&lOLOOI OF THE WHEAT STEM SA'WFU . CEPHUS CINCTUS NORTON.

NEIL DEVLIN HOLMES

A 'lliESIS

submitted to

OREGON STATE COLLEGE

in partial f'ul.fillment of the requiremente for the degree or

DOOT

Itnfmror of Xntorol$t In Obrrgr of lhJor

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&rlrrrn of Ermrfircnt of Entorolog[

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ghrlnrrn cil 0&ool Oirdurte 0orulttm Redacted for Privacy Drrn rf 0ra&rto &bool

Drtr Dmlt 1r paurat.{--|, !fpr{ by ltrr Arl,urn AOKNOWLEDG 'NTS

~e following acknowledgements are gratefully made; to Dr. Charles H. Martin for his most patient and helpful criticisms of the preparation of the material used in this manuscript; to the following members ot the Field Crop Insect Section, Science Service Laboratory, Lethbridge, Alberta. Dr . 0. • Farstad, Officer in Charge, for his essential guidance based on long personal expert..

ence in the wheat st~ sawtly investigations, to Dr. R. w. Salt for his excellent criticisms and susgestions concern­ ing this manuscript, and to Dr. G. A· Hobbs tor his assist­ ance in checking the final copy. The writer is especially indebted to Mr. L. K. Peterson for his invaluable assistance in the experiments described, and for his help in checking the accuracy of the statistical analysis. All photographs were taken and prepared by the Photographic Section, Science Service Laboratory, Leth­ bridge. The Cereal Breeding Division, xperimental Farms Service, at Lethbridge and Regina were most helpful in providing land and other assistance for many or the experi­ ments described in this thesis. The writer is indebted to Dr . w. c. Broadfoot, Director, Science SerVice Laboratory, Lethbridge, for his cooperation, and to the Division of En tomology, Science Service, Canada Depart ent ot Agriculture tor permission to use the data presented in this thesis. 'l'ABLlll OF CONTENTS Page "DtTRODUC'l'I ON ••• _. ••••••• • • ••••• .••••••• • ••••••• :• .• .•• 1 LITERA.ruRE REVI E'N ...... " ••••••••••••••••• • ••• 2 Taxonomic Position ...... 2 Synonymy .•••.., •••• " ...... 2 History ot Damage •••••••••••••••••••••• 4 Lite History ••••••••••••••••••••••••••• Damage ...... , ••••••• 16' Hosts •••••••••••••••••••••••••••••••••• 20 Parasites •••••••••••••••••••••••·•••••• 2:1 l!NVI.RONIIl!NTAL FAO'l'ORS AFFECTING THE ADULT •••• • ••• 2; Effect ot Wea ther ••••••••••••••••••••••••••• .2; Cage Experiment •••••••••••••••••••••••• 2.4 Field Observations on Adults ••••••••••• 26 Host Selection by the Female Sawtly ••••••••• Oviposition in Rescue and Red Bobs Wheat Varieties •••••••••••••••••••••••• Percentage ot stems infested •••••• Number ot eggs per. stem ••••••••••• Oviposition site •••••••••••••••••• Infestation and resistance •••••••• Oviposition in Red Bobs and Thatcher Wheat Varieties •••••••••••••••••••••••• 40 Percentage of stems infested •••••• 41

St~ diameter and oviposition ••••• 41 Oviposition site •••••••••••••••••• 44 Page Factors influencing host selection ••••••••• ~ •••••••••••••• 45

Sex Ratio • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 46 Effect of Date of Seeding ••••••••••••• 48 Date of seeding and stub dlamet·er ...... Time or infestation and sex ratio •••••••••••••••••••••••••••• Stub diameter and sax ratio •••••• Explanation ot variation in sex ratio ••••••••••••••••••••••.••••• 57 :Population Density ••••••••• •• •••••••••••••• 58 Factors Influencing Multiple Oviposition ••••••••••••••••••••••••••• 59 Effect ot Varying Adult Densities in Cages •••• " •••••••••••••• • • • • • • • • • • • • • • 60 Effects or handling adults on infestation •••••••••••••••••••••• ENVIRONMENTAL FACTORS AFFECTING '!HE EGG AND m.M.A.rrtrRE !,.A.RVA • • • • • • .,• • • , • • • • • • • • • • • • • • • • • • • • • • • 66 Effects ot \Veather ...... 66 Egg and Larval Survival in Rescue 1Nh eat • • .• • • • • • • •.• • •.• • • • . • . . . • • . . • • .•.... . 68 Egg survival in solid and hollow parts of Rescue stems •••••••••••• Larval survival in solid and hollow parts of Rescue stems ••••• 73 Larval survival in Rescue and Red Bobs ••,.••••••••••••••.•••••••• .,. 15 Survival in Rescue ••••••••••••••• 76 The nature of Rescue resistance •• 78 Page

Strains ot ~ephus cinctus •••••••••••••••••• 79 1951 Experiment ••••••••••••••••••••••• 80 Infestation and cutting of infested stems ••••••·•••••••••••• 81 1952 Exper iment ••••••••••••••••••••••• 84 Infested stems cut by l arvae ••••• 84 Comparison of inf estations a t Lethbridge and Regina ••,•••••••••• 87

19,5; Exp~r1ment ••••••••••••••• • ••••••• 88

Co~parison of infestations at Let hbri dge and Regina •••••••••••• 89 Tunnelling ••••••••••••••••••••••• 89

l'aras1t i em of sawfl y larvae • ~ •••• 92 Comparison of infested stems cut at Lethbridge and Regina ••••••••• 92 Comparison of Results for 1951, 1952 , and 1953 •••••••••••••••••••••••••••••• 93 Nature of the difference between the two sawfly stocks •••••• • ••••• 9; DIVIRONMENTAL FACTORS AFFECTING '!HE MATURE LARVA , l'REPUPA , AND PUPA •••••••••••••••••••••••• 9& The Effect of Weather •••••••••••••••••••••• 96 Spr ing Exposure •••••• • •••••••••••• • ••• 96 Weather conditions dur ing exposure ••••••••••••••••••••••••• 100 Development at time of exposure •• 100 Mortality and diapause from exposur e ••••••••••••••••••••••••• 100 Effect of second period ot diapause on adult size ••••••••••• 105 Page Comparison of laboratory and field results •••••••••••••••••••• 10.) Application of result s to control recommendations •••••••••••••••••• 107 Fall and Winter Exposure •••••••••••••• 108 Wea ther during exposure •••••••••• 108

Mortality from exposur e • • • • • • • • • • 109

• • • • • • • • • • •• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 111 BIBLIOGRAPHY • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 116 ECOLOGY OF THE WHEAT STEM SAWFLY, CEPHU§ CINCTUa NORTON

INTRODUCTION

The wheat stem _sawfly, CepbYJ sinctUJ Nort., has been studied quite intensively since it first became an important economic pest of wheat. Two early workers, Norman Criddle (8 to 13) of the Canada Department ot Agricultun e and c. N. Ainslie (1) or the u. s. Department of Agriculture, made so many excellent observations that much of the work since that time has consisted of enlarge­ ment and refinement or their original findings. Notable exceptions have been the development of the sawfly~resist• ant wheat variety, Rescue (50) 1 and the study of larval diapause (;6). However, even these advances might be traced back to the two original workers. Both Ainslie (1, p.26) and Criddle (13, p.3) remarked on the resistance of Triticum gurum to wheat stem sawfly damage, and Ainslie

{1, p.l6) reported on larval diapause of ~ c1nctyJ al­ though he did not describe it as such. The wheat stem sawfly exists in three distinct microhabitats. The adults ~ ive outside the host stema, the eggs and tmmature larvae inside the growing wheat stems above ground, and the mature larvae and pupae inside the base or the dead host stems at or below ground level. This thesis deals with the effects of the environmental factors that are operative during each of these phases. 2 LITERATURE REVIEW

Taxonomic Position

In North America the family Cephidae (Hymenoptera) . contains four genera (52, pp . S?-89):-

CeanoceRhus Konow - larval habits are unknown .

~ti gia Soh1pdte - larvae bore in raspberries, b ackberries, roses. Janus Stephens - larvae are pith borers in woody plants such as poplar, willow, ·_ viburnum , and rose. .. . Cephus Latrielle - larvae bore in grass stems.

Four species belong to the genus Cephus:­

c. oinotus Norton • wheat stem sawfly. Nat1ve, -- limited to western North America . c. olavatua (Norton) - native. Reported from -- Oalit., Idaho, Ore., Wash. c. pygmaeus (Linnaeus) - European wheat stam -- saWfly. Introduced to Conn., ass., N. C., N• Y • , Pa . , Ont • ~ (Trachelus) tabidus (Fabricius) - black grain stam saWf!y. Introduced to Del,, Md • , N • J • , N • Y • , Pa • , Obio , Va • .

The studies presented hers are restricted to Cephus cinotus.

S~nonm

Cephus cinctus was described in 18?2 by Edward Norton (4}., p.88) from a single male specimen (Fig. 1). 3

DWAaD KOBTOII.

oll.-Jat. eell, wlal'la Ia without croee DerYUN; Ullder wiDS' with two iDDer oella, ~elr lueeoiMe ..U loDJ &Dd reMiYiDI Ule crou-Denure withiD the tip ula~ · Var. 9.-J'iret joiat of uteDDIII black; all the femora with a wide black kDd. Near Cordon, Mexioo. (Prof. Sumichrut.) Two apeoimena • ....,....,_•s••a&a. NortoD. Var. 9 .-The bual half of third aDd the two bual joiDte of anteDDill rufou1; labrum aDd two 1pote aboYe, part of tegul•, bue of metatboraz, ftnt Yi1ible lllllll•Dt of ter1um rufou1, the whole edge of oollar, a large •pot beDeatb &efullt, bual platel aud tipe of ter1um, white; leg• u iD ezcaMic 1 wiDp more 1moky, uDder winsa without inner cell, their lanceolate cell Dot ooiDcidibJ with crou. Denure, but withdrawD u usual ill Macrophya; 1culptare ud form u In cz. CGMta, Texas. (Belfrage.) One specimen. LepllJ"-• ftllya, n. ap. 9 .-Length 0.30; br. wings 0.«15 inch.-Antenn• 13 -joiDted, black. Color yellow-browu; a lunate mark through ocelli, touching bue of each antenne, tcutel, metathorax aod band on 6nt segment of tergum, 1pot on breut and lower half of venter, black; !ega pale yellowish, tarsi tipped with black, bioder tarsi darkett; wioga faintly1moky. Antenn• abort, quite thickened in middle, taperio1 to eoda, 1ubeerrate beoeath; bead not u wide u thorax; body quite 1tout; •port 1imple; Janceolate cell of wing• closed iD middle, 1upetiolate, without oblique crot~-line. Te.ua. One specimen. (Coli. Am. Ent. Soc.)

~eplla• elae&a•, n. ap. t, .-Leogth 0.2M; br. wiog• 0.~6 incb.-Color black; a square spot on the nuua, a spot curYing arouod each lower orbit aod on the middle of each man­ dible yellow; tegule and a spot under each wiog, uoder Ule Deck, oo pectus, the 1idea of bual plate•, an irre&ular deDtate baud wide1t rot 1ide1, oD the llrat, teeoDd and fourth aud on the aides of third, fil\h and 1ixUl, aDd apical seg­ mentl of ter1um, aod on the apical ed1e of each segment of vertex, yellow; legs yellow, growio1 reddi1h toward• the tani, trochanten and the anterior pair of femora before, black; wiDg 1moky. Antenn111 alightly ~lavate, 18-joioted. Colorado. One specimen. (Coli. Am. Ent. Soc.) X7ela eaea, n. ap. t, .-Length 0.30; br. winga 0. 72 incb.-Antenne black, head and thorax brooze, with purple relleetiona, greenish about'tbe face : labrum and palpi pale reddish; abdomeo 1hining 1teel-blue; legs ferruginous. binder tibie blackish. Third joint of antennlll three time1 u long u the six remaining joints toge ther bual joint arcuate; head and thorax delicately, closely sculptured; claws with a strong inner tooth; wings hyaline, nerYurea as in tricolor. Texas. Five specimens. (Coli. Am. Ent. Soc. ) This may be a nriety of tricolor. On one of the wings is a sup· plewentary marginal cell.

Fig. 1. Original description of C. cinctus. From "Norton, Edward. NotesoilNOrth American Tenthredinidae with descrip­ tions of new species. ·rrans. Amer. Ent. Soc. 4 : 77-86. 1872." 4 The type is deposited in the Academy of Natural Sciences, Philadelph1 • SynonymJ and present status of _c...... oinctus.,...... 1s shown by Ross (52, p.88) as:-

Cephus cingtus Norton, 1872 Cephus occidentalis Riley and arlatt, 1891

Cephus ~raeqicheri Ashmead , 1898

In 1895 Fletcher (24, pp .229~230} collected

. adults of ~ oinotus from tumbling mustard heads at Indian Head, N. W. T. These specimens were inoorreotl7 determined

as~ pzgmaeus (Linn.). In 1905, ~ oinetue collected tram

Western Canada were determined to be~ oocidentalia (27, p.l66).

History of Damage

Adults of .2.:. oinctl\§ were first reared from native grasses by Koeble at Alameda, California, in 1690. Riley and arlatt (51, pp.l77-176) warned that these insects might change their habitat from wild grasses to cultivated small grains. The next report was trom Canada, where Fletcher (24, pp.229·2,0) recovered adUlts trom the heads of tumbling mustard at Indian Head, N. w. T. The first sawfly damage to wheat was reported from the area ot Moose 1aw, N. w. T., in 1898 (25, p.l20). In 1903 Fletcher (26, p.l72) stated that sawflies were distributed trom. the Rocky Mountains to central anitoba. Reports ot increas­ ing damage came from Manitoba and SaSKatchewan in 1905 and 1906. By 1907 the wheat stem sa ly was reported to be the most important pest at •heat in central anitoba where it caused losses up to 50 per cent (2?, pp .l66-l67) and 8, p.ll56). Ainslie (1, p.3) reported that widespread sawtly damage occurred in North Dakota in 1909. The sawfly damage steadily increased in Alberta, Saskatchewan, Manitoba , North Dakota , and ontana. During the worst years, between 1938 and 1944, the annual loss in estern Canada trom saw• flies was estimated by Farstad (49, p.232) to be 20,000,000. At present the area of economic importance ot -a. oinotua covers part of Alberta, Saskatchewan, Manitoba , Montana , and North Dakota. The distribution ot wheat staa sawfly in Canada in 19.53 is shown in Figure 2.

gte Historz

The life history ot ~ _c.in_c_t~u"s was first described

by Criddle (9, pp .237-238). Eggs are deposited inside the host st by the saw-like ovipositor (Fig. 10, 11, 12). It the stem is hollow, the egg is usually placed against the wall of the pith cavity (Fig. ~). In solid stems, a small hollow space is created by the female, and an egg deposited in it. Generally each female lays only one egg in each stem. but is not deterred by previous oviposition by other females . The egg hatches in three to 10 days. T.ae larvae .- LEGEND %Infestation 0-5 6-24 2 5-39 40-100

....., --'1.-t:.. ______"""_ ­ y WHEAT m SAWFLY .INFESTATION 19~3

Fig. ~ 7

Fig. 3. Eggs and first instar larva of ~ cinctus.

