAA. The apparent absence of any residual effects of demeËon-s-methyl was especially evident in warner periods of the year (February-March) when the temperature was favourable for rapid increases in numbers of SAA; with both rates of application ln these months, increases ln densit,ies of SAA in the

second week after applicat,ion were commensurate with those in untreated areas (Appendices 4.3 to 4.7). This absence of sufficient residual effect sometimes necessltated two applications of chemical insecticide withln a five r¡eek regrowth period to maintaln densities of SAA below the requlred 60 SAA per stem of lucerne, e.g. in T49-66 ln March 1978 (APpendices 4.4 atd 4.5) and 1n February 1979 (Appendix 4.7). These data suggest Ehat demeton-s-nethyl at the low rates of application may act as an effectÍve contect insecticide providing

good knockdown of SAA, rather than as a systemic insecÈicide whlch could be -92- expected to provide a longer residual effect. After Èhe end of April 1978, the lower ra¡e of appllcation r\ras used because of its si¡nilar efficacy but lower cost compared to the higher rate. The percentage mortaliEy of SAA v¡ith demeton-s-uethyl in 1979 was signifieanËly lower (P(0.05) than in 1978 and the regression in Figure 5.1 shows a signlficant d,ecline in the effectiveness of demeton-s-methyl fron 1978 to 1980. This decline was nainly attributed to the energence of insecticlde- induced resístance in SAA, a siroilar occurrence t,o that experienced in the U.S.A. after t\.{o to three years of intensive use of organlc phosphates againsË

SA.l\ (Stern and Reynolds f958). At Culburra, there appeared to be only a relatively low level of resistance 1n 198O because the rnortality obtained '¿ith the same dose of demeÈon-sreghyl r¡tas still about 70%. Ilowever, in early 1982 high levels of resisÈance to a number of carbamates and organic phosphates were confírmed in SAA from lrrigated lucerne stands at l,anghorne Creek, 95 lo NI'I of Culburra, and at Keíth, 45 kn SE of Culburra. These resistances were measured in laboratory bioassay t.ests and included a LZJ| reslstance to demeton-s-methyl at Langhorne Creek; this level of resistance is sufficient Eo cause lor¡ levels of mortallty of sAA in the fÍeld r,fíth the recommended rates of applicatlon of demeton-s-ne¡hyl (V. Edge, pers. comm.). Resistance Èo chem{cal insecticides vras expec¡ed to develop more rapidly in SAA 1n irrigated lucerne stands than in

dryland lucerne Pastures because of the more intensive use of lnsecticides there. The low level of resistance at Culburra ln 1980 is unlikely Co have

developed Èhere because only a small amount of chemical lnsecticide was used at the experimental site and the quantlties used ín commercial dryland lucerne pastures around the slte l¡ere minimal. The apparent low level of resistance may rather be attributed to natural ironl-gration of resistant SAA from irrigated lucerne stands in the Keith or Langhorne Creek regions, or both. -93-

100 x x* I Itt* Y =97'3 - 02¿.X x x r=-07t+ ØÍs0 Ë80 x x x x =ÉTo x o e 60 0\\o

50 1978 1 979 1980 Time of opplicotion of insecticide

FIGURE 5.1: Decrease in percentage mort,alicy of SAA using 37.5 g a.c. ha-l derneton-s-methyl fron 1g7g to 1980, Culburra.

(537") There r,ùas one occasion ln nid-February 1979 when a lower nortality was obt,ained with 37.5 g a.c. t.-l; this lower mortaligy Íras rnainly attributed to raln, of which 1.6 m fell just after appllcatlon and 22 nn fell during the next day. This lower mortallCy r*as noE included in the calculation of the rean percentage mortall-Èy given in Table 5.1.

The rapid emergence of resistance to chemical insecEicides in SAA at Culburra supported the need to develop a control strategy' even for the short- term, which relied on a number of tactics and not only a unllateral approach involvíng chemical insecÈicide. 5.3.2 Influence of grazing The deleterious effecEs of sheep grazlrtg on the density of sAA in dryland Iucerne pasture are evidenÈ from the reductions 1n the densities of SAA during (Appendices to mosE of the weeks of grazing in the period, January to ì4ay 4.3 4.7). The onty times in three years :.Jnat grazing did not reduce the densíEy of

SAA were in T* and T4O-U9 ln February 1978 (Appendix 4'4) and in T1SO-ZOO tn February 1978 (Appendix 4.5). GrazTrrg'appeared to be a useful tactlc to include ln control strategles for SAA, but was not necessarily reliable for high -94- levels of mortalíty of SAA. The percentage mortality of SAA caused by grazlng at each time of grazíng in each treatment was estimated from the mean density of

SAA inrnediately prior Eo and aft,er gxazír,g, respectively. Iligh levels of norÈality, greater tlnan 951l and usually greater than 98%, were only obtained with severe grazirtg where practically all of the lucerne herbage was consumed by the sheep, e.g. all Ereatmerits in Ùfarch 1978 (Appendix 4.3), TN, T46-66 and

TfaO-ZOO in April 1978 (Appendix 4.4), T* and 1¿O-60 in April L97B (Appendix 4.5) and T¡ and Ty in l"larch 1978 (Appendix 4.6). Ttre frequencies of percentage mortality of SAA attributed to less-severe grazítg are presented in Figure 5.2.

30

I 20 u C o J 10 U L LL o o o o o o o r.l) (\ (Yr { !o I È\ @ or o) I I I I I I I I I ô¡ (Ð { l.r) (.o r\ @ cD

o/o mortolitY of SAA

FIGURE 5.2: Frequencies of percentage mortalities of SAA attrlbuted to less-severe grazlng wlth sheep from 1978 to 1980, Culburra.

The percentage nortallEles used in Èhis frequency dlsEribution were restrlcted to mortalitles at those times of less-severe gtazlng when initial densl¡ies of SAA exceeded about 10 to 15 SAA per stem of lucerne. Any changes

ín densities of SAA with lower initial densities were not consÍdered to be reliable estimates of the influence of grazlng. The level of mortaliEy wiEh

less-sevete graztng ranged fron 14 to 957", but the 90% nortallty, or more, which was attained wit.h chemical insecticide in 1978, occurred in less tt:,an 207" of the -95- gxaz1rrLg periods. The increases in the density of sAA in T¡ and T49-69 ln February 1978 (Appendix 4.4) with less-severe grazing trtere due to selective graz1;,g by sheep. In Ehat gtazing period, sheep naínly fed on leaves of lucerne and left the coarser stems, as described by Arnold (1960); SAA survived and reproduced on Èhese stems during grazíag, though they did not increase in numbers, as expected, during the week afÈer gtazing. OR a few occasions' densities of SAA decreased, or at least did noÈ increase in Èhe second week following less-severe grazirtg, but this adverse effect of less-severe grazLng ott the subsequent increase of SAA dld not necessarily prevenÈ densiEíes of SAA exceeding the low threshold recommended for Ehe naintenance of lucerne (Section 4). The levels of mortality of SAA due to different intensities of gtazíng, other than severe grazíng, could not be predicted. l"fultiple regressíons relating nortality with less-severe grazing to mean temperatures duríng gtazing, initial densitles of sAA, initíal stem lengths and reductions in stem length were not significant. Results from the grazLng experiment at Culburra vtere contrery to those of

Bishop et aL. ( l98O) r¿ho found thaÈ grazing dryland llunÈer River lucerne pasture with sheep at three differenÈ sÈocking lntensLties in north-western Ner¡

South çales failed Èo reduce the numbers of SAA, relative to ungrazed areas.

The nain reason for Ehe lack of differences in their experiment apPeared to be the very low densities of SAA prior Eo grazing. Their experiment r'Ias conducted 1n August-September and densities of SAA were 1.6 to 8.6 SAA per 208 ct2 of Iucerne pasture, which is probably equivalent to less Èhan one SAA per stem of lucerne, as estlmated at Culburra. In addition, Èhe densities of SAA ln their quadrats each 208 ct2 of lucerne experirnent \üere estimated fron only ftve ' pasture, pêr replicate at each tirne of sanpllng compared to 30 quadrats, each

one sEem of lucerne, per replícate samPled each tlne l-n the experíment at -96-

Culburra. The small sanple size used by Bíshop et aL. ( 1980) would have gíven thelr samples a low precision and hence allowed them to detect only very large differences between means. Thelr conclusion that gtazLr.g by sheep failed to reduce numbers of SAA can not Eherefore be accepted as a generalisatíon. 0n Lhe other hand, Bishop et aL. (1980) did show Ln another experlmenÈ ÈhaÈ heavy grazing with cattle reduced densities of bluegreen aPhid, Aeyrthosiphon kondoi Shinji., by up to 937., win1.eh agrees in principle with the results obtained at Culburra with SAA and severe grazlrtg. Ihe percentage mortaliEles (up to g37.) of bluegreen aptrid with heavy grazíng in their experinent !ùere lower than the percentage mortalities (greater than 9B%) of SAA r,rith severe grazing in the experimenE at Culbürrâo Thts difference in levels of nortalLties úay be due to differences ln the severity of gtazLng beÈween the experiments.

In the second experinent of Bishop et aL. (1980), the shortest mean length of Iucerne sten was 14 nrn afÈer 10 days of heavy gtazing' whereas virtually all of the lucerne stems f¡rere consumed by the sheep after seven days of severe gtazirlg at Culburra. Severe, periodlc grazLng of lucerne is an acceptable nanagement pracÈice in the culture of lucerne, and Langer and Keoghan (1970) considered ÈhaÈ there \ras no advantage in leaving residual leaves. For thís reason and wlth the

Erends obtained in Ehe above data from Culburra, severe grazLtg can be considered as a tactic for the control of SAÀ ín dryland lucerne pastures in the Upper-South-East. Ilowever, gtazLng ls only useful to quickly reduce numbers of

S1y¡ and usually does not prevenÈ SAA fron increaslng l-n numbers immediaEely after grazLag during Èhose times of the year favourable to SAA' The lncreases

in numbers of SAA after grazLng are atÈributed Èo females survivÍrLg gxazLrLg and inrnigrant alates. The use of gtazirng as a tactlc for the control of SAA agrees wlth Penmanet aL. (1979) who lncluded grazing, especially in wlnter' as a control tactic for bluegreen aphld in lucerne Pastures Ín New Zealand. They -97- also suggest Lhat grazirrLg 1n the spríng to coinclde with rapidly increasing numbers of BGA could reduce the need for subsequenË application of chemical insecticide, buÈ they do not provide evídence Èo support thls suggesËion. 5.3.3 Influence of resl-staût cultlvars of lucerne

Sarnpling SAA on SAA-resisÈant culÈivars of lucerne at Iogan Rocks was liniÈed to three resístant cultfvars and IIunEer RLver because of available resources. The three cultivars were selected to provide wlnter-dormarit (CuF 101) lucernes (I^IL 318), winrer-acrive (WL 514) and highly winter-active ' and Èo test cultivars whlch were being gro\ün by seed gro\.{ers and would probably be some of the first sources of seed available ln substanÈial quantiÈ1es for re- sowÍng pastures (CUF 101 and m 3f8).

Numbers of SA,l\ on each culÈivar in weekly samples from Decernber 1979 to

June 1980 are gfven i.n Figure 5.3. A range of denslty of 40 to 60 SAA per sÈem of lucerne is also drar¿n across the graph to demarcaËe Lhe threshold below which

SAA should probably be maintaíned to allow the perslstence of llunter River lucerne plants (Sectlon 4). As expected, densities of SAA on Ifunter River greatly exceeded Èhe Ehreshold soneEimes, and reductions in densiÈy were due Èo either grazing (as shown), naxlmun daÍly temperatures exceeding 4OoC in the third week of February (Section 7), or a shortage of food due to damage by SAA in early-April. ùlean densitles of SAA on all the resistant cultfvars remaLned well below the Èhreshold; they reached about 20 SAA Per stem on l^ll, 318 only twice and on lf1. 514 only once, and other:wlse remafned below I0 SAA per stem of lucerne, I,fith reslstant culÈivars, the highest nean densttles of SAA e7s¡s Minly due to high numbers of aphids on relatively few plants in the pastures, e'g' less

than about 2O7" of plants wlÈh trÍL 318 and I0% wlth CUF f01. By conÈrasÈ' high

numbers of S|,¡\ oceurred on more ttran 957" of the plants in llunter River pastures

when SAA was abundant. This dífference in the proportion of plants heavily -98-

(J G G I I 300

200

100

o c L ETì oJv o a l+0 - o E X o r o tli\ I L /\ oo' XI X 10 /r I I t}(- I I U1 I I \ I I I o5 a I I oL I I -o I E I a ) I z x /'( X a

0

20

t-A1s

Ê10o cq o o 0 Dec Jon Feb Mor Apr. Moy Jun

19 79 1 980

Hunter River x---x wL31g .-. cuF101 .---. WL514

FIGURE 5.3: Mean denslty of SAA on dlfferent culÈivars of lucerne and mean ÈemperaÈures beÈween sampllng times from December 1979 to June 1980, Logan Rocks. -99- lnfested erith SAA beE\¡reen the resistant cultivars and lfunÈer River generally agrees with Lake and Kaehne (1982, unpublished), who t,ested the resistance of a number of SAA-resistant culËivars of lucerne by scoring, as a percentage, the numbers of plants in each of five classes ranging from very resistânt, to suscepÈible for each cultivar. They found that 281l liL 3L8, L4% CJ.JF l0I and L07"

IIL 514 plants nere suscepÈible to SAA and they attrlbuted the dl-fferent levels of suscepttbllity to the dffferenÈ parenÈages of Ëhe respective cultfvars. Ktndler and Schalk ( 1975) also found that nost planEs of the resistant cultivars that they tested were either resistant or suscePtible to SAA; they consldered that stand persisÈence and yield were dlrectly related to the percentage of SAA. Plants 1n the resisEant plants with antiblosis or non-preference .for cultfvars at Logan Rocks whlch lüere susceptible to SAA would probably be k1lled by SAA rs-ithin a couple of years, thus leaving stands of lucerne wlÈh hÍgher leve1s of resistance to Èhe current bíotype(s) of SAA. Ilowever, loss of susceptible plants nay also alter pastures from viable Eo non-viable, on the basis of plant density, mainly because of Èhe low rates of seedlng used Èo establish dryland lucerne pastures and the inabllity of establlshed dryland lucerne pastures Eo replace lost plants (Leach 1978). ThÍs tendency to rion- vlability can be nininised by proportlonally increasing Èhe rates of seedlng of cultivars known Èo have a high level of susceptlble Plants ¡ ê.8. I^IL 318, or by only sowing cultivars wit.h the highesÈ percentages of resistant plants in their populatlons.

The mean temperatures for the periods between samplfng Èimes were calculated as the mean of the daíly mean temperatures Eo test whether the levels of resistance to SAA of the resistant cultivars sanpled at logan. Rocks were reduced at temperatures below 15oC, as shown wl-th some oÈher SAA-reslstanÈ culÈlvars by Mclfurtry (L962). The mean temperatures are gl-ven in Figure 5.3, resistance of and. even though some means were less than 15oc' the lever of -r00- each cultivar did not appear to be reduced by these lower temperatures. The resi.stant cultivars ¿fse nâinÈalned high levels of resistance on the infertile sand at Logan Rocks. Apart from the problem of plant density which mey arise with rresistanEr cultivars that have a high proportion of susceptible Plants, the 1or¡ numbers of

SAl\ on the culÈivars of lucerne at Logan Rocks confl-rm the lmportance of reslsÈant cultlvars in the manegement of SAA in dryland lucerne pasÈures fn the Upper-South-East. Selection of the most profiÈable resisËant cultivars t,o use in the regLon will rely on the perfornance of Èhe different cult.ívars under grazíng and this performance can only be deteruined from comparaÈive fleld trials, such as that at Logan Rocks, and fron landotJnersr experience over time. 5.4 References Anon. 1979. Sumnary of crop and pasture pest conÈrol recommendations. Dep. Agric. Físh. S. Aust. 8u11. No. 7/79 Arnold, G.W. 1960. Selective gtazLng by sheep of Ewo forage species at dlfferent stages of growth. Auet. J. agríc. Res. 11: 1026-1033. Bartlett, B.R. I958. Laboratory studies on selective aphlcides favouring natural êûêmlss of the spotted alfalfa aphid. J. eeon. Ent. 5t: 374-378. Bíshop,4.L., GreenuP, L.R. and lloltkamp, R.H. 1980. Managenent of Aeynthosiphon konda¿ ShinJJ-, blue green aphtd, and Therioaphie trLfoLií (Monell) f. maeulata, spotted alfalfa aphid, by grazlng and cutting lucerne. Auet. J. eæp. Agríe. Aním. Hueb. 20t 710'716. Ilagen, K.S. , VikÈorov, G.A. , Yasauatsu, K. and SchusÈer, M.F. L976. Biologlcal control of pests of range, forage and grain crops. In, Theory and Practl-ce of Blological Control. Ed. C.B. Huffaker and P.S. I'lessenger.

Academic Press Inc. 788 pp.: 397-422. -101-

Hatpaz, L. 1955. Biononics of Therioaphis maeuLata (Buckton) in Israel. J. eeon. htt. 482 668-67 I. Ilelgesen, R.G. and Tauber, M.J. L974. Pirimicarb, an aphicide nontoxic to

three entomophagous arthropods. Enuiron. Ent. 3: 99-101. Klndler, S.D. and Schalk, J.M. L975. Frequency of alfalf a plants I'rith combined reslstance to the pea aphid and spotted alfalfa aphid in aphid-resisÈant

culËivars . J. eeon. Ent- 68: 7 L6-7 L8. Langer, R.II.M. and Keoghan, J.l'í. 1970. Growth of lucerne following defollatlon. Proc. N.Z. GnassLd. Aes. 322 98. Leach, G.J. 1978. The ecology of lucerne pastures. In, Plant. Relatíons in Pastures. Ed. J.R. I.Iilson. C.S.I.R.O. Iu¡st. lfelbourne : 290-308. Mclfurrry, J.A. 1962. Reslstance of alfalfa to sPotted alfaLfe aphíd in relaÈion to envlronmental factors. HiLgardia 32: 501-539. Nielson, M.W. an{ Barnes, O.L. f961. Population studies of the sPotted aLfalfa aphid in Arizona in relatíon to Èemperature and ralnfall. Ann. ent. Soe. Am. 542 44L-448. painter, R.H. 1954. Some ecological aspects of the resistance of crop plants to insecÈs. J. eeon. Ent. 472 f036-1040. Penman, D.R. , Rohitha, B.E. , I.Ihite, J.G.II. and Smallf 1eld, B.l"f . L979 ' Control of blue-green lucerne aphid by gtazlng nanagement. Pvoe. 3211Å. N.Z. Veed and Pest Contn. Conf. : 186-191. Reynolds, H.1. and Anderson, L.D. 1955. Control of the spotÈed alfalfa aphid on alfalfa in southern Californl-a. J. eeon. Ent. 482 67I'675. Reynolds, Il.T., Snith, R.F. and Swift, J.E. 1956. Insecticides for alf a1f a aphld. CaLif. Agnie. l0: 11-12. Russell, J.S. 1960. Soils of South Australía - Èhe deep sands. J. Dep. Agrie. S. Auet. 61, 298-307. -102-

Snith, l,{.V. L972. Ttre ecolory and utilization of dryland lucerne PasÈures on deep sands in the Upper South East of South A¡strel1a. ì4.Ag.Sc. Thesis.

UnlversitY of Adelalde. 247 PP. Stern, V.M., van den Bosch, R. and Born, D. 1958. New control for alfalfa aphid. CaLíf. Agric. 12: 4-5, 13. Stern, V.M. and Reynolds, H.T. 1958. Resistance of the spotted aLfaLfa aphid

Èo certain organophosphorus Ínsectlcldes in southern Californla. J. êêofl. Ent. 51: 3L2-316. Swincer, D. 1977. Spotted alfalfa aphld. Dep. Agrfc. Flsh. S. AusË. Fact Sh' No. 85/77. trIilson, C.G. , Sr.¡1ncer, D.E. and !ùalden, K.J. L982. the inÈroducÈ1on of Trioæye eompLarlatzs Qullis (Ilymenoptera: APhidlldae), an l-nÈernal parasite of the spotÈed alfalfa aphid, into South .\¡stralla. J. Auet. ent. Soe. 2I'. L3-27. -r03-

SECTION 6: INFLIJENCE OF PRADATORS AND PARASI1tsS Oil lEE DET|SIIIÍ OF SAA IN

DRYI.A}ÍD LITCERI{E IN lEE ITPPER-SOT'TT-EAST OF SOI]TE AIISTRALIA

Sum¿ry

predator-exclusion experimenEs demonstrated that Èhe most important role of native predators, mainly the hemerobiid, Mícnomte tas¡røniae (Walker), and various specfes of spiders, rùâs the naintenance of very low densities of SAA in lucerne pastures durlng sprlng. Reasons for the effecÈiveness of predators Ín sprlng lncluded (a) the predators abllity to be actlve and to lncrease in numbers at lor¿ temperatures in early-pring and (b) an lnitially favourable pred¿:uor/SAA ratfo in early-sprfng due to exËremely low numbers of SAl\ survlving wfnter in dryland lucerne pasËures.

The naÈive cocclnellid, CoeeineLLa repanda, Thunberg' Iras present during the sumner but Tras not capable of conÈrollfng SAA below the economic threshold in rotationally gtazed. lucerne. Attempts to augment predation by C' nepandø' through Iess-sevete grazLng, thus providing a less-disruptive environment for C. nepartdo,' were not successful .

Durlng autumn, levels of parasitl-sn and predatlon of SAA were low and were considered to be unimportanÈ at thaÈ tlne, especially as numbers of SAA were decltning \{.ith Èhe onseÈ of low ambient temPeratures. The introduced parasite' Trioæge eonrplanntl¿s Quilis, dÍd not effectively control Sfu\ below the economic threshold in dryland lucerne Pastures aÈ any Èime'

The lneffecÈiveness of predaÈors and the paraslte ln dryland lucerne pastures Ln summer and autumn led to the conclusion that any sErategies developed for Èhe short-tern control of SAA in susceptible, dryland lucerne pastures in the upper-south-EasÈ should not be consÈralned by a desire to conserve predators or parasl-Èes durLng suDtrpr and auÈumn. -r04-

6.1 InÈroductlon

I,then SAA was f lrst recorded ln South Australia Ln L977, considerable

enphasis was placed on the importance that native predators and lnÈroduced

parasites of SAA nay have ín the control or mânagemenÈ of SAA. Much of Ehe

speculaÈion rüas based on experÍence in the U.S.A. where 1t had been clalmed that both native predators and introduced parasites lrere substantl-al factors in Èhe control of SAA, especlally prior to the wide-spread use of cultivars of lucerne

resis¡ant Eo SAA during the 1960's (Ilagen et aL. I976b, Neuenschwander ¿ú aL. L975). Native predators were held to be nainly responsible for the

conÈrol of SAA during the spring and autumn (Ilagen et aL. f976b) buE did not

prevent economic outbreaks of SAA ln the most favourable times of the year for

SAA or prevent relnfestation after the use of chemical insecticides (Dlckson et aL. 1955, Snl-th and llagen 1956). The nain predators were Coccfnellldae' especially Hippodatnia spp., followed by Chrysopidae, Anthocorldae, Nabidae and Syrphidae, (e.g. Goodaxzy and Davis 1958). Three hynenopterous parasit,es of SAA were introduced inÈo Callfornla 1n the

nld-195Qrs and, withln a reasonably short period of Èine, parasltes becane establtshed over wlde areas of the U.S.A. due to both naÈural and man-aided dispersal (Angalet Lg7O, Barnes 1960, van den Bosch et aL. 1959). Ttre species of parasites were Tríoæys eoîrpLana.t¿s Quil1s, Praon eæsoLetum (Nees) and ApheLinus a.s7ehis llalker . T. eotnpLana,t¿a generally domlnated the other two specles (ltagen et a.L. f976b) and was Èhe most effecÈive in controlling SAA (van den Bosch et aL. 1964), though dlfferent species did show differenE clirnatic adaptations and there were regions where specles oÈher than ?.

eompLd,71øtlz6 were most abundant (Force and l"lessenger 1968, van den Bosch ¿ú

aL. 1959). I{hen SAA was first discovered in South A¡rsÈralia, an lntensive program was inítiated to rear large numbers of T. eontpLartatue, l-ntroduced from Callfornla, and to release then over as wide a geographical range in the state -105- as possible (lüilson et aL. L982). The introduction of this parasit,e was ao attempt to ¡¡ininise the impact of SAA on leguminous pastures ' especlally lucerne, until culÈivars susceptible Eo SAA could be replaced tsith resistant cultivars. This section descrlbes the influence of natlve predators and ?. eompld.naþuÊ oî the denslty of SAA ln dryland lucerne pastures in the Upper- South-East of South Australla. Initlally, regular sampling identifled potential predators of SAA and Ëheir relatfve abundances, then an experlment was carrl-ed out to test wheÈher nodifted grazing of lucerne could be used Èo augment predators during summer, especlally the coccinellíd, CoeeineLla repand'a' Thunberg. This section also discusses prpdator-exclusíon experiments which demonstrated thaÈ the unexpected low denslties of SAA in spring (Section 3) could be nainly attribuËed to predaËors. T. eotnpLanatus was released ln the experinental site and, although the specles became established' data are presented which suggesÈ thaÈ ?. eoîIpLanntue Ls not a significant facÈor in controlllng densities of SAA below the econornl c thresholds for SAA in dryland lucerne pastures (Section 4).

6.2 IdentÍffcatlon and Äbuodance of PotentÍal Predators of SAA 6.2.L l{aterl.ale and nethods Ihe ldenÈlffcation of potenÈial predators of SAA and Lheír relative abundances were evaluated durlng 1977 /78 l-n the maín grazing experiment set uP in llunter River lucerne-based pastures at Culburra 1n nid-October L977. Details of the experfmental slte and design are provlded l-n Section 4. Ìüeekly estl-mates of the density of predators !Íere m¡de from 18 October to 6 December 1977 uslng calico sweep nets, 380 nn in dlaneter wLÈh a L.2 m handle. CalLco sweep nets were used so that the herbaceous lucerne could be sanpled by beaEing most of each plant within the sarnpling area raÈher than only the upper Parts of the plant, as would happen with fine gavze nets. All sarnpllng was carried out at a - r06- sfmilar tiue of the day, between mid-morning and nid-afternoon' to reduce variaÈions in abundance due to dlurnal activity of any predators (Dumas et aL.

Lg62), Èhough other factors influencing the efficacy of sweep nets (SouÈhwood

1978) were appreclated, especially variatlons ln weather conditlons. The low probabiliÈy of detecti.ng nocturnal predators¡ ê.g. henerobilds, by only sampling durlng the day l¡as also recognised. Ten lots of 20 sÈandard 90o sweeps were taken fron each treatment area Ln each of the four flelds using straÈifled rand,om sanpling. The number of predaÈors or potentfal predators in each lot of

20 sweeps lrere counted and recorded. AfÈer 6 Decembet 1977, the number of predators were estimaÈed on 12 January and 16 March 1978 fron Èen lots of teri sr,reeps per treatment area, and on 7 Apr1l. and 31 May 1978 fron vl-sual estimates of the number of predators in 20 discreet clumps of lucerne Per treetment area. The sampling for potential predators of SAA in the experimental s1Ëe v¡as iniÈieted prior to the detection of sAA in Èhe site, not only to provide an early indlcation of those native predators which nay be useful Ln controlling

SAA, but also t,o flrst detecE SAA in the slte (Section 3). 6.2.2 Reeults The Èhree nain predators sampled fron l8 October Èo 6 Decenber 1977 lÙere: (a) Nabis kinbergií Reuter (Fanily Nabidae), fornerly known as il. (=Tropíeo¡tabie) taemartieus and of ten nis-identLf led as N. eapeíformis C'erûa (I'Ioodward 1982a'b).

(b) Mienormte tasmd.niae (I,Ialker) (Fantly lleneroblldae). (c) Coeeínel\a Thunberg (Fantly Coccinellldae). "ePand.a' Ilowever, the number of each species was relatl-ve1y low, e.g. relatively low compared Èo the number of sinilar predators found in irrigated lucerne in Callfornl-a by Neuenschwander et aL. (1975). /V. kinbergii 1¡4s nâinly found during OcÈober but only at densiÈl-es less Èhan about four per 20 sweeps; after that, only occasional lndíviduals were caught,. During October, N. kínbeTg¿¿ -107 - is probably boÈh PhytoPhagous and predatory on larvae of the noctuid, HeLioth¿s punctiger tr'Iallengren (Samson and Blood 1980). M. tasmaní.ae, maLnly adults, ltere eaught in the lasË two weeks of 0ctober at densiÈies less than about one per 20 s$teePs. This would eertainly be an under-estlmate of the abundance of the specles because of lts nocturnal behaviour and the time of sanpling.

C. repandø. began Èo appear ln very low numbers, less than a mean of 0.5 per 20 sweeps, in late-OcÈober and remained at that low density until mid-

January. From nidl,larch to the end of l{ay, C. reparld.a, \ras more abundant (Appendfx 6.I), probably because of a positive response to increased densiEies

of SAA after mld-January (Section 3). Ilowever, the abundance of C. repandø. was low compared to SAA, whlch had mean densLties in excess of 600 SAA per stem of lucerne during some regrowth periods (Sectlon 3); and it seemed to have no controlling influence on the numbers of SAA, as indlcated by the severe losses of dry naEter of lucerne herbage aÈ that tine (Section 4) ' Other potentlal predators detected tn L977/78, but in extremely low

numbers, vrere the small coccinellLd, Diomtl noteleens Blackburn, and the

syrphids, Símoeyryhue gnandieornis (Macquart) and MeLangyna oiridíeeps (!faequart). 6.2.3 Dlscugsion The data gíven in SecÈion 5, 1n relatiori t,o the grazing experiment initiated in October L977, Lndicate Èhat severe gtazlrrrg and the appllcaÈlon of chemical insecÈlcide caused severe perlodic reducËions in the numbers of SAA

in some treatments. Ihe reason for the low numbers of C. repanda' in these t,reatments l¡ras probably indirect and was probably caused by the reductions ln

SAA numbers grossly disrupting Ehe reproductive and survlval pattern of C. repandø necessary for the persistence and increase in numbers of C. nepandn. NoÈ only would the reduced density of aphids reduce Èhe survLval -r08- rate of all stages of C. repanda,, buÈ it. r¡ould also depress Lhe birth rate of C. repandn because Èhe seÈtlenent, maturation of ovarioles and oviposition of C. repandn, llke that of other predaEory coccinellids, is greatly dependerit on criÈlcal densities of essential prey in Èhe inmedíate vicinit,y; oÈher stimull appear Èo be of mlnor influence. Adults will also elEher enÈer diapause or rnigrate in the absence of suffl-cienÈ prey to stimulate ovipositl-on (Dixon 1970'

Ilodek 1973, Ilonek 1980, and Maelzer 1981). These deleterÍous effects on

C. nepandn caused by decreases 1n the numbers of SAA, together with the rapld colonization and l-ncrease in densiÈies of SAA, more t,han saturated the abll1ty of C. nepanda to control SAA; thus illustratlng the problems of disrupÈive agricultural practices on the persistence. and effectiveness of natural enemles (Price f981). 6.3 A¡snentatlon of C. reoattãø Durlog Su¡rrer 6.3.1 MaterLals and æthode In 1979. an experinent was conducted at Culburra to ÈesÈ the null hypothesis that intensity of grazjrng with sheep did not decrease Ehe abundance of C. repanda, and the control it exerted on SAA durlng summer. Four treatment areas, each 90 n x 200 n, which had sinilar densities of lucerne plants and were not being used for the darnage assessment experimenÈ (SecÈlon 4) were used. The treatments, replicated twlce' llere: l. Rotational severe grazlng: standard I week gtazed, 5 weeks

regrolùÈh. 2. LighÈ gtazíng: rucerne gtazed frorn 200 mm to 100 nn sÈem length' 3. Light mowlng: lucerne mowed fron 200 mm Èo 100 nm stem length. 4. Llght grazlng plus ehemlcal insectlcide: li¡cerne grazed fron 200 m

to 100 mm stem length and demeton-s-methyL (37.5 g a.c. ha-l¡ applied when Èhe mean density of SAA reached 40 to 60 SAA per stem of lucerne. -r09-

5. Light grazLng plus complete control of SAA wlth chernical insectlcide: lucerne gtazed frorn 200 mm to 100 nn sEem length and demeÈon-s-nethyl (75 g a.c. ha-l) regularly applled Èo mafntain lucerne plants virtually free of SAA'

TreatmenÈ 3 was set up in a fenced area, 40 m x 40 rn, approximately 1n the centre of the area used for Treatment 2, and all mowing lüas carried out with a flail motrer set 100 mm above Èhe soil surface and mounÈed on a nín1-tractor; the cuÈ herbage was removed from t,he experimental area. All gtazing was carried ouË wlth a stocking rate equivalenÈ t,o five dry-sheep-equivalenÈs (DSEs) per hectare; the dates and number of days of grazing at this stocklng rate in each

treaÈment were recorded for eaeh gtazlng !ime.

