BIOLOGY of EUROPEAN EARWIG FORFICULL Atjrictjl.ARIA. L

BIOLOGY OF EUROPEAN EARWIG FORFICULL ATJRICtJL.ARIA. L.

WIlE REFERENCE TO ] PR).ATORY ACTrnTi ON

DAON-HOP APHID PEORON HUTtJLI (sciiax)..

JO HOWARD BTON

Thesis submitted. for the degree of Doctor of Philosopby of

the University of London.

lye College, September, 197J4.. University of London. -1-

£BSTR

The biO1o r of the European earwig, orfiou1a auricuLaria L, was studied in two coulnercial hop gardens at Wye College in Kent. The effect of predation by earwigs upon P. bumuli populations both in the field and the laboratory were investigated. Observations were also made on the effects of the organophosphorous iriaoctieide dimefox on earwigs In the field and In laboratory experimts.

Earwigs were found in all areas of the hop garden but their distribution was not uniform end the highest numbers occurred at the garden edges The duration of nymphs]. inatara, ount of earwig feeding damage to the hops and incidences of parasitin end disease of F. auricularia were assessed during 1972-1973. A limited rvey of earwig rmmbers in seven hop gardens in S.E. Kent was also made. Earwiga were shown to climb hop bines of at

least 5 m., but the numbers caught In cardboard traps aroui4 the binea &epouded, among other things, on the frequency with ithich the traps were eirn1nd. The inacrofauria of Silks Garden was investigated using pitfall traps and. found to consist mainly of ground beetles (Carabidae) which were 12flh1ie1y to contribute much towards predation of P. humuli on the bines. Foods eaten by earwigs were shown by stomach contents analyses to consist intthly of hop aphids, green algae, fungi and hop tissue. The effect of dimefox upon field populations of P. auricularia was studied, with inconclusive results. However, laboratory experiments thawed that climefox applied to the soil was to.o at doses much lower then field applioation rates. Laboratory feeding experiments were made at 200 ± 2°C. with auricularia using P. hwm.i].1 as prey, and the effect of varying 'the prey:

predator ratio was investigated in ms11 plant experiments. Various methods -2-

of exclusion were used in attanpts to evaluate the importance of predation by earwigs upon P. l'ujmCLi In the field. The aphid population density on insecticIde-free hops usually increased enormously, Ca11R(Tg prnatux'e defoliation of the infested plants. However, in the Ntusery Garden in 1973, after one soil application of a systemic insecticide in early June, mobile predators maintained the resurging aphid population at low densities.

Predator evaluation experiments In Silks Garden In 1973 and l9?l attempted to use only one d.iinefox application, but this failed to control the aphid population in both years and, unfortunate:Ly, a subsequent treatment cemple- tely ellmlnMod the aphids ithith obscured treatment differences,

The results are discussed with reference to the part that F. auricu- ls4 could play In an integrated system of control for T. humu)j on COEnercjal hops. AEDGF2ENJ

This work was carried out with the support of a research grant frca the Agricultural Research Council, to ithom I am grateful.

I would like to t,hnk all the people itho have helped, criticised and encouraged me during the experimental work aixl preparation of this thesis, especially :-

Dr. D.S. Madge, Biological Sciences Department, Wye Colloge,

for his supervision and guidance of this work.

Dr R.A. Neve, Hop Research Department, Wye College, for hia advioe and for arranging the field survc. Ifr. R.F. Parrar, Hop Research Department, Wye College, for edvice on some of the technical aspects of hop growing.

Messrs. B. Wella and 3. Haynee for much help with equipnent

and preparing the Piguxea.

Mr 3. Marshall for taking most of the photographs. Mr. P. Haimnoth of the British Museum (Nature]. History) for

identifying most of the Carabidae and Staphylinidae.

Pinal3y, I wish to thank n wife Clandia, for field recording, correction of grairunax, typing this thesis and for her understanding and encourag nørt tbroubout.

TABLE OP CONTS

Pate

ABSTR.A.CT .. 9• I• 9...... 1

______. . 9. 9• .9 9. 3

GE1IER.AL ThTRQDUCTIOR •. .. .. •. •. 10

SECTION I — R%rIEV OF THE LITHRATUEE ...... 12

Introduction .. •...... 13 Classification and Synonymy ...... •. 15 Distribution of L auricularia ...... 17 (a)Passive spread by man •...... 17 (b)pljgbt ...... • •• 18

(o) Dispersal ...... 19 Morpho1or •. ., ...... 22 Life-cycle of F. auricularia .. .. •. .. 24.