Fig. 4. Mature larva of ~ cinctus. 8 move up and do\~ inside the stem, tunnel the nodal plates and destroy any eggs or other larvae present so the. t only one individual finally survives in each stem. 'l'Ae nwnb er ot larval instars is variable in various hosts; Farsta4

(l/ , p . 68) reports five :tn Marquis \'~heat . In August when the wheat 1s nearly ripo, tbe larvae stop feeding. First they move to the bastt of the stem where a circular cut te made around the insid$ ot the stem, the upl'er part of the stub (basal part of the stem) is plugged with frass and a cocoon is oonstrueted. The stem soon falls OVE!Ir and the stub remains in the soil. The stub is generally cut by the larva. just at ground level (11g • .5 , 6) . The mature larva can be distinguished from. the immature larva only by the gut. In the immature larva, the gut is a distended tube filled with green plant material. When the larva becomes mature, the gut is emptied of its contents. 1$ contracted to a narrow thread • an.d loses its Malpighian tubules (}3). In both mature and feeding stages, the larva has a eharaoteristie S•shape .. (Fig. 4) . The winter is spent in an obligatory diapause that is broken only by a period of low t~perat~es . Salt (,56 . p .•?6) obtained 95 per oont emergence from stubs stored at 10° c. for 90 days. The larva is capable of re•enter1ng diapause in the spring 1t unfavourable conditions such as high temperatures exist" If this happens, the larvae must unde.rgo another period of low temperatures before resuming 9

Fig. 5. Sawfly stub. Fig. 6. Sawfly stub. Split to show Cocoon opened cocoon. to show larva. l.O development (6 , p. 77) and 56 , p . 82) . Larvae have been reported to survive tor as long as three years and five months under laboratory conditions (1, p . l6) . With favourable conditions in late April or early May, the larva straightens out and becomes quiescent . This is known as the prepupal stage. After a short period, the skin is cast and the pupa emerges (Fig. 7). The adult appears approximately two weeks later. The adult chews a hole through the plug in the stub and escapes (Fig. 8, 9) . Although adults have a well for.med gut , which is mueh more specialized than that of the larvae, they do not have to feed in order to mate and pro­ duce viable eggs . Adults have been observed occasionally with their heads in flowers of various weeds, and also drinking 'from moist soil, but the necessity of suoh be­ havior is not known . Most or all nutrients required for growth, reproduction, and other aotivities are obtained during the feeding larval stage. There is only one generation per year, although under unfavourable conditions a generation may require two years. The normal life cycle is shown in Figure 13 and the time of development from mature larva to adult at 2;0 c. in Figure 14.

• 11

Fig. 7. Development from prepupa to pupa.

Fig. 8. Adult female, ventral and dorsal views. 12

Fig. 9. Adult male and female, mating.

Fig. 10. Adult female ovipositing. 13

Fig. 11. Stem split open to show ovipositor in .§.ill.

Fig. 12. Diagram of ovipositor, ventral view. DV, dorsal valvula; IV, intermediate valvula; VV, ventral valvulae. LIFE HISTORY- ~.cinctus

EGGS

FEEDING LARVAE

MATURE LARVAE

PRE­ PUPAE

PUPAE

ADULTS

APR. MAY JUNE JULY AUG. SEP. OCT.

Fig. 1} PERCENT 100" .. " ,..s-, ,,...... " . '-<.., / '\ . 90 "<~ I ' •• ~~ • i \ • 80 \ / \ \ I \ \ I \ • 70 \ /·-·, I \ •• ' /. ·, I \ .• \ I \ I • • 60 ', / \ ! \ .• .y\ \ t' 50 I , V ; \ ,r, : \ 40 . ' I . : \ / \ I I . . \ / \ ! ' ... \ 30 I \ I \ : I I • . \ ' I '. I \ , • ' 20 'J \ \ / \ \ ~~ .. \ /' .;:,".' \ 10 ~ " \ \ ~\)~' ' .... \ .,.~.· ' ~., ...... -- ~.- .· ... ,., .r- --­ ' 0 5 10 15 20 25 30 35

Fig. 14. Time required for development from post-diapause larva to adult at 25° c. ... .

16 Damage

The wheat stem sawtly produces two types ot damage . The main type is the cutting of host stems before the farmer would normally do so himself. In addition to heads lost on the ground, heavy rains may produce sprout­ ing from heads in contact w1 th the soil ( 20, · p . 6) • To prevent such loss, the farmer must cut his crop while it is . still in the late dough stage. This may produce a loss in Jield and a lower grade. In the Regina plains area ot Saskatchewan swathing is the common practise because or the high incidence ot 9.:, oinctua. Illustrations of damage are shown in Figures 1; to 19 . The second type ot damage is reduction in yield and quality of kernels as a result ot larvae cutting the vascular bundles and reducing the nutrients supplied to the head . Seamans !1 !!• (;8, p. ; ) reported that, in the average season, a 10 per cent loss 1n yield, a reduction of one 8rade, and a lower weight per bushel is caused by saw... fly larvae feeding in the stems. Occasionally sterile "white heads" are produced. Criddle (lO, p . 22) reported that sawfly larvae produced "white heads" in grasses, but seldom in wheat or rye unless these crops were late- sown . In 1953 "white heads" were observed in winter wheat . The top internode in these plants was tunnelled so intensivelr 17

Fig. 15. Wheat stem sawfly damage, Barons, Alberta, 1952. An example of marginal damage.

Fig. 16. Wheat stems cut off by c. cinctus. ­ (From the same location as shown in Figure 15.) 18

Fig. 17. Wheat stem sawfly damage, Nobleford, Alberta, 19.52. 19

Fig. 18. Wheat stem sawfly damage, Nobleford, Alberta, 1952.

Fig. 19. Wheat stem sawfly damage in experimental plots in the sawfly nursery, 1953. (Situated next ~ to field shown in Figure 18.} 20 that the stems were translucent; and the vascular bundles completely severed. goats

OepAua cinctus has been reported to infest the following species of grasses and also flax (1 , p . 8) 10 , pp. 22- 23) 18, pp . 383- 386) and 19 , pp . 216- 227) :­

Tribe Festucae Bromus 1nerm1e - brome grass festuoa sp .

Tribe Avenae D!scham;esia sp . Avena sativa - cultivated oats

Tribe Agrostidae Phleum ;eratense - Timothy Calama&£ostis sp.

Tribe Hordea

A~ropy~on caninum b dasystaohyum A. elon~atum A. occ! entale r:: &riftielisrl ~ ;eauciflorum - slender wheat grass A. repfqS - quaok grass A: richardsoni - bearded wheat grass I7 smithii - western wheat grass ~it1oum aestivum - common wheat T. durum ... durum. wheat T. stelta - epelt or emmer wheat Sica e cereale • cultivated rye Hordeum! j~batum - foxtail ! . vulgare - cultivated barlef Erxeus canadensis - wild rye 21 Tribe Hordea Continued

E. condensatus E. innovatus L .ma-.c....o_un='l.-.1

Criddle (11, pp.l76-177) reported that ~-r-io_h_a_r_d- -soni was a preferred host in sandy soil and ·----A. smi.th11...... in richer soil. Farstad (17, pp.68-69) reported that A. elongatum and Phleum Rratense are resistant to sawfly.- Criddle (13, p.3) reported brome to be resistant, oats and winter rye 1 une.

Parasites

Cephus cinctua is known to have seven hymen­ opterous parasites. They are:­

Ichneum.onoidea Braconidae Bracon ceph1 (Gahan). (28, p.l8) Bracon 11ssogaster Muesebeck, (40, pp.l49-151) Iohneumonidae Scambus detritus (Holmgren), (32, p.3}9)

Chalcidoidea Eulophidae Pleurotropis utahensis Crawford, (1, p.23) I Eupelmidae Eupelmella vescioularis (Retzius), (29, p.57) Eupelmus allln!i (French), (13, p.7) 22 Eurytomidae Eur1toma atripes Gahan, (29, p.37)

or these species, Bracon C!J>hi is the most important , and in some areas has effectively reduced severe sawfly infestation• (42 .• p .l03). ENVIRONUPNTAL FACTORS AFFECTING 'lHE ADULT

The adult ot Cephus oinctus spends most of its lite outside its host plant. Conseq1ently such weather conditions as light, temperature, 1nd velocity, air pressure, and precipitation affect this stage directly. T.he host plant exerts an i mportant influence on ovtpo ition sit e and oviposition frequency . Population density is a factor in the environmental resistance of this specie • The following discussion deals with these factors.

Effect of weather

As with other insects the activity of the adult of the wheat stem sawfly is limited by weather eonclitiona. Manson (38. pp .lOl-106) reported an increase in sawfly mergence after a rainfall because the plug in the stub was softened enabling the adult to escape more easily. Criddle (10, p . 2l) stated that adults required aunshin for ovi• position and that activity was retarded below 60° F. Ainslie (1, p. l9) found that sawfly adults were most active between 10 a .m. and 2 p . m. Seamans (59, pp.433-4,4} tated that sawfly activity was stopped when the sun was clouded over or 1hen heavy winds were blowing- Adult aotivity was confined to calm periods or sunshine between 64° and 'oo r. Although general observations had been previously made on the effect of weather conditions, yet we do not know

,. 24 precisely how weather tactors affect the mating and ovi­ position of the wheat stem sawfly. As a. result we have been unable to obtain satisfactory mating and oviposition in the laboratory. The study of effect of weather on .. mating and oviposition was attacked by two methods: (1) Host stems ere exposed to sawfly adults tor a certain period, at the end of which oviposition rrequenc7 waa correlated with a continuous temperature record, (2)

Parallel observations of adult activity and weather con~ ditiona.

Case .Experiment

., A series of two-toot-square plots, each with four rows of spring wheat, were covered with cages at Nobleford, Alberta, in 1953. All plots were caged before the sawfly flight began. On each day during the flight period, one plot was exposed to the wild sawfly populations by r oving the cage. After exposure or two to 4} hours, 50 stems were selected at random from the plot and examined for infestation.. A recording hygrother.mograph was placed in a Stevenson weather screen next to the plots,. The legs ot the cage were cut dow.n so the hygrothermograph was at the level ot the second internode or the wheat plants. Tb.t

results are reported in Table 1. ~ Table 1 shows that very little oviposition

occurred when the air temperature as be~ow 70° F. On .ble 1. lnfeetatlona ot 50 atas ot wheat exposed to a Wild sawtlJ latlon at intervals during the flight period

sure a;eu per infested t total ht-a. ioteatad atea, June 25 2 1 l. 0 1' J8 l.O ;Fune 26 21 21 0 0 2 ... 1.0 1une l'l 22 22 0 0 4 8 1.0 ltme 29 43 42 1 0 1 2 1. l'une ,-o 17 11 0 0 0 0 o. July 2 6 0 0 1M 84 2., Jul.J ) 22 20 '2 0 J! 00 l-.1 1\ll.J 4 21 21 0 0 2 . 4 1.0 l\111 ' }2 29 0 105 82 2 • .S 7u.ly 7 24 14 10' 0 210 'a 4.} 2& 20 a 0 }0 44 3"\ll7 aa ~-· ltll.J' 10 35 u 6 a· 11 )4 1.0

Sntl.J flight almoat compl$ted bJ lul7 8, only a tew adult• at111 :t'lJinS• 1\') \.71 26 J'une 25, when the temperature exceeded 70° F . for one hour, 19 eggs were laid, and 38 per cent of' the stems were infested. From 1une 25 to July 2, the temperature exceeded 0 70 F . for only one hour, and during that hour the wind velocity ot 2.5 to 30 m.p.h. was sufficient to restrict adult activity. Two-thirds of the eggs for the total period ere laid on July 2, 6, and 7 when the temperature exceeded 70° :r. for a total ot 19 hours. Correlation and regression coefficients were calculated from the number of hours above 70° F. and the number of eggs laid. The correlation coefficient of 0.954 was significant at the one p.er cent level. The regression line is shown in Figure 20. Infestations of the last two plots were com­ paratively low, although the temperature was well over ?0° F . tor much of the exposure periods. By this time (July 8) only a remnant or the p9pulation remained , and most temalesl remaining alive had laid almost all of their eggs. Relative humiditi.es ranged between 28 per cent and ;6 per cent during the periods of maximum oviposition.

Field Observations on Adults

In addition adults were observed during the day •. Temperature, wind velocity, light, and air pressure were recorded at the site ot the observations.. The temperature was ta.ken in the Stevenson cage (air temperature), on the 27

NO. EGGS y

100

90

80

70

60­

50

40

30

20

10

oL---~----~----~----+------4----~----~ 2 3 4 5 6 7 8 X HOURS OVER 70° F

Fig. 20. Regression line for number of eggs of c. cinctus laid, and number of hours above 70° F.-­ 28 surface ot the soil exposed to direct sunlight (soil sur­ face temperature) , and in the shade of wheat plants at the l evel of the second internode (shaded temperature) . These temperatures were taken lith mercury ther.mometers . Air pressure was recorded with ~n anaeroid barometer, and wind velocity with an anemometer . Ligh t was measured in foot• candles vdth a light meter.

Changes in adult activity appeared to be more closely associated with changes in the temperature at the soil surface than with cha es in air temperature. This indicates that radiant energy from direct sunlight may be an important factor in sawfly activity. When the air temperature was 68° F ., the sun covered w1 th a cloud, and the soil surface temperature 740 F. , most adults were inactive. However, as soon as the sun emerged, the soil surface temperature rose to 79° F., and the adults immed~ ­ ately became active. When t he soil surface temperature was 122° F . and the air t perature 98° F ., all the females and most males were inactive. Immediately a cloud passed over the sun both males and females became active. Observations of tbe effects ot temperature on adult activity are summarized below;­ 29 Adult aotivitz Air Soil Shaded od... temn . surta.oe tem.:2 . . tem12. Fliaat atins ;eosition 68°F . 7&C?. 740f. None None None

68~. 78o:F. 76~. Fair None None 68°F . 84<7. 78'7. Good Fair Slight 70°!'. 86°r. BoOJ.i'. Good Good Good 74°F. 96°F. to lOOOJ'. 80~. Best Best Best 98°r. l22°F. Slight None None

ales w•re active over a wider tanperature range than were f~les, J4at1ng took place at lower temperatures than did oviposition,

I Most oviposition occurred when the wind velocitJ was less than five m. p .h. Some oviposition took place When I the wind reached 20 m.p.h., but most individuals remained stationary on the stems and leaves of the wheat plants. Oviposition and mating occurred readily in the absence of measurable changes in air pressure. No pattern ot selection or oViposition sites in relation to light could be determined. Fema~es oviposited and mated as readily in shaded as in non- shaded locations. Direct sunlight is probably most important because ot ita effect on raising the temperature of the adults. Pepper and Hastings (4;, p .lO}) found that the body temperatures of two species o~ grasshoppers was raised o.;0 c. to 110 c. above the air temperature by the action of direct sola~ ;

30 radiation. Sawflies oviposited readily when the light

intensity was 4, 500 toot ~ candles . Optimum conditions for mating and oviposition ooourred when the unshaded soil surface tsmperature was between 96° F . and 100° F. , the temperature in the shade Of the plants at the level of the second internode 80° F, , and the air temperature between 70° F. and 98° F .

Host Selection by the ~emale Sawfly

The variety and stage of development of the host plant are important factors in wheat stem sawfly oviposition. Criddle (10 , p . l8) observed that tamales WQ\lld fly a con­ siderable distance through wheat to oviposit in a natural host . Ainslie (1, p . 26) suggested that mature stems of durum wheat might be resistant to oviposition. Mitchener (41, p . 754) reported that the tour- year- average sawfly' infestation of durum wheats in Manitoba waa 19 . 3 per cent and of aesti~ wheat 33 . 7 per cent., Platt and Farstad (49 , p. 236) found significant differences in infestations in different varieti$8 of wheat , but no single variety was significantly lower at all stations. T-hese differences were expressed only where infestations were less than 50 per cent. The stage ot host development is important in differential sawtly oviposition~ ·Ainslie (1 1 p~l9) reported that sawfly eggs are seldom laid in stems with heads ~ . }1 l!'arstad (17, p . 68) concluded that oviposition is limited

by stage of development of plant and diameter of stem. Early sown wheat is more heavily infested than later seeded heat . Farstad (20, p.5) reported average infestations ot 15 per cent in wheat seeded before May 20 and 13 per cent in meat seeded after that date. Jacobson and Farstad (34, p . 91) showed that the percentage of saw­ fly in:t'estation of Apex heat decret;tsed with lat r dates of seeding. Experiments were conducted in the spring of 1953 to determine the influence of three varieties of wheat on . sawfly oviposition. Thase varieties were Red Bobs, Thatcher, and Rescue . Red Bobs and Thatcher are both hard red spring

wheat varieties, which are hollow- st~ed and susceptible to the wheat stan sawtly. Rescue is also a hard red spring wheat , but it is solid-stemmed and sawfly resistant . The first part· of this work is conc erned with the effect ot Rescue on oviposition and the second with a comparison of oviposition in the two susceptible vari·eties of Red Bobs and Thatcher.