The experiment rüas set up on 29 January 1979 and densLtles of C. repanda

and SAA were esËimated weekly from 5 February to 4 June L979. Ttre denslty of

C. nepandn was estlm¡ted by visually inspecting 10 random clumps of lucerne per replicate during the day of sampling and counÈing the numbers of adults ' larvae, pupae and egg batches of c. repanda in and around each clump' Estinates of Èhe densiEy of SAA were made by cuttlng 20 stens of lucerne' chosen at random, pêE replicaÈe and countlng the number of aphlds on each stem

separately¡ €rs descrfbed 1n Section 3. The Èimes of grazLng, mowlng or applying chemical insectl-cide Ín the respective treatments are shown ln Figure 6'1'

The abundance of C. repartdn in each repl!.caÈe was expressed as the nunber of predator-days fron 5 February to 4 June L979. The number of predator-days in (excludlng each replLcaÈe was estlnated by drawlng a graph of predator numbers

egg batches) against t,ime for the above perlod for each replicate and then

neasurlng Ëhe area under the curve wlth a planlmeter. The area Ï,ras corrected to predator- the number of predator-days using a standard area of a known number of

days. The mean numbers of predator-days per treatment were compared statistlcally with a one-way ANOVA. -110-

6.3.2 Results

The numbers of SAJ\ and of C. repanda, in each of the four treaÈments in the augmentation experlment are given in Figure 6.1. Aphid numbers in three of the treatments decreased drastically whenever they reached 200 to 600 aphids per sren (see Figure 6.I:(a), (b) and (c), respectlvely). These reducÈíons ofÈen occurred before grazLtg or mowing, and they occurred when predator numbers were low and when the weather was favourable for increases in aphíds. Ilowever, when the reductions tn the number of SAA occurred, the plants had obviously been . severely damaged and so Èhe reductions have been attrlbuted to deterioration in food quality caused by the aphids thenselves. A sinilar densLÈy-regulaÈing process has often been recorded in populations of other aphid species (e.g' Gilbert l9BO, Ktran 1979). The deterloraËion in food quality (reduction in aphid

numbers) was particularly evident from two to four weeks afÈer each light

grazLng or mowing because the lighter grazLng or rnowlng assured a relatlvely high density of residenr SAA whlch rapidly infested and killed developlng nodal shoo¡s of lucerne. By conÈrast, with severe grazLng, the roortalÍty of SAA was high durirtg grazing and the relaÈ1vely low number of survlvors infested basal shoots which are more vigorous than the above nodal shoots. The 1o¡'r numbers of aphids on vigorous shoots of lucerne after severe graztng meant that reductlons of in SAA due to poor food quallty only occurred during the Dost favourable time the year for SAA (February-l{arch) and only after four weeks slnce grazLag (Figure 6.1(a) ).

The nurnbers of C. repattda, were higher ln those treatments wlth light

grazLng or nowing compared to ÈreaÈments wLth elÈher severe grazLng or chemical lnsecÈlcide (Figures 6.1(b) and (c) conpared to (a) and (d), respectlvety)' The (P dlfference betr,Jeen the two sets of treatments rtas statistlcally conflrned < 0.05) by comparlng the number of predaÈor-days (= number of c. repandø x (Table number of days) Ln each treatment durl-ng the period of the experiment - 111-

(o)

600 6 SG SG SG 5 I I

I

I t,

I I 3 I

I l 2

I '1 o 100 c Lo )U (b) s00 5 o o- E LG LG t, 2 o I U E (¡, I (J 3 3 oL J , o- I 2 o Id E a\ R o 100 7'f 1 Ut x s oL v. o- s (c) o 6 (n o LM LM o 5 oL L -o o t, E -o 400 ) )Ê c c C 3 3 o C o o o I 200 I I 100 I 1 z)- \:.u -./ | zt-

(d) 50 5

I I L G I I I t, j I J J t J I 3 I 3

I 20 I ? I t 10 I a ¿a

Feb. Morch Aprit Moy

FIGI]RE 6 .I : l"lean densities of SAA (x-x) and C. repandn' ('----') i-n Ehe four treaÈmenÈs of the predaEor augmentatlon experiment at Culburra' L9792 (a) rotatlonal severe grazLng (SG), (b) lighc grazitg (LG), (c) light mowing (LM) and (d) lighÈ grazlng plus chenlcal lnsecticide (I). -Lt2-

6.1). The ¡nain reason for the hfgher numbers of. C. r'epand'a' in the Èreatments conslsting of lfght grazLng and mowing r¡ras undoubtedly the higher numbers of SAA which generally occurred in these treatmefits compared to the other two treaËnents (Figure 6.1). Ilowever, the mean density of d. Tepand.a, vras very low, usually less than tl.fo per clurup of lucerne' even 1n the more favourable t,reatments. The higher densiÈy of. C. repand.a ofl one occaslon at the end of April in the treatment rrtth llghÈ mowing was inexplicable and was not due Eo ironlgrant adults, as could be expected, buÈ was rnainly due to larvae (Figure 6.2(c)). Although the visual methods used to esÈimate densittes of C. repand'a' LrL this experiment would under-estimate real. densities (Fraser and Gilbett L976), d,ensities were obvlously not sufficíent Eo narkedly reduce the numbers of SAA in any treatment. Ttre apparent oscillatory relat,ionship between SAA and C.

repanda. in the lighÈ graz1rng and mowing treatments (Figures 6'1(b) and (c), respectively) was different from the inherent predaÈor/prey oscillaÈions discussed by lluffaker (1958), and others. The ptedatot/prey oscillations demonstrated by ltuffaker ( 1958) are caused by a reciprocal dependence of the prey and predator populations which results l-n osclllations in the densities of both species where peak densities of the predator follow peak densitl-es of the prey, regardless of other factors in the environrnent. At Culburra' the reductions in numbers of aphids followlng their peak densities 'lrere maínly a¡tributed to unfavourable food quality induced by aphid damage, as discussed earlier, and noÈ to C. ?ePand'a'.

The EreaÈment wiÈh light roowing r¿as included 1n t,he experiment as a check for lfght grazLag in the event Ehat sheep did not satisfactorily gtaze |u)lle lucerne from about 200 to 100 nn stem length. llowever, the light grazlag was reasonably unlform across Ereatment areas and was successful' The sinilarity (Figures between the Erüo treatments lras reflected by slnilar denslties of SAA -r 13-

TABLE 6.1 The number of predator-days for C. repand.a' pet repllcate and the mean number for each treatmenE in the predator augmentation experiment at Culburra, 1979. Also glven is the LSD at P=0.05 for the dlfferences beÈween neans.

Number of predator-days from 5.2.79 to 4-6-79 TreatnenÈ Replicate 1 RePlicate 2 I'leantk

Rotatíonal severe grazing 560 700 630 b Light grazíng 2000 2370 2180 a Light uowi-ng 2040 2650 2340 a Light grazing plus 450 660 560 b chemical insecticide

LSD (0.0s) 730

* Ùfeans followed by sane leÈter are not signiflcantly different' P<0.05 (F3,4 = 26.20)

6.I(b) and (c)) and sinllar numbers of predaÈor-days in each treatment (Table 6.1). The age-structures of populations of. C. Tepandø in the different t,reatments are presented ln Flgure 6.2. They suggest that C. repand.a, completed two discreet generations durlng Èhe period of the experlment ' !ü-iÈh Èhe beginning of the second generation in late-l"farch to early-April. The times for each generation in the fleld appeared longer than the 19.7 days esÈimated for C. repanda in the laboratory at 25oC by Tlng et aL. (1978). This dffference could be due to lower mean temperaÈures in the field and the extra energy expended by larvae for catchlng prey ln the fteld rather Èhan in confined arenas in the laboratory. -LL4_ (o)

80 SG tro SG

60 o E o )o 40

o 20 o o. )E C' (h)

o 80 -Í LG LG LG oL o- 60 I

/.0 tÈ d a- o 20 l- ()

o (c) a =) 80 LM LM ! o 60 ! C -13I o 40 o o o-) o- 20 o o l_ o (d)

o 80 T I I I oL I i'i I I t -o 60 E z) 40 odults pupoe 20 torvoe

Feb Mor APn Moy

FIGI]RE 6.2: Age structure of C. repartdø. 1n t,he f our treatments of the predator augmentatLon experfment at Culburra' I9792 (a) rotauional severe grazíng (SG), (b) llght' gtazLtg (LG), (c) llght mowlng (Ll{) and (d) ltght grazing plus cheml-cal insecEicide (I). -l 15-

6.3.3 Discussion Of the nany dÍfferenÈ tactícs used Ëo augment natural enemies (Ables and

Ridgeway 1981, Iluffaker et aL. Lg77), nodificatlon of grazLag dryland lucerne pasÈures appeared Eo be a reasonable approach to increase the effectiveness of

C. nepanda,1n conÈrol1tng SAA durlng suÍImeÌ. This inference was suggested because C. nepanda was Èhe rnosÈ abundant predator detecÈed in L977/78 durJ-ng periods when SAA reached its highest densities, but lts abundance lüas restricted by the disruptlve effect of severe gtazllrg. Light grazLag (200 to 100 sten length) was a treatment which attenpted Eo provide an environment wlth a contlnulty of SAA which may stimulate better perslstence and reproducÈ1on of C. repandø in dryland lucerne pastures, for reasons discussed ln SecÈ1on 6.2.3. This experlment demonstrated that the abundance of C. repand'a. could be lncreased during sunner wlth llghl gtazlng rather than severe gxazing, but ,¿lensities were still too low to offer any reasonable control of SAA' The feasibllity of augmenting natural enemles as a tactic in the control of a Pest noÈ only relíes on an effective reductlon ln the density of the PesË' but also on the compatabiliÈy of Èhe tactic wlÈh oÈher pest cont,rol tactics and agronom{ c practices and Production. The Èrealment, consisting in theory of Itght gtazl-rlg plus complete control whether of SAA wíth chenlcal lnsecÈiclde, was included l-n the experiuent Èo test grazLng used to augment the number of C. reduced the the llght "epand'a' productlon of lucerne herbage and grazlng Potential of pastures comPared to

sEandard, severe gtazlrrg. Ttre treatment Itas not successful because Èhe hlgh innlgratlon rate of SAA fron nearby areas and the lack of resources to regularly spray the treatmenÈ area did not allow Ehe treatmenÈ area Èo be maintained free

of sAA durlng that summer. Eowever, the inftuence of ltght grazLng on the grazLng potentlal of lucerne pastures could be tested by comparing the number of -ll6- days that 300 sheep \tere grazed in each of the other tvto treatments wlth líght grazlng (Treatments 2 and.4) and in the treaÈment wl-th severe grazLng (TreatmenE l) during the experiment. Each of the pastures in the Erro treatments with llght grazfirtg could only be gtazeð. once for tr¡to days while the pasture 1n the treatment with severe grazing \ras grazed on three different occasions, including the grazÍng at the end of the experlment (Flgure 6.1(a)), for seven days at each occaslon (Table 6.2). Dlfferences in the numbex of gtazing days between pastures vrhich were either severely or ltghtly grazed with sheeP \üere nainly

attributed Eo differences ln the production of lucerne beeause most of lhe avaílable herbage ln the pastures during sunmer ls lucerne herbage' The quanÈities of lucerne herbage produced in Ehe treatments with lighÈ mowing and light gxazlng, respectively' \üere visually slmilar'

TABLE 6.2 The dates of. gtazLng and numbers of gtazíng days for 300 sheep on each treatment area during the predator augmentatlon experlment aÈ Culburra, 5 February to 4 June 1979.

Treatment DaÈes of Grazing Number of grazlng daYs

Rotatlonal severe grazing 12.03.79 - 19.03.79 7 ) 23.04.79 - r.05.79 7 ) total = 21 4. 06. 79 - LL .06 .79 7 ) LighÈ EtaztîE 7 .04.79 - 8.04.79 2 Light grazing plus 12.03.79 - L3.03.79 2 chenical insecticlde

The lower production (grazing days) of pastures wiÈh light grazLtg was partly antieipated because such grazLtg stlmulates a less-vigorous regrowth of lucerne from nodal buds rather Ehan Ehe more-vigorous regrowÈh from basal buds -TT7 - which occurs \^rith severe grazlrtg (Langer and Keoghan 1970), and because sheep were only allowed Eo gtaze the top 100 m of lucerne plants r¡ith Èhe light grazítg. Part of the advantage of severe grazing was also thaÈ the sheep remained Ln the pastures for seven days at each tlme of grazing whieh allowed

them to consume dry pasÈure resfdue produced by annual pasture specles in the previous spring, in additlon to lucerne herbage. Both the inabtlity of the lncreased numbers of. C. ?epdnda stimulated by light graz¡ng to control SAA during sulrmer and the deleterious influence thaÈ light grazltg ha¿ on the herbage production of lucerne pastures clearly sho¡¿ed that augnentation of C. ?epandn, by nodifying grazing management was not a useful Èactic for the conËrol of SAA in dryland lucerne.pastures' 6.4 Influence of Predators on SAÀ 1a Sprfng and Sunrner prevlous sampllng demonstrated thaÈ SAA occurred in unexPecte-dly low

numbers during spring in dryland lucerne pastures; Èhe possible reasons for these low numbers \rere noË lLsÈed earlier (Section 3). Ilor'rever, predaÈors Ìtrere considered to be an inportanÈ factor in controlling numbers of SAA at that time, nainly because (a) there were no other obvious components of the environmenÈ, except food quallty, which could have conÈrolled numbers of SAA and (b)

predators conÈrolled SAA during spring in some areas of the U.S.A. (Hagen et aL. f976b). Thus, predaEor-exclusion experlments were conducted to test whether predators controlled SAA in spring because correlatlons between denslty

changes (or densiEies) of the host and natural enemies ln an aree are not usually reliable (DeBach 1958), and the only satisfactory measuremeriÈ of the influence of natural enemies tn the field is to use palred comparlsons of Plots having naÈural enemíes present rüith plots where naÈural enemies are absent or inhibited (DeBach and ltuffaker 1971). -118-

6.4.L Uaterials and methods Four predator-exclusíon experlments rtere conduct,ed in dryland llunter Rlver lucerne pasÈures at the Culburra experimental site at different tímes Eo determlne the influence of predators on SAA ln spring and summer.

(i) Erperiment 7

The first experimenÈ was set up on 1 September 1981 in lucerne-based pasture rvhich had been grazed two weeks previously. The treatments lüere: l. Closed cage - designed to exclude all parasites and predators. 2. Open cage - designed to be comparable with the closed cage in TreatmenÈ I but to allor¿ parasites and predators free access to the aphids 3. Open cage plus DDT - designed to be the same as the open cage ín Treatment 2 but to prevent parasites and predators free access to the aPhids bY including DDT.

Each cage was 460 mm x 450 rorn x 660 nn high and was deslgned to be placed around one lucerne plant. A closed cage had all the sides and top covered with fine nylon gauze to exclude predators and parasítes of SAA. Open cages had

Eauze on three sldes only and were placed in a manner to protect the experimental plants and SAA from prevaíllng wlnds. There were four replicaÈes of each treatment, and at the start of the experlment, 12 similar lucerne plants were selected at random wlthín an area of about 80 n x 80 n Èo allocate to the 12 cornbl-natfons of treaÈments x replicates.

Each planÈ \das pruned to 10 main stens per plant and then caged. Any grass was removed from around those plants allocated to closed cages and then the closed cages and the lucerne plants and soil in them were thoroughly sprayed wi-t}:. 2.57" synergised pyrethrfn prior to caging, to kill any predators or parasites which may have been presenÈ. The base of the lucerne plants and soil 1n the oPen cage plus DDT treatment lrere sprayed with 0.52 DDT. -1 r9-

On 8 September 1981, tr.ro newly-emerged, aPterous adults of SAA were placed on each of the l0 stems in the cages to give 20 fernales per cage; this density was noÈ rnarkedly higher than field densities of SAA at that tirne, but Ehe age structure of the experimental cohorts of SAA would be different from and would have a greater reproductlve potential than the fleld population.

The experl-ment was termlnaËed on 6 October 1981 when Ehe plants of lucerne in the cage-s were destructively sampled, after about t\ùo generations of SAA determined from daily mean Èemperatures durlng the experiment, to estimate the

E,otal numbers of SAA Per cage (replicate). To take a sample, the cages were planÈs lifted on one side, whlEe paper was initially placed under the lucerne ' the stems cut and placed in plastlc bags -and then the paper and surface of the soil were vacuumed for SAA. SAA were washed off the stems and counted in the laboraËory, as descrlbed in Section 3. The vigour of each lucerne plant was assessed visually at the tlme of sampllng and recorded. Ttre densities of SAA in ¡he surrounding field population rüere also estimated at the beginning and end of the experlment by counting the numberg of SAA on 30 randomly selected sEems of lucerne at each time.

(i¿) EæPeninent 2

A second experimenÈ was conducÈed in November-December 1981. The treatments were the same as those in the first experimenÈ and Èhe methods r¡ere sirnilar, excePt thaÈ: (a) 0.5% dlchlorvos rather than Pyrethrin was used to spray Ehe closed

cages. (b) piÈfall traPs slere used for trapping potential predators to assess their ldentification and relative abundâocês'

TwenÈy-four pitfall traps, each consisting of an aluminium can,

63 m dl-ameter x 125 mm deep and open at one end, were buried flush inEo the sand at the base of the randomly selecÈed lucerne plants on -120-

22 October 1981. The Eraps were fllled to about t!¡o-thirds wíth' 27" formalin and a little detergent. (c) lucerne plants erere ûoÈ pruned to 10 stems per plant' (d) 25 newly-emerged, aPterous female SAA r¿ere put into each cage.

This second experímen r¡tas seÈ uP on 5l{ovember 1981, SAA put into the cages on 11 November 1981, and cages sampled for SAA on 22 December 1981'

(i¿¿) EæPeriment 3 The third experimenÈ \üas conducÈed in January 1982 and r¿as the same as the second experiment' excePÈ that: (a) the treatment wiEh open cage plus DDT was omiÈted. (b) temperatures i-n the open and clpsed cages ¡vere measured each hour

w1Èh thermistors and recorded on a Grant@ chart recorder; a thernistor rías placed amongst the lucerne herbage in each type of cage and out of direct sunlight' This third experinefit was set up on 6 January L982, SAA put inÈo cages on 13 January L982 and sampled for SAA on 26 January L982.

(io) EæPeriment 4 The fourÈh experiment was conducted in February-l"larch 1982 and was similar to the second experiment, except that, the treatmenÈs lüere: I. Closed cage - as fn ExPeriment 2' 2. Open cage - as in ExPerlment 2' the 3. Open cage with longitudlnal Pttfall traP across Èhe open side of cage plus SAA - to deternlne whether apterous SAA emlgrate from Èhe

cage.

4. Open eage wlth longltudinal pitfall EraP across the open side of the

cage mlnus SAA - to determing whether apÈerous SAA innigrate to the

cege. -L2L-

There were three replicaÈes (cages) for Treatmerits 1, 2 and 3 and two replicates for Treatment 4; each cage was seeded \.tlth 20 newly-energed, aPterous fenale SAA. Thls experiment was set up on 17 February L982, SAA put into the ceges ort 24 February 1982 and cages sampled for SAA on 17 March 1982. The treaÈments and the expected effects of the treatments on predators in the four predaÈor-exclusion experlments, together with Èhe Presence or absence of pitfall traps in the pasture in each experiment, are gLven 1n Table 6.3.

TA3LE 6.3 The treaÈments and theír expected effecÈs on the occurrence of predators in the four predator- exclusíon experimenÈs conducted at Culburra from SepÈember I98I to t"."h Lg82, together htith Èhe presence or absence of pitfall traps in each experinent.

TreatmenÈ Expected effect ExpÈ. I Expt. 2 Expt.3 ExpÈ. 4 of treaÈroent Sep-OcÈ Nov-Dec Jan Febl'far on predators

Closed cage + + + + Open cage + + + + + Open cage + DDT + + Open cage with pltfall trap - plus SAA + + + - ninus SAA +

Pitfall traps + + + l-n pasture

+ predators, treaÈment or plÈfa1l traps Present - predators, Èreatment or pitfall traPs absent -122-

(o) Analgsis of dnta Data from Experiments 1, 2 a¡1d 4 were analysed separaÈely wlth a onerùay The AI{OVA using a logarithnic transfornation of data to stablllse varlances' data from Experlment 3 were not analysed because hlgh temperatures in all of the cages killed most of the aPhids. 6.4.2 Reaulte lhe results of Èhe predaÈor-excluslon Experlments I, 2 and 4, respecÈlvely' are given |n Table 6.4 as the mean numbers of SAA per cage afÈer 35 days tn Experlment 1, after 41 days ln Experlment 2 and after 21 days in Experiment 4' Large differences in numbers of SAA occurred in Experiments 1 and 2 betlüeen treatúenÈs treaÈments wlth closed cages from which p¡edators \,{ere excluded and !ülth open cages lnto r¿hich predagors lüere allowed access and were expected to occüro Interpretation of such data from oPen/closed cage experinents can be mlsleadlng due to (a) innlgration and emlgratlon of aphids wlth Èhe open cages but not closed cages Q"faelzer 1981), and (b) to cages inEerfering with slgnlficant behavloural and ecologtcal characterlstics of both predators and prey (DeBach et aL. 1976). Ilowever, the experiments aL Culburra were carrled out at times when densiÈies of SAA in the field were very low (Table 6'4) and with feer alates, thus minimising the effects of imrnigration; and emigration was also minimised because densities of SAA in open cages lüere not sufficlent to stimulate crftlcal productlon and dispersal of alates. Furthentrore, the behavfoural characterlstlcs of SAA were unlikely to be affected because low large initlal numbers of apterae llere used Ln Ehe experiment, and the relatively cages cages were expected to produee slnilar envlronments wiÈhin open and closed For (e.g. temperatures in plant foliage were all within + loç of each other)' SAA beÈween Ëhese reasons, the signlfieanÈ differences (P < 0.05) ln numbers of demonsÈrate open and closed cages are most likely Eo be real and they clearly that predators were the key factor !n mafntaLnlng SAA at low numbers during

s pring. -L23-

TABLE 6.4 Final nean numbers (x) and log numbers (1og x) of SAÀ per cage in three predator-excluslon experinenÈs at Culburra, v!2. Expt. I (Sept.-Oct. 1981), Expt' 2 (Nov.-Dec. fgSf), and ExpÈ. 4 (Feb.*lar' 1982)' Also glven are (a) LSDs at P=0.05 for dlfferences beEween mean numbers based on the log numbers of SAA per cage and (b) field densiÈl-es of sAA on lucerne plants around the experimental cages.

Final mean number of SAA Per cage

Treatment Expt. l Expt. Z Expt. 4 (35 days)* (41 days ) (21 days)

x log x x log x x logx

Closed cage 890 2.87 31500 4.45 500 2.52 Open cage 70 1. 83 150 1.85 60 1.7 L Open cage + DDT 90 1.87 9 0.5 3 Open cage with pltfall traP 90 r.87 - plus SAA 20 l. 10 - rninus SAA

rsD (0.0s) 0.41 0.96 0.63 (F2,9=20.85) (F2,9=37.32) (F3,12=5.88)

0.6 Field SAAÎ 0.0 - 0.5 o.o - 2.4 0.2 -

* time fron seeding cages w1Èh adult SAA to destructive sarnpling of aphids and plants wlthin cages. t mean number of SAA per stem of lucerne: beginning - end of experlment' - treaÈment noÈ lncluded ln experimenÈ. -r24-

An unexpected outcorne in Ehe first t\do experimenÈs was that the mean Èo or numbers of SAJ\ in the treatmenÈ, oPen cage plus DDT' vlere either equal less than those in the treaÈmefit with open cages only. The numbers in treatment with DDT were exPected to be sinj-Iar to t'hose in the closed cages sAA because DDT was expecÈed Èo control ground-dwellíng predaÈors but not affect probably on Ëhe plants. The m¡in reason for Èhe failure of this treaEment was the toxlc effect of DDT on sAA r¡hich was subsequenËly shown in experiuents conducted by J. Samoedi (perso comm.); thts treaÈment was not lncluded in fuÈure experiments. Experiment 3, whÍch was carried out in January, failed because in all cages there were 10 consecutlve days with maximun temPeratures equal to or exceeding 3goc due to high ambienÈ temperatures aÈ Culburra; these high tenperatures killed most of Ehe aphids (Sectfon 7). Data fron pred,ator-exclusíon Experlment 4, which was set up in February/March, !üere expected, from previous experience (Section 3), to show that the large rates of increase of SAA during summer would swaEP any controlllng lnfluence of predators, and Ehat consequenÈly the flnal numbers of Table SAA would be slnilar in both open and closed cages. Ho¡úever, the daEa in 6.4 lndicate Èhat there were significantly more Sfut (P < 0'05) in the closed cages. on the other hand, overall numbers of sAA (Table 6.4) were much lower than expecÈed for thls tlme of the year when the raÈe of increase, (rr), of

SAA ln cages was about O.fO g/g/day (Sectlon 9). Ttre lower numbers were att,rlbuted to periods of above-average dafly maximum temPeratures whfch linited the rate of increase of SAA (Sectlon 7). Under these conditions of stress for

SAA, predators v¡ere consldered to more effecÈively control SAA than could be

expected durl-ng February/lfarch fn most years when the weaÈher was more

favourable for SAA. -125-

It was mentioned earlier that neither irnrnigratlon nor em{ gratlon of SAA were likely to occur durlng the predator-exclusion experimenÈs. Open cages with pitfall traps were included ln Experlment 4 to Eest ¡¡heÈher there was inmigration or enigration of apÈerous SAA into or out of the cages due to walklng. SAA were not found in Èhe pltfall traPs and the final numbers of SAA ln the open cages seeded with SAA did not differ from those ln open cages r¡ithout pltfall traps. The hfgher than expected number of SAA 1n the cages wiEh pltfall traps and not seeded wlth SAA was m¡1nly due Eo one replicate being more heavily infested (Appendlx 5.2), probably due to an imrnlgrant alate or alates. pltfall traps were included in Experiments 2, 3 and 4 to determine which

preda¡ors were presenÈ 1n the dryland luc,erne pasture Èo move into the open

cages during the experiments. Some predaÈors were caughÈ in Èhe traps and Ehe

numbers of three types of predaÈors - M. taenørtíae, C. repanda and spiders - caught per day begínning in November 1981 are given 1n Figure 6.3.

Numbers of M. tasnøniae peaked 1n early-November (Figure 6.3(a)) but' unfortunately, pttfall traps r¡rere riot, used for the firsÈ predator-excluslon

experimenE to show whether M. tasn¡niae !Ías Present earlier in the season' the M. ta.smaniAe Ls llkely Èo be present earller l-n the season because {t has exËremely low thermal Ehreshold for development, of z.goc (sanson and Blood LgTg). In addltlon, M. taemaníae ls líke1y to be lmportant in the conÈrol of

SAA 1n SepÈember-Oc¡ober and possibly durlng early-November because it has a hlgh efficl-ency of capture of aphlds and 1s llkely to be a more efflclenÈ predalor at low prey densitles than are other predators (Maelzer 198f)'

Neuenschwander (1976) also suggests that the low tegperature thresholds of

development of irnrnature stages of hemeroblids lend them as possible blologl-cal control agents agalnst aphlds very early !n Èhe season when other predators and parasites are lnactlve. -L26-

(o) M. éasmaniae' (odutts + lorvoe)

2

(odutts + lorvoe ) o (b) C. reponda.. E 2 o- o L

o L o 1 o ! o L o-

o

Lo -o ( E ( c) Spiders odutts + Juveniles ) ) c 2

C o o

Nov Dec Jon F€b. Mon

FIGIIRE 6 .3: l-lean numbers of (a) M. tasmaniae, (b) C' repanda' ar.d (c) splders caughÈ in pitfall Eraps during the Ehree predator-exclusLon experlmenEs at culburra conducted during t,he perlod November t98l to March 1982' -L27 -

Ttre numbers of c. repand.a. (Figure 6.3(b)) were very low durfng the five sAA the monËhs of sampling and were probably due to very low densLÈies of in field during that period, as discussed under the previous heading. The most conslstently trapped predators during Experlments 2, 3 and 4 were spiders (Figure 6.3(c)) and the highesÈ numbers of splders trapped were species fn the fantlies Lycosidae, Gnaphosidae and Llnyphiidae (Table 6'5)' Splders 1n

Èhese fanilies are ground-dwelltng and are more llkely Èo be trapped in piÈfall

traps than Èhose inhablting plant folfage. There were 21 dlfferenÈ specles of spiders trapped during the sprlng/summer period whlch was considerably less Ehan the 57 species collected tn lrrÍgated lucerne durlng Lhe sane season in New SouEhtr.Iales(AusÈralia)byBishopandEoltkanp(1982).ThlsdÍfferencecouldbe explained by envlronmenÈal dlfferences beEween dryland and irrigated lucerne stands, and Èo the use by Blshop and lloltkamp (fbid.) of both vacur:m sanpling durlng the day and continuous piÊf411 traPplng' 6.4.3 DÍacuselon The use of pltfall traps for quantiÈative evaluaÈ1on of predators has been critlcised because caÈch slze !s tnfluenced by a wide range of physical, environmental and behavioural factors apart from the síze of the population (Southwood 1978), but Greenslade and Greenslade (1971) considered that' although ptEfall traps have dlsadvanÈages, the disadvantages are not necessarlly so great as sEated by sone workers and need Èo be balanced agalnst thelr sinpllcity and ease of operation. More recently, Ienskl (1982) opposed the criticism Ehat pitfall Èraps cannot be used to estimate or comPare populatfon densities because capture rates depend on activLty as well as densl-ty. Ile claimed thaÈ an "activity abundance .(captures per traP per day)" nay be nore lmportant than true densl¡ies, slnce the lmpact of the population of predators on its prey and competitors ls a function of acÈivlty as well as denslÈy' The same reasonlng

was used t,o conclude that spiders were probably inportanE fn nalnÈalnl-ng low i28

TABLE 6.5 The number of each species of spider found in tIùenty-two pitfall traps at certain sampllng times durlng t"rvo predator-excluslon experíments at culburra, vfz. Expt. 2 (Nov.-Dec. 198I) and Expt. 3 (Jan. 1982).

Total Nuober of each Species fn 22 Traps Species Nov.8l 8.12.8I 15.12.81 22.12.81 t3'1.82 20'l'82 Total

3t2 Lycosldae 237 Trochoaa erpolíta ínPedita 58 2t 2l 70 33 34 I 25 Geolycoaa epencerí L7 I 6 l8 C. godeffroYí 2 6 4 6 t6 ceoLgcoea sp. 2 4 4 I lt Artor4ø. sp. 3 6 I 5 G. propítin 2 2 266 Gnaphosldae 5 I r88 Gnaphoeidze ep. I 57 26 90 o 48 Anzacì.a, ep. I3 5 2L l0 l8 Gnzphoaídaa ap. 2 3 2 I 9 II Myatúru sp. I Megatryrcnecíon sg. I Llnyphitdae 106 106 )eteariue reLanoPggíue 22 58 l4 lt Therldffdåe 8ó 50 Steatofu groaea 4 4 6 9 l3 L4 z4 Lactrodeetue haaeelti 2 IO 4 8 L2 Eutgopeie sP. 3 2 58 Clubionldae 57 Corrinomta sg. 9 8 t2 9 20 I Chirucanthitn 26 oxyopldee l8 26 OÊAopee sp. (2 üPenue) 2 2 1t DlcÈynldee ll Ðíctyt'ø ap. 2 3 6 I Saltl.cldae I Saitie sp. 2 I Èliturgldae i Mítunga ep. -129- numbers of SAA durlng spring and early-sunmer in dryland lucerne Pastures ' All spiders ere predatory and they have been reported to feed on different species of aphlds in different croPs (e.g. Bishop and Blood 1981, Vickerman and Sunderland 1975). Serological tests, as carrled out by Vickerm¡n and Sunderland

( 1975), would be useful to confirm Èha! spiders are feeding on SAA aË Culburra' 6.5 Abundance of. bí'o4,18 eofip Laru,tue 1o Drylaad Lucerne Pasture 6.5.L l.f¿terials and ¡ethods T, eonpLana,tuy was released aÈ the experlmental site at Culburra ln 1978 on 24 and 28 April, 5 and 23 llay and 12, 23 arrd 30 June. At each Èime of release, lucerne herbage infested wiÈh parasiÈised SAA and mrmmies of

T. eornpLana,tus was harvested from a primary release site for T. eonrpLana.tus

aÈ Meningte (!f1lsoî et a,L. 1982), placed in an insulaÈed container and

lmmediaÈely taken Èo Culburra. AÈ Culburra, the infested lucerne herbage was dlvtded lnto approxlnately four portions and a portlon \üas Placed ln the centre of each of those treatment areas whlch lüere not treated with chemical insecticlde 1n any exPeriments. At Ehe times of release, lucerne plants in these areas rüere naturally infested with SA.l\ (Section 3). On 12 June 1978, the cut lucerne wlÈh parasLtes was placed in a cage' I m x I m x 2 m, and covered with fine gavze, over lucerne plants ínfested l^71th SAA' The cage was renoved after two weeks. The abundance of 1". eonpLallø.tus LrL the experimental slÈe was subsequenÈly

esÈLmated by uslng slüeep nets Eo detect adults' sampllng munmies and dissecting fourth-instar saA for larvae of the paraslte, as follows: (a) sanpling for adult Parasltes was done wl-th sweeP neÈs thaÈ were the

same as those used Èo sample predators (sectlon 6.2.1) excePt that

they were nade wiÈh flne gauze net and not calfco. Twenty loÈs of t0

standard 9@ sweeps rüere rned,e at the experimenËal site each week from 8 APril to 23 June 1980. -1 30-

(b) Counts of mummies of ?. eonlpLarlatL¿7 orL steÍlÉi of lucerne were uade

r,rhenever lucerne plants r{ere sampled for SAA, predaEors and/or herbage production during Èhe four years of experiment,s at Culburra followlng the releases of f. eotÍPLanøtus ' (c) ApproximaÈely 1200 fourth-instar sAA from treatment areas T* and

TU (i.e. treatment areas \,{'ith no or few applications of chemical insectlcide, respectively - Section 4) were dissected for parasites from 12 June 1978 to 7 July L978; thl-s total comprised nearly all the

fourÈh-lnstar SAJ\ sampled in those ÈreatmenËs. From 8 January to 1g June Lg7g, abouÈ 38 500 fourth-instars were dissected; this Eotal represented 96 different samples of fourÈh-instar SAA from 18 sampling

Èimes spread throughout the p.tio¿. In 1980, 525 fourËh-instar sAA were dissec¡ed fron 20 different samples of SAA collected from the experlmental site on 8 þril, and 73 vrere dissected from sarnples

collected on 5 l"faY. Detect,ion of larvae of T. compLartatus by dissecting fourth-instar

SAA was successfully tested wlth parasitised SAA from laboratory cultures and, for this reason, this rnethod of detecting parasites in

SAA was not considered a rnajor linitlng factor in the deEection of larval Parasítes in the field. 6.5.2 ResulÈs Following Ehe releases of ?. eOrnpLat'øtua at Ehe Culburra experimental site from April to June Ig78, a sLngle adult was detecÈed in a sweeP-net sanple on 7 November 1978, but then ?. eonrpLana'tul was noÈ detected as adults' of mummies or larvae 1n fourth-instar SAÀ during the 1979 sunrner; the sightlng only one adult suggested ÈhaÈ the parasite had not established in the area' or at least had not increased ln densities that could be detected by the methods of sampling. During the 1979 spring, densLt,ies of sAA were very low and -131-

T. eornpLaTntue vras not found,. On 29 January 1980, one ?. eonlpLann'tL¿s mummy was detected, but it was not unEil early-April 1980 that ?. eotnpLartatus was againdetected.AdultsandformummlesweredeEectedfromAprfltoearly-Junein very low numbers (Table 6.6). Ttre highest number of mumnies r'ras recorded on 12 May 1980 and represerited percentage parasitisms ranging from only 0'87" t'o 2'47" in the different replicates saurpled. However, these estimates of percenËage parasltism ere crude and are based on a comparison of the numbers of mummies with the es¡imated numbers of SAA per sample uniÈ (clunp of lucerne)' Such estimates of percentage parasitism may noÈ indicate the true parasitism rate becauseparasiËemtrmmiesaresuscePtibleEopredationand,also'mummies resulting frorn parasitism of previous generations of aphíds nay still be inÈact on the plants. However, the numerous dissections of fourth-instar SAA collected at different tlmes durlng summer, autumr and early-winter fron 1978 to 1980 did not yield larval ?. eoîrpLanatus, thus confirmfng exÈremely low levels of

parasitlsn of SAA in dryland lucerne pasture.