Oviposition in Rescue and Red Bobs Wheat Varieties

The wheat stem sawfly cannot be satisfactorily reared in the laboratory. Therefore most studies on infestation, hatching, and larval survival were conducted in the field . • :·

Alternate 10- foot rows of Rescue and Red Bobs wheat were seeded in a saWfly "nursery" at Nobleford,. Alberta. The nursery was adjacent to a field of wheat heavily infested with sawflies in 19.52 (Fig . 18 , 19) . All observations were made on a sawfly population that was not influenced by artificial conditions such as caging, ete .

Samples ot stems were selected at random, split long1t udi ~ nally, and observed under a dissecting micros cope tor egg mortality and hatching,

Percenta&e of .stems 1nt:epte4: The effect ot host on reduction or increase in oviposition could be an important factor in sawfly resistance. Red Bobs is a susceptible hollow- stemmed variety in which sawflies readily oviposit . Because each row of Rescue had a row of Red Bobs on either side, any preferential oviposition effect could be easily observed.

The percentage of infested st~s of both varie­ ties in the test are recorded in Table 2 which shows t hat percentages of stems infested at Nobletord under field conditions were almost the same for the two varieties ot wheat . These results agree with those obtained previously I with caged and uncaged sawflies (Tables 3. 4, and 5) . Resistance to oviposition is not an important factor in resistance of Rescue to the wheat stem sawtlJ. Tables 2 to 5 show that differences 1n percentage ot ......

3J

..

f bl.e 2 . I.atestat1oa o.t twt> varieti•e ot whe ' at Nobletord in l9iJ

~------

Table -'• Infestation of tour wh t varie• ties 1n the sa 17 nurserJ · at seott,,., Saakatch. wan, 1n l.?!ifl

• Tba:toher · 153 ,, :rqu1e 162 6a. Reacue 14J ?J Oh1noo:k· 144 ,,

, .. ,.

'ble 4., Infeata.tion ot tou11 whoat ve.r1et1ea itltested .., wi'Oh equal _sawtlJ popt.llati on~.,und er casea at L.ethbrldse in l95u­

.!'ln~t.r

Thatcher 704 ,... 626 84 Red Bobe Jlj 496 'J RaSC'-\18 J;l '''a , ·1! ' 92 tol

• Totals ot two plots tor eaoh treatllent• ._ Results we:re 'l'llilllea.41ng here. One plot waa 1!11"ttate4 '1 par c•at ud tihe othe%' 95 per oen,.

fabl..e !h Intes.ta.tlon ot "'a.rieties oasect a~aratelJ'

· ;e;,er ·· au =- r · M:a u 2 3!1 IG filS J II 'li'A· 2 J i \I'=£1 I l 1 ,. OitS · etaa Jsl-. aata, 4 Looattoa• , ) ~El!tz: _ . .. _.ttll8o1121JJ9 •., inteaitd, 1,$1 Lethbr1da• ThaboheJ" ?80 '11 Red Boba JJ1 Rea.oue ,,. Go14.-n Ball Jll 14n 1,,2 I.ethbl"lttge REU\J0\1. 1514 ,, Gelden Ball ,,, ,, Belin• Resou.e ,, 11 Go·l.4en BaU 6!)0 1,,, Lethbr-14&• Goldftl'l Ball 918 '',, i.na Gol4en Ball 1?,, ,, 3.5 infested stems are greater between years and stations than between varieties. This agrees with previous reports of Platt and Farstad (49 , p. 237). Even where infestations ranged from 60 per cent to 76 per cent, there were no differences in percentage of stems infested among resistant and susceptible aestivum hosts .

Number of eggs per stem: A comparison of the number of eggs in stems of Rescue and Red Bobs was made at Nobleford in 19.53 (Table 6) .

Table 6. The number of sawfly eggs laid in two wheat varieties at Nobleford in 19.53

Date No . of stems Mean no . of eggs= examined Variety examined per stem

July 9 Red Bobs .50 7. 4 July 9 Rescue 50 3. ; July 14 Rescue ,50 3·1

Table 6 shows that twice as many sawfly eggs were laid in Red Bobs stems as in Rescue stems. However , there was no difference between these two varieties in percentage of stems cut by sawflies• ninety per cent or the stems were cut in both varieties. Therefore, the increase of 3. 1 eggs per stem in Red Bobs did not increase sawfly survival in that variety. f

Oviposition site: Studies VIera made to det,ermi.ne if out­ side stem diameter and solidness of host stems influenced oviposition. Fifty Rescue atams from the plots were split · longitudinally and the length of hollowness• measured (Table ?) .

Table ?. Hollowness of 50 Rescue atams at Noble­ • ford • July 8, 1953

I - , f Hollo~ess (om.) in internod.e:I 1 2 3 Mean 1. 6 2.1 o.a Range O. l-8. 6 0. 1-11 . 3 o. o- 12 .1 o. o-10 . 3

X Numbered from the crown .

As ..expected from previous reports (46 , p . l47) Rescue stems were more hollow than under drier, sunnier conditions. When the solidness in Rescue stems breaks down , it does so. first in the upper part of the internode. Table ? shows that considerable hollowness had developed in Rescue stems in the plots. The measurements were from the upper nodal plate in each· internode down the internode as far as the hollowness extended . The _second and third internodes had means of 2 . 1 em . and 2. 3 am . of holl owness respectively. Because of these results, the forecast was made that sawfly resistance of Rescue in the plQts would break down . Subsequent results showed this forecast to be correct . 37 Because these Rescue stems had a considerable

portion hollo t in each internode, they were ideal for testing of the effect of solidness of st m on oviposition

site. A comparison of the oviposition sites in stems ot Rescue and Red Bobs is shown in Table 8.

Table 8. Oviposition sites in 50 stems of Red Bobs and 50 stems of Rescue, at Noble.ford, luly 9, l95J

Per cent ot eggs Total no . in upper four om . Varietz of eggs of the internodes

Red Bobs 371 Rescue 168

• Laid in the hollow region.

Table 8 shows that distribution of eggs along

the internodes was not influenced by host variety. In bot.h varieties app:rox:imately 40 per cent of the eggs were laid more than tour em. below the node. In Rescue 40 per cent of the eggs were laid in pith, although there was adequate hollow space available tor all the eggs deposited in this variety. Apparently the females did not select for hollow­ ness when they chose the oviposition site. The behaviour of females while selecting an ov1­ position site was the same in both Red Bobs a·nd Reseue. First attempts to oviposit were "USUally made in the upper

.ft'·

·. • • . .. I ·, . 38 part of an internode. \Vhen the stems became more ature, the upper section of internode apparently became too difficult to penetrate, and, although attanpts would be made at oviposition, the female would move down until she located a more easily penetrated part of the internode. In older plants more eggs were laid in the upper internodes and in the lower part of these internodes. In Rescue stems , the pith apparently ottered considerable resistance to the ovipositor, as penetration in the solid parts of the inter­ node took longer than in hollow stems. There appeared to be as nany females on the Reseue as on the Red Bobs plants. Examinations were made to determine the diatri• bution of eggs per internode of' Red Bobs and Rescue (Table 9) .

Table 9· number ot sawfly eggs per internode ot two varieties of Wheat at .Nobleford in 19.53

No . ot · No . of ;eer internod:l Variety Dat! stems "'1 e=~~ !

Red Bobs June 30 2.5 0 26 32' 1 Suly 9 ;o 36 243 7.5 l Rescue July ; 2.5 1 10 4 0 July 9 50 24 66 6.5 1.5

I Numbered from the crown.

Table 9 shows that most eggs ere laid in the second and third internodes of each host variety. In Red 39 Bobs, the number of eggs in the third internode slightly exceeded those in the second on June 30, but on July 9 the reverse was true. In Rescue more eggs were laid in the fourth internode in Red Bobs. On July 9, the number ot eggs in the second internode of Red Bobs was almost four times that of eggs in the seoond internode ot Rescue. The total number of eggs in the first, third, and fourth inter­ nodes of Rescue was 104, 1n the same internodes of Red Bobe a total of 112 eggs were laid.

Infestation. - - ...,...... ,.and resistance: Tables 2 to 5 show that where sawfly infesta.tions were 60 per oent or higher, there were only small differences between resistant and non-resistant varieties 1n percentage of infested stems. Although Rescue was more resistant to oviposition than Red. Bobs, this is only or academic interest at the higher levels of population. Infestations as h1gh as 75 per oent oan develop in one year from a previous infestation of 10 per oent (Farstad, 1945). In view of this potential rapid increase, any resistance to oviposition to be of value must be operative at high;er infestations. This is not so with either Resoue or Golden Ball. The differences in infestation among years and stations were frequently higher than that among varieties (Table S, 1952 and 1953). Spring wheat oannot normally be 40 seeded early enough to be resistant because the earliest seeded fields are usually more heavily infested.

Oviposition in Red Bobs and Thatcher Wheat Var1e,:t1es

Red Bobs and Thatcher varieties are hollow- stemmed bread wheats susceptible to sawfly damage . Red Bobs di ffers slightly from Thatcher in susceptibility. The sex ratio of the sawfly population from Red Bobs is normally predomi­ nantly female while Thatcher usually favours malesA Because of differences in sex ratios .and sawfly-susceptibility, a comparison between these two varieties in frequency of ovi­ position was conducted in 19;;. Alternate rows of Thatcher and Red Bobs were seeded six inches apart at Nobleford, Alberta, adjacent to sawfly- infested stubble from 1952 . Plastic screen cages, approximately two feet square and three feet high, were placed so that each would cover two rows of each variety ot wheat . The cages were placed in position before the saw­ fly flight so that sawflies ware excluded from the plots until time of exposure. One cage was removed on each day during the flight . After exposure , which varied trom one to three days (see ']able 10), 2.5 stems of each variety were examined for sawfly oviposition that had occurred during the period. Stems of Red Bobs and Thatcher were selected at random from adjacent plots on four dates during the sawfly

, ­ . '

41 flight ~ Stem diameters at various locations of the inter• nodes were measured with a m1 crometer caliper. \ • Percentase of stems inteste4: Table 10 shows that the total percentage of infested stems was slightly higher for Red Bobs than for Thatcher. On June 30 . 88 per cent ot the Red Bobs stems were infest$d compared to ,56 per cent tor the Thatcher stems. On July 10. 16 per cent of the Red Bobs stems and 52 per cent of the Thatcher stems were infested. During the remainder of the test. differences in the 'percentage _of stams infested were small• Red Bobs generally had a greater• mean number of eggs per stem than did Thatcher. The mean number of eggs per stem for Thatcher exceeded that for Red Bobs on only two dates. • Neither variety showed a definite peak of Sl.lita• bility for oviposition, although Red Bobs appeared to be most attractive early in the flight. and Thatcher at the end of the flight.

Stem diameter and oviposition: Measurements of outside diameters of Red Bobs and Thatcher were made to determine if there was a relation between stem diameter and ov1­ position preference (Table ll) , Table 11 shows that the mean stem. diameter ot • · Red Bobs was greater than that of Thatcher and that the number of sawfly eggs was greater in Red Bobs than in •

.. 42

Table 10.

·; i ]j J . • 1 ;, =·= '1 1 : 'ill; I ; •' ~an no. o. ot e t.ll..S ner p.eroent. Date Va~- eggs in ..!D9t!!d., etz . 2' et June 1' }4 2.4 14 'o 1m 44 ·a.o 22 i3 JUlJ l f 84 I,., 24 ,, RB 10, 14.2 25 100 lnly 2 T 48 12 .4 20 80 '6 2·5 22 88 1ulr 3 T 16 1., 12 48 14 l., ll 44 July 4 . 'l 1 1.,0 1 4 RD 2; 11.0 . 2 8 JulJ 6 T ;3 2.1 20 eo BB 52 .e., 21 84 1ulJ 7 1' 9? 4.0 24 16 125 4., 2.S 100 1Ul7 8 lt l..l ll 44 ' 18 1.6 ll 44 lttl1 10 18 .1.4 52 ' '1 1.8 l'4 1&

Total 'f ,,3 2.6 1)9 61.a··· RB 421 2.9 143 6J.

~ - Thatoh•r wheat • RB • Red Bobe Wboat

.. -

, I Table ~1 .. co. ison ot outalde stem diameter-s and 1nteatat1on bJ CeR14apa c1notua at NobletoN 1n 19.)'

Above tirat 1Wle 26 :!hatcher 25 2.6 o., l.O uode Be4 BoW- 2' -a-..t 0-.-9 -2-4­ Above second lune 26 Thatcher 50 2"'0 0.6 node Red Bobe so 2.) o.6 -­ Abov• oroe lune 29 Tbatoher 25 2.2. ' . 0 .. 2 41 Red Bobe 25 2. 5 0 . } '8 Bel.ow th!.rd lu.ly 8 Tha~cher 2.S 2. 2 12 n04e ' Red Boba 25 2. 4 - 18

~ \.).1 ...

,· .44 Thatcher stems . For this reas n stem diameter may be a

factor affecting suitab~lity o a host for oviposition.

Oviposition site: Oviposition sites in the two varie­ ties were compared on two date • ·'l'he stems exam1n.e4 o.n the first date were exposed to sawflies from June 20 to June ;o. those examined on the second date were exposed. from July 8 to 4uly 10. 'fwent - rive stems ot each variety were examined on eaoh date. R sults are reported in Table 12 .

Table 12. NW!U> er ot sawfly ot two variet

Date Variet

June ;o Red Bobs 0 40 l 69 Thatcher 0 23 l 39 J'uly 10 Red Bobs 0 0 6 1 'l'batoher 0 4 12 2 1' The pattern of sel.ec on of oviposition site was similar in both varieties. N·o laid in the t1rst internode and only a few in the fourth. The third inter­ node was tavcnured tor ov1pos1ti n on both dates . For th• final observation.none s were laid in the seeoli4 internode of Red Bobs, and only tour 1n the second inter­ node or Thatcher stems• . 45 Factora influencis& ho$t sel ct1on; Red Bobs was more suit­ able for sa~ly oviposition than Thatcher during most or the sawtly flight. These varieties differed in stam diameter and internode length. It is possible that either one 01' both of these factors influence the female sawfly in her selection of a host stem for oviposition. It does not seem likely that chemical attraction is responsible for the observed differences. Sawflies will oviposit in a wide range ot hosts trom grasses t~ flax, and under laboratory conditions they have attempted to oviposit in wooden sticks and glass rods. Diameter ot the host stem appears to be important. During the first part ·of the flight, more mature stems and those of larger diameter are preferred for oviposition. At the end of the tlight, preference is shown for less mature and smaller diameter stems. This will be discussed further under the next section (Sex Ratio) . Toward the end ot the sawfly flight in 1953, females wer• observed attempting to oviposit in fairlJ mature Red Bobs stems. The diameter ot tb.e Be stems appeared to be too large for the females to obtain sufti· c1ent purchase to insert the ovipositor. Resistance to penetration by the ovipositor in these stems further increased the difficulties ot the females . Variations in size of females complicate the host diameter-oviposition relationship. Because ot this it 46 may be difficult to determine optimum di am~ters of stems f or oviposition.