TABLE 6.6 : The total numbers per sample of both adults and mummies of. T. eottqlarultils in dryland lucerne pastures fron April to June 1980' Culburra.

Det,e Adults/100 sweeps Mummíes/8O clumps of lucerne

8.04.80 L4 0 8.05.80 I 0 I 2.05 .80 I 62 20.05.80 I 26 .05.80 : 1 2. 06. 80 4 0

5 .06.80 0 0 23.06.80 0

not sampled. -L32-

6.5.3 Discussion The numbers of T. contpLanatus were so low at Culburra that one cannot decide whether the parasfte established at the time of the releases or whether there was subsequent lnnlgration of adults to the area (adult ?. eotnpLanatue are capable of dispersing long distances, I,lllson et aL. 1982). HoweveÊ, T. eontpLanøtzs is evfdently not an effecÈive bloconËrol agenÈ for SAA tn grazeð., dryland lucerne pastures in the Upper-South-East because lt was absenE during summer when SAA was most abundant, and occurred ln only low numbers in

Èhe autuûi when Èhe numbers of SAA were already decllning due to cooler ambíent temperatures. l.Iilson et aL. (1982) reported nrch higher levels of parasitism of SAA 1n lrrigated lucerne; up Eo 867" based on dissecËions of fourth-lnstar SAA. Most of thls parasitism occurred in late-sunmer and autumn, which was sinllar to Èhe llnlted data obtal-ned at Culburta. T. eontplartø.tzs is also nainly found in the field during autumn in the Mediterranean reglon (Aeschllmann 1981). Ttre effect of T. conrpLanatue Lt conËrolling the abundance of SAA and its influence on SAA-lnduced damage Eo irrigaEed lucerne was tesÈed by I'Ialden et aL. (1n preparatlon) in South Australia in Èhe sunmer and autumn of 1980 ln experiments w1Èh field cages. Itrey demonstrated that I. eontplann'tue dld not control SAA durlng suûtrer, but did reduce Èhe abundance of SAA in autumt and consequently lnduced an increase in the yield of lucerne at Èhat time. RecenÈ field studies in lrrigaÈed lucerne stands Ln South AusÈralfa by

Samoedi (pers. coÍutr.) further suggest that ?. eotnpLartatug is more efficl-ent with lower host/parasLÈe denslty ratios; Sarnoedi thínks that the inabllity of

T. eonrpLanatue to prevent raptd increases ln denslties of SAA 1n summer ls due to a hlgh host/parasÍte density ratio during late-sprl-ng and early-summer. Ile attrlbutes Èhis high ratto to a reducÈlon in Èhe abundance of I. eotnplanntue in sprlng due Ëo predaÈion of parasltised SAA. His data generally agree wfth those of l.Ialden et aL. (1n preparatlon). Samoedi also indicated that -133- hyperparasites signiflcantly reduced ehe rate of increase of T. eotttpLanntus' a factor which always has the undesired effect of raisíng the hosÈ equillbriuu density (Ilassell 1978). FacÈors causing a lower level of parasitism of sAA in dryland Pastures than 1n lrrlgated sÈands in autu¡n¡r are not known, but differences in the levels of hunidity and temperature between the trrto tyPes of crops l-n summer nay be important. During sunmer, Èhe humídLtles would probably be much lower and the

t,emperatures hlgher in dryland lucerne pastures than in irrigated lucerne stands. Such differences would be caused by a conbinatlon of the waterlng of

Èhe irrlgated stands and Lhe less dense herbage and severe gtazíng of dryland pastures (Slatyer and I'fcllroy 196f ). In addítlon, ?. eoÍrpLanntus may either or enÈer dlapause over summer (K.S. Ilagen' pers. conm', Schllnger and Ha1l 1960) else it may not survive the harsh envl-ronment of gtazed dryland lucerne during

supmer, and x¡Ay therefore need to relnfest dryland pastures each autu¡n' If this re-lnvasion is required each yeaÊ, then the tlme taken for ?. e1Î'tpLAnatus to reinfest a pasture and t,hen increase in number could ParÈly account for Èhe lower peak levels of parasitlsm recorded 1n dryland pastures compared to irrlgated stands ln autumn. In croP sysÈems elsewhere, there are numerous examples where natural enemLes more effectively control a host in one region

compared Ëo another, and the dífference 1n effíciency can be related to differences ln the weaÈher between the two reglons (l'fessenger and van den Bosch r971). Wllson et aL. (1982) studied Èhe establishment, dispersal and fncrease of

T. eornpLana,tus in South Australia and concluded thaÈ ?. eoÍtpLanatus dlsplayed all the qualitles of an effective biological control agent; Èhis

conclusion rùas based on a number of behavioural and ecological attrlbutes of

boÈh the paraslte and sAA. l'lany of the attributes that they lncluded for T. eorrpLana.tus have prevlously been considered essentiaL for an effectlve -r 34- natural enemy¡ ê.g. Huffaker et aL. (1971), Itagen et aL. (1976a) and van

Emden (1966). Ilowever, I,laage and llassell (1982) used maÈhematlcal models to ídentify and examine those attributes of parasttes and hosts which 1ed to successful biological control. They identifted that a number of Èhe attribuÈes consídered by the above authors¡ ê.$. searching efficiency, fecundlty and larval survival of the parasite, were "key contributors to the depression of host equilfbrta and/or to the stabill-ty of the inÈeractions"; but Èhey warn that "ecological and evolutl-onary Èheory cautlon us against the slnplistic conclusÍon

thaÈ a good parasltoid should have a high searchlng efficfency' high fecundity, high larval survl-val and so on". They considered that successful parasltes not only vary in all of these characters, but often show sÈraÈegies which couple high values of one with low values of another, and concluded that a

good. parasite for biological control appears Èo be one which ls ¡sell adapted to exploit the particular distribuËion and density of its host. Experience rüi;h T. conpLana,tus in the experlment aÈ Culburra and observations l-n oËher dryland lucerne pastures in the region suggest that ?. eotrPLanatae does not have a suitable stralegy to be a good biologlcal control agent for SAÀ in dryland lucerne Pastures in South Australía. The fallure of T. eontpLanøtus to effectively control SAA ln dryland lucerne.pastures ln the Upper-South-East is contrary to experlence in eastern- AusÈralia where ?. eonrpLanatuÊ Ls considered to be a successful parasite in borh dryland and lrrigated lucerne stands (Lehane L982). The consldered efffcacy of T. eoîrPLarlatus LrL eastern-Australia ls based nalnly on the occurrence of relatively hLgh levels of PercenÈage Parasftlsrn of SAA by

T. eOntpLaÌ1.atus and lolú numbers of SAA in Èhe fleld, rather than on more definitl-ve data. Ttre low numbers of SAA nay have been due also to environmenÈa1 factors other than ?. eoîrpLanatue. Further reasons for the difference in the

effLciency of T. e7îrpLa,na,tl,¿a betlüeen the two regl-ons of Australía are not obvlous. -135-

Inundatfve releases of ?. eomplanatul at critical tfmes of the year for

Sârl\, a tacÈic discussed by Knípling (1979) for control of other pests, mâY increase the efffcacy of T. eornplana,tua fot the conÈrol of SAA. Ilowever, inundatlve releases of ?. eorrpLa?1ntul are noE consldered to be economically feasible with presenË resources, both research and commercfal, thus providing another example where the use of periodic mnss releases of natural enemies is prinarlly inhlbtted by econoutc rather than ecological reasons (Stlnner 1977). 6.6 The Role of Natlve Predetore and Introduced Parasitee I'n the C¡ntrol of

SAA ln Drvland Lucerne Paeture 6.6.1 Predators

The imporËanÈ role of natlve pr-edators ln dryland lucerne pasEures lras to maintain populatLons of SAA at low numbers durLng spring. The predators fnvolved were malnly the hemerobiid, 14. taemaniae, and various species of splders. The effecÈlveness of the predators at thls time was clearly denonstrated by the data from a series of experlments with field cages which allorsed a eomparÍson between the increases ln the numbers of aphids with and without predators, respectively, and 1n which there was a reasonable assurance that the ecologl-cal events in Ehe two Eypes of cages were lndependent. I'Iith such experlments, differences 1n prey denslËy beE\.reen the two tyPes of cages are useful to measure the net effects of predaÈors (Gilbert et aL. L976), but the data do not explaln Ehe components of predation leading to Ehe end result (Ilolling 1959). Ilowever, Èhe ltolling rnodel Ls too detalled for use with field data and the only predation models that have been used 1n the fleld, apart from the recent one of Frazer et aL. (1981), lnclude variatlons of the Bombosch

¡nodel (e.g. Tamaki et a.L. 1974, Tanaki and Long 1978, van Emden 1966)' The

Bombosch model has only three components of predatlon, viz. synchronisation of predator and hosÈ, voraciÈy of predator, and reproductLve raËe of hosÈ. I'¡1th

aphidaphagous insects, van Emden (ibíd.) considered that Ehe effects of the -1 36- latter two components were conÈrolled by the first conponent buÈ he also used the Bombosch model to show thaÈ envlronnental factors which influenced the voracity of predators and the rate of lncrease of aphlds were important' The success of predators, especlaL|y M. taema¡t'iae, in controlling SAA 1n dryland lucerne pastures durlng sprfng aPpears Èo be due malnly to (a) Uhe predatorr s abiltty to be acÈlve and Eo increase 1n numbers at low Èemperatures - especially at tenperatures aË which the aphidrs rate of increase in numbers 1s not high (Sectlon 9) - and to (b) the extrenely low numbers of SAA whlch survive the winter in dryland lucerne Pastures together with an extremely low probability of inmigrant alates in early-spring (Section 3.3.1) so that the predator/prey ratto 1s relatlvely high. In early-summer, higher daily mean temperatures favour more rapld increases

in Èhe number of SAA Èhan 1n sprl-ng and, from then and throughout Èhe rest of

summer, the potentlal rates of increase of SAA are too high for predators to effectlvely control them. The most conmon predaÈor durlng sulnmer is the native coccinell|ð,, c. Tepanda., buÈ this specles only occurs ln relatively low numbers. part of the reason for fEs low abundance in pasture is periodic severe grazlng which dramaÈically re,cluces the number of aphlds necessary to stLmulate the persistence and reproduction of. C. fepand.a' in the pasture' Less-severe gtazLllg ensures a continuity of SAil\ and increases the number of C' ?epand'a" improve buÈ the lncrease in number of C. repanda 1s not sufflcient to markedly iEs effecÈiveness as a conÈrol agent. The lack of effectlve predation on SAA durlng surtrmer reflects Èhe paucLÈy of natlve aphtdaphagous predators adapted Èo feedtng and reproduelng on aphids at thaÈ tine of ttre yåar; prior to the establishmenÈ of SAA in L977, the densities of most speeles of aphids ln South Australla peaked Ín spring and

autumn and r¡ere low in summer (l'laelzer 198f). By contrast, ln souÈh-western U.S.A. the cocfnellids, Hippod.a,nia spp., are act,lve during summer and were -L37- important 1n the control of SAA when SAA first esÈablished in the area' though unfavourable predator/SAA ratios did occur ln nid-sunmer in some regions (Ilagen et aL. f976b). Ilowever, 1n Canada, where Hippodnntiø spp. do noÈ occur' noÈ to conÈrol oÈher aphidaphagous coccinellids , CoeeíneLLa spp. ' were able pea aphld, Aeyrthosiphon piewn (Harris), ln lucerne stands (Frazer and Gllbert Ig76). They concluded Ehat "slnce the cocinellid-aphid relaÈionship is unstable and incapable of a steady state, !üe cannoE expect, the coccinelllds Èo keep aphid

numbers low for any length of time . ... to use ladyblrds as effective and

permanent agent,s for biologlcal conÈrol, Ise must direct their naÈural behavlour to quite afi unnatural end." Etazet et aL. further studied the same Ínteractlon as Frazer and Gilbert (L976) and similarly concluded that "the intrlnslc lnstabllity of the predaEor-prey relationshlp nakes it very difficult to use coccinellids alone for biological eontrol of aphíds throughouÈ the

seeson. "

The more effective control of aphtds by Híppod'atnia spp. compared to

CoeeineLLa spp., as descrlbed above, would be due Partly to differences ln the reproductLve dornancles of species ln the Èv¡o genera. Specles of

Híppodnmí,4 have a facultat,ive reproductlve dornancy and nay respond reproductively when sufflcient aphíds are Present; they are more sensiËive to the presence of aphids than species of CoeeineLl¿ whlch enter an obligate

dornaney during summer and do not react to Ehe abundance of aphids in that season (Snlth and llagen'1966). In addition, CoeeineLLa spp. are not as

abundanË in the fleld, in Californla at least, durlng spring and auÈumn even

though specLes l-n boÈh genera are actlve (SniÈh and Ilagen 1966). 6.6.2 Tactica for naaagemeot of SAA The introduced parasLte, T. eotnpLanntue, vÍas also lneffective for the

control of SAA during suÍrmer. So, l-n the future, SAÄ-resl-stant culÈlvars of lucerne ¡v-Ill be the naln tactLc used to mânage SAA tn pastures ln the Upper- -138-

South-East (Section 5.3.3). Ilowever, where the new cultlvars are not highly

resistent to SAJ\ or if fuÈure biotypes of SAA evolve whleh ean damage the ner¡ resistant cultlvars, a further control straÈegy w111 be required and m¡y include augmentation of predators, lf econornícally feasible. If predators are Èo be more important ln the future, predator/ptey models

for SAA sinilar to Èhose developed for various specíes of aphlds and predators on sugar beer, and potatoes by Tanakl et aL. (1974) and Tamaki and Long (1978) nay be useful for short-term predictlons of the expected inPact of predaÈors on a SAA prior to naklng declslons on the need to use some other tacÈlc¡ e.8.

chernical l-nsecricide. The nodel of Tamakl et aL. (L974) can predict Èhe

number of aphl-ds in a given number of days. The prediction depends on (a) estimaÈlons of l-nitlal denslty of aphids, (b) predaÈor Por,rer (i.e. the

number of predators |n dlfferent classes of voraci¡y ntrltiplled by Èhe respecËive'feeding capaciEy of each class), and (c) predaÈor efficiency. Tanakl-

and Long (1978) increased the precision of the model of Tamakl eþ aL. (L974); they included the lnfluence of tenperature on both the rate of increase of prey

and on the feeding response of the predators, and also included the influence of prey density. The orlglnal model was also converted to a temperature-drlven nodel which gave Èhe new model an lmproved predl-cÈive capaclty over short perlods of tirne. The appll-catlon of such models depends on practical (econonl-c)

neÈhods to estfmate the densltles of aphlds and predaLors in commercial situations; the need to estinate these denslÈtes would currently be a problen ln dryland lucerne pastures because of the dlfflculties in efflcfently sanpling

both SAA and predators ln the lerge area6 of low-productivity Pasture on each property. Crofr (I975) used a dífferent approach to predict Èhe probability of effectfve control of phytophagous n1Èes by a predatory ml-te 1n apple orchards, and thus to predlct the need to use another control tacÈlc. Ile determined the -r39- levels of probability of control for a number of different predator/prey ratios and related each level of control to the Èolerance level of the pest miEes on apple trees. If the predator/prey ratio is such thaÈ the probability of biological control 1s hlgh, the density of nites will likely renain below the tolerance level and oÈher control tactics are not required. Sinilar to the models discussed previously, the use of this type of model to predict the need predators, for the control of SAA in for t,he application of tactics ' oÈher than dryland lucerne pastures is currently restricted by the lack of suiÈable methods to estimaÈe t,he denslties of aphids and predaÈors in corumercial pastures' Finally, the lack of conErol of SAA ln dryland lucerne pasture by predators the and parasites in sumner and auËumn suggests that any strateg"y developed for short-term control of SAA in susceptible dryland lucerne pasture in Sou¡h Australia should not necessarily be constrained by a need to Protect naÈive predators and ?. eompLd'na.t¿¿s during these seasons'

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I,Iaage, J.K. and llassell, 14.P. L982. Parasitoids as biological conÈrol agents - a fundamental approach. Patø.eitoLogy 84: 241'268' Iüalden, K.J. and,tr{lltshire, D.J. Ihe regulaÈory influence of an internal hynenopterous ParasiEe' Trioæys eonpLanat¿e Quilis (Ilynenopt'era: Aphidildae), on rhe sporred alfalfa aphid, lTterioaphie tn'ifoLü (Monell)

f. maeuLata. (In PreParaËlon). I,lilson, C.G., Swincer, D.E. and l^Ialden, K.J. 1982. The introducËion of

Trioæys eonpLd.rlø,trzs Quilis (Ilyrnenoptera: APhiditdae), an internal parasite of the sPotted alfalfa aphid, í.nto South Australla ' J' Auet' êrlt. Soê. 2Lz L3-27.

I,Ioodr¡ard, T.E. L982a. The ident.ify of Èhe species coÍlmonly known Ín Australia as Nabis eapsifonnzls Gernar (Ilemlptera: Nabldae). J' Auet' ê1Lt' SoC'

2lz 143-146.

ltoodward, T.E. 1982b. Nabie kinbergíi Reuter, the q¡rrefiÈ name for Tropieonøbie nigroLineatue (Distant), and its Australian distributfon (Iterniptera: Nabidae). J. Aust. ent' Soe' 2L:306' -146-

Appendix 6.1 : The total number of C. Tepand'a' per sample from 12 January L978 to 31 May 1978 in each treatment of the grazlrtg experimenE in dryland lucerne pasture at Culburra.

Field Treatment C. repandn/l0o sweeps C. repanda'/2o clumps lucerne

L2.r .78 16 . 3.78 7 .4.78 3I .5.78

0 weeks* 3 weeks I week 3 weeks

7 I TO 0 29 7 T¿o-oo 0 5 (14)t I 5 Trgo-zoo 0 o (8) I 9 10 TV 0 L2 2 5 r¡eeks 2 weeks 0 weeks 2 weeks 13 15 2 To I 6 T¿o-oo I 1t (14) I (1s) 7 Trgo-zoo 0 10 (14) 3 (ts) I 0 TV I 20 0 (r5) 4 weeks I week 5 weeks I week L7 5 3 To 0 I T+o-oo t 0 2 (8) t 0 I 4 (8) 6 T r go-zoo Tv I I 0 (8) 5 3 weeks 0 weeks 4 weeks 0 weeks 7 4 T0 I 0 7 (7) rao-oo 0 I 15 (22) 3 I 2 (8) 7 (7) T rgo-zoo 0 Tv t 0 5 10

* time after gxazLng. in 1 ( ) number of days from last appltcation of lnsecticlde for sAJ\ control currenÈ regrowth Perlod. -147-

Appendlx 6.2 ¿ Flnal numbers of SAA in each eage (rePllcate) in three predator- exclusLon experfuents aÈ Culburra, vLz. Expt. 1 (Sept'-Oct' 1981), Expt. 2 (Nov.-Dec. 19Sl) and Expt. 4 (Feb.ì"far. 1982) '

Final numbers of SAA Per cage Treatment Replicate Expt. I ExpÈ.2 ExpË. 4

Closed cage I 633 14460 232 2 366 48490 362

3 747 3 1500 r282

4 r80 I + 1r6

Open eage I 53 24 52 2 60 15 38

3 65 296 32 4 98 245 108

Open cage + DDT I 110 33

2 83 2

3 L32 2

4 25 0 open cages with pitfall traPs - plus SAA I 72 2 32

3 L77 4 - nlnus SAA I 2 40

treatment not included ln experiment. + all SAA dead due to death of lucerne. 148

Appendix 6.3 The age and sex distribution of each species of spider found in the pitfall traps at certain sarnplÍng times during two PredaÈor-excluslon experiments at Culburra, ví2. Expt. 2 (Nov.-Dec. 1981) and Expt. 3 (Jan. 1982).

Number of splders

20.1.82 Specles Nov.8l B.t2.8l 15.12.81 22.12.3L 13.1.82

J*c¡g J d g J d g J d q J d 9 J cr I

Lycostdae '¿ Tt ochoea erpolita ínpedita 242141236I8 63 4315991987 GeoLycoaa epenceri l6 I G. godeffrogí 2 I 4 23r Geolycoaa sp. 44 6 A?toria sp. 3 I G. propití.a, 2 2 Gnaphoeldae t, Gnaphoaidøe sp. I z 46 5 6 35825 7571 Anzací.a sp. 9 4 z 3 13 4 41242 Gnaphoeidae sp. 2 ) I r246 Myanãtv ep. lllT Meganyr.cmecion sp. Linyphlldae I o e t eaviu o ne Larøpy g iue 715 23 35 95164 TheridÍldae Steatodø gtoaea 4 l3zfl 2 LZ13I0l Lacttodectue haseeLtí 2 824 5 J Euryopeis sp. I I6 Cl-ubfontdae Cort'inorøm sp. 243242264 545105 Chíra,canthiøn Oxyopidae )Wopes ep. (?anoenue) 2 4 Ì8 Dlctynldae Díetyttø sp. 3 4 2 Salcicidae Saitíe sp. z 5 Mlturgldae Mitutga ep.

* - Juvenlle -149-

SECTION 7: LETEAL INELTIENCB OF EIGE TEITPERATT]Rß OIT SAA II{ DRYI.AìID LIICERNE

II{ lEE IIPPER.SOINE-EAST OF SOI]18 AUSTRALIA

Sunoary

Both the reductions ln densiEies of SAA in dryland lucerne pastures at Culburra during some periods r¡1th high naXlmum temPeratures and evidence overseas of the deleterious effects of high temperaÈures on SAA suggest that daily maxlmr:m temperatures equal to or greaÈer than 38oC for two or ruore consecutive days are lethal to SAA. To measure mortality in relation to temperature, stem cages lrere nodified Èo provide temperatures higher than ambient, teEperaÈures in the field; buÈ the increases ln maximum temperatures during the course of the experlment were not sufflclent for Èhe Purpose.

Reasons are given to suggest that lethal hígh ÈemperaÈure may have been the key factor causing low numbers of SAA 1n pastures in the Upper-South-East during ghe summers of 1980/81 and l98l/82. Ilowever, these reesons are based on Èhe relaÈionship between frequency of periods wiÈh temperatures greater than 38oC and the abundance of SAA in the field; experlmenÈs are necessary to determlne whether 38oC ts the lethal threshold Èenperature and to quantify the lethal effects of different lengths of exposure to temperatures higher then the threshold temperature. DaÈa are also required on the acclimatlzatlon of SAA co high tenperatures. -r50-

7.L Introductlon The lethal influence of hígh tenperaEure on SAA, especially during Èhose perlods of the year when SAA ls potenÈially most abundantr mâY be an important factor determining the population dynamics of SAA in lucerne-based pastures in

Èhe Upper-South-East 1n sone years. lfumerous researchers have studied the lnfluence of temperaÈure on the rate of development and fecundlÈy of SAA, but most have not measured the lethal effect of high temperaÈures on SAA. Earpaz (1955) staÈed thaÈ severe khamsln wind.s in Israel can kill greater than 90% of a population of SAA; severe khansln winds are hoE, dry desert winds whlch have Eemperatures exceeding

4OoC, relative huntdities less than 30% and last for at least four days. Other references to the lethal effects of high temPeratures on SAA are more general, e.g. maxlmum daily Ëemperatures in Arlzona were frequently over 38oC,

rundoubtedly SAA sometimes reaching 46oC, and had some detrimental effectf on (Nielson and Barnes 1961); exposures to Eemperatures greater than 38oC ln California srere tdeleterious' to SAA - the duratLon of exposure was not given (Messenger 1964); htgh temperaÈures, e.g. one day with a maximum of 49.5oC and tlarge several days wlth mexlma of 46oC or hlgher, mâY have caused reductionsl in numbers of SAA l-n the Inperlal Va11ey in California (Dickson et aL. 1955). This secÈlon describes the relationship between high mnximum ÈemperaÈures and the survival of SAA 1n the maín gxazíng experlment aË Culburra from 1977 /78 to 1979/80, and an unsuccessful field experiment which was designed to quanÈ1fy the lethal effects of high temperatures on sAA. The secÈlon also Proposes a hypothesis to explain the unusually low numbers of SAA in the field in South Australia during the summers of 1980/81 and 198I/gZ' -r51-

7.2 Influence of Da1lv tlaxLmum Temoerature on the Densltv of Field SAA

7 .2.L Ma terLals and methods The influence of high daily temperatures on the uumbers of Sfu\ 1n the field was evaluated from weekly changes in the numbers of SAA ln various treatment areas in the grazing experiment 1n Ilunter River lucerne-based pastures at Culburra from OcÈober L977 to June 1980. The experimental site and methods for the grazing experíment are described in SecÈ1on 4 ' The dates when daily maximum temperatures, measured in a standard Stevenson screen, were equal to or exceeded 38oC during the above period llere recorded; then, the rate of increase in the number of SAA per day during each of those

weeks whlch included t,he above dates was.calculated for each treatment âEêâr

Each rate of increase, r, Iùas calculated from the equation: log"Na - Log"No r= t

where No = number of aphíds on the flrst day of the week' N. = number of aphids on the last day of the week, and t = number of days. Rates of increase of SAA r¡ere only calculated for SAA in treatment areas where any changes in the number of SAA during the week with a day or period of

days wfÈh a maximum tempereture(s) equal to or exceedíng 38oC could be attributed nainly to temperature and not to other factors such as grazLrrg, chemical insecticide and funnigratlon or emlgration of alate SAA' The follor¡ing numbers of rates of lncrease of SAA during weeks with dífferent perlods of exposure of SArl\ to temperatures equal to or greater than

38oC were made ln 1978 and 19792

(a) for one day of maximum temperature greater than 38oC - 7 comparisons for the week includlng 14 January, 1978. - 16 comparisons for t,he week including 3 January , 1979. - 3 comparisons for the week including 2 January, 1979. -t52-

(b) for three days of maximum temperatures greater than 38oC - 9 comparlsons for Ehe l¡eek including 9-I1 March' 1978' Slnilarly, the rate of lncrease of SAA ln each of the above treaÈment areas day or was calculated for each week immediately following each ¡¡eek \{1th a period of days \tith a high tenperature(s). Each of the rates during the following weeks was taken as the expected rate of increase for SAA in the respectlve Èreatment area for that time of the year in the absence of

temperatures equal to or greater than 38oC. Bet.ter estlmates of the expected rates of increase of SAA nay have been the rates during Èhe respecÈl-ve weeks lnnediately prior t,o the weeks with the high tenperaÈure(s) because such rates the ¡vould exclude any deleÈerlous effect.s that hlgh temPeratures nay have on to subsequent raÈe of reproducÈion of SAA. Ilowever, data were noÈ available calculate the rates of Íncrease of SAA in most of the treaEment areas (a) immedtately prlor to the weeks with high temPeratures because either (¡) tne detatled sanpling of SAA had not been initlated in the experinent' or ín the treaÈment areas had been grazed' or sprayed wtth chemical insectlcÍde previous week. Differences between the nean rates of increase of SAA durlng the week j-ncludLng the hot day(s) and Èhe followlng week were eompared separately for

each perlod with hlgh tenperature(s) using studentrs t-tesÈs. 7.2.2 Results ThedailymaxlmumÈemPereturesequaltoorexceedíng3SoCwhichwere the recorded aÈ Culburra fron October 1977 to June 1980 are shown in Figure 7'1; and days of mean densÍËles of SAA in some Ëreatment areas on both the first last followlng week each week includlng these days wlth hlgh tenperaÈufes, and of the increase of ln each case are glven |n Appendices 7.I to 7.4. Relevant rates of at SAA could not be calculated for the weeks includlng hlgh tenpereÈures Culburra on 3 February 1978 because the whole e:çerLment lúas sprayed wlth paraÈhion to control wingless grasshoPper; or on 28 Decenber 1979 because -153- estimates of Ehe densiEy of SAA prior to and afEer the high temPerature llere too

1ow (less than one SAA per stem of lucerne) to show statisElcal differences in density; or on 19 and 20 February 1980 because the experiment r^las heavlly gtazed vri t,h sheep .

t 1977 I 78 /.5

to o --39" e- 35 o L J o L 1978 t 79 o o- 45 E o 40 E - -3go J 35 Êi o E 1979/80 è'õ o ô5

40 3go

35 Dec Jqn Feb Mor

It recordings commenced lr.1 , 78

FIGURE 7.1: The dai-ly maximum temperatures equal to or exceeding 38oC which were recorded at Culburra from OcËober 1977 to June 1980.

The mean daily rates of lncrease of SAA during eaeh of the four weeks wíth either a hot day or a period of hot days where rates could be estimated,

together vrith Ehe rates of increase during the flrst week following each of

t,hese weeks are shown in Table 7.1; these mean rates $lere calculated from the -r54- grouped rat,es of increase of sAA in each t,reatment area for each week (Appendices 7.1 Èo 7.4). The only negative nrean rate of increase of SAA r¿as durlng the week tncluding one hot day on 14 January 1978 and this raÈe was signLfÍcantly less (P < O.0Ol) than the mean rate during the following week' day(s) The numbers of aphids increased during the other three weeks wLth hot ' though the values of t in Table 7.1 demonsEraÈe that Ehe mean raÈes of increase in two of the weeks, one week including three hot days on 9-11 March 1978 and (P 0'10) Ehe other including one hot day on 2 February Lg7g, were both less <

Ehan the mean rates durl-ng each of the following weeks; so Èhe high tenperaÈure probably did at least retard the rate of increase of aphids at these tlnes' By contrast, however, the Èenperature which.exceeded 38oC on 3 January 1979 díd not fnfluence the nean rate of íncrease of sAA compared to Ehe mean rate in Lhe followlng week.

TAsLE 7.1 Mean rate of increase of SAA during various weeks includíng either one or three days with dally maxímum temperature(s) equal to or greater than 38oC and the mean rate during the following week' resPectively' at culburra in 1978 and 1979, and the value and significance of Ë used to compare the raÈes in each pair of weeks'

Date(s) of No. of Mean rate of lncrease of SAA* during: days wlth days Èr, Signiflcance temp. > 38oc tr{eek lncluding I,Ieek following > 38oc temp. > 38oc temp. ) 38oc

P<0 .00 I 14.r.78 I - 0.08 0. 16 t t2=6.83 P<0. r0 g-11.3.78 3 0.03 0. l4 t 16=2.00 t3O=0.15 NS 3.L.79 1 0. 20 0.19 2.2.79 I 0.01 0.19 E4 =2'49 P<0.10

NS - rates of increase fiot signtflcantly dlfferent at P(0.05 -r55-

The mean rares of increase of SAA (0.I4 to 0.19 o/o/day) during each of Ehe weeks followlng a week wtth high temperaÈure(s) l¡ere useful to demonstrate the Ínfluence of hlgh temPerature(s) on the rate of increase of SAA because the nean ratea durlng t,hese weeks were sÍ.milar to raÈes of increase (0'13 to 0'20 for SAA during the course of another experiment which was ++o/o/day) estimated conducted at Culburra in March-April 1981 ln the absence of daily temperatures greater than 38oC (Sectlon 9). Ttre equation used Eo calculate Èhe daily rates of increase 1n both the I98I experiment and 1n this section was the same, and in both cases the aphids were living on lucerne regrowÈh which was about tIüo to flve weeks old. l,Íean daily temPeratures above 38oC were e:çected to cause greaEer reductions in the nurnbers of SAA ln the fteld than shown by the mean rates of lncrease presenËed ín Table 7.1. Part of the reason for only one negative mean rate of lncrease (14 Jariuary L978, Table 7.I) nay be EhaÈ any negative raÈes which rüere measured 1n indivldual Ereatment areas at oÈher Èlmes were statlstically obscured. For example, durlng the week with three days of t,enperature greater Ëhan 38oC, Èhe nean rate of íncrease estirnated fron Èhe

nean rates 1n each treatment area was positive' even Èhough the rates of

increase of SAA were negatl-ve in three out of four of Èhose treetment areas

whlch had a mean denslEy exceeding 100 aphids per stem on Ehe flrst day of that

week (Appendix 7.2). A regresslon of the rate of increase of SAA agalnst the

mean denslty of SAA on the first flay of the week for each Èreatment area for this week was signíficant (P < 0.05) (FÍgure 7.2). This relatíonship demonstrates that the lnfluence of high Ëenperature on the rate of increase of to SAA is density-dependent; temperatures exceeding 38oC are more lethal aphlds in populations of hlgh densitles than of lotr denslties. This density- 1979 not dependence !ûay also be a reason for Ehe hlgh tenperature on 3 January l-nfluenclng the rate of lncrease of sAA (Table 7.L); the mean denslties of sAÀ -156- in each treaËEent area on Ehe first day of the week includlng that day of high

Èemperature were low, e.g. the densiEy of SAA exceeded 10 aphÍds per stem of Iucerne in only two out of 16 treatnent areas (AppendÍx 7.3). High tenperatures may be more lethal to SAJ\ when they occur in high densities rather than in low densiEl-es because the aphids are probably more stressed at hlgh densities due to (a) greater compeÈltion betrùeen aphfds for resources and Co (b) reduced food qualiÈy caused by the large numbers of aphlds feedfng on the lucerne plants.

025

0.20 ¡ x x 0.15 Y= 0'153-0'0013x x r 0'78. 0.10 x =

tn 005 x o oø 0 x o g (J -0'0s .s I x o o -0.10 o É - 0.15 x - 0.20 50 100 1s0 200 2s0 Meon density of SAA

FIGURE 7.2: The relaÈionshfp betwee.q the rate of increase of sAJ\ at l{ culburra durlng the weed lnclucllng the three hot days on 9-1I March 1978 and the mean density of sAA on the first day of t.hat week. -r57 -

In addiÈlon to the above densiÈy-dependence, the different stages of regrovrth of lucerne in the treaÈment areas at each time with high tenperaÈures may have also obscured any effects of high Èemperature on Èhe survival and

reproduction of SAA because high temperatures nct ouly act directly on aphids but also indirectly through their host plant (Ilodek et aL. L972)' The differenÈ stages of regrowth in the treatment areas were caused by the rotatlonal grazLng used 1n tine gtazLng experinent (Sectíon 4). Another factor which nay influence the lethal effects of high temperatures on aphids is the temperature regime prior to the occurrence of hlgh temperatures; temperatures prior to the htgh tenperatures nay or m¡1r not al1ow aphids to become

acclimaÈizeð. to the hlgh temperaÈures. As early as 1919, Chalne noticed that a

sudden rise in temperature to 37oC, or above, caused whole populatlons of the rose aphlð., Macrosiphon ro7ae (L.), on roses to die rapidly whereas a slower

rlse t,o the same temperagure produced nr¡ch lower mrtalíty (Broadbent and Ilollings r95r). Acclimatization of insects to uPper lethal temperatures has been discussed more recen¡ly by Bursell (1974) and he conslders that

acclimaÈ1zaËion ls likely Èo be of considerable significance to insects living in their normal habitat, e.g. the tLme of the day durlng which crltical

teDperaÈures are likely Èo be approached w111 be preceded by hours during which the fnsects w111 be exposed Èo hÍgh sub-lethal temperatures, thus enablfng a certain amourit of physlotoglcal acclimatlzation !o occur. SufficienE data were not avallable w-tth the above sanplLng at Culburra to test the above two

phenomena. 7.2.3 Dlscuselon Ttre sample data from the grazltg e:

June 1980 did not demonstrate Èhat dally maxlmum Eemperatures greaÈer than

3BoC caused high mortallties of SAA. Ilowever, the data did show Èhat Lhe rate of increase of SAA can be either unaffected or reduced by one day \ülth a maxl'mtrm -r58-

aphids in temperature greater Èhan 38oC (Table 7.1), and Ehat the number of populations of sfuL with high densities can decrease following three consecutive The for the days wiLh temperatures greater than 38oC (Appendlx 7 .2), reasons varlable lnfluence of high temPerature on populations of SAil\ are not explaÍned by the liníted data, but some of the observations suggest that aÈ least two conseeutive days with naxirna greater than 38oC nay be required to narkedly the reduce the denslÈy of sAA in Èhe field. This hypothesis was supported by on marked reducrion ln the density of sAA (260 to 60 aphids per sten) days with Ilunter Rlver lucerne PlanÈs at Logan Rocks following Èhree consecutl-ve

temperatures above 38oC tn February 1980 (Section 5.3.3). 7.3 I€thal Ef fect of Hish Tenperature on SAA 1u Fleld CroPe The tenuous data in sect,l0n 7.2 and the evidence of the effect of high 1964' and temperatures ou. sAA 1n the u.s.A.(Dicksot et aL. 1955, l"fessenger Nlelson and Barnes 196l) and in rsrael (Ilarpaz 1955) suggest the hypothesls tha' : 38oC is the threshold lethal temPerature and that the Percentage day mortality of sAA increases wl-th lncreasfng exposures of greater than one wlth a daily maximum temperature equal to or greaÈer than 38oC' where the An experlment rÍas deslgned to Èest this hypoÈhesis in the field high temPerature combined l-nfluence of both the direct and indirect effecÈs of The design of this on SAA were likely to be measured (Ilodek et aL. L972). (1980) when they measured experlment was sinllar to that used by Tamaki et aL. green peach the impact of hlgh temPeratures on the population dynanics of the They modified field cages to aphid , Mgzue pereieae (sulzer), ln the fl-eld. provlde a range of daily maximum Èemperatures 1n the cages higher than ambLent given Èime tepperatures. A cohort of aphids was then placed ln each cage for a in a manner t,o give a series of cohorts of aphlds exposed to dtfferent of aphíds Èemperatures for different perlods of Èime. The levels of survlval were compared' exposed to each combinatlon of temperature and exposure time -r 59-

The stem cages descríbed in Sectlon 9.2.1 were rnodlfied to test the influence of high temperatures on SAA. The nodificatíons included coverlng different percentages of the gauze sides and tops of Èhe cages wlth clear' cellulose aceÈate sheet. Ilowever, the nodified cages did noÈ sufficiently

increase maximum temperatures in the cages above the ambient temperatures in the field, so the experiment was not successful. Ttre naln reasons that the cages did not reach high enough ternperatures appeared to be (a) the small volume of air ln each cage - any ventlng of the cage probably allowed a rapid exchange of al-r between Èhe lnside and outside of the cage, thus reducing the accumulation of sufficienL heat ln the cage, and (b) shading by lucerne plants because of the relaÈively snall slze of the cages compared Eo the height of the lucerne plants' Further sÈudies of this type would require nuch larger cages. 7.4 ELsh Tenpereture aûd the LoP lfr¡nberg of SAA Ío the UpPer-South-East I'n 1980/81 and 1981/82 In dryland lucerne pastures ln the Upper-South-East, SAA usually occurs ín low numbers durLng wl-nter, increases ln numbers during December and reaches peak

numbers in the January to March period (Section 3). In 1980/81' SAA followed this general pattern of actfviEy in lrrigated lucerne stands in the coastal

Langhorne Creek regl-on but aphids rlere not detected in irrigated and dryland lucerne pastures in the lnland areas of the upper-south-EasÈ until early*larch'

Regular intensive sarnpling for SAâ, was not carrled out during the f980/8I spring

and sunmer but vlsual observatl-ons of lucerne by nyself, DisÈrict Agrononists

and landowners conflrned these occurrences of sAl\. In late-January and early- February IgSlr landowners growing irrigated lucerne for hay l-n the Langhorne

Creek reglon complained of some of the highest densltles of SAA that they had

experl-eneed l-n thelr lucerne stands; the high densl-Èl-es were partly due to the first, occurrence of insecticide-induced resistance 1n SAA in South A¡stralla (Section 5). By contrast, there was less than one SAA per sÈen of lucerne l-n -160- dryland lucerne pasture at the experimental site at Culburra 1n mid-January

(Section 3) and SAA was noE detected in other dryIand lucerne Pastures or in irrlgated lucerne stands around Kelth durLng January and February (B. 8u11, pers. comm.). By rdd-March, however, SAA was abundant ln irrigated and dryland lucerne stands |n the Upper-South-East (8. Bull, pers. coûrn.) and in nÍd-Aprll the nean density of SAA exceeded 1 000 SAA per stem of lucerne in some treatments 1n an experiment r{ith SAA in dryland lucerne pasture aÈ Culburra (Section 9, Table 9.5, Experiment 1). A key factor deter¡ninlng the dlfference in abundance of SAA between the cooler, coasÈal Langhorne Creek reglon and the hotÈer' inland KeiÈh and Culburra reglons ln January and February t98l coulj be the daily naximum temperatures during this perlod. Figure 7.3 shows the frequeney of days wlth maxima

exceedlng 38oC durlng Èhe 1980/Sf summer at both Menlngie (near Langhorne

Creek) and Keith (Bureau of Ìfeteorology). The most obvlous difference in Ehe frequency patterns ls the greater occurrence of periods wíth t!üo or Dore consecutive days having maxinr:m temperatures equal to or greater than 38oC up untfl nid-February at Kelth than aÈ Meningie. I suggest Ëhat these regular periods of high temPeratures rvere lethal Èo a hfgh proportion of SAA and

maintained SAA at low densitles during January and February in inland regions of the Upper-South-East; SAA did not have sufficlent Èime to lncrease Lo numbers that could be easl-ly detected in lucerne pastures after eaeh perl-od of unfavourable high temperature and before the nexÈ. In l98l/82, the dally mexinum temperatures durlng January and February were

above average at both Keith and l"fenl-ngLe. Thls tirne, the frequencles of perlods wlth at leasÈ t}¡o consecutive days equal to or above 38oC were sfnilar at Meningle and Keith - the nain difference in the hlgh temperaÈures was thaÈ lGith had more days wlth naxlmum temperatures above 38oC and usually higher roaxima

Èhan Ìleningie (Ftgure 7.3). Durtng Èhis perlod, SAA was not apparenÈ ln -161-

Meningie 1980 /81 /.5

lro - 38" 35

lGith 1980/81 45 y¿0 3go o35 J o o o. 34sE Mening e 1981t82 E r- 40 iE -- 3go E3s

I Keith 1981 / g2 15

10 - -360 35 Dec Jon l-eÞ. Mor

FIGURE 7.3 : The dafly naxlmum temperatures equal to or exceeding 38oC which r{ere recorded at l{eningie and Keith from December to }farch in 1980/81 and L98r/82.

irrigated or dryland lucerne stands at both Langhorne Creek and the inland Upper-South-East regions. In addition, SAA remaLned at low densities in both reglons for Èhe rest of thaÈ sumrer and auÈumn. The reason for the low numbers throughout late-summer and autumn is noÈ knot¡n but nay be parÈly due to a low -L62- fecundity of aphids following excessively hot períods' as suggested by llarpaz (1955). If the fecundity and consequent rates of increase of sAA were reduced by the high ternperatures, then the controlling influence of either predators, grazing or uowing for hay on SAA may have been more effectÍve than in years wiËh cooler sunmers and hlgher rates of increase of aphlds, Ehough there is no evidence t,o suPport this proposal .

The reason for SAA not being abundant in the early-summer of 1981 and ín

the whole summer of 1982 is based on Èhe proposal that two or more consecuÈive

days above 38oC can cause severe red,uctlons in the density of SAA. An experiment to test this proposal was unsuccessful; experiments are necessary to

deÈermlne whether 38oC is the lethal Ëhreshold temperature for SAA and to quanÈify the ínfluence that exposures to differenÈ lengths of time above Èhe threshold teqperature have on the density of SAA. Information is also required on the acclfnatizatLon of SAA to a 1ethal high temperature caused by prior exposure to sub-lethal high temPeratures. 7.5 Referencee Broadbent, L. and Holllngs,1"1. 1951. The influence of heat on some aphids. Ann. AppL. BíoL. 38: 577-581- Bursell, E. 1g74. Environmental aspects - temperature. InTlne Physiology of

Insecta. Ed. Ì,f . Rockstein. Academic Press. Vol. II. 568 pp.: l-41. Dickson, R.C., I¿ird, E.F. and Pesho, G.R. f955. The spotEed alfalfa aphid' HiLgandia 24: 93-117. Harpaz, L. 1955. Biononics of TherLoaphís raeuLata (BuckÈon) in Israel. J. eeon. Ent. 48: 668-67L- Ilodek, I., Ilagen, K.S. and .rt., ,td.rr, E.F . Lg72. l"fethods for studying effectlveness of natural enemies. In Aphld Technology. Ed. It.F, van Emden. Academic Press. 344 pp.: 147-188. -163-

Messenger, P.S. L964, Ttre lnfluence of rythnlcally fluctuating ÈenperaÈures on

the developmenÈ and reproductlon of the spotted alfalfa aphld Therioaphie rø.euLa'ta. J. eeon. Ent. 572 7L-76'

Nielson, 1"1.üI. and Barnes, O.L. I96f . Population sÈudles of the spotted aLfaLfa aphid fn Arizona ln relatLon to temperature and ralnfall. Ann. ent. Soe' Am. 542 44L-448. Tanakl, G., I,leiss, M.A. and Long, G.E. 1980. Impact of htgh temPeratures on the populatlon dynanics of the greeû peach aphtd ln field cages. EnÙíron. Ent. 9: 331-337. -r 64-

Appendix 7.1 The mean density of sAA in each treatment area on both the first and last days of the week including the hoE day on 14 January 1978 and of the following week at culburra, and t,he correspondíng rates of increase of SAA in each treaEment area during each week.

I.Ieek including hot day T'leek following hot day (beginning 9.1 .78) (beginning I6.1 .78)

RaÈe Density of SAA* Rate of Density of SAA* of .L increaset r-ncrease I First day Last daY Fírst day Last daY

5.8 3.8 -0.050 3.8 10.4 0.144 5.9 2.5 -0.122 2.5 10.2 0.201 5.7 2.8 -0 .l 01 2.8 13.9 0.229 3.3 2.1 -0.065 2.1 10.6 0 .231 25.0 29.6 0.o24 29.6 42.2 0.050 36.9 10.3 -0 .182 l0 .3 35.7 0.177 70.0 36.4 -0.093 36.4 52.2 0.05I

* mean number of SAA per sÈem of lucerne ' t natural logarithrn of rate of lncrease in the number of SAA per day ' -r 65-

Appendix 7.2 : The mean denslÈy of SA\ in each treatment area on both the first and last days of the week including t,he three hot days on 9-11 March 1978 and of the following week at culburra, and the corresponding rates of increase of SAA in each treatmenc area during each week.

I.Ieek includíng hot daY I,Ieek following hot day (begínning 6.3.78) (beglnning 13.3.78)

of Density of SAA* Rate of Density of SAA* Rate increase t lncrease t First daY Last daY First day Last daY

0 .051 244.0 146.0 -0 .07 3 146.0 209.0 95.4 190.0 0.099 190 .0 146.0 -0.038 r37.0 153.0 0.027 I53.0 250.0 0.070 8.7 26.2 0.158 26.2 238.0 0.315 o.252 12.5 40.9 0.169 40.9 238.0 0.229 111.0 71 .4 -0.063 71 .4 355.0 0.107 59.5 57 .0 -0.006 57 .0 120.0 0.083 29.7 93.2 0.163 93.2 167.0 o.177 161 .0 43.4 -0.1 88 43.4 150.0

* mean number of SAA per stem of lucerne' t natural logarittun of rate of increase in the number of SAA per day ' -r66-

first Appendix 7.3 The mean density of SAJ\ in each treatment area on both Ehe and last days of the week including the hot day on 3 January L979 and of the following week at culburra, and the corresponding rates of increase of SAA in each treatment area during each week.

I,Ieek lncluding hot day trIeek followLng hot day (beginníng 2.1.79) (beginntng 8.I.79)

Rate of Density of SAA* Rate of Density of SAA* lncreaset increaset Ftrst day Last daY Flrst day Last daY

0.074 7.7 19.2 0.152 19.2 32.2 0.057 25.9 35.4 0.052 35.4 52.9 28 .1 0.070 6.4 17 .2 0 .165 L7 .2 4.4 9.0 0.1 l9 9.0 26.2 0 .153 0.123 2.6 8.0 0 .187 8.0 I8 .9 0.168 1.3 8.5 0.313 8.5 27 .6 0.095 9.9 32.2 0 .197 32.2 62.6 4.0 26.4 0.315 26.4 32.8 0 .03I 0.288 2.2 7.6 o,207 7.6 57 .2 0.380 2.2 6.9 0.191 6.9 98.5 0.268 6.4 l5 .0 0 .141 15.0 98.I 0.8 3.4 0.241 3.4 55.0 0.396 0.240 5.1 35.4 0.323 35.4 189.8 0.230 15 .6 35.4 0 .I37 35.4 165.2 0.286 2.6 4.2 0.080 4.2 3l .0 0 .197 2.8 18 .8 0 .317 18.8 75.0

* mean number of SAA per stem of lucerne' t natural logarithn of rate of íncrease in t.he number of SAA per day. -t67 -

Apoendlx 7.4 The mean density of SAJ\ in each treaEment area on both the first and last days of the vreek includíng the hot day on 2 February 1979 and of the following week at culburra, and the correspondlng rates of increase of SAA fn each Èreatment area during each week.

IÍeek lncluding hot daY I,Ieek following hot day (beginning 29 .L.79) (beginning 5 .2.7 9)

Rate of Density of SAA* Rate of Density of SAA* increaset increaset First day Last daY First day Last daY

6.9 10.9 0.065 10.9 55.0 0.231 8.5 5.2 -0.070 5.2 45.8 0.311 0.036 205.0 251 .0 0.029 25I .0 323.0

* mean number of SAA per sÈem of lucerne' 1 natural logarittm of rate of increase in the number of SAA per day ' -168-

SECTION 8 : INFLIIENCE oF FOOD QUALIIY ON Itsß ABIII{DANCE OF SAA DITRING SPRING

IN DRYIÅIiID LUCERNE UC THE IIPPER-SOT'TE-EASI OF SOT],E AT'STRALIA

Sunnary

previous sampling for SAA demonstrated that SAA was usually scarce in dryland lucerne pastures in the Upper-South-East during spring. Ttre unexpected low numbers of SAA at that tine could not be explained, but m¡y have been related to predators and/or unfavourable quality of lucerne Plants for SAA.

An experiment using potted and field lucerne Plants compared increases in numbers of SAA on Ehe regrowth of lucerne plants 1n sprJ.ng r¡ith lncreases in numbers on regrolúth of plants whlch were Pre-conditioned in environments slmulating winter and sumer, respecÈively. RegrowÈh fron plants ln the different treatments \ùas expeeted to differ physlologically and, thus, dífferenÈtally lnfluence survival and reproductlon of sAA.

The experlment was unsuccessful, mainly because pre-conditioning Plants 1n dlfferenÈ environments influenced the physiology of the plants at that time but any effecÈs of Èhe dffferent envlronments on Ehe plants did not continue into the next regrowth phase. The experiment did noÈ elucidate whether the quality of lucerne linlEed the numbers of SAA in sprl-ng' -t69-

8.1 Introductlon The seasonal abundance of Sfu! in dryland lucerne (cv' I{unter Rtver) pastures in the Upper-South-East of South Australia was determined by regularly sampling lucerne pastures for Èhree years (Sectíon 3). The unexpectedly low have densitles of SAil\ durlng spring could not be explained at that stage but may

been related to the quality of the lucerne plants for SAA and/or the influence of predators. The densíEy of host plants has been recognised for many years as an

importanE factor influencing the population dynamlcs of phytophagous insects

(Hough and Pimental 1978) and there is general agreement that the physiological status of the host plant is also a signif.icant variable (Southwood 1973). Many in studies have suggested that increased levels of soluble nitrogen, especially the form of certain amino acids, ín plants stimulated higher reproduction and survival of ínsects (Feeney 1970, Kennedy 1958, I'fcClure 1980, van Emden and Bashford 1971, lfhite 1969), though there does appear to be an upper Ehreshold of nitrogen for increased fecundity (Auclair 1965) ' The value of a host plant for growth and reproduction of insects uray depend not only on the presence and quantlties of various essential compounds but also on the balance between them (Ilouse 1969). Plants often also contain high herbivores concentrations of chemicals which may not be used as resources by the but rather may provlde defences against herblvores by reducing the dlgestibility (Cates of the plants or disrupÈing the metabolic processes of herbivores 1980) '

The biochemical conpositíon of a speeies of plant varles under dlfferent in the conditions and at dlfferent seasons of the year, and the nany changes plants could behavlour and abundance of insects associated with such changes in This suggest that the diet was often far from optinal (Southwood 1973) ' year can influence of sub-optimal quality of host plants at certaln tirnes of the -r70- be important in deEermining the dynamics of insects (Dickson 1977, Feeny I97O' trIebb and Moran 1978, Schoonhoven I969).

In Ehe upper-south-East, the quantlty of lucerne in dryland pastures is abundant during spring, but daÈa were not avallable to determine whether its quality adversely influenced the survival and reproduction of SAJ\ in that

envlronment at that time. This section describes an experl-ment which aEtempted to t,est the hypothesis that the quality of lucerne did limit the abundance of

SAA in dryland lucerne pastures during spring'

The experiment compared (a) increases in numbers of SAA on regrovrth of lucerne followíng spring weather and (b) increases on regrowth of lucerne on plants whtch had been pre-condltioned in.growth cabinets with environmenËs

slmulaÈLng winter and sumrner, respectlvely. The comparisons were made at the attempted to same tlme during spring in the field. This experimental design

maximise Èhe advantages and minimise the disadvantages of two different methods ¡shich could be used to measure Ehe seasonal influence of food quality on the rate of increase of sAA. one method to deÈermíne the influence of food quality grovtn under a on the rate of increase of inseets measures the effect of plants, range of artificial conditions, such as constant daylength and temPerature' on insects in the laboratory; many such experlments have been carried out wiÈh a on number of different inseet species but they do not provide much information the importance of the plant in the field as an element of the environment influencing population change (van Emden and üfay 1973). The other meÈhod times measures rat,es of lncrease of insects on plants in the field at different of the yeer; the data from such experiments may be compounded by other either components of the environment which differentially affect the insects' directly or indirectly, at different times of the year and whlch cannot be manipulated or controlled. -T7 I-

8.2 Materl-als and Èlethods The experiment was conducted in spring 1980 with both field and potted plants of llunter River lucerne. The treaÈments were: I. Spring regrowth - fíeld plants 1n the field' 2. Spring regrowth - potted plants ln the field'

3. Summer regrowth - potEed plants in a growEh cabinet. 4. winter regrowth - potted plants 1n a growth cabinet. Field plants , 12 yeats old, provided regrowth in spring for TreatmenL 1. This treatnerit r¿as included as a comparison to poEted plants in TreatmenÈ 2 which vrere similarly allowed Eo grol^t normally in spring. The potted plants which were used to simulate the quality o.f regrowth during spríng, summer and winter, respectivelyr rlere two years old'

The mean dally maximum and minimum temperatures and daylength for each pre-conditioning Ereatment are given in Table 8.1. The values of temperature

and daylength required for the winter and summer pre-condltioning treatments were interpolated from meteorologícal tables which included estimates of the paramerers for latitudes 35oS and 4OoS (f.ist l95l) - the Upper-South-East of growth cabinets South Australla is about 3605. The lntensiEy of light in the plants were rúas not regulated, but was adequate for normal plant gtowth' The spring not allowed to become water-stressed at any time. Potted plants for the regrowth treatment l¡rere pre-conditioned in the field at the Northfield Research Laboratories, near Adelaide, and the field plants were |n the experlnental síte at Culburra. Preparations for the experimenE started on 31 October 1980' To provide plants for Treatments 2, 3 and 4, lucerne plants in pots, 200 um diameter x 200 into mm deep and 3 plants/pot, and with five weeks regro\tth were stratified then Ehree lots of visually unl-foru pots of plants. One pot from each lot was give four randomly allocated to each of the Èreatments r¡iÈh potEed plants to -L7 2-

TABLE 8. I Temperature and daylength reglmes for the differenÈ pre-condiÈioning treatmenÈs for lucerne plants ln the ffeld and ln Pots ln growEh cablnets ' respectively '

Treatment Mean temperature (oC) Ifean daylengÈh for each perlod of days

l"lax. ìfin. l-15 L6-29 30-3s

Spring (field) 22.L 14.2 13h 45n 13h 59n l4h l3n Spring (pots) 25.6 L4.7 13h 45n l3h 59rn 14h 13¡n Summer (pots ) 30.0 L2.5 I4h 35n 14h 20m f4h 5n I¡llnter (pots) 15.0 5.0 th 45n 10h 0n 10h 20n

repllcates per treaEment. All herbage was cut from each plant, each plant Itas fertilLzed w1th Aquasol@ (t g l,-1) and then placed in the allocated pre- condl-tioning environgent (Table 8.1). Sln{larly, four uniform plants were selected in the field at Qrlburra ln âll âfêâ câ. 40 n x 40 m, and all the herbage of each Plant was removed. Each planÈ was allowed to regrow for five weeks and Ehen the herbage tras agaln removed. This tlne, the number of sÈens, number of stens wlth floral buds, number of s¡ems with flowers, and dry mâÈÈer (D4) per plant' resPectively' were estfnated and recorded. All the Pots were then transferred to Culburra where they were placed 1n the fleld amongst Èhe field experinental plants' Each pot was embedded flush Ln the sandy so1l and enclosed l-n a cage, 450 m x 650 nn x 540 m high and covered w-ith fLne gauze, to preclude predators and parasites. Stnllar\y, a cage \{as placed over each field plant' Each cage had a sliding perspex fronÈ to provlde access to the plants for Èhe additlon of SAA' The perspex front faced south to nlnlnize overheaÈlng of the cage' Each potÈed plant was watered from outsl-de Èhe cage through a funnel and hose to avold -r7 3- disturblng Ehe aphids (Plate 8.1), and was not allowed to become $teter-stressed throughout the experiment. Maxlmum and rolnimum ÈenPeratures anongst the lucerne herbage in the cages in each treatment were estlmated with a Èhermistor placed 1n one cage in each t,reatment and attached to a Grant@ recorder. The inside of each cage, including the plant and soil, Itas sprayed twice wfth 0.5% dichlorvos, lnlËially when the cage vras placed over the planEs and Èhen aft,er one week, to control any predators or parasiÈes of SAA which may have been presenE inside the cages. Each cage was seeded with I0 newly-emerged female SAA on 23 December 1980, two weeks after each plant r,las cut and caged. The plants 1n each cage were destructlvely sanpled to estimate toÈ41 numbers of SAJ\ per cage on 13 January 1981. Ttris sampling was carrled ouÈ after about t\üo generaÈions of SAA, as est,imated from mean datly tenPeratures in the ceges. The stems were taken to the laboratory where SAA were washed fron them and counted, as in Section 3.2.1. Following the removal of stems, âoY aphids on the soil surface within each cage were collected wl-th asplrators attached to a suction pump. At the same time as sampling for SAA, estimates were rn¡de of the number of stems, number of stems vtlÈh floral buds, number of stens with flowers' and Il'( per plant, respectively. The different parameters in each of the Èreatments, except where stated, rrere stat,istically conpared uslng ANOVAs with a log (x + l) Èransformation of daÈa to stabllise varlances, where'applicable. 8.3 Results

8.3.1 Rate of iocrease of SAA There were no significant differences (P<0.05) in the final rnean numbers of SAA per cage between treatments (Table 8.2). The flnal numbers of SAA 1n the replicates (cages) for each treatnent r{ere varlable and were lower than expected, even in Èreatments whích should have favoured reasonable increases in t,he numbers of SAA, e.g. summer regrowth. -17 4-

a PLATE 8.1 A cage, including Èhe waterlng system and pre-condiËioned potted lucerne plant with all of its herbage removed, which was used l-n the experiment at Culburra Èo determine the influence of food quality on the rate of lncrease of SAA. -17 5-

TABLE 8.2 Final numbers of SAA per cage (replicate) and the final mean number Per cage for each treatmenÈ after approximately Et'Io generations of SAA ln Èhe field' Culburra, 1981.

Treatnent Number of SAA per cage

Rep. I Rep.2 Rep.3 ReP.4 l'lean*

Sprlng regrowth (field) 48 93 200 82 r06 Sprlng regrowth (pots) 366 73 320 L22 220 Summer regrowth (pots) 129 433 101 233 224 I,Iinter regrowÈh (poËs) 73 267 143 73 139

* I'feans not significantly dlfferent aÈ P(0.05 uslng 1og (x + 1) transformation, F3,12 = 1.02.

Ihe lack of dlfferences in the numbers of aphlds ln the different treatments suggests that the various pre-conditioning daylength and temPerature regimes given to the plant,s in the differenÈ treatmenÈs did noÈ signiflcantly l-nfluence the physiological status of the plants Ín the treatments. For this reason, the properties of the plants were analysed ln sone deÈail. 8.3.2 ProDerties of the Plants (¿) After p"e-eondítioning The ínfluence thaÈ the different pre-conditloning environments (Table 8.1) had on Èhe raÈe of developnent of lucerne regrowÈh are glven in Appendix 8.1

and summarised in Table 8.3. The number of stems and IM per plant for field plants were not lncluded in the analyses because Èhese plants were larger and nore productive than the younger plants 1n the poÈs. For the plants in poEs' the number of stems per planÈ did not differ (P<0.05) between Ehe differenE

treatments, br¡È Èhere were large dlfferences in the percentage of stems wiEh -r7 6-

TAsLE 8.3 ì,feans and rean log (x + l) of various properties of the regrowth of lucerne plants after five weeks pre-conditioníng in the different treaÈments, together wlth LSDs aE P = 0.05 based on log (x + 1) or x for the varlous properties and the corresponding F values, 8. I2.80, Culburra.

Treatnent No. stems % ste¡ns wi-th % sEens with IM per per plant floral buds flowers plant (e)

x log(x+I ) x log(x+l ) x 1og(x+l )

Spring regrowth (field) 35 .0* r3.3 1.02 0.0 0.0 9.4r, Spring regrowth (pots) 12.8 r. 13 26.4 1.42 24.L r.34 5.8 Summer regrowÈh (pots) 1I.2 1.05 10.3 0.81 16. r l.12 4.1 I,Iínter regrowth (poÈs) 10.3 r.05 0.0 0.0 0.0 0.0 2.8

LSD (0.05) NS 0. 58 0. 30 r.2

F F2,9=15. I F-value Fj 6=0.54 3,L2=9.98 F3,12=56.45

* Not included in analysis. NS - Èreatments not significantly dlfferent aÈ P(0.05. floral buds and the percentage of stems wlth flo!üers; and Ehere l¡ere also significanË dlfferences (P<0.05) in Ill per plant beÈween treatments' The most obvious dlfference was that plants subjected to r'rlnter conditions remained vegetative and had a slower raÈe of grolJth which was reflected by the total lack of stens wlth floral buds or flowers and the low ll'f per plant' respecÈively. Plants in all other Èreatments advanced to the reproductive stage, with planÈs in sone treatmenÈs developing more Èhan others' There lùas an unexpected difference in the s¡age of floral development betr¡reen field and potted plants in sprlng weather. The faster rate of reproductive developnent in -r77- potted plants in sprLng compared to field planÈs was attributed Èo the pots being left 1n the field above Èhe ground at Northfteld during the pre- condltloning period. The roots of the plants l-n these pots would have been at htgher tenperatures than the roots of field planÈs in the soil at Culburra. In addftlon, Èhls dlfference in temperature could have accounted for the sJ-rnilariEy !n the reproductive development and IM between poÈted Plants in the spring and suÍurer Èreatments. Nevertheless, the data did suggest thaÈ the different pre- conditlonlng treatgents did produce seEs of plants at different physiological stages and, presumably, with different biochenlcal conpositions.

(i¿,) After ínfeetatíon î'tith SAA The final IDI productlon and physiological stages of plants in the different

Èreatments following exposure to SAA were similar (Table 8.4, Appendix 8.2). The pre-condiÈioned planÈs dld not dlffer (P < 0.05) 1n herbage yield or reproductlve development once they were allowed to regro!ü 1n the sane environnent in the fleld. The close sinilariÈy in the reproducÈ1ve development of the plants is especlally evident from the total mean percentage nunber of stems per plant w'iÈh floral buds plus flowers, ví2. approximateLy 64%,677.,507" and, 66% for the spring (fiefd), sprlng (pots), sunmer and winter regrowth treaÈnents, respectivelY. 8.4 DLscussfon The nethodology in this experlment was unsuccessful, partly because Pre- conditlonlng plants in differenÈ environments for flve weeks aPParently only influenced the physlology of Èhe plant durlng thaÈ Perlod' and any effects of those environments on the plants dtd noÈ contlnue Lnto the next regrowth phase. The design of cages and the relatively high anbient temPeratures during that part of the experiment l-n the field were also attrlbuted to the fallure of the experl-ment. I'faximum daily temperatures in lucerne herbage ln the cages were up

; tOoC trtgtrer than those in a Stevenson scrêên. This increased Èemperature resulted ln naximum temperatures ln the cages exceeding 40oC for four -17 8-

TAsLE 8.4 Means and mean log (x + I) of various Properties of the regrowth of lucerne plants in the dlfferenÈ treatmenÈs after infestation v¡ith SAA ln the field at Culburra, together with LSDs at P = 0.05 based on 1og (x + 1) or x for Ehe varfous properties and the corresponding F values, 13.f.81.