Sex Ratio

Farstad (16. pp . 206- 207) reported that only females of Ce2hus oinctue were present in the Nobleford region, and that these individuals were capable of pro­ ducing f emales uniparentally. In laboratory experiments the occasional uniparental female has been reported (39, p, 57) . Ma ckay (38) has shown that mal es are haploid and females diploid . Flanders (23 , p ,l35) reported that a basic method of sex control in Hymenoptera was utilization of sperms stored in gravid female to change the sex of undeposited ripe eggs from al (haploid) to female (diploid). Farstad !! !!· (21, p. 27) reported the etfeetsot four varieties of wn eat on sex ratio of th wheat at saw­ fly at tour stations tor five years:-

Varietl Sex ratio ran6e (~/9 ) Ap ex 0.90 - 0.9? H4191 1 . 60 - 2 . 61 Red Bobs 0.39 - 0.5.5 Golden Ball 0 . 09 - 0 . 27

At Scott, Saskatehewan, the saWflies from Red :• Bobs and Golden Bal~ were consi~tently pr•edom1nantl7 tamale, and those t rom H4191. male. The sex ratios from Apex varied from 0,60 to 1.10. ... 47 McGinnis (39 , p. 56) reported that infesta­ bility of Red Bobs was influenced by the age of the plant. J'aoobson and Farstad (}4, pp . 90- 92) reported the effect of date of seeding or Apex Wheat on sex ratio. Although the population from the two earliest dates ot seeding was predominantly female, adults emerging tram plants seeded later were mostly male. The s.hift ot sex ·. ratio from fe la to male was correlated With date of seed• ing and was probably a result of the time of 1nfeatabil1ty of the host. The females that oviposited in later- seeded plants ere probably ~ated because the males had disap­ peared, or it mated, had exhausted the eperm. rece1•ed during an earlier mating. Attempts have been made to obtain a positive . correlation bet~een stub diameter and sex ot emerging saw­ flies. Wall (61, pp. 273- 274) reported results from measuring the stub diamete.rs of six varieties of wheat from three stations. She stated that diameter ot stub varied with the variety but not with the station. Tbe average stub diameter from which females emerged was 2. 6 millimeters as compared to 2 . 4 millimeters tor males. Eckroth and toNeal (1.5, pp . 400- 404) reported that sex ratio was not correlated with stub diameter within variety. 48 Effect qt Date ot Seeding

In 195~ an experiment was conducted to determine the effect ot time of infestation in relation to the saw­ fly flight period on sex ratio of surviving progeny . Fe• male sawflies select .stems in the early boot stage for ovi­ position in preference to ate s that are either more or less mature. Consequently , ttme of infestation can be controlled by modifying host development with date ot seeding, Two varieties of wheat , Red Bobs and Thatcher, were seeded next to a natural sawfly infestation at Noble­ ford , Alberta. Red Bobs was chosen because it has con­ sistently produced mostly females, and Thatcher because it has favoured males. The two varieties ere seeded in tour randomized blocks, each consisting of four plots ot ed Bobs and tour plots of Thatcher. Two guard rows were planted on the ends of each block. Plots were single ten­ foot rows . One block. was seeded on each ot the following dates: May 7, May 14, May 21 , and May 28 . When the wheat was ripe, stubs from each plot were collected and stored separately in moist soil at 10° c. In January they were placed at 2·5° u. and the .numbers of stubs, and the number of emerging adults of each sex were recorded. Outside dianeters of stuba trom which adults had emerged were measured at the upper end with a micrometer caliper. 49

Adults did not ~er g e from stubs of two Red Bobs plots and one Thatcher plot. The per cent males for these plots were calculated by the missing plot technique (}o , p. 262) . Complete results are shown in Table 1}. Percentages of males ware oonverted by the "angular transformation" (60 , p. 449) and analyzed by t h e analysis of variance methods (7 , pp . l8- 2j) . Results are shown in 'rable 14. Significant differences at the one per cent level were obtained between varieties and between dates of seeding . A significant difference was shown in the inter~ action of varieties by dates, Sex ratio was influenced by both variety and date of seeding , but the influence of the two varieties was not unifor.m (Fig . 21) . The percentage of males was higher for Thatcher than for Red Bobs at eaoh . date of seeding. . "Least significant differences" at the one per cent level for percentage of males were calculated tor each variety (Table 15) . Within each variety the difference in percentage of males was significant at the one per cent level among all four dates ot seeding . Date of seeding exerted a highly significant effect on the sex ratios of the surviving populations, The percentage of males increased significantly with the late­ ness of seeding and consequent lateness ot infestation. In Table 13

Percentage of male sawflies from two wheat varieties seeded on four dates

R e d B o b s T h a t c h e r

Date Total No . adults Percent. Mean stub Date Total No. adults Percent . Mean stub seeded stubs emerged males diam. (mm.) seeded stubs emereed males diam. (rum.) ·--·------­ May 7 1B8 162 39 2.74 May 7 183 169 46 2. 28 139 120 33 2.87 214 0 4~ 2,41 132 107 29 2.85 257 217 45 2. 35 140 ll.L_____J.§______E_~R 240 _?QL__ _ _5E_------b3Q.. 599 504 35 2.79 894 588 47 2.34

May 14 148 123 46 2. 99 May 14 230 196 65 2. 50 125 112 2. 94 205 167 65 2.44 158 0 !~ 3.02 238 200 70 2. 37 11~ 20 4l 2,28 222 164 7.2 --- 2,4l 546 325 44 2.98 900 727 68 2.43

May 21 164 123 61 2.90 May 21 222 191 84 2.44 160 130 61 2.94 240 204 84 2.40 142 123 2. 98 237 202 80 2. 52 162 0 ~~ 2.9Z 221 202 82 2,2z 628 376 62 2.94 970 804 83 2.41

May 28 103 86 77 2.75 May 28 15~ 129 92 2.36 120 105 76 2. 72 16 144 93 2. 25 112 96 75 2.88 177 149 91 2.34 112 105: 66 2.§§_ 112 28 21 2,2z 452 392 73 2.75 610 520 92 2.31

*calculated by the missing plot formula x • ~~ + f~ - T (q - 1) .ble 14..- Analys-is at variance between datea, var1eti·ea• and replica~ea tor percentag-e or mal

Source DF s us .,. u .

Bet. Reps. J l~JO l.:JO 0 ...40 ,.12 Bet. Val" . 1 1;198.0,) 1,.198.0.) 365.26JU( ,5 .12 ~0. , , .

Bet. Datea .5tl7J~.S5 1,0;7-.8) 156-.2.5:** ' ,3 .86 ' RxY '} 18.01 6. 00 1.8) ,.86 '·'' x» 9 4?•42 5·27 1.61 }.18 ' VxD 60 .. ~4 20.}1 b.l9* }. 84 RzVxD 9' 29.jS }..28 '·'' tal. Jl. 4;.S3l.42

\.n...... ­ t • of ' 52

PER CENT MALES 100

90

80

70

60

50

40

30

20

10

MAY 7 MAY I 4 MAY 21 MAY28 DATE SEEDED

Fig. 21. Mean percentages of males of c. cinctus from two wheat varieties seeded on four-dat es. Table 1.5

hnalys1s of variance of oercentage of ~ales between treatments within varieties

R e d B o b s T h a t c h e r

;) ource DF ss MS F Fll ::,ource DF ss MS F FH bet. reps. 3 15.64 5.21 0. 94 6.99 Bet. reps. 3 6.27 2.09 0.70 6 . 99 bet. dates 3 1,258.42 419.47 75.44U Bet. dates 3 1,976.07 658.69 220.3<>" Error 9 50.09 5. 56 Error 9 26.89 2.99

Total 15 1,324.15 Total 15 2,009.23

Mean percentage Mean percentage Date males (converted) L.S.D.:U: Date males (converted) L.S.D.:U

May 7 36.09 5'.40 May 7 43.57 3.97 May 14 41.84 May 14 55.58 L4ay 21 51.80 May 21 65.)0 May 28 59.09 May 28 73.33 ,...

'"' .._

.54 both Red Bobs and Thatcher, females predominated in the plots infented first and males in those infested last.

D.ate of seeding and stub diameter: The ,covariance between per cent males and stub diameters of ~erged stubs was calculated separately for both wheat varieties (Table 16) . Within both varieties, mean stub diameters were not correlated with per cent males. Stub diameters were significantly affected by date of seeding . Diameters of stubs from plants seeded on May 7 and May 28 were approximately equal, and were less than those from plants seeded on May 14, and May 21 . Th mean stub diameters ot Red Bobs varied from 2. 72 mm . to 3. 02 mm ., and of Thatcher from 2. 25 mm . to 2. 52 •

Time of infestation and sex ratio: The ~eaults obtained ' . are a measure of "mass interactions": Becau·se most indi- · viduals laid in the stems were destroyed by cannibalisni and parasiti~ , only a small proportion of the original popula­ tion was measured for sex ratio. It is probable that the first laid are most likely to survive by destroying eggs and smaller larvae. Location ot eggs may exert an influence on hatching. These• and other factors influence the sur­ viv1ng popu1ation. Differences in the sex ratios of adults from Red Bobs and from Thatcher appear to be the result of ed Bobs being infested earlier than Thatcher. From the sex ratio Table 16 hnalysis of var:ance and covariance of mean stub diameter and ue rcentage of male sawflies

R e d B o b s T h a t c h o r

R e p 1 i c a t e R e p 1 i c a t e 1 2 3 4 1 2 3 4

Treatment X y X y X y X y Treatment X y X y X y X y

May 7 2.74 38 . 65 2 . 87 35 . 06 2. 85 32 .58 2. 72 38 .06 May 7 2.28 42,48 2 .41 43 .45 2. 35 41.96 2. 30 45.86 May 14 2. 99 42 .71 2.94 42,71 3. 02 42.13 2. 95 39 . 82 May 14 2.50 53 . 61 2.44 53 . 91 ? . 37 56 . 48 2.41 58 . 05 May 21 2. 90 51.35 2. 94 51.3 5 2. 98 53 . 73 2. 97 50 .77 May 21 2.44 66 . 27 2.40 66 .27 2 . 52 63 . 58 2 . 27 64.60 May 28 2.75 61. 34 2 . 72 60 .67 2 . 88 60 . 00 2. 66 54.33 May 28 2. 36 73.78 2 . 25 74 . 77 2. 34 72 . 84 2 . 27 70 . 34 x • sLub diame ter y : percentage of male s converted by angular transformation

Source DF SS x ::;sy ::;sxy Source DF SSx SSy SS xy l:!et. reps. 3 0 . 03 15.64 0.11 l:!et . reps. 3 0.02 2.67 - 0.17 oet . treats. 3 0.15 1,258 . 42 - 3 . 07 Be t. treats. 3 0 . 05 1,945 . 52 -1.35 ~rror 2 0. 02 20 ,02 -0,06 Error 2 0.04 32.22 -0 .18 Total 15 0 . 20 1 , 324.15 - 3 . 02 Total 15 O.ll 1,984.14 -1.70

Source )riSy Fx Fy Source MSx MSy MSxy r'x Fy F* FaA:

Bet. re ps. 0 . 01 5. 21 0 . 04 6.99 Be t. reps . 0.007 0 . 89 -0 .06 1.75 0.22 3. 86 6.99 Bet. treats. 0.05 419.47 -1.02 Bet. treats. 0 .017 648 .51 -0 .45 4.25* 162 . 53aa: Error 0 . 002 5. 56 -0 . 02 Error 0 . 004 3. 99 - 0 .02

SSXY r • l/~(::;=· ::;=· x~)~(S~S=y7) • -0.059 (not s ~ gnifican t ) r = -0. 151 (not significant) \.TI \.TI ...... ,

results the peak of infestation apparently occurred about one week later in Thatcher than in Red Bobs for eaoh date of seeding.

Stub diameter and se~ ratic:u: Although mean stub diameter and sex ratio w1 thin the two varieties were not correlated, the ef'feet of stem diameter may still be an important :factor.. Tbe maximum differenc-e 1n stub d.iam.eter within

treatment for Thatcher was 0 ~ 15 mm . and for Red Bobs 0 . 22 mm. However , the differences between the two varieties were much larger as shown in Table 17.

Table 11. A comparison ot mean stub diameters of two. wheat varieties seeded on four dates

pate ot seed1nf Maf·1 Mai 14 ::;MaY 2 Difference in m.ean stu.b dia­ meter between ' varieties (mm.) 0.4.5 o.;; 0. 44

The differences in mean stub diameter& were much

greater between than wi~hin the two varieties. In every

case Red Bobs stubs were larg~r , and a lower percentage o~ malea emerged from these stubs• • It ·is interesting to compare stem diameters of these varieties in June (Table ll) with the stub diameters. Because the plants measured in J"une were seeded on J.lay 7 in • 57 the same nursery as the sex ratio plots they are comparable to stubs from plants seeded on the first date, i . e ., Kay 7. The measurements are compared in Table 18 .

Table 18. Comparison of stub and stem diameters of two wheat varieties

I F :~an fiam,£ers (mm.) : Date ,Measursent Illite ate er Red Bobs• June 26 Aboye first node 2 . 6 June 26 Abofe second node 2. 0 June 29 Abo'lie crown 2 . 2 Sept. Stub 2. 3

1bese data show that stub measurements were indicative of stem diameter measurements at time of infes­ tation. Red Bobs stems were larger than Thatcher stems at infestation time and at maturity.

EXPlanation. I of variation in sex ratio: The sex ratio was completely reversed in both varieties by changing the time of infestation. The effects of variety (at least of these two) on sex ratio are not absolute but dependent on time of infestation. Previous data and observations showed that stems of larger diameter tended to be infested first . This then would explain the differeno·es in sa:x ratios trom the two varieties. Red Bobs stems are lareer than Thatcher stams, are infested before Thatcher stems, and favour females , while Thatcher favours males•.. .58 The data support the theory that the sex ratio ot the surviving progeny are dependent on the sex ratio ot the adult population. At the beginning of the flight, males predominate and at the end of the flight, f~ales. • Consequently chances tor fertilization decrease toward ·the end of the flight. Because unfertilized eggs produce males, • and fertilized eggs produce tamales,, chances tor females are greatest early in the flight, and males at the end. It seems probable that the sex ot an individual is determined before it leaves its parent. Therefore a variety may influence the sex ratio only by its time of peak infestability in relation to the .tlight and by ita effect on differential larval survival. It is possible that a variety by ·some chemical reaction could influence the sex ot the egg, but no data are available to support this hy pothesis.

Population Density

The fecundity of females of Cephus cinetus varies d~reotly with size of individual and host variety (22). Under normal conditions all or most ot t he 40 to .50 eggs contained in each female a r e laid. Because a female will usually lay only one egg in eaob s t em, 40 to .50 stems can be infested by a single individual. Where the normal sex ratio ot one male to one female occurs. the potential increase is 20- to 25-told in one year. This inorease 59 seldom, if ever , occurs because of environmental resistance from weather, parasitism, host resistance, and population density . Ot these, population density is probably the most important single factor.

Factors Influencing Multiple O~iposition

Sawflies oviposit readily in previously infested st s , and where high levels of adult population occur, over 30 eggs in a stem are commonly found. No matter how many sawfly eggs are laid in a stem, almost without exception only one larva will survivt in that st • In a previous section it was reported that Red Bobs received 7. 4 eggs per staa and Rescue ; .6 eggs per stem. Ninety

I per cent of the stems ot both varieties were out by sawtly larvae, i . e ., a survival of 0 . 9 larvae per staa. The reduction of sawfly population in Red Bobs was 88 per cent and in Rescue 75 per cent. A host ~riety that is more attractive tor oviposition may cause a greater reduction in population of the sawfly than a less attractive variety.

Jacobson and Farstad (34 1 p . 9l) reported mean infestations and survival ·ot sawfly in Apex wh eat. Their data showed no correlation between number of eggs per stem and larval survival. In a resistant host, chances tor a stem t9 be cut by ~ cinctus are probably increased b7 increased oviposition 1n that stem. No evidence is avail­ able concerning this matter. bO The sawfly lays most of its eggs in stems in the margins of fields. Infestations decrease progressively from the source ot infestation, and rate of decrease 1a negatively correlated with population pressure. Graphio illustration ot marginal infestation is shown in Figure 1;. T.his habit is utilized tor trap crops that are seeded as controls between infestation source and main crop. In estern Canada, soil drifting and low pre­ cipitation are important agricultural problems. Crops are seeded in narrow strips at right angles to the prevailing wind . Each strip is seeded only every second year and is left fallow in alternate years to conserve moisture. Adults emerge from the stubble and move into adjacent newly . planted strips. Obviously more margins are available for infesta­ tion with strip farming than with large blocks ot neat. As more stems are available for oviposition, fewer eggs are

laid in each stem resulting in increased sa~1t'ly populations. Most areas for which strip fanning is recommended are also the areas of heavy sawfly infestation.