Ïreatment No. stems % stems wlth % sterns with Ill per per plant floral buds flowers plant (e)

x log(x+I ) x log(x+l ) x log(x+l)

Spring regrowth (fleld) 33.5* 57 .l 1.76 7.3 0. 65 4.4* Sprlng regrowth (pots) 9.9 1.03 35 .0 r.46 31 .8 1.44 3.7 Summer regrowth (poÈs ) 8.0 0.94 32.7 l. 50 17 .4 0.75 3.4 tr{inter regrowth (pots) 5.0 o.77 59.7 L.77 5.9 0.35 3.5

LSD (0.05) 0. 19 NS NS NS

F2,9=0.13 F-value Fc o=5.07 F^J, Lz'^=2.51 F3,12=2.03

* Not included fn analysis. NS - treatments not slgnificantly different at P(0.05.

consecutlve days durlng the ntddle of Èhe experinent. Such Èenperatures would have undoubtedly caused a reduction in the numbers of SAÀ in the cage and nay have reduced the subsequent fecundity of fenales (SecEion 7). The use of relatlvely heavy gauge perspex for a stlding door aÈ one end of each cage was considered to be responsLble for the excesslvely htgh ternperatures ln each cage because the perspex acted as a heaE sink, even though each door was faced away from the sun. -L7 9-

The experiment did not elucidate the influence of the quality of lucerne in the population dynamics of sAA in dryland lucerne in the upper-south-East durlng spring.

8.5 References Auclalr, J.L. 1965. Feeding and nuÈrition of the pea aphid, Aegrthoeíphon pietun (Ilomoptera: Aphidae), on chemically deflned diets of various pll and nutrlent levels. Ann. ent. Soe' Am' 58: 855-875' Cates, R.G. 1980. Feeding patterns of monophagous, oligophagous and polyphagous insect herbivores: the effect of resource abundance and plant 462 22-31. chemístry. )eeoLogia - Dixon, A.F.G. 1977. Aphíd ecology-life cycles, polymorphism and populatíon regulatíon. A. ReÐ. EeoL. & Sget' 8: 329'353' Feeny, P. 1970. Seasonal changes in oak leaf tannins and nutrients as a cause of spring feedlng by winter moth caterpillars . EeoLogy 51: 565-5é1. Ilough, J.A. and Pimental, D. 1978. Influence of host foliage on development' survival and fecundity of the gypsy moth. EnÐiron. Ent. !-z 97'102' I{ouse, II.L. 1969. Effects of dlfferenE proportions of nutrients on insects' Ent. ery. & aPPL. l2z 651-669.

Kennedy, J.S. 1958. Physiologlcal condition of the host-plant and susceptibility to aphid atÈack. Ent' ery' & appL' 1: 50-65' InsÈitute List, R.J . l95t . Smithsonian l"feteorological Tables. Snithsonian ' I^lashington. 527 pp. host suiEability for elongaEe I'fcClure, Þ1 .S. 1980. Foliar niErogen: a basis for hemlock scale, Eiorirta eæte'rrcL, (Homoptera: Díaspididae)' EeoLogy 6l:

7 2-79 .

Schoonhoven, L.l"f . 1969. Gustation and foodplant selection in some lepídopterous larvae. Ent' eæp' & appL' L2z 555-564' -1 80-

Southr¿ood, T.R.E. 1973. The insecÈ/plant relaElonship - an evolutionary perspective. fTt, Insect/Plant Relationships. Ed. H.F¡ Vâlt Emden. Blackrsell Scientific Publicatlons. 215 pp: 3-30. van Emden, II .F. and Bashford, l"f.A. 1971. The perfornance of Bretsicoryne

braeeíeae and Myzue pers¿ed,e in relation to plant age and leaf amino acids. Ent. etp. & appL. l4z 349-360. van Emden, II .F. âDd I,Iay, I'f.J. 1973. Ilost plants in the population dynamics of insects. In, Insect/Plant Relationshíps. Ed. II.F. vâo Emden. Blackwe1l Sclentific Publícations. '215 pp: 181-191.

I,Iebb, J.ll. and l'loran, V.C. 1978. The lnfluence of the host plant on Ehe

population dynamics of Acizzia nusseLlae (Honoptera: Psyllidae). EcoL. Ent. 3: 313-321. Iühite, T.C.R. L969. An index to measure weather-induced stress of trees associat,ed wlth ouÈbreaks of psylitds in Australia. EcoLogg 50: 905-

909. -t 8I-

Appendlx 8.1 Estimates of various propertíes of the regror¿th of lucerne plants in each repli-cate after five weeks pre-conditioníng in the dlfferent treatmeriLs, 8.12.80.

Treat.ment Rep. No. stems Z stems wiÈh % stens with DM/p1ant per plant floral buds flowers (e)

Spring regrowth I 54.0 1.8 0.0 L2.6 ( field) 2 35.0 8.6 0.0 L0.2 3 33.0 15.2 0.0 ll.7

4 18.0 27 .8 0.0 3.2

Mean 35.0 13.3 0.0 9.4

Sprlng regro\{th I 11.0 30.0 36.3 5.7 (pots) 2 l2 .0 25.0 19.2 5.2

3 l6 .3 I6 .6 26.4 6.8 4 ll.7 34.2 14.5 5.3

I'fean r2.8 26.4 24.L 5.8

Summer regrowth I ll.3 0.0 38.0 4.8 (pots ) 2 L2.3 5.7 13.8 3.8 3 l6 .5 7.9 6.1 5.0

4 4.7 27 .6 6.4 2.8

l"lean IT.2 10.3 I6.l 4 I

I,Iinter regrowth I 11.0 0.0 0.0 3.2 ( pots) 2 9.7 0.0 0.0 2.1

3 9.7 0.0 0.0 3.0

4 10.7 0.0 0.0 2.7

Ìlean 10 .3 0.0 0.0 2.8 -r82-

Appendix 8.2 Estimates of various properties of Ehe regror¡th of lucerne plants in each replicate after lnfestatlon wl-th SAA in the field at Culburra, 13.1.81.

TreatmenE Rep. No. stems % stems with % stens wlth DM/p1ant per olant floral buds flowers (e)

Sprlng regrordth I 62.0 64.5 1.6 6.4 ( f ield) 2 36.0 41.7 0.0 4.0 3 l8 .0 61 .1 22.2 5.4

4 18.0 6l.l 5.6 I.6

l(ean 33 .5 57 .l 7.3 4.4

Spring regrowth I ll.0 L2.l 45.4 4.0 (pots ) 2 7.3 54.5 13.6 3.4 3 8.7 57 .6 l5 .4 3.8

4 12.7 15.8 52.6 3.7

I'f ean 9.9 35.0 3l .8 3.7

Summer regrorrth I 7.7 30.4 52.2 4.3 ( pots ) 2 12.7 36.8 0.0 4.4 3 6.0 16.6 0.0 1.6

4 5.7 47 .O L7 .6 3.3

Mean 8.0 32.7 17 .4 3.4

I,linter regrowth I 6.7 45.0 0.0 4.3 (pots ) 2 5.7 47 .0 23.5 4.1 3 3.3 70.0 0.0 2.5

4 4.3 76.9 0.0 3.2

lulean 5.0 59.7 5.9 3.5 -1 83-

SECTION 9 : LIT'E TABLES AIÙD RATES OF INCREASE OF SAA ON DRYLAND LUCERNE IN

TEE IIPPER-SOUTII-EAST OF SOUTE AUSTRALIA

Sunmary

The fecundities and survival of female SAA in leaf cages on different ages of lucerne regrowth in the field lvere compared at different times of the year. The fecundity was not influenced by the age of regrowth wíthin the five-week regrowth períods used to manage dryland lucerne pasÈures for gtazlng buÈ it was influenced by the tfme of the year - SAA rtas most fecund in March-April and least fecund in June-July.

Life tables r¡rere prepared for SAA on dryland lucerne plantsi the values of the innate capaciÈy for increase, rm, calculated frour these tables demonstrated tha¡. tenperature and food quality were favourable for increases in density of S|,l\ during winter, spring and summer, though the value of r, !'ras not related to temperature; the highest value occurred in March-April when Ehe mean tenperature r^ras an unexpectedly low 15oC. Reasons for a hlgher value of r* at a relatively low temperature lrere aEtributed to a higher quality of food for SAA and, perhaps, a different physiological condition of females during ì'farch- Aprll compared to other t.imes of the year.

Comparisons of the values of r* with rates of increase obtained from populaÈions of SAA both in stem cages and naturally occurring on field plants showed that the innate capaclty for increase !Ías not realised in the field; much lower than expected rat.es of increase occurred in the fleld in Septenber- October and November-December r¡hen the rates were virtually zero, and ln June- July when the rates \rere negative. Reasons are given for these differences. -184-

In March-April, when SAA was most abundant, acEual rates of increase of populations of SAA declined with lncreaslng densities of SAA; thís decline was attributed to deterlorating food quallÈy caused by SM-lnduced stress on the lucerne plants. Other fnEraspecific factors rmy have also been operaÈing wiEh SAA, e.g. the production of snaller, less fecund adults and increased emLgration of alates with increased densities of SAA.

The fecundlties and values of r, for SAA on dryland lucerne plants at dlfferent mean Èenperatures are compared w1Èh t,hose from studies wiÈh SAA in the U.S.A. and in Israel. -185-

9.1 InÈroductlon An understanding of the population dynamtcs of pests underlies the development of integrated pest managemenË prograns (Flint and van den Bosch f981). In practical terms, this undersÈanding can be achLeved with empirical studies, though the use of llfe-tables, key factor analyses and nodelling nay give confidence to such studLes (tlay L972). Llfe-table analyses have been used to establish differences beËween specfes of aphids as well as the effecÈs of hosÈ plants on the population dynamLcs of aphlds (tr'razer L972>, and Èo compare

the effects of dlfferent mean temperatures and hunldlÈ1es on the populatlon dynamies of SAA (Graham 1959, l"fessenger 1964b). However, neither lif e-table studies nor other similar studies have been carried out wiÈh SAA in dryland lucerne pastures to provlde a more fundamental understanding of the populatlon

dynamics of SAA in such pastures. For this reason, I determlned life-tables for

SAA on dryland lucerne plants aÈ different Èimes of the year under field

condlÈlons using caged aphids. Innate capacities for lncrease calculated from l1fe-tables are theoretical

maxlmum rates buÈ those calculated for SAA were expected to provlde mainly a comparison of Ehe influence of Èemperature and quallty of lucerne on Èhe aphfds at different Èlmes of the yeaÊ. Theoretlcal rates should also be Eested, if

posslble, agal-nsÈ actual rates of increase Ln the field at Èhe same time (Birch 1948); conparlsons of the theoretical and actual rates of increase of SAA can then l-ndicate whether Èhere are other envlronmental facÈors whose lnfluences have been missed ln calculat!.ng Èhe theoreÈlcal raÈe of increase of SAA at the different times of the year. Any large differences between the two estimates of rates of increase would suggest that there is an lmportant factor(s) lnfluencing

the populatÍon dynamics of SAA other than Èhe direct lnfluence of temperature and/or food quality experienced by aphfds in Èhe cages. -r 86-

Food quality was expected to be one of Ehe najor influences on the rate of increase of aphids within the cages because of the physiological changes in the lucerne regrowth caused by agíng (van Enden and Way 1973) and because of the likely differences in the plantrs physiology at different times of the year.

The physiological changes in lucerne plants in dryland pastures are possibly greatest in late-spring to early-autumn; durlng this time, pastures after are allowed to grow for flve weeks between each grazíng and, during this period' the regrowth changes fron an acEively growing, vegetatlve stage Èo a stage of floral |nítiation. The aphids are mosE abundant during this period of change to floral inítiaEion. The ain of this section r,{as, therefore, to determine populatíon growÈh statistics for SAA on different ages of regrowth of lucerne in Ehe field at different times of Ehe year to elucidate t.he role of environmental factors, especially temperature and food quality, 1n the population dynamics of SAA in dryland lucerne pastures.

9.2 }faterlals and Methods

Four experiments were conducted in 1981 during Mareh-April (Experiment I), June-July (Experiment 2), September-October (Experinent 3) and November-December (Experiment 4) on l3-year old l{unter River lucerne plants ln a dryland lucerne- based pasture growing'at ¡he experimental site at Culburra. In each experlment, there were 10 treatments comprísitg 2 types of cages (leaf and stem) x 5 initíal ages of regrowth of lucerne (2,3, 4,5 and greater Èhan 5 weeks). The age of regrowth (=AR, say) treatments are deslgnated AR2, AÚ, AR4, AË and AR6, respectively. AR6 r¿as not included in Experiment 2 because regro\{th of this age was stunted and had shed most of iEs leaves due to unusually low rainfall.

Newly-emerged apterous female SAA were confined indlvídually in the leaf cages, and t,heír age-specific survival and fecundity curves were used to esÈimate the theoretical innate capacity for increase, Ím, of SAA' - r87-

Newly-ernerged apterous female SAA were confined in each stem cage (five per cage) to estímate the rates of increase of populaÈions of SAA for at least trlro generations ín an envlronmenÈ free of parasites and predators. In ExperinenÈs I and 2, there $ras one area (block) 15 m x 30 m, per age of regrowÈh, and in ExperimenEs 3 and 4, there were thTo areas (blocks), each 15 n x 15 m, per age of regrowth. In each experiment, there were eíght leaf cages (replicates) per age of regrowth, so there were eight per block in Experiments

1 and 2 atd four per block fn Experiments 3 and 4. The number of stem cages Per age of regrowth varied in the different experiments; there were 12 each in AR2,

AR5 and AR6 Ín Experlment l, 13 each in AR2 and AR5 in Experinent 2, and 12 each (6 per block) in ¡nZ, AR5 and AR6 in Experíurents 3 and 4.

During the perlod of each e"perirent, samples of SAA were also taken from natural populations of SAA within the areas with differenÈ ages of regrowÈh, and the data from these were used to estimate the crude rates of increase of the naÈural populat,ions.

9.2.L lypes of cages

(i) Leaf eage

A leaf cage (Ptate 9.1) was made r^rith two cylindrical sections, each l0 m long, of clear perspex tubLng, one section securely fttÈ1ng inside the other. The section with the smaller dia¡neter was the base of the cage and was atÈached to a wire peg, as shown in PlaÈe 9.2, and Ehe larger section was used as a lid

Eo the cage. The internal diameÈer of the cage was 44 rnm and provided sufficient area for a ErlfollaÈe leaf of lucerne to lay flat in the cage. Corresponding U-shaped grooves 1n the side of each section allowed the peÈiole of the leaf to pass through.. The petlole was wrapped 1n cotton wool to seal thls part of the cage. The top and boÈtom of the cage Iüere covered wlth flne nylon Eavze to provlde aeratlon but to exclude parasites and predators of SAA. -r88-

PLATE 9. I: A leaf cage used to enclose a female SAA on a trlfolaEe leaf of lucerne in the four experlments measuring the fecundity of SAA in the field at Culburra, tg8f. -189-

Leaf cages çere put on expanded trifoliate leaves, free of SAA, on seParate lucerne plants r¿hich were selected at random within the areas of different ages of lucerne regrowth.

(ii) Stem eage A sten cage (PlaÈe 9.2) was a modifl-ed clear plastic, cylindrieal container, 66 * inÈernal diameter, wiEh a softer Plastic screwtop lid. The

cage was nade frorn (a) the líd, whlch acted as the base' (b) a 55 m length of thaÈ end of the container which screwed into the lid, and (c) a wire frame which r,¡as att,ached to sectlon (b) of Èhe container; the frane r{as covered r,r'ith fine nylon gauze which was initially attached to the end of the container with rubber bands. After Experiment 3, Line gauze was glued Èo the container. The height of

the cage was 270 nrm. The base had a hole, 8 rm dl-ameter' bored in the centre through which a stem of lucerne could pass; a radial sectlon' 5 * w'ide, was cut out of the base to allors the base to be slipped onto the bottom of the stem. The base also had three other holes whtch vlere covered w'ith fine nylon gauze to irnprove ventilation Ln the cage. After the base was slipped onto Èhe stem, the hole around the sten rras sealed with cotton wool and the radial section, whlch was cut out for the sten, was sealed wtth \üaËerproof adheslve electrical tape.

The base was held in place with three wire pegs lrhich were placed equidistant

around the circumference of the base and then pushed into the soil; Èhe pegs were fixed to the base wit,h a strip of the adheslve ÈaPe. The t.op of the cage could be put into place or removed easfly by screwlng or unscrewing iÈ ínto the

base.

Stem eages were placed on índlvldual stems on separate lucerne plants

approxlmately one to Èlro weeks prlor to the addltion of SAA; the planEs rlere

selecÈed at random withl-n the different treatment areas and Èhen a stem arising frorn the centre of each crovrn was used. tr{hen each cage was fLrst posítfoned' the stem of lucerne and the inside of the cage r,rere thoroughly sprayed with -190-

PLATE 9"2: A stem cage used to enclose a population of SAA on a stem of lucerne in Ehe four experiments meaèuring the rate of increase of populations of SAA in the field aÈ Culburra, 1981. -19 r- either water-based pyrethrfn (L7" a.c.) or dichlorvos (0.57" a.c.) before the cage was sealed; this spraylng was done to control any parasiËes or predators of SAA which may have been on the caged stem.

9.2.2 SAA for cage treatnetrts Newly-energed, nulliparous, apterous ferneles were used in each cage. These aphids were obtained from a laboratory culture of SAA which was maintained on poÈted lucerne at abouÈ 25oC. (Reasonable genetic variability of aphids in the culture was mainEalned by regularly addlng first insËar nymphs from adulËs collected in the field ). Seven days prlor Èo the beglnnlng of each experiment, about 100 adulÈ apterae ¡vere allowed to larviposit on excised trifoliate llunter River leaves for about 16 hours during the night. The leaves \dere on slightly da4 fllter paper ln petri dishes and kept at about 25oC. The resultant first-instar nymphs, approximately 300 to 400, were transferred onto caged bouquets of lucerne stand.ing in water, and then reared at 25oC + loC; this rnethod provided a sufficient number of adults aPParently of the righÈ physiological stage at the start of each experlment. 9.2.3 Ase of lucerne regrowth The dtfferent ages of lucerne regroutth for-each experlment were obtained ín the lucerne-based pasture by sequenttally mowing a different area of pasture

each week 1,¡igh a rotary lawn mower and removing all the cut herbage. The age of regrowth ln the areas deslgnated AR6 in the different experlments varied from about severi to l0 weeks, depending on the time of the previous grazing ln each experfnental area. 9.2.4 Temperature Thernistors, atÈached to a Granto temperature recorder' Ilere placed in an fndivldual leaf cage, stem cage and amongsÈ herbage in an uncaged plant, respectively, to neasure daily meximum and ninimum temPeraÈures in each environment. Each thernfstor was placed under a lucerne leaf Èo shield 1t from -192- direct sunlight and the temperature measured by each thermistor was recorded on a chart every 30 minuÈes. The daily maximum and uiniuum temperatures estinat.ed from these charts were used Ëo calculate the mean dally temperatures. The mean of the mean daily Eemperatures for the course of each experiment was taken as the mean temperature for each experiment. The temperature in a sEandard

Stevenson screen was also recorded by the Grant@ recorder as well as contfnuously by a therrnohygrograph, as a check for the values recorded by the

GranE@ recorder.

9 .2.5 Tfne of Eow{1n,g the paetures and Btart of each experiment The dates of nowing the pastures and the start of each experiment (i.e. when the aphids were added to the cages) !{ere:

Treatment Expt. I Expl. 2 Expt. 3 ExPt. 4

Date of mowing pasture:

AR5 9.02.81 9.04 .81 28 .07 .81 29 .09 .8 1

AR4 16.02.81 15 .04 .81 4.09.81 6.10.81

AR3 23 .02.8r 22.04 .8r 11.08.81 13.10.81

AR2 2.03.81 29.04.81 18 .08 .81 20 .10 .81

Experiment started on: 19.03.81 29.05.81 I .09 .81 5.I I .81

9.2.6 Tfne and nethode of sanpllng aphlds

(¿) Leaf eage The aphíds within each cage were flrst inspected three to four days after

seven days except in the start of each experimenÈ and then approximately every ' ExperimenÈ I when the aphids l{ere usually inspected every three to flve days -193-

(Figure 9.1). At. each Eime of inspect,íon, Èhe petiole of the caged leaf was cut, the cage was placed over a tray and opened, all nyrnphs t¡7ere removed with a fine sable hair brush and placed in a labelled vial of 80% ethanol' and Ehen the surviving adult Ì{as returned to the cage on another trifoliate leaf on the same plant. A record was kept of the number of nymphs produced per female and wheEher or not Ehe fenale r¡ras alive each time. Any female which was missing or r¿as dead at the time of f.he first inspection was replaced with a newly-emerged, nulliparous, apterous female.

(ii) Stem eage

The mean numbers of aphids per stem cage for each age of regrowth with stem cages were estimated after an expected onp, two and three generat,ions of aphids' respectively, in Experlments I and 2; after one and two generatlons, respectively, in Experlrnent 3; and after four generations Ín Experiment 4.

The expected number of generations at each time of counting the number of aphids was estimated from the mean temperature in the cage and the time taken for the development of nymphs at dlfferent temperatures (Messenger 1964b). At each time that the mean numbers of SAA per cage \^tere estimated, at least four cages llere removed from each age of regrowth and the aphlds in each cage were counted. To remove a cage, Èhe three pegs around the base were removed, the stem was cut under Ehe cage \rith a scalpel and then Ehe unopened cage was put int,o an insulated container and taken back to the laboratory; Èhe aphids were then washed from the inside of the cages and off the sEems of lucerne and counted' as fn Section 3. The times of sampling cages for SAA, and the numbers of cages sampled in each age of regrowth at each sanpling time for each experiment are given ln Appendix 9.3. (íii) EíeLd popuLatíon

The mean numbers of SAA per stem of lucerne in the fteld populations of SAA were estimated within the areas with different ages of regrowth using the rnethod -r94- descrlbed in Section 3. In each experiment, 20 stems of lucerne per age of regrowth were randomly sampled. The times of sanpling the field populations of

SAA ln each experiment are glven in Table 9.5. 9.3 Results 9.3.I Fecunditv and survival of SAA lu leaf cages The number of progeny for each female on eaeh age of regrowEh in each of the four experiments ís given in Appendix 9.1, and the mean number and the mean square root of the number of progeny per female for each treatment in each experiment are given in Table 9.1. Fecundíties are only given for those females

1n each experiment whlch (a) survived to at least the second time of inspection of aphids, (b) produced at least l0 proge¡y, and (c) were not mlssing during the experiments - the bodies of dead females were easily seen in the leaf cages. These consEraints were applied to minimise any bías of data which may be caused by deleterious effects of handling and/or caging aphids; such constraints were not considered unreasonable for this type of study in the fíeld. The mean fecundities of the lndividual female aphids in leaf cages on each age of regrowth r¡rere compared with a l-way ANOVA for each experiment. A 2-way ANOVA was then used to test for differences in fecundities of adults on each age of regrowth, AR2, AR3, AR4 and AR5, between the four experiments (i.e. between different times of the year). In each of the above analyses' a square-root transformation of data was used Eo transform each set of data Èo an approximately normal distribuÈlon. In Experiment I (March-Apri1), the mean number of progeny per female in leaf cages on regrowth lnitlally older than five weeks (AR6) was less (P<0.01, 84,29=7.17, Appendix 9.2(a)) than the mean numbers of progeny per female on the younger regro\{ths in the experínent. Thls lower number of progeny per

fenale in AR6 was attrl-buted to a more rapid deterioration of the quality of this regrowth as the experiment progressed, compared to the younger regrowths; -195-

TABLE 9.1 Mean numbers and mean square root of numbers of progeny per female ín leaf cages for the five regro$¡th treatnents in four experiments at

Culburra, 1981, vlz. Expt. 1 (l"farch-APrtl) , Expt. 2 (June-July), Expt. 3 (Sept.-Oct.) and Expt. 4 (Nov.-Dec.). Also given are the signlfLcant dlfferences between various mean fecunditíes of aphids on different ages of lucerne and at different times of the year.

Treatment Mean number of progeny per female, Mean* (age of regrowth x and /5, 1n: .AR- in weeks) ExpÈ. I Expt. 2 Expt. 3 Expt. 4

x /xt T x /* x /* x /* x /x

AR2 92 9.44y 25 4.95 47 6.63 74 8.46 60 7 .37 AR3 93 9.54y 26 4.93 52 7. 10 75 8.52 61 7 .52 AR4 91 9.49y 38 6 .06 58 7 .58 84 9.07 68 8.05 AR5 83 9. 09y 35 5.80 5r 6.95 49 6.79 55 7. 18 AR6 4L 6.402 77 8.77 57 7 .s5 58 7 .62

l{eant' 89 9.39a 30 5.35d 52 7.07e 70 8.20b (excludinC AR6)

AR6 not fncluded ln Experfment 2. * I'feans (excluding AR6) not signif icanÈly dif ferent aL P>0.05 (F3,9=3.40). 1 Means (excluding AR6) followed by differenÈ leÈters noÈ signfficantly different at P(0.05 (F3,g=45.7I). LSD (0.05) = 0.88 Expt. 2 vs Expt. 3. LSD (0.05) = 0.84 Expt. 3 vs Expt. 4. LSD (0.05) = 0.76 Expt. 4 vs Expt. l. 11 I'feans (excludlng overall nean) followed by dtfferent letters are slgnLficantly differen! at P(0.05 (84,2g=7.17). LSD (0.05) = t.52. -r 96- the leaves of plants in AR6 senesced and were shed due Èo both the physiological stage of the plants and the damage caused by the field populat,ions of SAA on the planÈs. The plants in the other treatments also carried hlgh nurnbers of naturally-occurring SAA during Ehe experiment (Table 9.5), buE these plants did not suffer severe damage and leaf shedding during the experiment, especially early in the experiment when larviposition was at a maxirnum (Figure 9.1(a)). By contrast, the mean number of progeny per female 1n AR6 in each of Experíments 3 (September-October) and 4 (Novernber-December) did not differ at P)0.05 Appendix 9.2(d), respectively) (tr4r22=I.38, Appendix 9.2(c) and F4 ,34=2.29, from ¡he mean numbers of progeny per female in AR2, AR3, AR4 and AR5. These data suggest that the fecundity of fernales was the same on lucerne regrowth greater than five weeks old, ê.gr in ungrazed pastures, and on regrowth less than five weeks old, e.g. iû roEatlonaLly grazed pastures, from September to

December, but rras less on older regrowth 1n March-Aprll when the quality of older regrowth for SAA rapidly deterLorated. In each experimenÈ, the mean number of progeny per female did not differ between AR2, AR3, AR4 and AR5 (table 9.1, Appendix 9.2). This lack of difference showed Ehat, the age of lucerne regrowth wiEhin the fíve-week regrowth period used to manage dryland lucerne pastures did not influence the fecundiÈy of S¡¡ at any t,ime of the year. For this reason, the fecundities of SAA in age- of-regrowth treatments AR2, AR3, AR4 and AR5 were pooled for eaeh experiment for uost of che analyses and population sEatistics discussed in the remainder of this section, even though the age of lucerne in these treatments exceeded five weeks by Ehe end of each treatmenE.

The fecundÍty of SAA did differ (P<0.05, F3,9=45.71, Appendix 9.3) at different times of the yeeî; the level of fecundity increased, in order, from June-July through September-October and November-December Eo a maximum in March- April (Table 9.1). -r97-

For each experiment, the ages and fecundlties of the females on each of the ages of regrowth AR2, AR3, AR4 and AR5 were pooled to determine (a) the proporÈion of fenales surviving each interval, x (i.e. Èhe age-specific survival rate, 1*) and (b) Èhe number of progeny produeed per female per day

a¿ Èhe end of each age l-nterval, x (i.e. the age-specific fecundity rate' n*), as descrlbed by Àndrewartha and Birch ( 1954). The fecundlties whlch were pooled were only those of females which satlsfied the above three constraints íncluded in the tniÈfal analyses, plus the constraint that each female also belonged to the origlnal cohort of SAA plaeed in the leaf cages for

each experiment. The age-speclfic fecundity curves for SAA varied narkedly beEween

expertmenÈs (Figure 9.l(a)-(d)). Th" r"*ìr,n dally production of progeny per female in Experlment I was about five progeny Per female aÈ a time when the adults erere about ttro weeks old; after Ehis tine, the number of progeny per female per day rapidly declined durlng the nexÈ four to five weeks (FLgure 9.1(a)). This pattern of larviposLtion r¡as similar to patterns obtained in other sÈudles with SdA, e.g. Graham (1959) and I'fessenger (1964a), buÈ the

maxlmr:;m datly fecundiEy at Culburra was abouÈ one Progeny per female less than in the other studies. The naxfmum fecundítfes betr¡reen SAA at Culburra and in the other studies may have been more comparable 1f the temperature ln Experiment t had been higher, as lras expecEed for the Elme of the erçeriment (see 9.4.1).

11he daily productlon of progeny per female 1n Experiment 2 was relatlvely constant throughouÈ the life of the adults (Flgure 9.1(b)) and Èhere was noÈ a definlte peak 1n the production of progeny, as in Experinent 1. In both Experlnents 3 and 4, there rüere apparent peaks of daily productfon of Progeny

when the adults r¡ere about three weeks old, followed by a decline in producÈ1on over the remal-nder of the perÍod of larviposition (Flgures 9.1(c) and (d)' respectlvely). -r98-

Mor, - Apr June - July

1.0 5

0'8 I

0.6 3 d x € I 0¿ 2 o x-)l-x-\--x\ ! 0.2 o+ lì \ oC ol I o o o Sept Oct Nov. Dec- L - - _o

E 1'0 5 =E ¿ C a l. ) v) 0-8 U ll.(U 0'6 3

0.4 2

0.2 1

0 20 /.0 0 20 10 60

Doys

FIGURE 9.I: The age-specif lc survival ( '-' ) and age-speclf íc fecundlty (x-x) curves for adult SAA in leaf cages in the four experl-ments at Culburra 1981, vlz. (a) Expt. I (l{arch-Apr11), (b) Expt. 2 (June-July), (c) Expt. 3 (Septernber-October) and (d) Expt. 4 (November-December) ' -r99-

The age-specific survival curve for SM in each experiment is also given in Flgure 9.I. The curves for Experiments 2, 3 and 4 ¡.rere similar (Figures 9.1(b), (c) and (d), respectively), suggesting that the different, mean t,emperatures during the experlments, viz. from lo.loC to 19.9oC (see Table 9.2) did not influence the survival raÈe of the adults. This flnding is contrary Eo E.hat of

Graham (1959), Harpaz (i955) and Nielson and Barnes (1957). Adults appeared to be shorter lived in Experiment I than in Ehe other experiments (Table 9.2) , and the rapid mortality of adults afEer three weeks in Experiment I (Figure 9.1(a)) may be related Eo the higher daily fecundity of females during the flrs! three weeks of Experlment 1; this higher fecundity probably caused the adults to reach Eheir physiologícal linits in a sho¡ter tine (Grahan 1959). Ilowever, i-n each experiment., the ranges of the survlval and reproductive periods of each cohort of aphids were similar (Figure 9.1). Also, in each experiment' Ehe pre- reproduetive period ¡sas short, as reported by Harpaz (1955) and others, and it was short because fourth-instar SAA contained embryos and parEuritíon usually occurred within a day of t,he final moult of fourth instars. Ilo$lever, contrary to some other studies, there was virtually no post-reproductive survival of adults at Culburra; Harpaz (1955) recor

(ì.) Leaf cage The age-specific survival and fecundity rates for SAA in leaf cages in each experiment were used to calculate the followlng staElstics (after Andrewartha -200- and Birch 1954):

Net reproductl-ve rate Ro 1*\ (progeny per fernale) ' T lmx Mean of adults xx duration ' 1*t*

Innate capacity for increase, r. = 1o8" Ro T Finite rate of lncrease, L = anÈilog. r,

The value of Ehese statistics for SAA in each experlment are given in Table

9.2 a¡¡ð. are theorettcal values related to the rate of increase of populaÈions of

TABLE 9.2 Various populaÈion growth statistics for adult SAA in leaf cages in four experimenÈs at Culburra, 1981' ví2. ExpÈ. I (March-Apri1), Expt. 2 (June-July), Expt. 3 (Sept.-Oct.) and Expt. 4 (Nov.-Dec.), together with the mean tenperature during each experiment.

Growth Expt. I Expt. 2 Expt. 3 Expt. 4 s tatis tic*

n 28 24 16 28 cRR (??) 89 30 52 70 Ro ( î/?) 84 29 46 7T E, (?/?/a"v> 0. 31 0. 18 0. 18 0.25 r ( ?/ Î/¿av) I. 36 t. 20 1. 20 L.2g T (days) 14.5 18.3 2I.L 17.2

Mean temperature (oC) 15.2 10. I 14.9 r9.9

:tn number of adults in each experlment. GRR - gross reproductive raÈe (= mean number of progeny per fenale). R raÈe. o neÈ reproducÈlve lnnate capaclty for increase. rm I finite rate of increase. T nean duration of adults. -20 t-

SAA. ,The mean temperature during the course of each experiment is also glven in Table 9.2.

SAA is parthogenetic and these staÈistics do not need to be corrected for a sex ratio. The values d.o not allors for the lnfluence of environmenEal factors such as crowding of aphids, differing age-structures of populatlons of aphids, natural ênem.rss and pathogens whLch may lnfluence the actual rate of lncrease of populaÈions in the fietd. Ilowever, the statistics are useful Èo deÈernlne Èhose times of the year whl-ch are theoretlcally nore favourable for lncreases in numbers of sAA Ehan other times of the year. The values of the innate capaclty for increase, Em, and the finlte rate of lncreaserÀ, of sAA in each experiment (Table 9.2) denonstrate Èhat the combinatíon of food quality and tempereture is nost favourable durJ-ng ltatìf,-April (Experiment l) and least favourable durlng June-July (Experinent 2). The contrlbutlon of each age group of adults to the value of r. for SAA in each ocperiment is glven in Table 9.3. The values of the percentage conÈrlbutlons demonstrate that the value of r, was mainly deÈermlned by the rate of larviposlËion withl-n the flrst Ewo weeks of adult life ín each experiment. For this rea€ion, the rates of increase of field populatlons of SAA immediately following caEastrophlesr e.E. Lhe host plants grazed by llvesÈock or the applicaÈ1on of chemical lnsectfcide, would depend on Èhe age distribution of the fenåles which survived Èhe catasÈrophe; higher lnttial rates of increase in aphid numbers would be expecÈed lf most adults whlch survived the catastrophe rf,ere younger than trvo weeks rather than older then tv¡o weeks.

(¿i) Stem cage

The number of aphlds in each undamaged sÈem cage on t\,so-\{eek (AR2) and five-week (AR5) old regrowth were pooled for each tl-rne of sanpllng in each experlment and the resultanÈ ilean numbers of SAA Per cage ¡sere used to estlmate the rates of increase, Etr, of caged populatlons of SAA at the different times -202-

TABLE 9.3 The percentage contribution of each age group of adults Èo the value of r, for SAA in leaf cages in four experÍments aE Culburra, 198I, viz. Expt. I (March-Aprll), Expt. 2 (June-July), Expt. 3 (Sept.-OcÈ.) and Expt. 4 (Nov.-Dec. ).

Expt. 1 ExpE. 2 ExpÈ. 3 Expt. 4

(x)* 7!ï (x) 7" (x) 7" (x) 7"

2.0 56.5 2.0 57 .9 1.5 25.4 3.0 85.4 6.0 29.7 7.5 32.2 5.0 26.3 9.0 8.6 10.0 10.2 14.5 7.7 10.5 35 .0 15. 5 5.2 13. 5 3.3 2t.5 1.8 L7 .5 11.1 22,O <0. I

17 .5 1.0 29.5 <0. 1 24.5 1.5 29.0 <0. I 22.5 0.2 36.5 <0. I 31.5 0.1 36.5 <0. I

26.5 <0. 1 42.5 <0. I 38.5 <0. l 43.5 <0. r 31.0 <0. r 49.5 <0. 1 45. 5 <0. 1 51.0 0.0 37 .5 <0. r 56.5 <0. 1 52.5 <0. I 44.5 0.0

* (x) - Pivotal age group (days). I "/" - percentage conÈributlng of each age grouP to Ehe value of fn'

of sarnpling at each time of the yeer. The rates of increase of SAA were calculated from the equation: .t, = logeNÈ-1o8"No

E

¡¡here No = number of aphids aÈ time zero, and N, = number of aPhlds at tlme t. The number of aphids aE each tine of sampling in each sEem cage on ages of

regrowth AR2 and AR5 were pooled for the sane reasons that the number of aphlds ln leaf cages were pooled - stem cages rüere not set up l-n ages of regrowÈh AR3 -203- and AR4. The damage to the relatívely large numbers of cages in Experiment 3 after 34 days (Appendix 9.4) was caused when rubber bands, which held the nylon coverlng onto the cages, perished and broke, thus allowing the coverings to be partly blown off the cages. Damage in other experiments appeared Eo be caused nainly by birds.

The numbers of SAA in the stem cages aE each time of inspectíon of cages for the four experimenEs are given in Appendix 9.4, and the rates of increase of

SAA calculated f rom these data are sho\^In in Table 9.4.

TABLE 9.4 Rates of increase of populations of SAA in steu cages for different times ín four experiments at Culburra, 1981, viz. Expt. I (March-April), Expt.2 (June-July), ExpÈ. 3 (Sept.-Oct.) and Expt. 4 (Nov.-Dec').

Experiment Time interval after Rate of increase the start of each of S¿\A experlment (days) r', (? /?/aav)

Experiment I 0 - Il 0 .31 t2-t9 0.25 20-27 0.11

Experirnent 2 0-18 0 .I5 19-46 0.04 47-60 0.04

Experiment 3 0-22 0 .15 23-34 0.25

Experiment 4 0-33 0.22 -204-

In Experimen¡ 1, the inÍtlal rate of increase of SAA in stem cages during the first generation was Ehe same as the Èheoretical rate, fr = 0.31, determlned from Èhe aphlds ln leaf cages (see Table 9.2). A sinllarity ln the two rates vras expected because the iniÈial age-strucÈures of aphids in the stem cages and in Ehe leaf cages used Èo determ{ne the value of r, were the same' i.e. 100% newly-energed adults. The lnltial rates of increase of SAA in sten cages in Experiment,s 2 and 3 (Table 9.4) were marglnally lower than r, (Table 9.2>. The lower rates nay be partly due to the experimenÈal method - only five adult SAA were initially placed in each stem cage and any Premature mortallty of the lnitial adulÉs, eíther caused by the handling of aphids or by some other means when the experimenEs were set.up, would reduce the calculated rates of increase; ealculations of rates are based on Èhe survlval of five adults. The rate of increase of SAA in stem cages fn ExperimenÈ I decreased as the e:çerlmenÈ progressed (Table 9.4); this sequential decrease in rate wag considered to be a denslty-dependent response, either due directly to conpetition beÈween aphids or lndirecÈly through Ehe deleÈerious effecÈ of aphlds on food quality - both stlmulated by lncreaslng nurnbers of aphlds in the cages with time (Appendix 9.4). In ExperlmertL 2, the raÈe of increase of SAA in stem cages also decreased after the first sampllng, but the decrease in raÈe was mgeh greater than in Experl-menÈ I (Table 9.4). Ttre dtfference ln the decreases 1n rates between the two experiments nay have been due to a hlgher mortallty of nymphs dr-rrlng E:çerimenÈ 2 than during Experirnent I for the following reason. the original fenales in the sÈem cages tn both experlments probably produced most of their progeny by the tlme of Ehe firsÈ sampling (Table 9.3), and subsequent rates of lncrease probably depended on the survLval and reproduction of Èhis progeny. If progeny did survl-ve and reproduce ln ExperimenÈ 2, then rates of lncrease in stem cages should have approached Èhe value of r, for SAA -205-

1n the sarrp experiment, as occurred in Experiment l. Any nortality of nyrnphs in

Experimen1 2 may have been due to the low temperatures duríng Ehis experiment - dat,a from experlments in Section I0 demonstrate that the survival of nyrnphs is low w1Èh low Eemperature. In Experiment 3, the raEe of increase of SAA in the stem cages !¡as higher between Ehe first and second sanpllngs than l-n the perlod before the flrst sampling (Table 9.4); the reason for thls higher raÈe ís inexplicable. The initlal sampling of stem cages in Experlnent 4 was delayed and occurred after about four generations of SAA. The rate of increase of SAA in t,he stem cages durlng this perlod was less t,han the value of r, in that experimerit, and the lower raÈe was probably due to a density-dependent response(s) stínulated by greatly lncreased numbers of aphids in each eage afÈer the four generations (Appendix 9.4), as discussed earlier. (¿í.í,) EieLd popuLation

Ttre hlghesE denslËies of field populatíons of SAA occurred during Èhe course of Experinent I in March-Apr11 (Table 9.5). The mean numbers of SAA per stem of lucerne l-n areas with different ages of regrowth in Ehís experiment lTere used to calculate Èhe crude raÈes of lncrease, rt, between sanpling Èlmes for fietd populations of SAA on the different ages of regrowth. The rates of lncrease were calculated separately for aphlds on each age of regrowÈh because the different ages of regrowth were obtalned by sequenEially nowing different areas of pasture and were thus exposed to aphids for dlfferent periods. The rates of increase Ìüere calculated lt-ith Ëhe same equaÈ1on used t,o calculate the rates of increase of SAA in the stem cages. SAA lras noÈ sufficienLly. abundanÈ 1n the fteld during the other three experiments to rellably estimate ratLs of increase of field populaÈions of SAA aÈ the tlmes of Ehose experiments (Table e.s). -206-

TABLE 9.5 Mean densities of SAA in the fíeld on the different ages of regrowth of lucerne in Ehe four experiments at Culburra, 1981 , viz . Expt . I (l'larch-Apr11) , Expt. 2 (June-July), Expt. 3 (Sept.-Oct.) and Expt. 4 (Nov.-Dec.).

Experiment Time of Mean number of SAA per stem of lucerne on regrowth: sanplingt AR2 AR3 AR4 AR5 AR6

Experlment I 1l 37 .8 25.3 57 .9 150.0 77 .8 t9 187 .0 299.0 321 .0 444.0 260.0 27 628.0 86þ.0 940.0 961 .0 624,0 35 r365.0 1504.0 r019 .0 500.0 423.0

* Experíment 2 0 11 .1 9.1 5.9 7.L I1 6.0 6.4 5.0 5.4 18 6.5 4.3 5.8 7.6 25 3.3 3.0 2.8 2.8 34 0.8 1.0 1.0 0.8

39 0.7 0.2 0.4 0.0 46 0.0 0.0 0.0 0.5

Experiment 3 7 0.0 0.0 0.0 0.0 0.0 26 0.0 0.0 o.2 0.1 0.0

Experiment 4 6 0.0 0.0 33 o.2 0.6

t Nurnber of days after the start of each experiment. * AR6 not lncluded in Experlment 2. - Treatment not samPled. -207-

The crude rates of increase of SAA 1n the fleld on the different ages of regrowth of lucerne aÈ different times durlng the course of ExperimenÈ I are given in Table 9.6. In this experimenÈ, the fnltl-al crude rate of increase of

SAA on each age of regrowth was less than both Èhe value of r* (Table 9.2) and the lnitlal rate measured in stem cages (Table 9.4), except for the rate ln AR3 which was slmilar to rm. Reasons for the lower lnitial rates of increase in the field probably lncluded Èhe adverse lnfluences of envlronmental factors which were presenÈ in Ehe fleld but not 1n the cages, and different age- structures of SAA between populations in Èhe field and in cages. Ttre crude rate of increase of field SAA on each age of regrowth decreased wiÈh t,lme (Table

9.6), simllar to the decrease in raÈes of lncrease of SAA tn stem cages in the same experiuent (Table g.4>. The crude rra"" of increase and the d.ecrease in these rates with tlme were slnllar in Èreatments AR2, AR3 and AR4. the raËes in

AR5 and ARó were also similar b¡t less Ehan the prevlous Èhree treatments, and the declfne in the rates of i.ncrease of SAA fn AR5 and AR6 appeared to be one sampling period ahead of the declines in AR2, AR3 and AR4. In the last sampllng perlod, there was a populatlon fcrashr (negatl-ve rate of lncrease) 1n AR5 and AR6; 1f sampling had been continued in AR2, AR3 and AR4, large reductlons in

Èhe numbers of SAA on each of Èhese ages of regrowÈh would have been ltkely during the nexÈ week. The reduction tn the number of aphids ln boÈh AR5 and AR6 during the lasÈ sanplLng period was nalnly attrlbuted to an lnÈeracÈlon between the age of regrowth and the density of SAA whlch caused a dramatic deterloratlon in the quality of lucerne herbage for SAA.

The denslties of SAA tn the field durlng Experiment 2 were low (Table 9.5); the ratee of increase for SAA on the different ages of regrowÈh were not calculated but there lùas a consistenÈ decllne in the numbers of SAA beÈween each age of regrowth durlng the experlment. At the end of the experÍment, the densities of aphids 'were so lo¡s that aphids lrere usually noÈ deÈected wlth the -208-

TABLE 9.6 Crude rates of increase of SAA on dlfferent ages of regrowth of lucerne ln the field during differenÈ intervals of time durlng Experlnent I (March-Apr11) aË Culburra, 1981.

Age of regrowth Interval of time Crude rate of lncrease EreatmenÈ for sampling SAA'I r'(?/?/a"y>

AR2 11-19 0.20 20-27 0.15 28-35 0. 10

AR3 11-19 0. 30 20-27 0.13 28-35 0.07

AR4 11-19 0.2L 20-27 0.13 28-35 0. 08

AR5 1r-19 0.14 20-27 0.10 28-35 -0.08

AR6 1I - 19 0.15 20-27 0.lI 28-35 -0. 05

* Days after starÈ of ocperl-ment. -209- nethod of sanpling. The envirorinent in the field was obviously unfavourable for

SAA durlng the course of this experlmenÈ. The Lnfluence of thís unfavourable envfronment rsas also apparent ln the low rates of increase of SAA (O.O+ ?/?/aa1 in the stem cages after the original females larviposiEed - Table 9.4). The decrease Ln numbers of SAA in the fleld conpared to the lncrease, albeiË small, 1n stem cages in Experlment 2 suggests Èhat Ehe stem cages nay be protecting the aphids fron an adverse factor(s) in the field, e.g. heavy rain.

The anomaly beÈween Èhe theoretlcal capacity for increase of SAA (positive) and the crude retes of lncrease in the field (negatLve) in Experiment 2 cLearLy shows that natural populations of SAA do not necessarily realise Eheir capacity for increase, as expecÈed, and that a comparison of the two rates of increase is useful to the understanding of the populatlon dynanics of SAA.

In Experiments 3 and 4, the mean densl-tles of field SAA on each age of regrowÈh srere extrenely low and SAA was usually noÈ detected wlth Èhe method of

sanpling (Table 9.5). The crude rates of lncrease of fleld populations of SAA

could not be calculated in Lhese experiments, but they lrere assumed to be

virÈua1ly zeroi Èhis assumptlon meanÈ that the rates dlffered greatly from those j-n leaf and stem cages in these experiments. Thls dlfference suggests that environmenÈal factors¡ ê.gr tenperature and food, lnslde the cages were favourable for SAA, but other factor(s) in the field were not. The roain factor

conÈrolling SAA in the fteld at the Èine of these experiments lüas probably predaÈors (Sectlon 6). 9.4 Dlscusslon

9.4.L Relatlonehlp between ratea of Lncrease of SA.A and some envl-ronnental factora at Culburra

(i) Tenpenature Temperature ls an important environmental factor which influences the fecundlty and longevity of insects, and thus the value of r, (Andrewartha and -2 10-

Blrch 1954); l,lessenger ( 1964b) shor.sed that the value of r, f or sAA increases up to an optÍmum rean EemperaÈure, about 3OoC, then decreases rapidly. The mean temperatures in the leaf cages at Culburra dld noÈ exceed the optimum temperature for SAA and, for Ehis reason, a positive correlaEion was expected between the value of r, and mean temperaÈure in the leaf cages. This relationship does not occur, nainly because Ehe highest value of r, occurred ln ExperJ-ment I when the mean temperature was only l5.2oC (Table 9.2). The low nean temperature in the leaf cages in ExperimenÈ 1 was unexpected for the tine of the year (March-April) and \,las not caused by the leaf cage r pê1n sê' The nean temperature in each leaf cage was similar Èo thaE recorded in a standard Stevenson screen during the experiment (Table 9.7), and boEh temperatures \rere considerably lower than Èhe average mean temperatures (neasured in a Stevenson screen) at Culburra for Ehat tine of the year' vLz. about 27oC Ln March and about 21oC Ín þr11 (Bureau of I'feÈeorology). Reasons for the departure from the expected posiËlve relationshlp between r, of SAA and temperature 1n Èhe series of experiments at. Culburra were not determfned but may have been related Èo dlfferences in the physlological state of females. in each experlment or Eo the food being ¡nore favourable Ín Experlment I than in other experiments.

(i.í) Síze of femaLe SAA Theore¡ically, the higher value of r, in Experiment. I could be due Partly to Èhe use of larger and more fecund females in thls experinent than in other experiments; many studies have demonstrated that the fecundiÈy of aphids increases wlth lncreased slze of fenales (e.g. GilberÈ 1980). The size of females used in each experimenÈ at Culburra was not comPared, but Èhe slze of females is not likely Eo be a contribuÈing factor to the larger value of r, in Experiment I because the differentlal fecundity related to size nay be a

secondary outcome from a functfonal relationshtp between slze and nortaliÈy of -2IT-

TABLE 9.7 Mean Eemperature and the daily mean maximum and minimum temperatures in a Stevenson screen, leaf caget stem cage and field plant during the four experíments at culburra, 198I, viz. Expt. I (March-Apr1l), Expt. 2 (June-July), Expt,. 3 (Sept.-Oct.) and Expt. 4 (Nov.-Dec.).

Experimenl Mean t.emperature (oC) (maximum-minimum)

St andard* Leaf* Stem Open field Stevenson cage cage plant screen

ExperLment I 15.7 15.2 l8 .0 19 .4 (23.9-7 .5) (29.6-1.9) (33.1-3.0) (33.4-5.4)

Experlment 2 10.6 l0 .1 l0 .6 ( 14.7-6.5) (t6.2-4.o) (t7 .o-4.2)

Experlnent 3 13.2 14.9 12.8 13.2 (17.8-8.s) (26.5-3.2) (22.4-3 .3) (t9.2-7 .2)

Experiment 4 L8.2 19 .9 18 .6 22.8 (22.t-14.2) (31.9-7.8) (28.6-8.6) (36.2-9.3)

* Mean temperatures in standard SEevenson screen and in leaf cages during the same period in each experiment, í.e. for 48 days ln Expt. 1,60 days in Expt. 2, 56 days ln Expt. 3 and 55 days ln Expt' 4'

temperature not measured. -212- adults (Taylor Ig75), and the age-specifl-c nortality curves of cohorts of SAA did not differ greatly between each experiment at Culburra (Figure 9.1).

(äü Host PLant The physíological staLus of host plants in each experiment nay be a further reason for the absence of a positive relatlonship between rate of increase of

S¡¡¡ and mean temperaLure. The host plant cari be a key factor ln determining the denst¡y of insects (Sou¡hwood L973, van Emden and l.Iay 1973) and numerous studies have related the rates of increase of aphíds and other insects to the chemical composition (or quality) of host plants aE different times of the year' to the ages of host plants and Eo the levels of stress of host plants (Dixon L977, Gilbert 1982, Ilough and Pinental 1977, McClure 1980, van Emden and Bashford LgTIr 1.Iearing and van Emden L967, Webb and luloran 1978). These studíes have demonstraEed Èhat Èhe raÈes of lncrease of many insecÈs' ineluding aphids' are oft.en related to the levels of soluble nitrogen or' more sPeciftcally' certain

âmJn6 acids in the hosÈ plant, and that levels of these substances vary with seasonal weather, age of the plant and insecÈ-induced stress. In dryland lucerne pastures at Culburra, the balance of nutrients for aphids such as amino acids and, perhaps, plant defence substances (Cates 1980)r IIEr] vary ln plants with the tíne of year, thus ínfluencing the value of r,n. An abundance of lucerne herbage during most tfmes of the year does noE necessarily mean that Èhe qualíEy of the lucerne 1s equally favourable for SAA at all tines¡ ê.$. larval feeding of the winter moth, Openophtera bnÌna,td L., is related to seasonal changes in the chemical conposition and ÈexËure of leaves - leaves are less favourable for larval grolrth during summer (Feeney 1970).

(ítt) Densíty of SAA The rates of increase of populatlons of SAA boÈh in Èhe field and in stem

cages J-n Experiment I decreased wlth increased densiEl-es of SAÀ. This lnverse relationship was nainly at,Èributed Eo reduced quality of lucerne herbage caused -2L3- by SAA-lnduced stress on the plants but nay also have been caused by intra- specifie competiEíon beÈween aphlds, e.B. productlon of smaller, less-fecund fenales due Èo competÍtion for resources betrseen aphids, and higher numbers of alaÈes of SAA enigrating fron field populatlons because of a higher Percentage productlon of alates with hlgh densities of SAA. The lnfluence of intra- specific conpeEltlon on the denslty of SAA was not Eeasured at Culburra buÈ the above effects have been experienced with oÈher aphlds¡ ê.g. the sycamore aphld'

Drepanosiphun pLatattoides (Schr.), on sycamore trees (Dixon L975) and the black cltrus aphid, Toxoptern eítr.ieidus (Kirk), on citrus buds (Khan 1979). The self-lnduced regulation of denslties of populations of SAA through the severe det,erloraElon of the qualiEy of lucerne and, perhaps, 1nÈra-speciflc competltion, is a most importanÈ determinant of the changes in t,he densities of populations of SAA durlng surnmer (refer to SecÈion 3 for other examples of thls type of decllne in densiÈies of SAA in lucerne pasËures ). 9.4.2 Couparl-son of rowth statlstics of SAÀ at Culburra aud ln other etudlea

(ü Eeeundity

The rean fecundities of SAA estfnated at Culburra were usually less than the fecundíties at comparable mean temperatures deternined ln other studles (Figure 9.2(a)). An exceptlon was in ExperimenÈ I when the fecundlty at abouÈ

15oC was sinllar Èo that determlned by Messeñger (1964b) ln Èhe U.S.A. and

Hatpaz (1955) in Israel. The fecundities of SAA in the field at Culburra rsere expected to be sinl.lar at comparable tenperatures to those in the two oÈher

studies rnenÈioned because each study was also conducted 1n fluctuaEing dally

temperatures, Èhough l,fessenger (1964b) used aphids on potted plant,s ín the

laboratory and tÃarpaz (1955) used aphids on potÈed plants on a Porch in ambl-ent weather. The quallty of field plants for SAA compared to potted plant,s may have caused the lower levels at Culburra - potted plants nay be consistenEly more -2r4-

(o)

125 a ÁÀ '-Á\ A 100 x o o+ À 75 X a o c o o 50 x IL / + o- a x 25 + o

(b)

o't,

a ,03 X o X o E o.2 t- X i 0'1

5 10 15 20 25 30 3s

M eo n temperotu re ('c )

I'lessenger ( I964b) fluctuatíng temPeratures in the laboratory o Graham ( 1959) constant Èemperatures in the laboratory ã Haxpaz (1955) flucÈuating temPeratures outside, potted plants + Dickson et aL (1955) fluctuaÈing ÈemPeratures in field cages x Culburra 1981 f luctuatlng temperatures tn fteld cages

FIGIIRE 9.2: The (a) trean progeny per female and (b) lnnaÈe capael-ties for increase, rm, of SAA at different mean tenperatures ln the U.S.A., Israel and the four experimenÈs aÈ Culburra, 198I. -2L5-

favourable for SAA duríng the year compared to field plants. Other reasons for the disparity nay include differences in (a) the biotypes of SAA in South

Australia compared to ln the U.S.A. and in Israel, (b) the cultivars of lucerne,

and (c) some other environmental facÈor(s) that influerices reproducÈion of SAA.

The fecunditles of SAA recorded by Graham ( 1959) were determined with aphlds in constant temperatures and were also less Èhan those deÈermined by Messenger ( 1964b) and llarpaz (L955) i but these differences vrere attributed to a differential influence beÈween fluctuatíng and constant temperatures on females

(l'fessenger 1964b). The lowest fecundities in Figure 9.2(a) were estinated by DÍckson et aL. (1955). Their estimates were nade with aphids ín field cages on lucerne plants and an unusually high proportion of fenales had low

fecunditles. Reasons rrere not. given for t,hese low values but, they Day have been

partly caused by poor adaptation of some females to the environment in the cages, especially as there sras a high lncidence of females whích "slnply disappeared".

(iü Innø.te eapaeity for increase of SAA The values of r, for SAA during ExperJ-nents 3 (l4.9oC) and 4 (f9.9oc) were similar t,o values in other studies at comparable mean temPeratures. Ilowever, the values of r, durlng Experirnents I (t5.2oC) and 2 (10.IoC)

were somewhat higher (Ftgure 9.2(b)). Ttre apparent higher values of r, for

SAA at Culburra may be caused by differences beÈween food quality and/or aphid physiology in Èhe field at the times of Experiments I and 2 and in the laboratory or other artificial environments used ln Ehe other studies. The

approximate method and not the accurate nethod (Andrewart,ha and Birch 1954) was

used to calculate Èhe values of r, for SAA at Culburra, and Èhe approxlmate

rneEhod may under-estimate the value of r* for SAA (Messenger L964a). Thus,

the higher values of r, for SAA at Culburra compared to values from studies 1n the U.S.A. suggesE.Èhat Ehe innate capacity for increase of SAÀ in dryland -216- pasÈures in SouÈh Australia nay be greater than 1n the U.S.A., Ehough confidence in thls comparison is reserved because of Ehe inherent problems in comparing field and laboratory data on aphids (Dixon 1977). 9.4.3 Rates of lncrease and the populatlon d5m¡ntss of SAA fn dryland lucerne tures

The values of r* for SAA at Culburra demonstrate that ÈemPeraÈure and food quallty were favourable for lncreases ln the numbers of SAA at all times of the year, though the conbined influence of these two facÈors varied lrith Ehe

t1¡oe of the year. Temperature and food were most favourable 1n sumner and least favourable in wfnter. During June-July (winter), the rates of increase of the

second and thlrd generatlons of SAA in stgm cages r{ere consÍderably less than the r, values from leaf cages; the large difference suggests Èhat the likelihood of survival of nynphs to the reproductive stage ís low r¿hen temperatures and/or food are unfavourable durlng winter. In additfon, the crude

rate of increase of SAA 1n Èhe f1¡eld lras negatlve and less than the small positive increase in the stem cages, thus suggesting that factors other than

temperaÈure and food, and which were excluded by stem cages, were also

unfavourable for SAA in winter.

From September to December (spring), the value of r, and the rates of

Íncrease of SAA in stem cages in Septenber-October and November-December were sinílar, suggesting that temperature and food are favourable for the survival

and reproductlon of SAA in sprlng. Ilowever, the crude rate of lncrease of SAA 1n the field was virtualLy zeto and was much less than the above Ëwo raËes. The

faetor(s) suppressLng the numbers of SAA in sprlng could not have been presenÈ in the cages and data Ín Section 6 shows that predators are the key factor ¡shich

controls the number of SAA in spring. The hlghest rates of increase of SAA in stem cages and fn the field occurred in I'farch-April (sunne.r) and the rates were slmllar to the value of r, -2r7 - in leaf cages. The environment at culburra was most favourable for sAA during time summer and early-autumn. However, as the density of sAA increased at this of the year, the raÈes of lncrease in sÈem cages and in the field decreased; the rates in the field decreased to such an extent that the numbers of SAil\ on the plants lrere reduced to very low levels. The collapse in the density of SAA in summer following high densities of sAA is a self-induced regulatlon of density by sAl\, mainly through the deterioration of food caused by their feeding. Iligh densities of sAJ\ nay also induce (a) the development of less- (b) fecund females caused by lncreased compet.ition betr¡een aphids, and increased emigration of aphids caused by an increase in the percentage production of alates, both of whích nay contribute to the reduc¡lon in rates of increase of

SAA at high densities. 9.5 References of Andrewartha, II.G. âûd Blrch, L.C. 1954. The DístribuÈ1on and Abundance Animals. Univ. of Chicago Press, Chicago' 782 pp' Birch, L.C.1948. The inËrinsic raEe of natural increase of an insect population. J- Aním. EeoL. I7z 15-26' polyphagous Cates, R.G. 1980. Feeding patÈerns of monophagous, oligophagous and lnsect herbivores: ¡he effec¡ of resource abundance and plant chemistry' OeeoLogía 462 22-31. Dlckson, R.c., Laird, E.F. arrd Pesho, G.R. 1955. The spotted alfalfa aphid' HiLgardia 242 93-117. Dixon, A.F.G. 1975. Effect of populaÈíon density and food quality on autumnal reproduetive activity 1n Ehe sycamore aphid, Drepanosiphrttn pLatanoídes (Schr.). J. Anim. EeoL. 442 297-304' Dixon, A.F.G. Ig77. Aphid ecology-llfe cyeles, polyurorphl-sm and population regulation. A. Reo. EeoL. Syet' 8: 329-353' -218-

Feeny, p. 1970. Seasonal changes in oak leaf tannins and nutrietts as a cause of spring feeding by winEer moth caterpillars. EeoLogy 5l: 565-58I. Flint, Ùf.L. and van den Bosch, R. 1981. Introductíon to Integrated Pest Management. Plenum Press. N.Y. and London. 240 pp' Frazer, B.D. L972. Life tables and intrlnsíc rates of lncrease of apterous black bean aphids and pea aphlds, on broad bear- (Homopterd': Aphidid-a-e). Can. ETtt. 104: 1717-1722. Gilbert, N. 1980. Comparative dynamlcs of a single-host aphid. I. The evídence. J. Anim. EcoL. 492 351-369. Gilbert, N. 1982. Couparatíve dynamics of a single-host aphid. III. Movement and populatíon structure. J. Anim. EeoL. 51: 469-480'

Graham, II.M. 1959. Effects of temperature and hunidity on the biology of

Theríoaphis ma,euLata (Buckton). Unítt. CaLif . PubLs. Ent. 16z 47-80. Harpaz, f . 1955. Bionomics of. I'Lterioaphis r¡aeuLata (Buckton) in Israel. J. eeon. Ent. 48: 668-671. llough, J.A. and pimental, D. 1978. Influence of host foliage on development' survival and fecundtty of the gypsy moth. Entliron. Ent. 7t 97-102. Ilughes, R.D. 1963. Population dynamics of the cabbage aphid, BretSieoryne braesicae (L.). J. Anim. EeoL- 322 393-424.

Khan, l"f .I{. Ig7g. Ecology of the black citrus aphid, Toæoptera eitn'Leidus (firtaldy) (Homoptera: Aphididae). Ph.D.Thesis. Univ. of Adelaide.

145 pp. McClure, tf.s. 1980. Foliar nitrogen: a basis for host suitability for elongate hernlock scale , Piorina eûterrul (Homoptena: ùLaepidíd.a'e). EcoLogy 61: 72-79.

Messenger, P.S. 1964a. Use of life tables in a bioclimatic study of an experlmental aphid-braconid wasp host-parasite system. EeoLogy 452 119- I31. -2L9-

Messenger, P.S. 1964b. The lnfluence of rhythrnically fluctuaEing temperatures

on the development. and reproduction of the spoEted alfalfa aphid' Therioaphis nøeuLata. J. eeon. Ent. 572 7I-76.

Nielson, I'f .tr{. and Barnes, O.L. 1957 . Life history and abundance of the spotted aIf.al-fa aphid in Arizona. J- eeon. Ent. 50: 805-807 ' perrin, R.ÙI. 1976. The populaEion dynamics of Èhe stinglng nettle aphid

Mierolophium ea'r-nosum (Bukt.) EeoL- Ent. 1: 31-40.

S1uss, R.R. 1967. Population dynamícs of the walnut aphid CTtnomaphís jugLandieoLa (KalE.) in nor¡hern California. EeoLogg 48: 41-58.

Sout.hwood, T.R.E. 1973. The insect/plant relatlonship - an evolutionary perspective. fn InsecÈ/Plant Relatlpnshlps. Ed. HrFo vâll Emden.

81ackwe1l Scíentific Publications. 215 pp.: 3-30' Taylor, L.R. 1975. Longevity, fecundlty and size; control of reproductive potential in a polymorphlc rnigrant, Aphis fabae Scop" J' Anin' EeoL. 44; 135-I59. van Emden, Il .F. and Bashford, ì1[.4. I971. The performance of Breoíeorvne

braseieae and Mgzue persieae fn relatíon to plant age and leaf amino acids. Ent. etp. e appL. l4z 349-360. van Emden, H.F. â11d Way, l'1 .J. 1972. Host plants in the populatlon dynamics of insects. In Insect/Plant Relationships, Symp' 6' Roy' Ent' Soc' Lond'

Ed. H ¡F ¡ vâtt Emden : 181-199 . van Emden, Il .F. and l,Iay, l'1 .J. 1973. Ilost plants in the population dynamícs of insects. In Inseet/Plant Relationships. Ed. H.F¡ Vâo Emden. Blackwell Scientlfic Publications. 215 pp.: 181-I91.

[,Iay, I'f.J. Ig73. Objectives, methods and scope of integrated control' Ïn Insects: Studles ín Population Management. Eds. P.W. Geier, L.R. Clark' D.J. Anderson and II .4. Nix. Ecol. Soc. Aust. Mem. l: L37-152. -220-

I,Iearing¡ C.II. and van Euden, H.F. 1967. Studies on the relations of insect and host plant. I. Effects of water stress in host planEs in pots on infesrarion by Aphis fabae Scop., Mgzue pereicae (Su1z.) and Breuieorgne brøssieae (L.). II. Effects of waEer stress in host plants on the feeundlty of lhyzus pers¿ea.e (Sulz.) atld BreoieorATle brassieae (L.) . Nature 2l3z 105I-f053.

Webb, J.[,J. and luforan, V.C. 1978. The ínfluence of the host plant on the popularion dynamics of. Aeizzia russeLLae (Homoptera: PsgLLidøe). EeoL. E?tt. 3: 313-321. -22r-

Appendix 9.I : Number of progeny per female SAA in each leaf cage on the different ages of regrowth of lucerne in the four experiments at Culburra, 1981.