Effect ot Varytns Adult Densitie!! in Cas,ee

In 19.52, an experiment was conducted to determine • the effects ot varying sawtly population densities over caged wheat . The purpose of this experiment was to determine the effect of population density of sawtly adults 61 on oviposition and larval survival, and the optimum adult population tor adequate infestations in standard sawfly cages.­ Four levels ot density, 5, 15 , 25 , and 50 pairs of both sexes, were caged over 'l'hatcher v.rhea t in standard sa~ ly cages, eaoh covering l/10,000 ot an acre. These collapsible cages are constructed of wooden trames covered with "Lumite" plastic screening of 20 x 20 mesh . They are ; feet high and approximately 2 feet square. Sawtly stubs from Thatcher wheat were collected in the s prin and treated so that adults began to emer e during the latter part of tune. Emerged adults were stored at 10° c. in jars containing moist excelsior. Because insufficient numbers of both sexes emerged simultaneously, it was necessary to store some individuals up to tour days. Each plot as covered with a cag e and received one· level of population. Th~ experimental design consisted of three randomized blocks, eaoh containing four plots. The blocks were infested on three dates because of limited numbers of adults. Dates of introduction of adults were:­ Block I June 25 Block Il - June }0 Block III July } When the sawfly flight was ended , the cages were removed . The plots were ha~vested on September 16 1 and the results are recorded in Table 19-. · .. Table 19. Comparison ot in.restation and suJ"vival or prDgeny of Cephus c1nctue at tour population levels caged over Thatcher whea~

0

·eall 232 190 121 1 }. 2 .. 1 258 · 186 m 2.c. 12 .,,' ·· >· .5 16• II 212 164 . 1}8 2 77 86 ) . 6 b.6

.PI I 242 84 ·40 8 l5 '2 t •• 1·2 . , . , I ••

ean o-t I & II 23.5· l.1J 12:5 1] 74 1' S• .5 1. 0 I l' I 211 166 '13 J.5 '11 6,S 7. 2 11. 1 II 227 1>3 ·84 1' ~9 73 6. 5 8. 9 III 226 112 72 9 ' I ~0 . 19 ,t, 1·2 j ea.n 22) 111 '' 1' 61 'll 6. ; ' · 5 I 262 46 1.6 .o 12 . 4 15. 8

Been 2J-S J9 1: 2 ' ·1 12. 0 f\)"" Because the number of stams per cage varied (Table 19), the percentage of infestations may be mis­ leading. An average of 190 stems were infested with 50 pairs of adults. In Blocks I and II with 25 pairs, a mean of 175 stems was infested. Results in Block III ~th 25 pairs appear to be influenced by factors other than popu­ lation density, and perhaps should be disregarded. Fifteen pairs infested a mean of 9. 2 st s per pair as compared with 12.0 for five pairs. Infestations increased with population level. Cag s containing 15 to 25 pairs received infestations of .50 to 77 per cent. Analysis of variance a conducted on the number of infested stsns per plot. B c use the plot with 2.5 pairs in Block III was obviously affect d by some \Ulexplain d tactor, the valu for this plot was calculated according to Goulden (31, p. 262) . Leaot significant differences at the one and five per cent levels were calculated. Results are shown in Table 20 . There were no significant differences bet een blocks, but the treatments varied significantly at the one per cent level. Highly significant differences in the number of stems infested were found between 50 and 1..5 pairs, and between 15 and five pairs. The numbers of st~s · infested by 2..5 and ;o pairs did not differ significantly. The percentage ot infested stems cut by larvae was similar for all four treatments , although multiple ble 20. Analysis ot variance ror n er o at intested per 1' l>Ulation level

lean no ~ Popul. t1on Block inrsst d level ~ ~ ~! stems ~ L 50 198 182 190 190.00 ~8 . 1; 4.5 . 08 2.5 186 164 168 l'/2.£1 15 166 133 112 1;?.00 5 19 )0 71. 60. 0

Source DF ' ss F

Bet. blocks 2 1,930.6? 965.)4 4 .•J4 .5.14 B t . tr t • 29 ,92 . 2j 9 .• 976 . 08 44. 8 1.78 :r~ rror l 1.336. 0 222 . b7 ot 1 · 11. ,,,194-.92 6,5 ovipositi on probably i ncreased With i ncreased adult popu­ l ations. T.h mean number of s t ubs produced wa s a s expected . Ca3en with only f ive pairs of adult sawfly a veraged 9.7 stubs per pai r, wher eas those wi t h .50 pairs ·

gave only 2.9 st ub~ per pa i~ •

.· Effects ~t handline adults on infestation: Although a4ulta' were treated oarerully, results show that handling had som.• detrilnental effects. Adults will chew each other whtn con- . fined, and some damage ot this type probably occurred. All cages could not ba infested on the same date, and varying periods of storage were required. When stubs are plant·ed in plots., and adults are not handled, better infestations are obtained. Unfortunately t he exact number of ei ther sex cannot be controlled; and emergence occurs over a period of time. ENVIRONMENTAL ACTORS AFF OTIUG THE .ooG D I TORE LARVA

Effects ot eather ..

Criddle (10 , p . 2l) reported that pr~ture ripening ot t he host plant as a result of drouth ill kill or stunt larvae of caphua o1nctus. tow, moist areas ot a field are less heavily out by sawfly than hi3her, dry • areas of the s e wheat field (12, p .20). Seamans (59, p. 435) reported that when plant growth was rank, sawfly larvae were apparently drowned 1n. excess sap in the lumen of the host stem. This is only a rare event as free wat r in a stem has been observed only occasionally by other workers. However , a wet July usually r esults in reduced infestations the following -year . Excessive drouth or moisture are both detrimental to the l arvae. Platt and Farstad (49, p . 242) reported high mortality or sa.wtly l arvae during seasons ot high rainfall when the plants were rank and succulent. Alt hough c. oinctus is present throughout - . Western Canada and United States ~ it is of economic impor• tanoe only in the short rasa region where annual precipi­ tation is between 10 and 20 inches. It causes little damage in wheat grown on irrigated land in this region•. Waather conditione affect larval survival in resistant hosts. Platt (46, p.l47) considered low light intensity during t he growing season to be the main factor 1n breakdown of Rescue- type solidness of stem an thus in the consequent breakdown of sawfly res1 stance. Rescue

~heat is not recommend d in the Regina plains area because of its tendency to lose sawfly resistance there. Farstad (49, p , 242) believed this breakdmm of resistance to be the result of lo ered light intensity in the area . Infested stems of Rescue and Golden Ball wer$ readily out by sawfly i.n cased plots in 1951 at Lethbridge. Adjacent unca d plots of these varieties retained their normal sawfly resistance. This could have resulted tram reduced light and , or; incr$ased moisture under the cages. In 1953 , 90 per cent of Rescue stems were out by

sawtly larvae at Nobleford , Alberta. . During June, 19 5~ , there were only 260 hours ot sunshine compared to a nor.mal of 277 hours tor this period. Rain fell on 20 days during

June, the total praoipitation was b.l} inches as oom~ared to a normal of 2 , 84 inches (;). These results will be

discussed further in the nex~ section. Larvae in hollow- ate ed varieties are favoured by mod rate precipitation during the growing season. In solid- ate ed hosts, they are favoured by cloudy wet conditions during the arly part of the growing season. Excesses of moisture or dxouth are both detrimental to larval s.urvival. 68 Ess and Larval Survival in Rescue Wheat

Before the development of Rescue wheat , the common bread wheat varieties (Triticum aestivum L. ) grown on the Great Plains area ot North America were hollow­ .stemmed and susceptible to sawfly damage . Kemp (35, p . ;6) reported that sa.wtly survival might be reduced in solid• stemmed wheats. Be was fortunate in obtaining differential survival because even in his susceptible checks larval survival was low . Kemp also dis­ cussed a group or solid- stemmed wheat selections obtained from New Zealand. These comprised ;8 linea, ot which two originated in New Zealand, and ;6 in Portugal, Spain, and

Morocco. Among these introductions was s - 615 (35 1 p . ;;) . Farstad {17, p . 68) tound that amount and con­ sistency of pith in the host stem influenced larval sur­ vival. He discussed the sawrly resistance of s - 615 and other lines. The inheritance of solidness in bread wheat stems has been inv estigated extensively (47 , pp . 216- 224) and 48 , p~ . 214- 220) . Larson (36 , p . l43) considered chromo­ somes of A genome to have little significance in solidness, moat of those of B genome seemed to be necessary for solid­ ness, and chromosomes ot C genome probably inhibitory. Platt, Farstad, and Callenbach (50, p.l54) reported that Rescue , a seleoti on from a cross between Apex and s-615 made in 1942 . was grown on a field scale in 1946 . The tive.year average sawfly cut was 9. 3 per cent for Rescue, 61 .9 per cent for Thatcher. Since that time a solid- stemmed selection from the s-615 x Thatcher oross was licensed under the varietal name of Chinook. This latter variety, although not quite as resistant as Rescue , qualifies for a higher grade and possesses drouth resistance. Sawfly infested solid.-stemme·d Rescue is c-om­ pared with. hollow-stemmed varieties in Figures 22 , 23, and 24. The exact nature of resistance to wheat stem sawfly is still a controversial issue. The following study was conducted to obtain preliminary information on this subject.

Rescue and Red Bobs wheat were seeded in alter­ nate rows adjacent to a natural sawfly infestation in 1953 . Periodic examinations of th se varieties were made to determine the fate of the sawflies in the stems.

Esg survival in solid and hollow partq of Rescue s t am~ : Resulto from observations on the effect ot Rescue wheat on hatching ot sa~ly eggs are reported in Table 21 . Those data show that only 3. 2 par eent of the eggs laid in Rescue failed to hatch by 1uly 21. At least one egg had hatched in each ot the 75 stems examined oa

.. ?0

Fig. 22. Comparison of wheat stem sawfly cutting in susceptible and resist­ ant hosts, both equally infested. (Kharkov winter wheat (left), Rescue resistant spring wheat (right).) 71

Fig. 23. Dead first instar Fig. 24. Longitudinal larva of C. cinctus in section of a mature pith of sOlid-stemmed wheat stem tunnelled Rescue stem. (Note the by larva of c. cinctus. small area tunnelled and The nodal plate is the discolouration of completely tunnelled, the adjacent pith.) pith cavity is almost filled with frass. 72 Table 21 . Survival of sawfly eggs laid in Rescue wheat at Nobletord in 195'

, &ite lio .6f stem~' ' No .oi' examined infested essa;

1u.1r 1,. ljO 64 .0 luly 21 248 96.8

* SawflY flight completed on that date. that date. The July 21 observations were ot eggs laid in the pith and of those laid in. the hollow seot1on of the stam (Table 22) .

Table 22 . Comparison of hatching or sa.wtly eggs laid in solid and hollow parts of Resoue stems by July 21

; -, _- -- _- r. -'~ : Ov.1pOSl.ti Oll

site ! :

Pith 12, 94.4 Hollow 122 99.2

Table 22 shows that the percentage hatoh of eggs laid in pith may be slightly lowered. However . thtt difference is so slight and both percentages are so hieh that it may be concluded that the pith had little effect. 73

Larval aurvi~al in solid and hollow parts of Rescue stems:

Stems or Rescue were e~1ned periodically to determine the fate ot larvae in solid and hollow regions. Until

J'uly ·23 the ~ourse or the larvae could be followed through the pith. fter that date , howev r , surviving larvae destroyed uch of the evidence. A comparison of survival in solid and hollow parts of Rescue stems is reported in Table 23. Table 23 shows that larval mortality in pith reached 72 per cent (ot individuals in pith) on July 23 .

Some redu~tion in survival in the hollow areas resulted from cannibalism. All larvae alive on July 21 were feeding in the vascular tissue region. Larvae tunnelling through the internode avoided the central pith and created a spiral tunnel between the vascular bundles and pith. As a matter ot interest the direction larvae moved when first hatched was observed in 21 stems of Rescue . even larvae started upwards and 23 down . Larvae tended to move away from the node nearest the oviposition aite. The d1 stance larvae had tunnelled is recorded in Table 24 . Table 24 shows that most of the dead larvae had failed to move more than 2 mm . from the oviposition site in the pith. These were all t1rst instar larvae. fable 2). Ce:m:parison ot larval survival. 1n &;lll4 and hollow portlona ot aescu.,e stems ate Nobletord in 1,-5}

11~ v 1"' .1 ~a a I ·t i c) u e 1 t • .. · I ·sa!ii a!eJii' · ,} I ' !I . O,­ I iO ... lin

· S~eras !{Wa not p ::t;4ij~' ",·: !~a· aoi · 'fJ ~t;~• "' . If~t ,,. . ~amin~ , ha.t~~4..._ , .Itf:ie u ~ , lat~hce4 .Jllv,. . laa,l .

July '14 .so 2-' J1 ll 8 Jl 4 lQlF ).;6 . !S 1 41 JA. 0 20 2 J\U.;v 21 JQ ,. 41 j' 1 81 14 luli 2:S ~0 0 -}2 .82 0 21 9 - ~~-~--~ ~ ..____.___ ~ ~ ----·------­--- ~~~ - - --­ --­---- -·· ­ ' ' ..t. .. ..______- -· .. -

I

-:) .f;o.

;.

.,p

;.. 75 Table 24. Mortality and tunnelling in .50 Re$OUe at~s, luly 23 , 19.53.

· No or arvae from eo n P1th AX£~•: : l)~ad .

1-2 9 68 1 Q 3·10 2 9 0 11-.50 1.5 ; ; '2 51-100 0 10 0 101-~00 1' 0 0 ' * Numcers probably redu.ced by cannibalism.

Larval survival in Re~gu§ and Red,Bobs: Further obser• - ( ­ vations were made on August 4, when .50 Resoue stems were examined for survival and tunnelling of internodes (Table 2.5).

Table 25. Tunnelling of ;o Rescue stems by August 4

1 t I ; No~ ol = No._ oi' intel1'!1odes living tunnelled .larw..e 0 10 l 42 2 13. ; ~ 4 0 .5 -0 'I'otaJ.. .71

,• 76 Tahle 25 shove that by August 4 , most living larvae had tunnelled only one internode in Rescue because of resistance to larval movement offered by the pith. The largest larvae ere 1n the bottom internode. In comparison , the hollow- stemmed variety, Red Bobst was completely tunnelled by August 3. Fifty larvae from stems of Rescue and 50 larvae trom stems of Red Bobs were measured . The mean length for ·those from Red Bobs was 7. 2t2 . ; mm . compared to 5. 6! 2. 2 mm . for larvae from Resoue . 'fhere was a trend tor larvae from Rescue to be smaller than those from Red Bobs . This may be the result of the lower nutritive value of Rescue ,

or because energy was ~tilized for tunnelling the pith ot Rescue at the expense or larval growth •. On August 12 , 100 Red Bobs stems contained 91 living lflrvae while 100 Rescue stems contained 116 living larvae, Only 34 per cent ot the Rescue stems were com­ pletely tunnelled. Sixty living larvae were in the first

internode, the remaining 46 larvae had fail~d to tunnel below the second internode.

Survival in Rescue: A summary ot survival in Rescue during the grOWing season ot 1953 is reported in Table 26 . Table 26 sho s that after the tirst major drop in surVival (from ; . 6/stem to l . l/stam) the level remained constant until cutting in September . The reduction ot ble 26 . , survival ot aawfly larvae in Rescue stems at .N obleford in 195~

1111¥ a so 41 lb'l - 3. 6 luly 14 .so 4' 24 126 ,.]. lulr l.6 a.; 25 - 34 .l. 3\ll3 21 15 7} ·- 160 2. 1 Jul.J 2} 50 47 .... 52 l.. l Au.st. 4 so 4'1 - .so 1.. 1 Au.g • . 12 100 100 - 116 .1 . 2 -Sep. ~ 100 100 - 90 o.­ .. Larvae had oomplet-ed cutting stems on this date.