Experiment Block Number of Progeny per female on age of regrowth:

AR2 AR3 AR4 AR5 AR6

ExperlmenÈ I I 52 9l 79 (l,larch-April) r00 80 72 45 56 L22 73 98 19 96 Lt7 104 86 20 148 56 96 89 31 68 66 76 84 r14 90 76 99 105 L12 83 48 * Experiment 2 I 13 44 39 29 (June-Juty) 30 43 39 25 10 36 r7 35 3i 37 46 11 19 I7 58 it L7 42 34 36

Experiment 3 I 20 22 r03 ( September-Oc t obe r ) 48 59 67 40 r07 72 62 62 6r 96 20 54 84 r00 2 60 86 5i 48 35 43 27 60 52 42

Experiment 4 t 80 65 L2r 51 2L (November-De cember) 84 78 .50 23 30 98 52 42 47 93 95 65 7L 106 2 86 86 85 55 56 27 27 85 29 r03 53 88 110 24 73 95 60 106 96 23

* ARó not included in Experl-nenÈ 2. - females elther dead before first sauplíng, produced less than l0 progeny or misslng (refer to Section 9.2.7). -222-

Appendíx 9.2 Summaries of the one-r¡ray analyses of variance testing for differences in the mean fecundities of Sfu\ in leaf cages on dtfferent ages of regrowth of lucerne in Èhe four experimenÈs at Culburra in 1981.

8o Experinent I (March-APril)

Source D .F. S.S. M.S. F-ratio

Treatment 4 5 I .079 L2.7 70 F4,29 7.168*** ltithin 29 5r.665 1.782 Total 33 L02.7 44

b. Experiment 2 (June-July)

Source D.F. S.S. M.S . F-ratio TreaÈment. 3 5.883 1.961 F3,20 = 1.350 NS Withln 20 29.051 1.453 Total 23 34.934

Experiment 3 (September-October)

Source D. F. S.S. È1 .S. F-rat io TreaEment 4 14 .5 83 3.646 FL ), = 1.379 NS I,Iithin 22 58.168 2.644 Total 26 7 2.7 5l

d. Experiment 4 (November-Decernber)

Source D.F. S.S. ll .s. F-ratio TreatmenÈ 4 29.7 05 7.t76 F4,34 = 2.288 NS l.lithin 34 106 .6 18 3.136 Total 38 r35.323

NS - treatments not significantly different at P ( 0'05) '-223-

Appendix 9.3 Sumnary of the 2-way analysis of varlance tesÈíng for dlfferences in fecundltles of adults on each age of regrowth of lucerne AR2, AR3, AR4 and AR5 between Ehe four experlmenÈs (= time of year)

Source D.F s. s. ìl .s. F-rat,io

3 227 75.753 F 45.714¡kt * TLne of year .259 3 ,9 = 3 16.890 5. 630 F 3.398 NS Age of regrowth 3 ,9 = Resfdual 9 14.9L4 1.657 llithin 87 t7 3.690 1.996

Total r02 432.7 53

NS - fecundities of adults on each age of regrowth not signl-ficantly different at P ( 0.05. -224-

Appendix 9.4 : Number of SAA in each stem cage on the different ages of regrowth of lucerne at different Eimes in the four experimenÈs aE Culburra, 1981.

ExperimenÈ Tine of Age of Nunber of SAA ln cage: ìfean number samplfng regrowth of SAA (days) I 2 3 4 per cage

ExpÈ. I 1l AR2 95 136 149 191 r43 (March-April) AR5 rr4 r57 186 r98 166 AR6 2LI 99 r32 r44 r46 19 AR2 40* r047 I 363 298* 1205 AR5 626 1824 721 950 1030 AR6 733 104 r r07 I 897 935 27 AR2 2098 29L3 4307 3706 3256 AR5 1418 L24L 3594 28LL 2266 AR6 1464 1590 L342 714 1277

I 2 3 4 5

Expt. 2 18 AR2 0* 77 63 80 5B 69 (June-July) AR5 81 84 80 106 87 8B 46 AR2 24r 226 194 162 206 AR5 286 254 341 266 287 60 AR2 24x 2* 499 228 363 AR5 202 704 471 539 479

Block I Block 2

I 2 3 I 3

Expt. 3 22 AR2 38 141 79 46 170 11t 98 ( Sept-0ct) AR5 r52 163 275 17r L7,\ r95 190 AR6 181 7L r48 55 178 rr4 r24 34 AR2 105* I 13'k 3170 27 47 25Yc 183 1 2582 AR5 3064 3290 l938t 4027 2842 1549r, 3305 AR6 2806 3r67 1886 924x 1620 3977 2709

Expt. 4 33 AR2 94Bs 9696 r37 I L7r, 697 12885 6826 (Nov-Dec) AR5 8403 7 556 2520 123 168 1223 3332 AR6 349 739 920 I 935 320 r37 5 940

- Cages not íncluded in ExperimenÈ 2.

* Number of SAA not included in means because of damage to cage. -225-

SECTION 10: TEE LOI{ER TEMPERATTIRE THRESEOLD FOR DEVELOPMENT AIID RATES

OF DEVELOPMENT OF NYMPIIAL SAA IIT SOUTE AUSTR.ATIA

Summary

The rates of development and the developmental threshold of nynphal SAA at low temperatures were determíned in constant temperature rooms by exposlng newly-born nymphs on lucerne plants Eo short períods of 1ow temperatures and then allowl-ng them to complete their developrnent at a hlgher, favourable temperature. The developmental threshold was estimaÈed at 3.loC; thís temperature is considerably lower than the thresholds estlmated for SAA in previous studíes where relationships between developmental rates and temperature were assumed linear for the whole range of favourable Èemperatures.

The rates of development of nynphal SAA were also determined in the field at different times of the year. The rates were'similar to the rates of development of SAA in fluctuatlng temperat,ures measured in other countries, but were loÌ{er than those measured with aphids from New South I'Iales and Vlctorla in ano¡her study. The dlfference in the rates of developmenE between SAA from South Australia and SAA from Ner¡ Sout.h l^Iales and Victoria was probably caused by a dlfference in the quallty of lucerne for the developmenE of SAA in each study.

The level of survival of nynphal SAA in leaf cages ln the field was high during sprfng and summer and low during aut.umn and wlnter. -226- l0.l Introductlon The teuperature threshold for development and rates of development of immature stages of lnsecÈ pests are useful statistics to predict or explaln their population dynamics in relatl-on Eo control programs (Messenger 1970). The temperature thresholds for development, i.ê. the temperature at whích the raÈe of development is zero, of a species ís widely accepted as Ehat temperature obtained from extrapolation of a linear developmental rate-temperature relation- ship determined in constanE temperaËures in the laboratory (Hughes 1963). Ilowever, the relationship between rate of development and temperature is only linear for Lhe favourable temperature range of the species and departs widely from 1t at lower and higher temperatures .(Logan and Hilbert 1983); rates of developuent aE low temperaEures near the theoretical lovrer threshold are usually not included in the deÈermination of the threshold. The main reason that rates of development are not determined at low t.emperatures in experinents is that long exposures to such temperaÈures may cause high mortaliEy (Maelzer 1974). In reality, shor¡ exposures to Ehese low temperatures may have no influence on the nortality or on the subsequent rate of development of the insect at a favourable higher temperature. I'faelzer (L974) described a method to determine the lovrer threshold for development of insects whtch overcame the lethal effect of cont,inuous exposure of lnsects to low temperatures; his method involves exposure of separat.e cohorts of insects to different low temperatures for dlfferent short periods of tlme aE each E,emperature, respectively, and then allows insecÈs in each cohort to complete their development at a favourable higher temperature.

IIe assumed that, if the influence of low temperatures on development \ras additlve, the regression of total duratlon of nymphal development at the l-ow plus at the favourable temperature on duratlon at the low Èemperature \^ras linear. The slopes of the linear regressions for each low temperature were used -227 - to estimate the rate of developnent at Èhe lor.v EeEperatures and Ehen the threshold temPerature for development. This secÈ1on describes an e>çeriment Èo determl ne Èhe lower tenPereture threshold for the development of SAA on potted lucerne at constant temperatures using the nerhod descrlbed by Maelzer (L974). The rates of development per day and survlval of nynphs of SAA were also estimaÈed 1n Èhe fteld at various Èirnes of the year. The st,atistics obÈained fron SAA ln the fleld are comPared with those obtained l-n other studles with SAA in AusÈralía, the U.S.A. and in Israel. 10.2 I'lre Rate of lÞvelopnent and the Threshold for Developneût of lilynphs of

SAA at Low Tenperatures 10.2.1 MaterLalg aad nethods An experlment to determlne the rates of develoPment of nymphal SAA at low temperaÈures and Èhe lower Èemperature thteshold for the development of nyrnphal

Sfu\ was conducted in constant-temperature cool roons and a plant grostth cabinet at the Northfield Research Laboratories. Ihe experlmental aphlds lüere reared on potted lfunter Rlver lucerne plants r¡hich were abouÈ three years old and had two- week-old regrowth at the beginnlng of the experl-ment. The experlmenÈ was conducted in two parts at dlfferent times because, durlng the flrst part' unforeseen lnsectlcidal conÈarninatlon l-n one cool room killed all the aphids in that room. The tv¡o parÈs of the experiment began on 23 November 1982 and 10 February 1983, respectlvelY.

In each part, a cohort of newly-born aphLds was exposed to each of the followlng treatments in the cool rooms, i.e. constant low temperature x exposure tlme to thaÈ low temperature, before exposlng then Èo 25oC fn a conÊtant Èemperature, plant growth cabLnet. The treatments were: -228-

Low temperaÈure Days of exposure to low temperatures oc Part 1 ParE2 48r014 481014

4 ++ + +

5 + + + +

6 + + + +

8 + + + +

10 + + + + + + + +

I2 ++ + +

Each cohort consisted of 30 newly-born nymphs, 0-2 hours old, which were contained ín three leaf cages (10 nymphs per cage) on expanded trifoliate leaves on one lucerne plant. The cages were the sâme as the leaf cage described in Sect,ion 9.2.L. Selection of the leaves for the cages on each plant $Ias not important because Harpaz (1955) showed that the duration of development of nynphs on the different perts of lucerne herbage was the same. The newly-born aphids were produced by fenales from the laboratory eulture of SAA discussed in Section 9.2.2. On each morning when each part of the experimenÈ sras set up, about 1200 apterous females were placed on excised lucerne leaves in petri dishes wtEh slightly moistened filter Paper and kept at 25oC. The fernales Ì{ere allowed to larviposit f rom 11.00 a.n. to 1.00 p.m., and the tlme of birÈh of the resultant nymphs ltas assumed to be 12.00 noon; this AE 1.00 Èime was taken as the beginning of each part of the experiment. P.rn. ' the nynphs \üere transferred to leaf eages using a moistened, fine sable hair brush. Each plant \ùith caged nymphs was allocated at random to a treatnent and placed at the requlred low Èemperature. In each cool room, the plant was positioned under a twin batten of 40Iù fluorescent tubes suitable for plant gro\{th (Phtllips PlanÈ Light@) vrhich r¡ras suspended about 250 nnn above Èhe Eop of -229- the plant. No planÈ was allowed Eo suffer moisture stress during the experiment. The temperature in a leaf cage on a lucerne plant in each cool room was measured each 30 minutes wlth a thermocouple and recorded on a lloneywell MultipoinÈ Recorder@, and the temperature r{as constantly recorded stlth a thernohygrograph ín the plant gro\üth cabinet.

(í) lnepeetíon of nYrnPhe The nynphs in each cage vrere flrst ínspecÈed just prior to them reaching the adult stage. The approximate time for adult emergence in each treaÈment \üas esEimat,ed from ny experience,w'ith Èhe time of nynphal development of SAA, as discussed in Section 10.3, and from the rlata of Graham (1959) and llarpaz (1955). Subsequently, nynphs were usually inspected each morning and afÈernoon unÈi1 they all emerged as adults. At each tine of inspection, the lids of the cages were taken off, all adults were removed r.r'lth a moistened fine brush and'then Èhe cages \cere resealed. The number of adults removed from each cage at each tl-me was recorded. (ii) AnaLyeis of data The rate of development of nymphal SAA at each low tenperaÈure ltas calculated thus (after l{aelzer I974)'. exposure Èo low temPerature let n, = number of days of ' n2 = number of days required for subsequent developmenE to favourable temPeraÈure the adult stage at the ' -L = rate of development at the low ternperature' and v1

t = rate of develoPmenÈ at the favourable temperature' v 2

then I = (r-k)/y 2 v I

r¡here k is the slope of the regression of (nt + n2) on nl. -230-

The median value of n, * n, for sAA in each temperature I,7as interpolated from visually fitted graphs of the logarithm of Ëotal time (in days) as a nymph, nl * n2.- on the probit value for the cumulaÈ1ve percentage

of nyrnphs reaching the adult stage. The developmental Èime for nyrnphs aE each

low temperature r¿as calculated from the reciprocal of the rate of developnent at

each ternperature. The Èhreshold tenpereÈure of development i-s that temPeraÈure for which k = 1. This temperature r¡tas calculated frorn a regression of the value of k on Èhe low Eemperature Èo whích Èhe nynphs r,{ere exposed. The percentage nortaliÈy of the nymphs after each period of exposure

t,o each- low temperature was calculated from the number of nyrnphs survlving

the exposure Eo each 1ow Èemperature. 10.2.2 Results The low temperatures recorded in the different cool rooms rüere 3.3 + 0.10, 4.7 + 0.10, 7.6 ! 0.1o, lO.1 + 0.10 and 11.8 + 0.loc, respectively, but sufficient data to determine the rates of development of SAA at low temperatures rüere only obLained from Èhe Èreatnents aE 4.7o,7.6o, I0.lo and l1.8oc. Data from the treatBents whlch lncluded exposure to either 3.3oC or 4.9oC could not be included 1n the analyses because all of

the nyrnphs died in the treatnents at 3.3oC w'íth exposure periods greater than four days, and 1n the treatmenÈ at 4.9oC with exposure for six days (Table I0.f). The rnortalities at, 3.3oC were aEtribuÈed to the deleterlous influence of continuous periods of exposures longer than four days at this low temperature, but the cornplete loss of SAA in Èhe 4.9oC t.reatment was inexplfcable.

Tlne median nunber of hours of the nymphal period, n1 * n2, for each cohort of aphids exposed for each period of time, n1, to each low ÈemperaÈure fs glven in Figure f0.1. These nedian nynphal periods were estimated from the -231-

TABLE IO. I Percentage mortality of nymphs of SAA exposed to low temperatures for varlous periods of time in the cool rooms aE Northfleld, L982/83.

Period of exposure % mortaliEy of nynphs to low temperature (days ) Low Eenperature (oC)

3.3 4.7 4.9 7 .6 10.I I1.8

4 77 50 43 6 3 37

6 100 7 7 I 100 57 47 57 63 27 10 100 80 70 30 50 10 r4 100 97 53

- not included in experiment. probit lines in Appendix 10.1, and, for reasons given above, only apply to cohorts of aphlds at the low temperatures,4.7o,7.6o, 10.10 and 11.8oC, respeetl-vely. The regression of the values of. (.1 + n2) on n1 for each low temperature (Flgure 10.1) was slgnifícant (? < 0.001). The rates of development of SAA at each low Èemperature elere calculated with equaEion ( I ) using the values of the slope, k, of the regressions for each temPerature in Figure 10.I and the tlme for Èhe development of SAA estimaÈed at a constant

25oC (t.e. 176 hours determined as Èhe ¡oedian tíne for 507" of the nymphs to become adults fron Èhe 25oC probtt l1ne ln Appendlx l0.l). The estlmated raÈes of development per day and the medi-an numbers of days for the development of SAA at the low temperatures and aÈ 25oC are gfven tn Table 10.2; the estimated rates of develoPment shol¡ that nymphs do develop at 4.7oC. -232-

600

g73X ( t,.fc, y ='170 + 0 r=0'998 ) s00 7.6oC: y=175+0847X (r=0.997) 'lQloQ: y = 176 +0.770X (r=9-996¡ o 11,8"C: y = 168 +O'782X ( r= 0 997) )L 100 o E

I

c.{ 300 +

L

200

100 100 200 300 /.00 n - hours

FIGURE 10.I: Regresslons of Eotal duratlon at low plus at the favourable Èemperature (n, + n2) on duraEion at the low tenperature (n1) for nynphs of SAA at varlous low Ëemperatures at, Northfield l98l/82.

The linear regression of the values of k (determine

The results of this experimenE show that Ehe nethod proposed by Maelzer

(L974) t¡as feaslble to deternine the lower temperature threshold of SAA and Èhe rates of developnent of SAA at low temperatures. However, the data from this experLment lüere nLninal for these determinaÈlons because of unexpected nortalities of SAA in some treatmenÈs and because esÈimatíons of the time for -233-

TABLE IO.2 The raEe of developmenE and medlan developmenEal time for the total nyrophal period of SAA at various low temperaÈures and at the higher favourable temperature, 25oC, NorÈhfield, L982183.

Temperature Rate of develoPnent l"fedian develoPmental (oc) (per day) tlme (daYs)

4.7 0.004 272.O 7.6 0.02I 47 .L 10. I 0. 032 3r.3 I r.8 0. 030 33.3 25.0 0. 137 7.3

1 .1 y = 1'086 - 0,028X (r= 0.9/.5 ) 1'0 x

k 0'9 x

0.8 x x

0.7 12 0 I I 1

Temperoture ("C ) I Threshold temperoture of development for nymphs of SAA

FIGURE 10.2: Regresslon of the value of k, slope of (tt + n2) on nl(Flgurel0.l),onËhevarlouslowEemperaturesto whlch nynphs of sAA vtere exposed aÈ NorEhfield I98L/82. -234- development of nymphs in the 10 and 14 day exposure period at 4.7oC relied on only one observation each; a further experiment is necessary to improve the accuracy of these data. Ilowever, 3.loC probably approximates Èhe lower temperat,ure threshold for development. of SAA because development of nynphs did occur at 4.7oC. Caopbell et aL. (1974) and others claimed that it is not practical to examine the rate of development of aphfds at low temperatures close to the threshold temperature of development because considerable mortality occurs aE

Ehese low temperatures and because there is selection for individuals which can develop at low Èemperatures. The first part of their argument \{as supported by

Èhe data fron the experiment wlth SAA benêuse increased exposure times at low t.emperatures usually increased the percent.age mortality of SAA (Table l0.l).

Ilowever, in future experiments the exposure of nymphs Èo 1ow temperatures for shorter periods of time t,han in this experíment should reduce E.he mortality of nymphs, and reduced mortality should minimlse selection for indlviduals adapted to low Eemperatures. Shorter periods of exposure Eo low temperatures should still provide suitable data to estimate Èhe threshold ternperature for development.

The t,hreshold tenperature of 3.loc for development of SAA estimated Ín this study \¡ras considerably lower Èhan previous estimaÈes of this threshold for SAA, e.g. in Australia,7.4oC (Hughes and Roberts 1978) and in the U.S.A., 8.5oC (Graham 1959) and 6.OoC (l'fessenger 1964). Each of the previous estimat.es are based on the assumpEion that developmental rate and temperature relationships are linear, and that, by extrapolation, the temperature which theoretically causes zero rate of development approxímates the lower threshold temperature for development. However, the relat.íonship between the rate of developmenÈ of SAA and temperature is sigmoidal (Messenger 1964), and previous calculatíons of lower temperature thresholds for SAA did not include -235-

measurements of rates of development at temperatures below the extrapolated thresholds. Graham (1959) recognised t,his problern and considered Ehat his estimate of 8.5oC was only a rrough'estÍmate of the actual threshold

temperature, and that the actual threshold temperature was 'probably somewhat

below this temperature | .

The more accurâte estimate of the lower temperature threshold for Sfu\ determined 1n thls study is useful to explain the population dynaurics of SAA, especíally in the cooler periods of the year. For example, the lower value of the threshold estimated in thls study compared to previous studies better explains the unexpected increase ln density of SAA over large areas of lucerne pastures in the Upper-South-East during the cool weather 1n June 1981. At the same time, the mean density of SAA increased from about 30 to 180 SAA per stem of lucerne in two weeks in the grazirtg experiment at Culburra (Appendix 4.4,

TN). This increase in the number of SAA was not d.ue to immigration of alaÈes from other areas and it \das not expected ln such a short tirne because the mean temperatures for Èhe two weeks at culburra were only 12.0oc and 13.6oc, respectively. This íncrease at mean temperatures from 12.0 to 13.6oC is especially difficult to explaln if the telnperature Ehreshold for development of SAA is as hlgh as 8.5oC, as recorded in previous studíes.

The estimates of realistic lower temperature thresholds rnay also be fnportant for use in mathematical models based on thermal sumrnations, e.g. day- degrees, above the threshold ternperature for development to predict the tine for development of insects at different temperatures (e.g. Gllbert et aL.1976, Hughes 1963). If the relaÈively high temperature thresholds for development of

SAA estimated prior to this study had been used to calculate Ehe physiologlcal time for the development of SAA in South Australia, the lnfluence of tenperature in determining the density of SAA, especfally in the cooler periods of the year, would have been under-estimated. -236-

10.3 Rate of Development and Survival of Nyuphs of SAA Ln the Field

10.3.1 Materlals and methods

Four experimenEs r¿ere conducted on llunter Rj-ver lucerne plants in Ehe

field at the Northfield Research Laboratories to estimate Ehe rate of

development and survival of each nynphal inst,ar of SAA. The experiments were

iniEiated on 19 June 1981 (ExperÍnent I),24 Septernber 1981 (Experiment 2), 16

March 1982 (Experirnent 3) and 17 April 1982 (Experinent 4), respecrively. The lucerne plants were about four years old and were in a pure stand of lucerne about 0.5 ha in area. The sEand was malnly rain-fed, and linited sprinkler lrrigation was applled durlng the driest periods of the year but not during each experimenE. The age of lucerne regro\¡rth aE the beginning of each experiment r^/as two weeks.

Newly-born nymphs of SAA were used at, the beginning of each experiment and obtained by the following method. AbouÈ 600 females were randomly selected from a laboratory culture of SAA (Section 9 .2.2) in the late afternoon prior to Ëhe beglnning of each experiment. The fenales rüere placed on excised trifoliate lucerne leaves in petri dishes with slightty noist filter paper and kept at 25oC; the fenales rdere allowed to larviposit on the leaves during the night. Early next ilorning, newly-born nymphs rdere transferred wiËh a moistened sable hair brush to l0 leaf cages (f0 nyrnphs per leaf cage) (Experiments t and 2), or to 30 leaf cages (10 nymphs per leaf cage) (Experirnents 3 and 4) in the field.

Each leaf cage (Sectíon 9.2.1) was placed on an expanded trifoliate leaf on an individual planti both the leaf and the plant were selected at random for each câgeo The mean time of birth of the nymphs was assumed to be 12 midnlght of the previous night and this time was taken as the start of each experlment.

The daíly maximum and urinimum temperatures were measured ín five leaf cages in each experiment wíth a thermocouple placed under Èhe leaf in each cage and connecEed to a Iloneywell Multipoint Recorder@. -237 -

(¿) Inepeetùon of nynrphs

In Experiment I, the nynphs in each cage r{ere inspecEed each three Eo four days after the start of the experiment to determine their stage of development.

In Experiment 2, the nynphs 1n each cage were inspected daily. In Experlment 3 and 4, nymphs were inspected more frequently than ín Ehe prevíous ttùo experiments; the nyrnphs 1n each of Ehree or four randonly-selecEed cages r¡rere inspeeted at least each morning and afternoon after the start of each experiment. The lnspecÈion of the nymphs in this relatively small number of cages' compared to the 30 cages in each experiment, at each tlme reduced the handling of each nymph and presuruably minimised any adverse effects that handling may have had ou the rate of development of the nyrnphs. The number of nymphs inspected each time (i.e.30 to 40 nyrnphs) was considered adequate for this type of study (Canpbe11 et aL. 1974).

At each time when nymphs were inspected, the petlole of the leaf contained in each cage wíth aphids t.o be ínspected was cut and the closed cage wiLh the nymphs was t.aken t,o t,he laborat.ory. In the laborat,ory, Èhe nyrnphs from each cage lrere transferred with a moist, sable hair brush Eo a labelled petri dish conEaining noist filter paperi the stage of developuent of each nymph was determined under a mlcroscope and recorded. The four lnstars of SAA were identifled by differences ln (a) Èhe number of longftudlnal rows of setae on the dorsal surface of the abdouen, (b) the size of the setae in the rows and (c) the area of the chitinised plate at the base of each set.ae. The first lnstar has two rosrs of seÈae less than the other insËars; the second instar has relatively smaller setae in the tr¡Io rows adjacenE to the t\¡ro central rows compared to the third and fourth lnstars; and the third insÈar has relatively smaller chitinised plates at the base of the setae compared to t.he fourth ínstar. An adult is easily separated frorn the nynphs by lts large sIze, relatively longer antennae -238-

PT,ATE IO.I The four nymphal stages of SAA and an apterous female showÍng the differences between the configuration and size of setae on the abdomen of each stage of development; first instar to fe¡nale in ascending order of size (25x magnification). t I t '.3. a a .t-.4.r.- d -239- and contiguous chitínised plates at the base of the setae on the dorsal surface of rhe abdomen (Plate 10.1). I{hen the stage of development of each nymph in each cage had been deÈermined, all the adulÈs nere removed and the remainlng nymphs were reÈurned to Èhe sane cage on another lucerne leaf in the field' (í¿) ArtøLysie of data.

The data from ExperlmenÈs 2 and 3 were used to calculate the median Èime for the development of each lnstar in each experiment using a linear regression of the age of nymphs (in hours) on the probít value of the cumulaEive percentage of nyrnphs developed,to the subsequent instar. The median time in hours (i'e' the time f.or 507" of the nymphs Èo reach each subsequent instar) was converted Eo days to give the developmental time in days, Y, and the rate of development per I ínstar \¡rere summed day i for each instar. The developmental times for each in each experiment Eo give t.he duratlon of the total nyrnphal p'eriod ' The data from Experiments 1 and 2 could not be used to determine the above statistics because there were insufficient lnspections of nymphs in each experlment for Èhe data to be reliable. The data from Experiments 3 and 4 provided esEimates of the rates of development of SAJ\ at only two meari temperatures and these lirníted data were not sufficlenÈ to d,etermine the influence of Eemperature on t,he rate of development of nyrnphs of SAA in South Australia. For this reason, the rates of developmenE of the total nynphal sÈage in the Ewo exPerlments lrere compared with the corresponding rates measured by Ilarpaz (1955), l(essenger (1964) and Nielson and Barnes (1957). Data from the latEer three studies were pooled to obtain a linear regression of the logaríthm of mean temperature on the probit value of the rate of development of nynphal SAA per day; 957" eotfídence liml-ts were calcrrlated for this regresslon. The regression, confídence llnlts and the retes of development of Sfu\ fron Ehe two experiments at Northfield were plotted on a -240- graph (Figure 10.3). Sinllarly, the developmental races for each instar obt,ained at Northfield were compared $rith the corresponding rates obtained by l"lessenger ( 1964) (Figure 10.4) .

The survival of aphids r^ras expressed as the Percentage of aphids completing

each nymphal instar and was calculated from the number of nyrnphs vrhich survived

each instar in each exPeriment. 10.3.2 Results and dl-scuselon

(i) Rate of deoeLopment of nyî1phs of SAA Alt of the nyrnphs ín each of the four experiments emerged as aPterae. The

median times for the development of each nymphal instar in Experiment 3 (March)

and ExperfmenÈ 4 (April)' estimated from the regressions in Appendix l0'2' are given in Table 10.3. The rates of development, both for each instar and for the

total nymphal period, are also given in Table I0.3; each corresponding rate is greater i-n Experiment 3 compared to Experiment 4. The higher rates r'rere

expecÈed in Experiment 3 because of the higher mean temperatures in that

experiment compared to Experlment 4, but the data were insufficient to test the relationship between (a) the rate of development of the total nynghal period and

mean temperaÈure, and (b) the relationship between the rate of development of

each fnstar and nean temPerature. The rates of development of the total nyrnphal period from Experíments 3 and 4 at Northfield were within t]ne 957. confídence liniEs of the regression of

mean temperature on Ehe probit value of rate of development of the Èotal nynphal

perlod of SAA calculated from the pooled data fron experiments ln the U.S.A. and in Israel (Figure 10.3). Sinilarly, the rates of develoPment for each instar in Experiments 3 and 4 were wíthin the 95% confidence lfmits of the corresponding regresslons of ilean temperaEure on the probit value of rate of development of

each insÈar derived frou the data of l'lessenger (1964) 1n the U.S.A. (Figure r0.4). -24r-

TABLE 10.3 Mean tempereture. and medlan rate of development and developmental time for each instar of SAA and Èhe total nynphal period in the field in ExperilDenÈs 3 and 4 aÈ Northfield, 1982.

Experiment InsÈar of Mean RaÈe of Developmental SAA teEperature development time (oc) (per day) (days )

Experiment 3 1 22.7 0. 348 2.9 (March) 2 27 .3 0.490 2.0

3 24.0 0. 387 2.6

4 r8.4 0.27 3 3.7 nynphal period 2r.3' 0.089 IL.2

Experiment 4 1 16 .5 o.289 3.5 2 17 .0 0.26r 3.8

3 t2.8 0. 195 5.1

4 15. 1 0.128 7.8 nynphal period 14.9 0.048 20.8

The conparisons 1n Figures 10.3 and 10.4 suggest Ehat Ehe relationships between the rate of development and rean temperature for each nymphal instar and for the toÈal nynphal period of SAA at Northfield are similar Èo the corresponding relationships lriËh SAA in the U.S.A. and in Israel. The rates of development of SAA at Northfield were expected to dlffer from those in the

U.S.A. because the est,imated tenperature threshold for development of SAA at

Northffel-d was lower than thresholds estinated for SAA l-n the U.S.A. (Section 10.2). The reason for the sinilarlty in the rates in Flgure 10.3 nay be that (a) the lower threshold temperature of development of SAA, as estímated at Northfleld, does not signlfl-cantly tnfluence raEes of develoPment at

Èemperatures considerably hlgher than the threshold temperaÈure - the -242-

2 (J e- o. E o

c 1 o y= -0.480 + 0'479 X o E (r = 9'940 )

JI

3.0 3.2 34 3'6 3'8 1,0

Probit of rote of development per doy --- 95Vo contidence limits x Culburro, 1982.

FIGI]RE IO.3: Regresslon and 95% confldence lirnits of 1og mean temperature on the probit value- of the raËe of developmenË of È,he toEal perlod of nymphal SAA derived from the pooled data of Harpaz (1955), Messenger (1964) and Nielson and Barnes (1957), and the raËes of developrnent of SAA fron Experiments 3 and 4 at Northfield, 1982.

temperaÈures at which the Èr,ro rates of development were estimated at Northfíeld were 16.70 and 21.3oC, respectively - or Ehat (b) the threshold ternperatures

for development of SAA at Northfleld and in the U.S.A. are similar, i.e. the ex¡rapolaÈion of linear relationships beEween the rate of development on temperature, as used in the U.S.A., does not provide a realistic threshold.

The above comparisons of rates are based on limited data from Northfield

and further experiments, simÍlar to Experlments 3 and 4, are required to determine the influence of Eemperature on the rate of developmenÈ of nymphal SAA in South Australla. Experiments 3 and 4 provide useful data for the deslgn of further experiments, especially data on Èhe frequency of inspections of nynphs

requlred to calculaÈe Ehe medlan tlme for development of each instar aÈ

different mean temperatures. -243-

1q)First instor (StSecond instor 2

__- -l x -¿t

o 1 Y=0'01 + 0'29X Y= 0'09 + 0'23X (t, L ( ( r 0.971) ) r=0985 ) = o Lo o- E (d) Fourth instor o (clThird instor 2 Ic E -¿l x

1 ql o J y =-0.14 + 0'29X y=-043+ 0'38X ( (r=0.971 I r=0'948)

5 6 3 t, 53t, Probit of rote of development Per 0 5 doy

--- 95% confidence limits x Culburro, 1982.

FIGTIRE IO.4: Regressions and 95% confldence limlÈs of log mean temperature on Èhe probiÈ value of the raEe of (b) lnstar d,evelopment of t,he (a) first insÈar ' second ' (c) ttrtra instar and (d) fourth instar of SAA derived f rom Èhe data of I'lessenger (1964), and Èhe rates of development of each instar of SAA from Experl-ments 3 and 4 at Northfield, 1982.

The rates of develoþment of nyrnphs of SAA in various constant temperaËures rather than in fluctuaElng temPeratures have also been deÈermined ln the u's'A' (Bishop and crockett 1981, Graham 1959) . These rates were not included in the regressions Ín Figures 10.3 and lO.4 because the lnfluence of flucÈuatfng of ÈemperaËures compared Eo consEant ÈeEperatures on the rates of development -244- aphíds is not clearly understood. Ifessenger (L964) found that exposure to fluctuating teuperatures caused the development of SAA to proceed faster than was predicted from the rates of development under different constant temperatures, as determined by Graham (1950). By contrast, CampbelL et aL. (I974) did noÈ find nuch difference between the developmental raEe6 of fÍve species of aphids, ot,her than SAA, at tenperatures that were either constant or fluctuating about the sare mean value, provided that the fluctuatlons did noË extend below the threshold ËemperaËure, and the nean teuperature T¡las not greaÈer than the optimum ÈemperaÈures for development. Stnilarly, Ilughes and Roberts (1978) found that alternaÈing Èemperatures did not enhance the rate of developrnent of SAA. Hughes and Roberts (1978) determined the rates of development of the Èotal nynphal perfod of SAA aÈ different temperatures ln a laboraÈory, uslng SAA from eastern.{r¡stralla (New SouÈh !ùales and Victorla). The rates determined in their study were higher at simllar mean Èemperatures than the rates determined at

Northfield r^rÍth SAA fron South A¡stralia. Ttre reason for the lower values for the rates of development of SAA in South Australia Iüas not determined but it was unlikely Ehat the lower rates could be atÈributed to dlfferent biotypes of SAA ln eastern Australia compared to South AusÈralla; the lower rates were more likely to be due t,o dlfferences in the qualiÈy of food for SAA between the t\.¡o studLes. I used plants of Hunter River lucerne ln the field, whereas Hughes and Roberts (1978) used dlscs of lfunÈer Rlver lucerne leaves floating on a culture solution. The excised leaves may be more favourable for SAA because of changes ln the chemlcal composition of Ehe leaves caused by excision. Canpbell et aL. (L974) vtarns thaÈ hosts used in a laboratory to determine the developmental tl-mes of aphids should be sinilar to those ln the field.

(¿,í) SuruioaL of nynrphe of SAA The data from the four experiments clearly demonst,rate that survival of nymphs was higher in Experinents 2 (Septenber-October) and 3 (March) than in -245-

Experiments 4 (April) and I (June-July). The difference in percentage survival betvreen the tr^Io lots of experinenEs I^ras partly attributed to (a) lower temperatures and (b) lower quality of lucerne plants for survival of nynphs in Experiments 4 and I compared to Experiments 2 arrd 3. The rean temPeratures rtere

14.9oC and 10.9oC ín Experinents 4 and I, respectively, compared to L6.7oC and 21.3oC in Experiments 2 arrd,3, respectlvely. The level of survival of each instar also varied between the tr,ro lots of experinents. In Experiments 2 and 3, there was a 100% survival of the first instar follor,red by a low level of mortallËy (

of nyrnphs with each instar whlch resulted in the low percentages of nymphs these ato (Figure 10.5)' eurerging as adults in each of "*n"timents

100

80 E60 ¿) l./', 40 o\-o 20

A D A 0 A D A D 2 3 l. ln stor of SAA

A +D : Sept. - Oct Morch , April , June -JutY

FIGURX 10.5: Percentage survival of each l-nstar of SAA ln four experlmenÈs ln the field at Northfield, viz. Expt. I (June-July f98l), Expt. 2 (Septernber-October I981)' ExpË. 3 (ì,farch 1982) and Expt. 4 (April 1982). -246-

The low level of survival of nymphs during June-July (winter) in Experiment

4 supporÈs the hypothesis in Section 9.3.3 that the reason for considerably lower ra¡es of increase of populations of SAA in stem cages conpared to the innate capaciÈy for increase, Em, of SAA in June-July l98l was partly due to the low survival of nymphs aE low temperatures in the cages.

10.4 Beferencea Andrewartha, H.G. and Birch, L.C. L954. The Distribution and Abundance of Anl-nals. Univ. of Chlcago Press. 782 pp. Bishop, J.L. and Crockett, D. 196i. The spotted alfalfa aphid in Virginía. Va. Agrlc. Exp. Stn. Tech. 8u11. I53.: 22 pp. Canpbell,4., Erazer, 8.D., GllberÈ, N., Gutierrez, A.P. and Mackauer, M. L974. Temperature requirenents of some aphids and their parasites. J. appL. EeoL. ll: 431-438. Gilbert, N., Gutierrez, 4.P., Frazer, B.D. and Jones' R.E. I976. Ecological Relationships. I{.H. Freeman and Company. 156 pp.

Graham, Il.l'f. f959. Effects of temperaËure and humldiÈy on Ehe biology of therioaphie naculaüa (Buckton). (Jníü. CaLif . PubLe. Ent.

16z 47-80. Harpaz, Í. f955. Bionomics of The'.ioaphis tTacuLa,ta (Buckton) in Israel. J. econ. Ent. 48: 668-67I. Ilughes, R.D. and Roberts, J.A. 1978. Temperature relationships of spoÈÈed alfalfa aphid. Lucerne AphÍd l,lorkshop. Tamworth. Dep. Agríc. N.S.W. 273 ppz 25-27. l"faelzer, D.A. L974. The rate of development of insects at temperatures outstde the favourable range. Abstr. Aust. Conf. Ecol. Grassld.

Invert., Arnidale, N.S.I^I . 92 pp: 7-8. -247 -

Messenger, P.S. 1964. Ttre influence of rhythnically fluctuating

temperaÈures on the development and reproduction of the spotËed alfalfa aphld, l,lterioaphis nøeulata. J. eeon. Ent. 572 7L'76. Messenger, P.S. 1970. Bíoclimatic inputs to biological control and pest

management programs. In, Concepts of PesÈ I'fanagement. Ed. R.L.

Rabb and F.E. Guthrie. North carollna state university Press, Raleigh. 242 pp: 84-99. Nlelson, M.trl. and Barnes, O.L. 1957. Llfe history and abundance of the spotred alfalfa aphld in Arizona. J. econ. Ent. 502 805-807. Taylor, L.R. L957. Tenperature relations of teneral developnent and behavlour Ln Aphie fabae Scop. ./. eqt. BioL. 34: 189-208. -248-

Appendix I0.1: Visually fltted lines used to determine the median Eime for cohorts of nymphs Eo euerge as adulÈs when they are exposed to various low Èemperatures for varfous periods of Eirne ' respecEively, and then exposed to 25oC; and for nyurphs conEinuously exposed to 25oC, all at Northfield I98L/82.

Doys r 400 tr'7"C 300 I 200 t, c¡ C + C I 400 7.6" C o 10 )g 300 I o 200 6 : t, o €. 400 10 .'10 C E 10 300 C I 200 6 o !,

oC 400 11,8c,C E 1t, o- o 300 10 7) I o 200 t, ! Lo 300 250C o E Cont inuous j: 200 ( port 1 + port 2)

100 30 35 r.,0 4.5 5.0 5.5 60 65 7-0 Probit of cumulotive 7o of nymphs becoming odu lts

t doys of exposune to low temperotune -249-

Appendix 10.2 Linear regresslons used to determine the median time for the development of each ínstar of SAA in the field ln Experiments 3 and 4 at Northfteld , 1982.

ExperÍment Instar of n Regression* r Probabllity

SAA

Expt. I I 4 Y = 1.47+0.073 X 0.934 P < 0.05 (March) 2 3 Y = I.81+0.053 X 0.995 P < 0.10 3 5 Y = 1.76+0.099 X 0.466 P < 0.30 4 4 \ = 2.2þ+0.028 x 0.950 P < 0.05

Expt. 2 I 7 Y = 0.93+0.198 x 0.960 P < 0.05 (April) 2 9 Y = 1.38+0.173 X 0.977 P < 0.01 3 10 Y = 1.89+0.117 X 0.981 P < 0.01 4 7 'l = 2.36+0.066 X 0.9 59 P < 0.05

* Each regression is the age of nymphs ln hours, Y, on the probit value of cumulative percenÈage of nynphs developed to the subsequent 'instar, X. -250-

SECTION 1I : A CONTROL PROGRAI,T FOR SAA IN DRN,AìID LUCERNE A}TD ITS

I}IPLEIEI.¡TATION IN THE TIPPER-SOI'18-EASÎ OF SOI'18 AUSTRâLIA

Sumary

When SAA first becane esÈabltshed in lucerne-based pastures in Ehe Upper- South-East, virtually all of the lucerne was the hlghly susceptible cultivar' Hunter River. Experience with SAA in the U.S.A. suggested thaË the mânagement, of SAA in lucerne pastures would lnitially rely on the integration of chemical lnsecticides and biological control, and then on reslstant cultivars in the longer term. A program for the short-teru conËrol of SAA in dryland lucerne pastures in the Upper-South-East r¡ras developed from data collected in field experlments over a three year period. The program relied on rotational, severe Erazi'îg of lucerne pasÈures with st,rategic use of low rates of chenlcal insecticlde when densitles of SAA exceeded an econom{ c Èhreshold density of 40 to 60 SAA per stem of lucerne. Native predators and an introduced parasite !üere not useful control tact,Lcs when SAA lras most abundant during suumer and autumn, Èhough predators did control SAA belo¡+ Èhe econonlc threshold denslEy during spring.

The control program rras not \ùídely inplernented by landowners because of Èhe cost and practical difficultles of applyfng the program over theÍr large areas of pasture, Èhe belief thaÈ nat.ive predators and introduced parasiÈes would effectively control SAA, Ehe future availabiltty of SAA resl-stant cultlvars and, ln sone areas, Èhe increased sowÍ-ng of alternaÈive cash crops, e.g. cereals and luplns.

Three years afÈer the establishnent of SAA in the district, virtually all of the llunter Rlver lucerne had been kllled. Ttre lucerne pastures are currently betng resown vrith SAA-resisÈant cultivars. If the extensive sowlng of these culËivars results in the selectlon of new biotypes of SAA whl-ch can damage the resLstant culÈivars, then Ehe data used to develop Èhe above program rnay be useful to rapldly establlsh new strategies Èo control any new blotypes of SAA whlle further resistant ctrlÈivars of lucerne are belng produced and sown in the areao -25L- ll.1 Introductlon

lfhen SAA flrst became established 1n dryland lucerne-based pasEures in the Upper-South-East of South Australia Ln Late-L977, vfrtually all of the lucerne

1n Èhe region was the cultivar Ifunter River, which ls hlghly susceptible to SAA.

Experlence wiEh SAA and susceptible cultivars of lucerne in the U.S.A. suggested thaÊ SAA would be a severe pest of lucerne pastures and that the menagenent of

SAA !n pastures in the Upper-South-EasÈ would probably rely on Èwo strategies - inlttally, on the integration of chenical and biological conÈrol (Stern eú aL. 1959) and, ln the longer Èerm, nainly on the replacemenÈ of llunt,er River lucerne with SAA-reslstanÈ cultlvars of lucerne (Ilagen et aL. 1976). The study of SAA described 1n this thests 1s nainly directed towards the developuent of a pest control program for SAA in susceptible dryland lucerne pastures which could be used in the short-tem prior to Èhe pastures being resown with resÍstanÈ cultlvars of lucerne. The time necessary to select and then resolù suitable resistant culËivars of lucerne in the 600 000 hectares of lucerne-based pasture in the region was estinated to be at least 10 years (8.D. Higgs' pers. comn. ). 11.1.1 Pest control

DurJ-ng about the last 25 years, researchers studylng pest control have been more a!üare than prevÍously of the advantages of fntegraEing tT,Io or more control tactics into a conÈrol program, rather than relylng on only one tactic, ln particular chemical insectl-clde. Orlginally, the term tl-ntegrated controlr was used Eo describe the lntegration of bíological and chenical conÈrols into a pest nanagement system (Stern et aL. 1959). Subsequently, integrated control was broadened to become synonymous wlth integraÈed pest nanagement (IPÎ'f) (Snith and Reynolds 1965). IPI'I seeks to establish how and why pest control should be effectfve (Kearns 1981) and can be defined as Ehe selectlon, lntegraÈíon and lnplenentation of various cheml-cal, biologícal and physlcal control tacÈics based on predicted -2s2-

economic. ecological and sociological consequences (BotÈrell L979). During the last decade, t,here has been a proliferation of definitions and descriptions of

IPM in the llterature (e.g. Flint and van den Bosch 1981, Ituffaker 1980, Metcalfe and Luckman L975, R¿bb and Guthrie 1970), but they are all sirnilar in their fundament,al concepts and objectíves; each definition or descript,ion aius to control pests in an economically efficient and environmentally sound Eanner, as defined by BotErell (1979).

IPl'{ is covered by the generalísed, all-embracing term of rpest managementl whLch 1s synonymous with pesÈ control (i'Iay 1973), and the sinple terms pest control or control program will be used in this sect.lon. These latter terms are preferred for the control of SAA in dryland lucerne pastures because the cont,rol of SAA in these pastures depends on indivÍdual control Èactics which are not dírectly integrated with each other, as implied in the term IPl,l.

LL.2 Data on the Ecology and Control of SA^ô, 1n Dryland Lucerne Pasture

The developnent of a control prograu for SAA ín dryland lucerne pastures included consideraElon of all those facÈors, both biotlc and abiotLc, in t.he system which rnay lnfluence Ëhe effectiveness and implementation of a control strategy for SAA; the progratr was developed from the followl-ng existLng knowledge'or data emanating from the field study on SAA in dryland l-ucerne pastures at Culburra: t,he phenology, production and nanagement of lfunter River lucerne pastures on siliceous sands (Snith 1972); economic returns fron grazed, dryland lucerne (Snith I978);

seasonal abundance of SAA (Section 3);

economi s thresholds of SAA (Sectíon 4);

monitoring field densities of SAA (trIalden et aL. 1978); - ínfluence of chenical insecticide on denslties of SAA (Seetion 5); -253-

influence of SAA-resl-stant cultivars of lucerne on densities of SAA (Section 5); - influence of predators and an introduced paraslte on densities of SAA (Section 6); - inftuence of weather on densiÈies of SAA (Section 7); population statistlcs from l1fe-table analyses for adult SAA

( Sectton 9) ; - tegperature threshold for developmenÈ and rates of development of nynphs of SAA (Section 10). This approach was similar to guldelines subsequently suggested by Bottrell

(1979) and Fllnt and van den Bosch (198f)., and used by van Emden (f978) in developing pesE mánagement programs in graín legumes. The value of life-tables compared to empirical studies in developíng control progranÉ¡ $ras questioned by t{ay ( L973> bur life-Eables rsere included in this study to provide stability to the information on the population dynanics of the current biotype of SAA which was obtained from other experinents in Ehis study (see trlay 1973) ' The population staÈistics from life-table analyses and other quantitative information on Èhe population dynamics of SAA ín this thesis rnay also be useful for any mathematical modelling of SAA in lucerne pasÈures; such nodelling could provide a Eeans to rapidly nodify Lhe control program if there is a future selection of biotypes of SAA which could darnage the resisÈant cultlvars of lucerne now being sot{n. The following sub-sections sumnarise the data fron the above studies which appeared most relevanÈ to the cont.rol of SAA ln susceptible lucerne pastures. ll.2.l The ranageuerrt of lucerne pasture

Eunter River lucerne is a semí -v¡lnter dormant cultivar of lucerne and is most productive during Èhe warmer months of the year. 0pÈ1m:m herbage -254- production of lucerne is achieved \.r'ith rotational gtazí-ng where the lucerne is severely grazed wlth livest.ock for one week and Èhen allowed to regrow for five weeks (six-paddock systen). This grazing system is used in large fields in the Upper-South-East which vary fron about 40 to 200 ha fn area.

Livestock production from these lucerne-based pasÈures is low w'lÈh concomm{Ëant low gross marglns per hectare. In addttfon, when SAA flrst lnvaded the region, available flnance to propertfes was generally linited due to Ehe prevlous Èwo years wfEh low ralnfall and low market values for livestock. Thus, the cost of inplenenting any control progran for SAA would have to be mlninal for aceeptance by the landowners.

11.2.2 Seasonal abundance and lnpact of SAA on lucerne pasËure

SAA is potent,lally nost abundant during summer and early-autumn and least abundant, well below the econonic threshold, in wlnter and spring. Population statlstlcs ori rates of increase of SAA fron life-table studies helped to explain thl-s seasonal abundance of SAA. Ttre abundance of SAA durlng summer may vary from year to year and this variation appears Eo be related to the nurnber of days with high lethal Èemperatures (>38oC) for SAA. In some years, the number of days above thi6 temperature appears to be sufffcient to prevent SAA from beconing a pest durlng suÍtmer. The seasonal abundance of SAA suggests that monlËoring of lucerne-based pastures for SAA should begin in about nid-

December.

Ttre production of lucerne herbage is significanÈly reduced when mean densitfes of SAA exceed abouE 40 to 60 SAA per stem of lucerne and, more lmportantly, repeaÈed exposures to densitles above thaÈ threshold virtually elininaÈe lucerne plants 1n grazed pastures after three years. Thís range of aphld densiËies is accepted as an economic threshold for Èhe control program, nainly because of the deleterious effects of htgher densities of SAA on the persisEence of lucerne plants. Persfstence of susceptible lucerne pastures rùas -255-

considered imporÈant because the cost of re-establishing lucerne on siliceous sands was high relatLve to the production from the pastures.

LL.2.3 Tactlcs for Èhe control of SAA ln lucerne pasture PredaEors, nainly a brown lacewing and various species of spiders,

conÈrol SAA below the econornJ-c threshold durlng spring and are most important

control agents at Ehat tine of the year. Ilowever, predators, nainly the

Eransverse ladyblrd, do not control SAA below the economlc threshold during

sunmer and autunn when the environment, especially temperature, is most favourable for SAA. Augmentatfon of the transverse ladybird durlng suumer \,üas atÈempted by lightly grazi-rg lucerne pastures at this Èime of Èhe year, but this nodified grazj-r'g practice dfd not effectively increase the level of control by thls predator, 1t only reduced the productlon of lucerne herbage. The lntroduced parasite, 7. conrpLana,tilg, sras established in dryland lucerne Pestures ln the Upper-South-East by 1979 buÊ only occurred in very low densities and did not appear to effectively control the densiÈ1es of SAA. Ttre aPParent Íneffectiveness of predators and the parasite to control SAA in summer and early-aut,umt is contrary Èo experience in the U.S.A. where ?. eonrpLantntus, plus t\ro other introduced parasites, and native predators, especially

Hippodnttia spp., did at leasÈ reduce damage to the lucerne, though failed to effect full economic cont,rol of SAA (Caltagirone 1981., Ilagen et aL. 1976). The only tactLcs whfch can be nanipulaÈed by landowners and are reliable for t,he control of SAA in dryland lucerne pastures are chenical insecticide and severe grazing wlth llvestock. Chernlcal lnsecÈicl-de initially achieved greater

Èhan 95% cont,rol of SAA. Ttre rnain lnsecticidal EreaÈmenÈs recommended for the conÈrol of SAA were low rates of applicatlon of demeton-s-nethyl or pirl-micarb. These ehemical insecticides were lnitfally selected nalnly because they were not as toxic to predators and Èhe parasiÈe of SAA at the recommended rates of -256- aPplication compared to some other aphicides. After about three years, a blotype of SAA, resistant to Èhese chemical insecticides, was selected in the field. Ttre resistant blotype probably emerged in irrigated lucerne stands, where the use of the above chemi.cal insect,lcides was far more intenslve than in dryland lucerne pastures, and then nlgrated ínto dryland Iucerne. The resistant biotype of SAA was found to be susceptible to chlorpyrlfos and rnaldison (nalaÈhion) (V. Edge, pers. cornrn.). These alternative chemical insectícides are more t,oxic to predaÈors and parasítes Èhan demeton-s-nethyl or pirinicarb but their higher toxicitles are not considered a problem in the control of SAA in drylald Pastures because naEive predators and the fntroduced parasite are lneffective when SAA is most abundanÈ.

Grazing \.tl-th livestock achieves high levels of control of SAA (>952), provided that the gxazíng is severe, such that. vÍrtually all of the green herbage is consumed by Èhe livest.ock. Lighter grazLng produces variable conËrol, ranging from an actual increase in densitles of SAA after gtazLng to reductlons up to 95%.

11.3 A Control Program for SAA in Lucerne pasture

The strategT to control SAA in dryland lucerne pastures is based on the six-paddock system of rotationaL grazing and mainÈaining the density of SAA below about 40 to 60 SAA per stem of lucerne. SAA is kept below the chreshold denslÈy by ensurlng that virtually all of the foliage of lucerne is removed durlng the week of grazLag, and then strategically applying ehenical insecticíde during Èhe flve-week regrolüth perlod only at times when the densiÈy of SAA reaches the threshold density. In years which are most favourable for SAA,

Èhree to four applicaÈlons of chenlcal lnsecticide nay be needed to maintain SAA belov¡ the threshold during the period January to þril. In some years, as fer¡ as one or two appllcatLons may be required, and occassionally, in sunmers with -257- sufficient nunbers of days wl-Èh maximum temperatures greater than the lethal

Èemperature for SAA (>38oC), severe grazLng alone nay be sufflcient. Successful appllcation of severe grazjr^g depends on the stocking raÈe of the properEy relative Eo the available herbage at t.he tirne of grazing. I.Ihere there is a shortage of livestock tor grazlng, lucerne-based pastures on a property can be ranked i-n order of importance. Criterla which may be used to rank lucerne-based pastures include the age, densLÈy and vlgour of the plants in a lucerne pasture and the suitabiliEy of the area for lucerne hay or seed productlon, or for alÈernative crops or pasture specles. TLrose pastures with the highest prioritles can then be severely grazed in turn to control SAA, dependlng on the available livest,ock. Cattle normally do not graze lucerne as severely as sheepi but severe gtaztng of pastures on properties with cattle can be achieved by first grazhg \üith cat,t,le and Ehen with sheep in the latter parc of the week of grazlng.

During summer when tenperatures are nost favourable for SAA, chemlcal lnsecticide usually needs to be applied wlthln tr¡o to three weeks after severe grazlng Eo naintain the denslty of SAA below the threshold density. At times when temperatures are less favourable, the density of SAA may not reach the threshold unÈll at least four weeks after severe grazLng. If the threshold denslty is not reached until at least four weeks after grazLng, the pastures can be severely grazed a week earlier than expected to control SAA rather than applying chenical insecÈfclde, thus savlng the cost of an addfÈl-onal applicatlon of chemical lnsecÈtcide. Repeated early and severe grazíng of lucerne pastures

1e not recommended because thls pracÈLce may reduce carbohydrate reserves ln the tap-roots of lucerne plants and reduce the vigour of the plants. Ilorùever, occasional early grazlng of pastures when SAA is most abundant can reduce the cosÈs of chernical insectlcide and should noÈ be Èoo physiologically deleterious -258- to the lucerne plants. Early grazírtg of lucerne pastures may also be used to avoid the cost of a second application of chemical insecticíde within a regrowth period during the most favourable time of the year for SAA; at this time, insectícidal treatments may be required in both the second and fourth weeks after grazítg because of rapid increases in the densíty of SAA.

ff gtazíng is not severe and all of the lucerne herbage is not removed, chemícal insectlcide rnay have to be applied within one week of grazing to protect young shoots of lucerne. The threshold for treatment of young shoots may be as lotr as 20 SAA per stem of lucerne; the need for this lower threshold was not tested in the study at Culburra because the pastures were usually severely grazed and chemical insecticide was not required until the shoots r¡lere well developed.

The first yearts daEa from Ehe experiment at Culburra lrlere used Eo develop an initial program for the control of SAA in lucerne pastures (Allen i978). This program was produced wiEh límited data to assist landowners r¿ith decisions on the control of SAA in the second year. The provision of a program after only one year was considered essential because there were no other alternative strategies available Èo protect llunter River lucerne pastures. In the first summer with SAA (Lg77 /78), landowners \^rere hesitant to control SAA wiÈh chenical insecticide without knowing the nurnber of applications that could be required; consequently, SAA severely damaged lucerne pastures in Ehe Upper-South-East in that year. At least the initial program indicated the nurnber of applícatlons which may be requfred in a year and also provided a basic strategy which could be irnproved wiÈh fsÈep by step rnodifications'as more data and field experience srere accrued (Rabb 1970). Further data díd not markedly modify the program buE supported the main principles ln the program. The initial control program was actively promoted by districÈ agronomists and nyself at group meetlngs with landowners, in the mass medla and during consultations with indívidual landowners. -259-

11.3.1 Problems !d.th the control program Three nain Èechnical problems were envisaged with this control program; they were - monltorlng the densiEy of SAA on propertles rfith large areas of

lucerne-based pasture ; insufftclent livestock to severely graze pastures in seasons \,lith

an abundant producËion of lucerne herbage; and - inablllty to severeLy graze the larger sandhllls in the Upper-South- East, for fear of drlft. Walden (1979) developed a method using inverse binonlal samplíng to rapidly estimate the density of SAA ln irrigated lucerne wiÈh accepÈable precision. UnforÈunately, his technique was no! applicable for the estimaÈion of densities of SAA in dryland lucerne pastures because it was too tedious in the much larger fields of dryland lucerne pastures conpared to irrlgated lucerne stands. Other sinple methods to reliably estimate densitles of SAA in lucerne pastures were not available and decisions on whether the numbers of SAA on stems apPear to exceed the economic threshold could only rely on subJective, vlsual assessment.

Visual assessment Day not be conpletely impracticable because of the relatively low threshold densities, but it ls not desirable. The problen of insufficienÈ ll-vestock in those years when there is an excessive growth of lucerne plants due to favourable sunmer rains can not be easily overcome and, in Èhose yearsr some damage and loss of lucerne herbage must be expeeted. The lncreased number of applications of chenícal insectfcide ín these circumstances would probably only be JusÈified ín those pastures whlch were golng to be used for the producÈl-on of lucerne hay or seed.

The nanagement SAA lucerne pastures on sandhills is diffleult of in ' especl-ally in large fields where the sandhills are not fenced off from less- undulatlng ground. In t.hese fields, severe grazLtg may noE be a useful Èactic -260- because of the risk of erosion, and any conErol of SAA will depend urainly on chemical insecticide. II.4 ImplernentatÍon of the Control Program 1n the Upper-South-East

the conËrol program for SAA was not widely implemented by landowners and, in the tern of l{ay (1973), the program was not feasible. The main constraint preventing the adoption of this program appeared to be the cost of chemical insecticide, though other factors also eontributed.

Prior to Ehe establishuent of SAA in the region, chemlcal insecticides were generally not required or considered necessary for the control of arthropod pests in dryland lucerne pastures, except for sporadic treatment of wíngless grasshopper or pink cutworm, Agnotis mtnln (ltalker). I,títh this background, landowners qtere cautious to embark on a program which involved not only the cosE of chemical insecticlde and its repeated application in a season, but also Ehe cost of labour necessary to adequately monitor pastures t.o det,ermine the optimuu time to apply the cheu¡ical insecticide. In addition, the cost/benefít ratío frorn implementing the prograr was often misrepresented by some landowners because they tended to consider only the total cost of the program, especially the cost of chemical insecticide, for their properties as a r¡ho1e and did not consider the likely benefits. The potential cost. of chenical insectícíde per property was high due t.o Èhe large areas of Ehe properties; this high cost r¡ras often further emphasized because of the difficulty to secure extra finance needed for the purchase of the chemícal insect.lclde and the high interest rates associated with such finance. The major economic advantage from protecting

Ilunter Ríver lucerne pastures from SAA was the better persl-stence of lucerne plants ln protected pastures compared to unprotected pastures. This informaËion only became apparent after three years with SAA and earlier knowledge of such a benefit may have stíurulaEed more landowners to adopt Èhe program in the first instance. The landowners' att.itudes to the cost of t.he control program vras -26r- probably also partly caused by Ehe absence of any cost/benefit analyses in the program; cost/benefit analyses could not be determined fron one season's data. Landowners are more likely to follow advice and implement control programs if the programs are presented in terms of economic advantages (Strickland 1970).

Resist.ance to adoption of chis program because of Ehe need for chemical insecticide is contrary to experience with the adoption of control programs in many other parts of the world; in other parts of the world, programs vlere often noÈ implemented because landowners rrere not confident to change from their reliance on chemícal insecticíde (Anon. 1979). Other constralnts on the program rrere the practical difficulties ín adequately monitoring SAA and applying chernical pesticlde during the most favourable times of the year for SAA because of the large areas of lucerne pastures compared to Ehe available labour; the premature and unfounded belief that native predators and introduced parasites would effectívely control SAA; the imminent availability of SAA-resistant cultivars of lucerne; and, in some areas, the use of alEernatlve crops¡ êrgo cereals and lupíns, Eo improve the flnancial situation of the property in the short-Èerm, at leasE. The few landowners who did adopt the principles in the program appeared to benefiE, especially in Èerms of persiscence of their lucerne-based pastures (4. Ileard, pers. coriltr.). After thrèe years with SAA, the density of lucerne, plants in their pastures was still economically viable even Ehough uost of the lucerne plants 1n unprotected, grazed lucerne pastures in the Upper-South-East had been killed. Any reductions fn planÈ denslty ln the protected pastures vrere maínly aÈtributed to periods of below average rainfall, overstockíng with

livestock and damage from arthropods other than SAA during the last five years.

Some landor¡rners improved the persistence of l{unter Rlver lucerne pastures by greaEly reducing the stocking rates of their propertles or strategically grazirtg

their lucerne pastures to control SAA w1Èhout the use of chemical ínsecticíde. -262-

In many cases, these practlces probably emanated from data from Culburra used to develop the control program for SAA. An economic analysis t.o crltically evaluate t.he control program was not made on the few properties which adopted the program because such an analysis

\des considered to be a useless refinement (Springett 1973). Virtually all the susceptible lucerne in the district was killed by SAA and other factors, and most lando\rrners would be resowing pastures with suitable SAA-reslstant cultivars of lucerne. Data in this thesís demonstrated the entomological value of SAA- resistant cultívars as a tactic for the long-term manageuent of SAA, and commercial use will determine their economic value for gtazíng.

Although the above control program was not widely implementpd, it may be a useful basls for future management of SAA 1n dryland lucerne-based pastures if there is an emergence of new biotype(s) of SAA which can damage the currenlly- used resistant cultivars. In the U.S.A., seven dífferent blotypes of SAA evolved which could damage formerly resistant lucerne cultivars. Any biotypes t,hat may emerge in South Australla are not expected to cause the severe damage that was experienced with the initial biotype of SAA in Hunter River lucerne pastures because 60 to 707" of lucerne plants ln resistant pastures should be able to withstand attack by a new biotype (Lehane 1982). In such a system, strategic use of severe grazing'only nay of fer reasonable control of SAA, thus reducing the reliance on chemical insecticide which ls needed wíth Hunter River lucerne. If the innate capacities for increase of the new biotypes on currently resistant cultivars are less than those of the initial biotype on llunter River lucerne, especially during summer, then predators may also be a more useful t.actlc than with the original bíotype ln Hunter River pastures. -263-

I 1.5 References

A1 len, P.G. 1978. Control of aphíds in dryland lucerne on sandy soils. Dep. Agric. Fish. S. Aust. Fact. Sh. No. 5l/78. 3 pp. Anon. 1979. Executive Suumary. In Integrated Pest Management. Council on Environmental QualiÈy. D.G. Bottrell. U.S. Gov. Printlng Office, I{ashlngton D.C. I20pp.: v-xi. BoÈtrell, D.G. 1979. Integrated Pest Management. Council on EnvironmenEal Quality. U.S. Gov. Printing Office, I^Iashington D.C. 120 pp. Caltagirone, L.E. 1981. Landmark examples in classical biological control. A. Reù. Ent. 26: 213-232. Flin¡¡ Þf.L. âtrd van den Boseh, R. 1981. Introduction to Integrated Pest Management. Plenum Press. New York and London. 240 pp.

Hagen, K.S., Vlktorov, G.4., Yasamatsu, K. and Schuster, Þf.F. 1976. Bíologlcal control of pests of range, forage and grain crops. In Theory and

practice of Biological Control. Eds . C.B. I{uf f aker and P .S . Messêrlgêt r Academic Press Inc. 766 pp.: 397-442.

I{uffaker, C.B. 1980. Ne¡,r Teehnology of Pest Control. John I^11 ley and Sons. 500 pp. Kearns, N.B.F.1981. A conceptual frauev¡ork for the analysis and treatmenE of insect pest problems. I'f.Sc. Thesis. Unlversity of Canterbury and Lincoln

College, N.Z. 92 PP. Lehane, L. 1982. Biological control of lucerne aphids. Rur. Res., C.S.I.R.O.

1 l4: 4-10. Metcalfe, R.L. âûd Luckman, lI.Il . 1975. Introduction t.o Insect Pest Management. John l,Iíley and Sons. 587 pp. Rabb, R.L. 1970. Introduction to the Conference. fn Concepts of Pest l.{anagement. Eds. R.L. Rabb and F.E. Guthrie. North Carolina State Unív., Raleigh. 242 pp.z l-5. -264-

Rabb, R.L. and Guthrie, F.E. 1970. Concepts of Pest Management. North Carolina State Univ., Raleigh. 242 pp.

Smith, M.V. I972. The ecology and utllization of dryland lucerne pastures on

deep sands in the Upper South East of South Australia. M.Ag.Sc. Thesís. Univ. of Adelaide. 247 pp. Smith, Ìf.V. 1978. Existing Hunter Ri-ver dryland lucerne stands - should they

be protected? Lucerne Aphid tr{orkshop, Tamwort.h. Dep. Agric. N.S.tr{.

273 pp.z 253-255.

Smith, R.F. and Reynolds, I{.T. 1965. Principles, definitions and scope of

integrated pest conÈrol. Proc. FAO Syn. on Integrated Pest Control.

l: ll-17. . Springett, B.P. L973. Biologfcal principles of insect management. Introductlon. .Iz Insects: Studles in Population Management. Eds.

P.úI. Geier, L.R. Clark, D.J. Anderson and H.J. Nlx. Ecol. Soc. Aust. Mem. 1: 3-6.

Stern, V.M., Smith, R.F., van den Bosch, R. and Hagen, K.S. 1959. The integrated control concept. HiLgardia 29: 81-101.

Strickland, A.II. 1970. Some economíc prlnciples of pest nanagement. fn Concepts of Pest lulanagement. Eds. R.L. Rabb and F.E. Guthrie. North Carolina State Univ., Raleigh. 242 pp.z 30-43. van Emden, II.F. L978. Ecological information necessary for pest managernent in grain legumes. In Pests of Graln Legumes: Ecology and Control. Eds.

S.R. Singh, H.Fo vârl E¡nden and T.A. Taylor. Academic Press. 454 pp.:

297-307 .

I,Ialden, K. 1979. I'fonltoring spotted alfaLf a aphid ln irrigat.ed lucerne. Dep. Agric. Flsh. S. Aust. Fact Sh. No. 5/79. 2 pp. -265- l{alden, K.J. , SwLncer, D.E. and l{ilson, C.G. 1978 . Descriptlon of an lnverse blnomial sanpling technique for the spott,ed alfalfa aphld ln lucerne. Lucerne Aphid I.Iorkshop, Tauworth. Dep. Agric. N.S.I{. 273 pp.z 66-67. trIay, 11.J.1973. Objectlves, methods and scope of lntegrated conÈrol. In Insects: Studies 1n Populatlon Management. Eds. P.trt. Geier, L.R. Clark, D.J. Anderson and II.J. Nix. Ecol . Soc. Aust. Mem. l: 137-152.