~ -.) 78 living individuals was greater in Red Bobs than in Rescue . In Red Bobs on July 9 there were 7.4 eggs per stem while on August 12 there were only 0.9 living larvae per staa. Parasitism accounted for six per cent ot the mortality, while cannibalism accounted for most of it.

The nature or Re scue resistanc .: Larval mortality from eggs laid in pith reached 72 per cent by July 2}. There­ fore Re scue was still resistant although examination of cutting data alone would lead to the conclusion that resistance broke down completely. Circumstantial evidence snows that larvae must feed in the vascular ~ssues in order to survive. Perhaps pith does not provide most larvae with sufficient energy to tunnel the tissues.

These results were obtained by comparison within the same stems. It does not seem probable that one section would be very different qualitatively in chemical eonstitu• ents from the adjacent section in the same internode in the same stem. The only observable difference was the extra pith, and this difference was positively related to increased larval mortality. 79 Strains of Cephus cinctus

Reports of strains ot insects capable of over­ coming host plant resistanc e are not extensive. Painter (44, p . }25) reported that strains of Hessian fl¥ (Phytophaga dest.ruotor (Say)) from different areas, ditf'er in their ability to infest different varieties of wheat . Harrington (31 , p . 22) reported that five biological strains ot pea aphid, Macrosiphum P!!!!. (Italt . ) present in the U. s . A. , differ in their size and fecundity . Beall (3, p . l;) reported that the multivoltine strain of PYrausta nubilal is Hubn . attacked hosts other than corn. The effect of geographic isolation on the development of races has been discussed by various authors (2 , pp. 608- 610) and 14, pp. l77- 181) . Farstad (16 , pp . 206- 207) reported that a thely­ tokus parthenogenetic strain of c. oinctus occurred in the Nobleford area ot Alberta. Callenbaoh (4 , p. 999) was unable to establish r esistant strains of sawflies 1n Rescue wheat ~ Platt, Farstad and Callenbaoh (50 , P •l55) reported that the five- year average out· by ~ oinctus ot Rescue at Regina was }6 . } per cent as compared to 1.8 per cent at Lethbridge. They postulated that these resul ts may have been caused by environmental effects on 'the host, vari­ ations in plant nutrition or inherent differences in the sawtl y popul ations. So • I n 1951, 1952, and 1953 the writer continued investigations of the factor or factors which cause the breakdown of resistance at Regina . It was first necessary to determine if a strain of sawflies existed in the Regina area that was more able to overcome Rescue resistance than sawflies at Noble:f'ord . Regina, Saskatchewan, is approxinstely 400 miles east of Lethbridge. Nobletord is 1.5 miles ·northwest of Lethbridge, and for convenience, will be regarded as the Lethbridge area. Both Regina and Lethbridge are in the dark brown soil zone in which moisture is the normal limiting factor tor plant growth. The low nitrogen con... tent of the soil becomes the limiting factor with exces­ sive moisture. The two areas are separated by the light brown soil area, and by a ridge of hills at the Alberta­ saskatchewan border which is mostly rang e land. The Regina area is a flat plain ot heavy clay soil, while the Leth­ bridge area varies from silty loam to clay loam .

1251 Experiment

Three varieties of !.:. aestivum (Thatcher, Red Bobs , and Rescue) and one ot T. durum. (Golden Ball) were each seeded in solid blocks. Each of the four blocks was divided into four plots; two infested with Regina sawflies and two with Lethbridge sa~l1es . Eaoh plot v;as two teet square, and was caged during the sawfly flight . The 31 sawfly stubs v-ere collected froFl Thatcher wheat in the two areas in the spring of 1951 . One hundred stubs were dug into each plot. The plot plan is shO\m in Figure 2.5. The experiment was conducted at both Lethbridge and Regina . Unfortunately the experiment at Regina ylelded no results . Because of the heavy snow falls , the plots could not be harvested at Regina in the fall. In the spring, the material that remained was so saturated with water that identification of stubs and infested stems was impossible. Therefore results for 19.51 were from the Lath• bridge station only.

Infestation and cuttins of infested stems: Results are reported in Table 27 . Although the percentage infestations of Thatcher were lower than for Red Bobs , the percentage of infestAd stems cut by larvae in the two varieties Mas very close for the two sawfly stocks. Golden Ball was the only variety in which con­ sistent differences occurred between treatments . Progeny of Lethbridge sawfl:i.es cut 20 per cent and 32 per cent of

the infested stems, ~hile 16 per cent and 14 per cent of

the infested stems were cut by progeny of Regina sawflies. 82 1951

LETH REGINA LETH LETH

REGINA LETH REGINA REG IN A

LETH LETH REGINA LETH

REGINA. REGINA LETH REGINA

RED BOBS GOLDEN BALL RESCUE THATCHER

1952

REGINA LETH REGINA LETH

LETH REGINA REGINA LE TH RES CUE

REGINA LETH LETH REGINA

LETH REGINA LETH REGINA GOLDEN BALL

) 1953

REGINA REGINA LETH LETH

REG INA LETH REGINA LETH

LETH REGINA REGINA LETH

REG INA LETH LETH REGINA

GOLDEN BALL

Fig. 2.5. Plot plans for sawfly stra1n - _:._·i men t s for three years. '!'able 27. Cutting and 1nfestat1vn of four tiheat varieties at Lethbridge in 1951 by l'ror;eny ot Cefhus cinctu~ c-ollected tram Leth6r. d~e and ttesin

---~-- - --~----source·----~------~-~---~-~Perciritaao Percentage tl'beat ot· Plot 1-l o . No . ntema stems infested , vftr1e~ sa,rliee no. stems inrested 1ntosted stems eut Red Bobs L6th. 1 17} 150 87 83 J 1;7 122. 8 ean JI etdn 12_) 112 1.58 150 I Mean H 1! 1hate1ter Leth. 13 184 11, 61 81 15 206 1}1 ,. ,.ean R~na 14 19J 1~.. i 16 1,, l.4} ui i Reso-ue Leth. 9 169 128 - 211 l bO Regina 10 148 l}O ll 22, 212 .!! Mean 1! I Golda Ball Leth. 6 92 11 20 7 t2 108 Mean Regina lc21 ?0 i I (X) i 120 9> \.).1 lteatl H II • 84 . 19.52 Experi.l:1ent

Because differences in survival of the two saw­ fly stocks were not demonstrated in Thatcher and Red Bobs , they wer e not used in 1952 . Rescue and Golden Ball were seeded in solid blocks. Each block was divided into eight randomized plots, four of "ll'fhich were infested with Leth­ bridge sa¥~11es and tour.with Regina sawflies (Fig. 25) . One hundred Thatcher stubs collected from the two areas in the s pring of 1952 were dug into eaoh plot . Standard cages were placed over the plots during the sawfly flight . Each treatment was replicated four times . and the experiment wa s duplicated at Lethbridge and Regina .

£nfest~ stems cut by larvae: The results from the 1952 experiment are shown in Tables 28 and 29 . The percentages of infested stems eut were con­ verted by the angular transformation (60 , p. 449) and analyzed as unpaired samples (30 , p . 40} . Re sults are sho\~ in Table 30 • A significant difference between percentages of infested stems out was obtained only in Golden Ball at Lethbridge. At neither station was a difference in sur­ vival shown in Rescue. ·.

Table 26. Co:J.parison of inf est ation ann cut ting b7 prose:nJ ot aephua cinctua troa R~mina and Lethbridge in t wo va~ eti es ot wheat' at 'tetiibrldie in 1952

. .. Ya..... 40- V,f WU.ft& ...'Q'~ QVV..IIM'U • ...._..._.VU"W'II"¥ g_....,,...,w"" _,.,..,..v .yv.v~ _vw-W:,.._.., "", ""' . I Golden Ball Leth. l 10] 100 1 97 'lfJ J 84 0 93 74 90 1 11 '8sl. 1 18 ·-· ' ' e~~ H' Regina 2 9} 84 0 -90 4 81 68 0 ' 84 109 101 1 ,,z: i 1.0& ,, 2 91. &2 '' (;b .ean -90 - Rescue Leth.. 12 200 184 ' 92 ·, 14 1'1, 111 0 91 zs 228 211 2' ') 70 u 197 1,, 2 99 ?3 llEJan H lf Regina 10 118 168 0 ,, ­ lJ 181 16.5 0 91 I~ lj 14, 1.47 0 4J 16 20.5 164 0 c JO (X) lieu -90 n "'

----~ --- - -~-~- - ~-~ ------· --­ ------~ • Table 29. Comparison of in fes~ation and cutting by progeny of !eepbus cinctus trom Regina and Lethbri dge in two varl. etiea of wheat at· Regina in 19.52

I I ~~ I I Source No .a!ema Percent. Percent. ·"""'" eat ot Pl.ot No. No . stems para- stems infested var1•ty _ sawtl,1~s~ - - ~no • .. ~~$X!l8 infe s1t~d aj.t1zed infested atems out Golden Ball Leth. l 14 0 1 10& it :i lt l} 6 7} 49 0 67 2.5 ''I 117 ,. 1 80 11 ean 7f -lj R&g1na 2 0 -12 4 %i :i 0 11 ll 62 0 SJ 8.5 l~ 0 12 12 -u' ' Meu'"- - Resou.e Letb. 9 91 5} 0 58 ll 11 ,, 81 0 84 12 12 ].04 85 0 32 14 129 94 0 7} 1'2 Jlean -15 -11 Regina 10 123 11, Q 92 -22 l} 120 61 0 j6 j 15 101 0 41 11 16 91 tl 0 ll Mean 6'1 -lJ CD - - 0"

...... Table 30. Analysis of percentage of infested stems cut by two sawfly stocks

Host 6bs. varietz Station t - Golden Ball Lethbridge ;.o4* Regina 1.04 Rescue Lethbridge 1.72 Regina 0.21

• Significance at the five per cent level • 2.4.5

Comuarison of infestations at Lethbridse and Resina: Both varieties were out and infested more heavily at Lethbridge than at Regina . Weather records from the Regina Sub­ station were examined . The maximum temperature tor the period from June 10 to June }0 was ?6° F., and on that day 0.01 inches of precipitation and 24 m. p . h. of wind were recorded. During Jul.y l to July 20 , maximum temperatures exceeding 79° F. were recorded for only five days. Although these records can only be used as indirect evi­ dence , it is indicated that good conditions tor oviposition did not prevail very often during the no~al flight period. The flight in the cages was delayed . The super­ intendent of the Regina station reported sawflies tlying in the cages late in July•. In adjacent sawtly nursery plots the percentage infestation was very low although adjacent 88 strips of wheat had been heavily infested in 1951. The emergence from these strips was approximately 8; per cent. The unfavourable conditions for sawfly flight and oviposition at Regina in 1952 probably had a consider­ able effect on the results obtained there. These results are probably not very indicative of what would occur in a normal year.

Golden Ball alone was used as host variety. Sixteen plots were seeded in randomized blocks at each of two stations, Lethbridge and Regina. Sawfly stubs from Thatcher wheat were collected from Regina and Lethbridge in September, 1952, and stored at Lethbridge over the winter. One hundred stubs trom each sawfly stock were tested for per cent emergence, sex ratio, and time of emergence. As a result of these tests. 116 Regina stubs were buried in each of eight plots and 125 Lethbridge stubs in each ot the remaining eight plots at eaoh station (Fig . 25) . Each plot was covered with a standard sawfly cage during the sawfly flight . In September the stems were split and data recorded. Percentages of infested stems cut were calculated by the sum ot stubs and stems containing parasitized larvae divided by the number ot infested stems . The sum ot the parasitized, cut, and tunnelled but uncut stems was divided 89 by the number of infested stems to give percentage of stems tunnelled. The category of "scars" was established for those stams in which the larvae failed to move out of the cavity made by the adult female for the egg (Fig. 2.3). The percentage of infested stems out was con• verted by the "angular transformation" and analyzed as unpaired samples for each station.

QQmRarison of infestations at Lethbridse and Resina: Data for the two stations in 1953 are shown in Tables 31 and 32. These results and those of previous years show no consistent differences in infestation by the two sawfly stocks. There was no relation between percentage ot stems infested and percentage of infested stems eut.

Tunnelling : The percentage of tunnelling was quite different for the two stocks of sawflies.

Table .33. Tunnelling of Golden Ball stems by sawfly larvae

Sawfly Mean per cent Range Station sto~}{ twmellints (per cent) Lethbridge Regina 32 .7 15.8 - 49.4 Lethbridge 62 .1 46.7 - 84.2 Regina Regina ,58.4 ;6.4 .. 71.4 Lethbridge 80 .9 68.6 - 91.4 ...

These results sho that more Le~hbridge sawflies than Regina sawflies survived the first instar. .. 90

Table 31 . Oomparison or two stock& of Og~h!B Q1pctue in Golden Bnll ~eat at Lethtiriase In 19JJ

7 , , , Jerqef~~{$- ...... n ested Sawtlr Stems Infested stems etem• • s~oek iytgetod stema . pu~ , par~eiti,ed , twmelle , ltegine. 91 1}., o.. o 'I·? ,o o.o 29 . & 20 .8 4. 2 l! ,.,'·' o.o 15.Jl·J ,. 14.~ 2. 1 ,1.9 ?'1 10. 4? . 2 25.4 "4·. 8' 41 .) I• I p . I o.o i ''24 &&0s -I Mean ,4.) 1S.8 a.o }2.7 '

Leth . 80 ,8.6 84,2 99 )0.4 .5.1 ,,.a ' 100 26 ., 11' ·. '; 51 ·1 ,, 28.i }. 8 92 1.7. 2. 2 614 ·.,' 100 );., 8.6 65 .7 ,, 4~ ., 10., .,

•;JI ' J J I 1.1 ­ 22 2 sl I I 4 . J I 22 ·~ ,. ean 9,.8 ,o., 6. 0 ,2.1

... 91

R•gtna 15•8 ,., t~ l2•l. ,.o ,,'1••.. 1J•1 o.,,o 64•7 ~l lb•1 1;,4 6J~J 19 1,42 1•4 JO•O 71 22~1 1•6 7lt4 J8 lJ•' O~H) ,,~4 nun • u '1i, e st: ,!b-i.l ' I ' ''ij! ,•.. ,Ai& . 't!il w - 1.: .. J~t6 - Keaa. 51•4 1&~4 2;7 ,,~,

Letll; bO .,.., •~ ~B~ -~ .' 1'1 .,., 1,0 ..., 50 27•J a.o ,•., ,., '91•4 1~ 4'*1 10• 11 )6.-&'" ~ ' l.•a 'J!l 40~1 a,t. lo;a Wlll!l!iill!li . u . Ill iMI . -- ~~l!· i~ - ~' Iii i' li$1 ~ •t ~ u ,,.,!~41 I .... ,o., ,,~, ,,, ?'8.•, . ~ .. !IL .. I . i -­ .. ' liiiiJII' ~ ' ~ ...,, . ; L I .. . ~ ~~ -- ..!!j .Uiillll\l I - ,. .. . •• I' -­ ' ·· - ~ ' 'ill 92 Parasitism of sawtlz larvae: l?ercenta e parasitism at both stations was higher i n plots containing Lethbridge sawflies than in those ot Regina sawflies (Tables 31 , 32) . These results serve as further indication of the differences between strains in that more larvae of thG Lethbridge saw­ flies were available for parasitism than tere those of the Regina stock. In plots containing Lethbridge sawflies, mean per cent parasitism was 6. 0 at Lethbridge, and 6. 7 at Regina , and in plots of Regina sawflies 2 . 0 per cent and 2.7 per cent, respectively.

Comparison of infested . E;~tems cut a,t Lethbridge and Resina: Percentages of infested stems out were converted by the dare sine" transformation and analyzed as unpaired samples . Results are shown in Table j4.

Table 34 . Analysis of infested Golden Ball stems cut by two sawfly stocks

o\ie . Station t t.. Lethbridge 3 . 94~ 2. 98 Regina 1 · .56** 2. 98

** Significant at the one per cent level.

The differences in larval survival between sawfly stocks at both stations were significant at the one per cent level. These results agree with those ot previous years. The mean percentage ot infested stems out by Regina sawflies was 16 per cent at both stations, and by Lethbridge sa\vflies at the two stations 37 and ;1 per cent.

Comparison of Results for 1951 ,_ 1952, and 1953

A summary or resUlts for 1951 to 1953 is presented in Table ;;. These data show that in each test• the survival in Golden Ball wheat of Lethbridge sawflies was higher than that of Regina sawflies. No significant differences were obtained between sawfly strains in Rescue , ed Bobs , or Thatcher.

Nature of the difference between the two sawfly stocks: The evidence for differential larval survival between the t o sawfly stocks is conclusive. Is this difference ' genetical? All sawflies used in these experiments were obtained from Thatcher wheat . The only differential treat­ ment was in environment of the host plants during the larval feeding staee. It is known that varieties influence fecundity of adults (22) . However, differences in fecundity were not demonstrated between sawflies from the two areas in these tests. survival of larvae in Red Bobs , Rescue , and Thatcher was the same for both sawfly stocks. Table :s;. Oonpe.r1son ot percentages ot' inf ested wheat st cut by two stocks ot Oaobus oinotus from ~951 to t;SJ"

19,1 Leth. - 78 so 19 19 78 81 27 ,1,~ 1952 Lethe - - - - 72 6} 11 Regina - - - - 11 13 1,5 u 1953 Lath. ... - -· - - - Jl 1 Resina -· - - - ­ - )7 16 ·----~- - -· ------'------~- ---~·- --~-----~ -- ~-~- -~ ------~~----~-- - ~- ~-- ·­ • L - Lethbridge sawtli - Rsll_ina aawtl1ea

"().,. 9.5 Time ot infestation may be a factor in differential survival. However , adults emerged at the same time from both groups. It has been suggested that the !.:. ..,d..ur-..-um.,. wheats possess an additional resistance to sawflies not possessed by the .!:.. aestivum wheata (1, p . 26) . This might be the reason that differential larval survival was expressed 1n the solid- ate ed durum , Golden Ball, and not in the solid- stemmed aestivum, Rescue . 96 ENVIRONMI!NTAL FACTORS AFFECTING 'IHE MA.TO'RE LARVA , PREPOPA , AND PUPA

The Effect ot: Weather

Weather is the most important factor in survival and development ot the mature larval, prapupal, and pupal stages. Uature larvae move up and down inside their cocoon in response to temperature changes . Soil around the stub provides an excellent insul a­ tion against extr~es of air temperature, and under normal conditions , the sawtly is well protected. The temperature at one inch below the soil surface seldom falls below 23° F . although the air temperature during winter often reaches minus 40° F . When the air temperature reaches 90° F . to 1000 F., the soil temperature may climb to 86° F . Excessive moisture is not £avourable for survival, as various fungi will penetrate the stubs and kill the larvae. Excessive dryness is also detrimental. The following experimental rewlt s are concerned with effects of weather during the spring, fall , and winter if the stubs are removed from their protectiv soil cover.

Sprins Exposure

Farstad (20, p . 6) recommended shallow cultivation to destroy wheat stem sawflies by exposing stubs on the soil surface. Salt (54 , p . 6}0) found that sawtly larvae died 97 after ·losing more the.n 40 per cent of their body weight through des1ecation. Susoept,.bility to desiccation increased progressively from the larval to adult stages. Because larvae absorbed contact moisture, Salt stated that precipitation during exposure would negate the effects of desiccation (5.5 , p. 6;8) . Farstad (56, p. 66) reported that some sawfly larvae returned to diapause when stubs were exposed b7 spring till age, or when drought conditiona existed. ~lt (56, P •71) snowed that , at 3.5° c_ , development was pro­ hib1ted, prepupae and pupae were deform.ed, and non- cliapause larvae re- entered diapause. These results (''• pp .63l- 6,9) and 56 . pp . 66- 86) were obtained under constant conditions ot temperature and hwnidity. It was decided to test the effect of exposure with larger populationa Wlder actual field conditions. This experiment was conducted during the. spring of 1948 at the Dominion E~erimental Sub- station, Regina. Saskatchewan , Four blocks of wheat heavily cut by sawtliea in 1947 were each divided into ten randomized plots. At intervals of two to tour days, all stubs in each ot four plot,s were dug up and placed in two 10- toot rows on the surface ot the soil where they were held in place with strips of stucco wire. Each plot contained 600 stubs and as each treatment was replicated four times, 2, 400 stubs were exposed on each date. The . plot plan is shown 1n Figure 26 . First exposure was on lay 9 and the last on June 4 . An extra group of 200 stubs were exposed on June 19 . One plot in each replicate was left undisturbed as a check. Random samples ot 25 stubs from each plot in each

replicate were split on the first day or e~osure and at regular intervals thereafter. Stages of development and mortaltty were recorded . Twenty-five stubs from each of the tour check plots were examined at intervals for com... parison ith treatments . On July 9, 100 stubs from each plot were spltt and examined . The remaining stubs were taken to Lethbridge and stored at a low temperature to break diapause of the surviving larvae . After four months they were placed at room temperature. ergence and sur­

vival ~ere recorded tor comparison with results of July 9. Measurements of body length, wing length, ovipositor length, and head widths were made on these adults for comparison with measurements of individuals that had emerged nor 117 the previous spring. Daily maximum t peratures were recorded with a maximum thermo eter placed on the soil surface no:xt to the plots. Other weather records were obtained from the Sub­ station.

' *~ . LEGEND

Plot Date 5 2 9 3 I 10 4 8 6 7 I MayS 2 II 3 14 4 18 7 10 I 8 4 5 3 9 2 6 5 21 6 25 7 28 8 June I 9 4 I 0 Check I 4 9 5 10 2 7 8 6 3

3 2 6 5 I 8 7 10 4 9

PLOT PLAN- SPRING EXPOSURE- REGINA, 1948

Fig. 26 100 Weather condi t iona during exposure: Maximum surface

t peratnres ot the plots varied from 75° F . to 120° F . (mean 100° F .) durine the exposure period . The mean maximum air t perature for May was 73° F . (range 53° F . to 90° F . ) and total precipitation was 0 . 03 inches. In

June the mean maximum air tempe r a ture was 74° F . (range 59° F . to 93° F .), precipitation was 2 .01 ,.nohes .

Developmen~ at time of eeposur~ : The stage of development of sawflies and the date of exposure of eaoh plot are reported in Table 36. Until May 21 most individuals were larvae or prepupae. Many prepupae were classified as l arvae because very early prepupae can not be distinguished externally. The first pupae were observed on May 2.5 . By June 4 only three per cent of the population were larvae.

Mort alitl and diaBause from exposure: Co~par1sona among treatments are shown in Table 37 . The se data show that rate of mortality was a cceler a ted i n the later stages ot development . Correspondingly , the final mortality was progressively higher with later exposures. Mortality in plots exposed between May 25 and June 4 ranged from 91 to 96 per cent. A comparison or mortality and diapause in 100 stub s from each plot on July 9 is reported in Table 38 and Figure 27 . Thes e data ru1owed consistent trends in percent­ age of mortality and diapause. few indivi duals completed . .. ,: , ...

101

bl• )6 . Stag o·t 4avelopmot and mrn:·te.litr ·o,f · 'Wh.at st&ra sawtlr trom 100 otube ~ t .time ot espo&ur ,

:: ; r·e. Plot lfJJI)i . . j -

l May 9 9l. 2 0 0 ·? 2 !tat ll. s, .e 0 0 ,, tAay l.4 90 Q G 0 10 '4 May 11 't l 0 0· ·? s ·1 U · ,1 0 0 0 I' 6 1 2' 51 )J 1& 0 1 May 28 ,. 29 0 lJ.' ·a June 1 11' I 18 6) 0 ·8 9 June 4 J 1 80 · j lltln., 19 2 l )8 $1' ·8 '

.. InoJ.~es par s1t1aeu larv •• •

,. 102 ..

Compar1son ot mortality of Oefihu! otnotua Table ''· exposed on different tla •• ­ :::::.4. :: ;; ; :~iit•Y~Sii:~ii ;;•;.~ 1 14 22 61 .J ll' 1 ll' )1 ''51 67 8'1 14 l.} 16 ., ,, 68 .ar 1'7 - 2' 46 &a 75 21 2.$ MaJ - ,, ,, ' ar 2.5 .. • 48'' 1J 91 I .. J 28 ... - ,, 91 96 lune 1 ...... - a, rune 4 - .. - ,, ''95 I tu.ne 19 ... • '18 - - ' Check 6 • 8 6 J a ltortal1ty (excluaive of paras1t1rsm) baat4 on 100 stu.be per date except tul1 9 • whiob 1a baaed on 400 st~bs per treat~ent. 103 Table ;8

Influence of time of exposure on sawflies tro• lOQ atubs oer plot exposed on different datu*

P e r c e n t a g t Date PUpae, exposed Plot Range Mortality Emerged Diapause adults

May 9 1 I 61 2 36 1 II 66 1 0 III 57 2 ~~ 3 IV 61 1 34 3 Mean 61 2 35 2 May 11 2 I 66 2 32 0 II 65 0 33 2 III 66 1 0 IV 72 1 ~i 1 Mean 67 1 31 1 May 14 3 I 69 1 27 3 II 66 0 31 3 III 67 1 30 2 IV 71 2 22 0 Mean 68 1 29 2 May 17 4 I 76 0 23 1 II 78 1 21 0 III 72 3 25 0 IV z8 1 21 0 Mean 75 1 23 0 May 21 5 I 83 0 16 1 II 85 1 14 0 III 82 1 15 2 IV 82 0 lZ 1 Mean 83 1 15 1 May 25 6 I 87 0 12 1 II 13 0 7 0 III 94 0 6 0 IV 91 0 2 0 Mean 91 0 9 0 May 28 7 I 2 2 1 II §~ 0 2 0 III 95 0 3 2 IV 26 2 2 0 Mean 96 1 2 1 June 1 8 I 94 2 3 1 II 93 6 1 0 III 93 6 1 0 IV C)() 8 2 0 Mean 93 5 2 0 June 4 9 I 95 3 0 2 II 97 2 1 0 III 93 6 1 0 IV 25 3 2 0 Mean 95 3 1 0 June 19 83 17 10 (Check) 7 8a 3 2

*stubs . exalllined on July 9 • 104

PER CENT 100

90 ~ ~TALI T Y ~ 80

70

60

50

40

30

___}2.J APAUSE 20

10

OL-~--~~~~~~~~~~--~~~~~~--- 9 II 14 17 21 25 28 4 DATE MAY JUNE EXPOSE D

Fig. 27. Percentage of diapause and mortality on July 9 of ~ cinctus ~xposed on different dates . 105 development and emerged even in stubs exposed on ay 9. The percentage larvae that re-entered diapaus~ decreased progressively with date of exposure. Adult emergence was very low in all plots except the last, which was exposed • on June 19. Seventeen per cent emerged from these stubs. Stage ot development and mortality was recorded for stubs stored in an ice house at Lethbridge . )(any larvae were destroyed by fungus and others failed to com­ plete diapause and develop (Table 39). However, results obtained showed good agreement with those or July 9·

Effect or second period ot diapause on adult si~e: Table 40 shows that individuals surviving a second period of diapause had aller body and wing len t hs than normally emerged adults. This is not unexpected as nutrients required for the extra period of diapause would be utilized for respiration at the expense of production ot adult tissues.

Conparison of laboratory and field results: Results obtained under field conditions agreed closely with those reported by alt (54, pp .622- 6}0 ). As his experiments were conducted at 40° c. and 0 per cent relativ~ humidity, emergence of adults was not · allow~d . Under field conditions fluctuating temperature and humidity permitted some develop­ ment to proceed and some individuals to emerge as adults. Presumably with cool wet conditions during exposure, more 106

bl 21notua t\et= ''· 1 l}

I = ' .te ·f~•n¥~&! ol ' ' ttil IJ ­ Dat• Lirln~ ~ r~a~t s.du~'f e!J?O!Bd :l@;i 2;: ,e§,•±J': ·.:t• • I ., t J' 8 24 Miq 11 )l 12 ar 14 29 21 0' .., 17 2) 1 11 1 21 16 0 12 MaJ 25 , 0 ar 28 2 0 1 lu.ne 1 2 0 0 luna 4 l 0 0

.. 107 .

Table 40 . Comparison of adults emer ed f ~m spring and fall diapause larva

I No . of ~easure- l~a!es emaies adults ment faII S];!rins Fal! s~rins 2.5 body length '1 ·' 7. 2 '1 · 7 ?.4 25 wing length 6. 2 ,5 . 8 6. 7 6. } 20 ovipositor l ength 1. 8 1. 8 20 head \vidth 1. 3 1 . ; 1 . 4 1 . 4

1c All measuremonts in mm. . individuals would complete development . Although temper­ atures in t his test were not extreme and 2 . 07 inches of rain f'ell during the exposure period; ood control of the exposed sawflies ;as obtained,

AEpl1cation of results to control recommendation~ : These results show the importance of proper timing o:r spring tillage to control the wheat stem sawfly. The best time for control wa.s between May 25 and June 4 . It would be preferable to ~lit the stubs and examined the individuals in order to arrive at the best time for exposure. Good control should be expected when 50 per cent or less of the population is in t he larval stage, and 5 per cent or less in the adult s~age . ... 108 Fall and Vinter Exposure

The next phase of this study was to determine the effects of date of xposure on tall and winter mortality of sawfly larvae. Stubs of both winter and spring wheat were used to co pare effects of different hosts on mortality. At intervals during August and September, 1948 , wheat stubs containing sawtly larvae were exposed on the .soil surfac at Lethbridge. 'l'wo thousand stubs were x­ posed on each of seven dates. Stubs from winter wheat were used on tour dates and spring wheat stubs on three dates. One hundred stubs per treatment ere examined at weekly intervals until October 1 . The remaining stubs were left on the plots over winter and examined on June ; . Temperatures ere recorded at the plots on the surface ot the soil with a maximum mercury thermometer.

e ther during exposure: The maximum soil surface temper­ ature during Au ust and September occurred on August 14 , when it r ohed l Z7° F . The mean maxi um soil surface t perature from Au ust 14 to October 1 v~s 100° F . (range 74° to 127° F .,) . J.Io preoipitation was recorded between August 14 and October 1 . ~··,

109

MortalitY from e!Rosur~: The comparatively high mortality (41 per cent) of larvae exposed on August 14 (Table 41) probably resulted from the high temperature of August 14. Many larvae in these stubs had just out the stems and had not yet secreted their cocoons . There was little variation among the remaining plots. The mortality reached 20 to 28 per cent after three to six weeks of eXposure.

Salt (541 p . 628) found a progressive increase i n resistance to desiccation during August followed by an approximately equal decrease during September . Except for the f irst date of exposure such an effect was not obserTed in this experiment. It is apparent from Table 41 t hat time of exposure had no differential effect on overwinter survival. Sawflies in stubs exposed in the fall stand little or no chance of surviving to the adult stage•

. . 110

Table 41. ortal1ty of larvae ot Ceph~ oi ctU! in atube exposed at intervale 1n'A.ugust an! s pt ·•r in 1948

: 2 Dat;e ~~~~~~~Yi 1p~.~~~l~~ti ~~~·~ !pJi~i:: ,.eao 9! Boat• . g: l l J :! :2 : ~ ~ . 1!4! Aug. 14 ww s 41 41 '0 '' ,58 60 60 100 Aug ~ 20 5 10 ll 20 22 23 22 - 100 Aug . 27 - 7 lS 19 2J a1 24 • • +OO Sep . 1 sw ; 18 19 28 .. ... - ,,8 S P• 2 ww '9 lJ 21 17 24 24 - ­ 100 Sep . s s 4 21 21 ...... - ioo Sep . 29 sw ...... - - - .... - ~00 .I - winter wheat sawfly stub& sw ~ epring wheat sawtly s~ub 111

SUMMARY

1. Optimum air temperatures for oviposition by Cephua g1nctus Nort. fell between 70° F. and 98° F. Mating occurred at lower temperatures than did-oviposition. Males were more active than females at higher and lower air temperatures. Mating took place as readily in the shade as in direct sunlight. Direct sunlight ensured adult activity at lower air temperatures but inhibited activity at higher air temperatures. Winds of 20 m.p.h. or more restricted adult activity. Mating and oviposition occurred readily in the absence or measurable changes in barometric pressure.

2. Although equal percentages of Rescue and Red Bobs wheat

stems were infested by ~ cin~tus, Red Bobs received twice as many sawfly eggs as did Rescue. This may h.ave been caused by the extra time required to penetrate the solid stems of Rescue with the ovipositor. In.Rescue stems, oviposition sites were not apparently influenced by the absence or presence of a pith cavity. Most or the eggs in Red Bobs were laid in the second internode while Rescue received most ot the eggs in the second and third inter• nodes. . The peak of infestation was probably earlier in Red Bobs than in Rescue. Although solid-stemmed wheat hosts showed some resistance to infestation this was not an

important factor in their resistance to ~ cinctus.

• .· 112 3. Red Bobs wheat variety was preferred over Thatcher variety tor oviposition by c. o1nctus during the early part of the sawfly flight period. This appeared to be the result of the larger diameters of Red Bobs stems as com­ pared to Thatcher stems. Larger and/or more mature stems were preferred for oviposition during the early part of the flight. During the last part of the flight. stems that were smaller and/or lees mature were preferred for oviposition, i.e. the requirement for a stem to be attractive for ovi­ position remains fairly constant throughout the flight. This was probably beoe.use older stems become more resistant to penetration by the ovipositor and beoause the larger diameters of these stems prevent the female sawfly from obtaining a firm grip during oviposition.

4. The sex ratio of surviving wheat stem sawfly progeny from two wheat varieties was controlled by date of seeding ot the host plants. The first-seeded plants favoured females, the last-seeded, males. Red Bobs gave a lower percentage or males for each date of seeding. This was explained by the differences in pe k of infestability of the two varieties; the peak occurring earlier 1n Red Bobs than in Thatcher for each date of seeding. Stub diameters were indicative of stem diameters at time or infeet~tion. Stub di meters were not correlated with sex ratios within varieties, but the ~ifferenoee in diameter between

. , 113 .. varieties were much greater than those within varieties. Red Bobs stubs were larger in diameter than Thatcher stubs. Time of infestation in relation to the sawfly flight is a major f ctor in determining the sex ratio of surviving saw­ fly progeny in sawfly-susceptible bread wheats.

S. Fifty pairs of adults of C. cinctus caged over eight row-feet of Thatcher wheat gave an average infestation or 82 per cent. Although this was not significantly higher than the infestation by 25 pairs, it was significantly higher than the infestation by 15 paire .or adults. Increased levels of adult populations in the cages resulted in decree.sing numbers of eurviving progeny from each pair of adults. The percentage of infested stems out by larvae, i.e. larval survival, was approximately equal for all four levels of adult population.

6. The hatching of eggs or ~ c1notus was not r educed in Rescue wheat. Eggs hatched as well when completely embedded in pith as in pith cavity. Larval survival was much higher from eggs laid in the pith cavity than from eggs laid in the pith in the same Rescue stems. Most larval mortality in Rescue occurred in the first instar. .Only larvae tha.t had fed in the vascular tissue survived. Larvae from Rescue were sm ller than those from Red Bobs . 114 . All evidence indicated that the influence of solidness on larval mortality is the main factor in Rescue resistance to . ' . ~ , > the wheat stem sawfly. ~ • '• > ·~

7• ~ cinetu§ from two widely separated areas in Western Canada, Regina, SaskatChewan and Lethbridge, Alberta, was differentiated by the ab1lity o.f the larvae to survive in the durum wheat variety, Golden Ball. The Lethbridge population was more virulent 1n this variety than was the Regina population. Tnis difference is probably genetical. Infestations of the four wheat varieties tested were equal tor the two sawfly stocks" there were no difference between

the two sawfly stocks in their ability to survive in Re~ Bobs, thatcher, or Rescue varieties of wheat. The break• down of sawfly-resistance of Rescue in the Regina area is

caused by environment.al faeto~s and not 'by a more virulent $train in that area.

8. When &.&. c~sctu§ was exposed in stubs on the soil ,surface - in the spring it was .found that the percentage of mortality increased with the later dates of exposure, Ninety-one to 96 per cent mortality oeeurred in sawfly exposed between

May 2~ and June 4 Percentage of spring diapause decreased with the later' dates of exposure. Thirty-five per cent of ' larvae exposed on May 9 re-entered diapause compared With one per cent of those exposed on June 4, These results ... . • a I . I

; , 11; stress the importance of proper timing of spring exposure to ensure maximum control of ~ · £!n£tus. The most susceptible period occurred when prepupae or pupae comprised 44 per cent to 87 per cent of the population.

9. Results from fall exposure of ~ cinctus in stubs on the soil surface showed that with the exception of the first date of exposure, neither date of exposure nor host variety gave a differential effect on larval survival in the fall. Individuals in stubs exposed to the soil surface over winter stood little Chance of surviving to the adult stage. 116 BIBLIOGRAPHY

Ainslie, c. N. The wheat grass~stem sawfly. Washington, u.s. Government printing office, 1920. 27p. (U.s. Dept. of agriculture. Bulletin no. 841) ·

2. Allee, • c. !1 !l• Principles of animal ecology. Philadelphia, .B. Saunderst 1949. 837P•

Beall, Geoffrey. Multiple generation pyrausta nyb1lal1s (Hubn.) on plants other than corn in Ontario. Seventy-fourth annual report of the entomological society of Ontario, 1943. pp.13..15.

4. Cailenbaeht J. A. Rescue wheat and its resistance to wheat stem sawfly attack. Journal of economic ento­ mology 44:999. 1952,

Canada Meteorological division. Dept. of transport. Monthly meteorological summary for June. Lethbridge, 1953.

6. Church, Norman Stanley. Initiation ot post•diapause development and re-instatement of diapause in Cephus I cinctyg Nort. Master's thesis. Bozeman, ontana state college, 1953· 88 numb. leaves,

7. Cox, Constance E. Handbook on statistical methods. Canada Dept. ot agriculture. Science service. Division of administration. Statistical research and service unit, 1952. lljp. (Its processed publication no. 3)

8. Criddle, Norman. The wheat~stem sawfly. Nor'-West Farmer (Winnipeg, Manitoba) Dee. 20, 1907, p.ll56.

--~~~--· Injurious insects of 1910 at Treesbank, Manitoba. Journal of economic entomology 4:236-241. 1911. 117 10. Criddle, Norman. The hessian fly and the western wheat­ stem sawfly in Manitoba, Saskatchewan, and Alberta. Ottawa, The King's printer, 1916. 23p. (Canada. Dept. of agriculture. Series B, no. 11)

11. • Further observations upon the habits of the western wheat-stem sawfly in Manitoba and Saskatchewan. Agricultural gazette 4:176-177. 1917.

12. • The western wheat-stem sawfly in Canada. Fifty-second annual report of the entomological society of Ontario, 1921. pp.l8-22.

13. ------~~~~· The western wheat-stem sawfly and its control. Ottawa, The King's printer, 1922. 8p. (Canada. Dept. of agriculture. Pamphlet no. o, new series)

14. DobzhanskY, Theodosius. Genetics and the origin of species. 3rd ed. New York, Columbia university press, 1951. 364p.

15. Eckroth, E. G. and F. H. McNeal. Association of plant characters in spring wheat with resistance to the wheat stem sawfly. Agronomy journal 45:400-404. 1953.

16. Farstad, c. W. Thelytokus parthenogenesis in Cephus cinctus Nort. (Hymenoptera:Cephidae). The Canadian entomologist 70:206-207. 1938.

17. • The development of western wheat stem saw­ ----f~l~y~(~C~e-p~hus cinctus Nort.) in vartoua host plants as an index of resistance. Ph.D. thesis. Ames, Iowa state college, 1940. (Abstracted in Iowa state college journal of science 15:67-69. 1940)

18. • Wheat stem sawfly in flax. Scientific agriculture 24:383-386. 1944. 116 Farstad, c. • and A. W. Platt . Reaction of barley varieties to wheat stem sawfly attack. Scientific agriculture 26:216-224. 1946.

20. et al. Control of wheat stem sawfly in the ____p_r_a~i~r~1~e--p-roVInees. Ottawa, The King's printer, 1945. ?p. (Canada agricultural supplies board. War ~time . production series no. 59 (rev.) )

21. , A. w. Platt and A. J. cGirmis. Influence ----o-f~w~h-e-a~t---varieties on the sex .ratio of the wheat stem sawfly, Cephus gigety§ Nort. (Hymenoptera:Cephidae). Eightieth annual report of the entomological society of Ontario, 1949. pp,27-28.

22. ---=--~:-:----' A. • Platt and D. s. McBean. Female length as an index of fecundity in the wheat stem sawfly, Cephus cinctu§ Nort . In Ms.

Flanders, Stanley E. Control of ·sex and sex•limited polymorphism in the Hymenoptera. The quarterly review of biology 21:135·143. 1946.

24. Fletcher, James. Report of the entomologist and botanist. Ottawa, Government printing bureau; 1897• pp.229-230.

--~'!----· Report· of the entomologist and botanist. Ottawa, Government printing bureau, 1898. p.l20.

26, ----~~----· Report _of the entomQlog1st and botanist. Ottawa, Government printing bureau, 1904. pp.l63-21S.

27. ----~~---~· Report of the entomologist and botanist. Ottawa, Government printing bureau, 1906. pp.l59-204.

28. Gahan, A. B. Description of a new hymenopterous parasite (Braconidae) • Proceedings of the ento·mological society of Washington 20:18. 1918. 119 29. Gahan, A. B. The serphoid and chalcidoid parasites of the hessian fly. Washington, u.s. Government print• ing office, 1933· 147P• (U.S. Dept. of agriculture. Miscellaneous publication no. 174)

30. Goulden, Cyril H. Methods or statist~cal analysis. New York, John iley and Sons, 1939. 2?7p.

31. Harrington, c. D. Biological races or the pea aphid. Journal of economic entomology 38:12•22. 1945.

32. Holmes, Neil D. Note on Scam~s detritus (Holmg.) (Hymenoptera:Ichneumonida~ a new parasite or wheat stem sawfly, Cephys cinctus Nort . The Canadian ento• mologist 85'c339. 1953.

33· -~~~--:--• Food relations o! the wheat stem sawfly, Cephus oinctus Nort. (Hymenoptera:Cepbidae). In press.

34. Jacobson, L. A. and c. w. Farstad. Effect of time ot seeding Apex wheat on infestation and sex ratio of the heat stem sa !ly~ Cephu§ oinctu§ Nort . (Hymanoptera:Cephidae}. The Canadian entomologist 84:90-92. 195'2.

Kemp, H. J. Studies or solid stem wheat varieties in relation to wheat stem sawfly control. Scientific agriculture 15':30•38. 1934.

36. Larson, Ruby Ila. . Aneuploid analysis or the inheritance of stem solidness in common wheat . Ph.D. thesis. Columbus, University of Missouri , 1952. 193 numb. leaves.

Mackay, Margaret R. Cytology and parthenogenesis o! the wheat stem aa fly, Cephus ainctu§ Nort. (Hymenqpteraz Cephidae). In Ms . 120 anson, G. F. A preliminary report on the effect ot rain­ tall on emergence of the wheat stem sawfly t Ce·phJ1§ cinctus Nort. (Hymenoptera:Cephidae). T enty•fifth and twenty-sixth annual report of the Quebec society for the protection of plants, 1934. pp.l01•106.

McGinnis; Arthur James. Sex ratio studies on the wheat stem sawfly, CftphU§ cinctys Nort. Kaster's thesis. Bozeman, Montana state college, 1950. 61 numb. leaves.

Muesebeek, Carl F. • Three ne reared Braoonidae (Hymenoptera). Proceedings of the entomological society or Washington 55:149•151. 1953·

41. itchener, A• . v. On the efteat o:r the wheat-stem sawfly, Cephus cinetus Nort., upon the spring wheat crop in western Canada. Scientific agriculture 8•751-756. 1928.

42. Nelson, • A. and c. w. Farstad. Biology of Bracon C§ph' (Gahan) (Hymenoptera:Braconidae), an important native parasite of the wheat stem sawfly, Cephug cinctus Nort. (Hymenoptera•Cephidae) in western Canada. The Canadian entomologist 85al03•107. 1953.

Norton, Edward. Notes on North American Tenthred1n1dae with descriptions of new species. Transactions ot the American entomological society 4t77-86. 1872.

44. Painter; Reginald H. The biological strains ot hessian tly. Journal of economic entomology 23&322-326. 1930.

Pepper, J. H. and Ellsworth Hastings. The effects of solar radiation .on grasshopper temperatures and activities. Ecology 33•96-103. 1952. ----~------

121 46.. Platt, A.. W. The influence of some environmental factors on the expression of the solid stem character in certain wheat varieties.. Scientific agriculture 22 t 139•151. 1941.

47. . , J. G.. Durroeh ana H. S. Kemp-. The inheri­ tance of solid stem and certain other characters in crosses between varieties of triticum vulgare. Scientific agriculture 26:216-224. 1941.

48. and Ruby Ila Larson. An attempt to transfer solid-stem from Triticum durym to ~ yulgare by hybridization. Se1ent1t1c agriculture 241214-220. 1943.

49. and c. w. Farstad. The reaction of wheat varieties to wheat stem sawfly attack. Scientific agriculture 26:231-247. 1946.

50. , C. W. Farstad, and J. A. Callenbach. The reaction of Rescue wheat to· sawfly damage. Scientific agriculture 28:154~161. 1948.

51. Riley, c. v. and c. L. Marlatt. Wheat and grass­ sawflies. Washington, tT.S. Government printing office, 1891. pp.l68·179. (U.S. Dept. of agri­ culture. Division or entomology. Insect life vo1. 4)

$2. Ross, Herbert H. Family Cephida • ln Hymenoptera of America north of Mexico. Washington, u.s, Government printing office, 1951. pp.87...89. (U.S. Dept. of agriculture. Agriculture monograph no. 2)

5'3. Row'her, s. A. The American species of the genus Cephus Latrielle. Proceedings of the entomological society of WaShington 19:139·141. 1917.

54. Salt, R. w. Moisture relationships or the wheat stem saw­ fly (Cenhus eincty; Nort .) l· . Some effects of desiccation. Scientific agriculture 26a622-630. 1946. 122 . Salt, :a. W. Moisture relationships of the wheat stem sawfly (Qepbus c1nctus Nort.) II. Some effects of ... contact moisture. Sc1enti.f1e agriculture 26:631-639 • 1946.

,6,. . • Some etteots ot temperature on the production and elimination of d1apa:us& in the ·wheat stem sawfly, Cephus cinctNs Nort. Canadian journal of research, D, 25;66~86. 1947•

57. SeaJnans, H. L. Experiments on the control of the wheat stem sawfly by parasites., Sixtieth annual report of the entomological society or Ontario, 1929,. pp.65'•67.

5'8. Seamans·, B. L:., G. F. Manson, and c. w. Farstad. i'he effect of the wheat stem sawfly (Cephus cinctus Nort .) on the heads and grain of infested stems. Seventy­ fifth annual report of the entomological society of Ontario, 1944. pp.lO~l6-.

5'9. Seamans, u. L. A preliminary rep.ort of the climatology ot the wheat stem sawfly .(ggppus cinctus Nort'.) on the Canadian prairies·. Scientific agriculture 25'J 432•45'7. 1945'.

60. Snedeeor, George w. Statistical methods. 4th ed. Ames, Iowa state college press,, 1946. 485p.

61. Wall; Alice :t.h The diameter of the wheat stem in relation to the length and sex of emerging sawfly (Qephys S!:Lfg~u§ Nort.). Scientific agriculture 321 272-277,. 9 2~ .

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