Behaviour .. •. .. .. •. .. .. 31

Peedizg habits and economic importance of P. E1riCm18.Xia.. 34. (a)Predatory habits ...... 38

(b) Attacic on plants .. .. 13

(o) Conc1uaic ...... ••

Eiitry into houses .. •. .. •. .. 4.7

Effect of pesticides on P. auricularia ...... 4.9 Use of traps to estimate earvig populations .. .. 51

Naturs]. enniee of P. auric'uleria ...... 54. Life-cycle of P. humu].i ...... 56 -5 —

Pate

SECTION II — STUDY 01 THE BIOL0(Y OF F. AtJRICULRIL IN

THE F]Z •. .. .. a. 59

FIff.iD EXFERIMENT. 1972 ...... 60

Introduction .. •. .. •. 60

)Tatericla czd Methods ,. .. .. 60

Results cth Discussion .. .. 62

Earwig population S. •. 62

Aphid population deve1oprent .. •. 67 Duration of stages .. .. 67

Leaf dainge •. 67

PIED EU RThENI. 1973 ...... 70

Introd.i.iotion ...... 70

Habitats studied i) Nursery Garden I. a. '10

Materials and Methods •. .. 72

Results •• •. •5 .. 5. 73

Earwig population .• S. a. 73

Effect of dimefox treathent S. I. .. 75

ii) Silks Garden .. .5 77

Materials and Methods .. S. •. 80

Results •. .. •. •5 .. 81

Cob plot ...... a. .!

Early Bird plot .. S. I. 'S

E)lge effects ...... a. .. 66

Leaf damage .. ., •. a. .. 88

Discussion .. .. 90

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Page

Natural ennies of P. auriculari .. ,. 93

Duration of stages .. .. 95

Height climbed by earwigs 'I .. 99

T1ii interval between trap assessments .. .. 106

Crowd fauna of Si3ks Garden .. 109

Dispersal experiments 1972 and 1973 .. .. 115

Earwig stomach contents .. .. 127

PIFID J'itIMN'I. ]Th, .. .. 137

Survey of earwig abundance In S.E. Kent .. •. 137

Locations •, .. .. •.138

Earwig rauiibers •. .. .. 138

Discussion and conclusions .. 139

SECTION Ifl - THE TOXICITY OP DINFOX TO FD D LBORATOI POPULTIOE OF P ICULRI& .. .. •. 142

LABORATORI XP.tTS.].97l...... 143

Introduction .. .. •...... ].43 )lateriala and methods ...... 143

Results •. •. •• 145

Contact toxicity to mele and. fncle earwiga .. .. 147

Puxnignzit activity ...... •. 148

Contact toxicity in two soil types ...... 149

Disoussion ...... •. 150

F.iD EXP±itfl'J. 1971k ...... 156

Introduction •, ,. •. 156

Materials &id methods .. •. .• .. 156 -7-

Results ...... •. 158 Earwig populations within c1osed and unclosed areas 158

Food-chain toxicity and toxicity of dirnefox vapour .. 162

Discussion .. •. .. 166

SECTION IV - T TECTIVEMFS OF F. AtJRICDLRIL IN REDtICING P. HUMtJLI POPJLATIO! ON HO} •. •. •. 168

LABCWORY wfl .. .. 169 Feeding experiments at 20°C. .. 169

Introduction •• I. .. 169

Methods •...... 169

Results •...... I. .. 170 Number of aphids eaten .. 171

Conversion ratios .. 172

Presh weight lettuce tissue eaten •. 174. Discussion •. 174.

Predator/prey experiments at 20°C. .. .. 176

Introduction •. .. •. 176

Methods ...... 177

Aphid s&zpling method ...... 177

Results and Discussion ., ...... 178

FD E2u'iKI!lE!1T. 1972 •. •. •.

Exclusion of earwiga bi greaae-b riM Tg hop binee •. 186

Introduction ...... Method.s ...... •. 186

-8—

Page

Results •. .. .. 187

Earwig nubers .. ..

Effect of the banding treabnont U. •. .. 188

Discussion .. U. .. 192

PIEaD 1973 ...... 193 Exclusion of aphid p:redators by caging hop bxies .. 193

Introd.uotion .. •. .. •. .. 193

Methods U...... 1914.

Exclusion cages •...... •. 194. Snp].ing methods ...... 196 Dimefox treatment .. .. 197

Results .. •...... 197

Natural ennies •, .. .. 198 aphid population development ...... 199 Cone weiits .. 199 Discussion .. 202

Hand rva1 of aphid predators from individual leaf pairs 203

Introduction .. •. .. .. 203

Methods •. •• .. •. 203 Treatmits - .• •. ,. •. 203 Results •. •. •. 2014.

Experimt 1 •. .. •. •. .. •. 204.

Experiment 2 ,. ,. .. .. •. 208

Experiment 3 ...... •. 209 Discussion .. •. 210

-9-

FJ) 2LEWJ1. ).97l ...... 212

Enoouragnent of earwig predation .. •. 212

Introduction .. .. .• •. .. •. 2]2

Methods ...... e 2]2

Positionirig of bathe ...... •. 213

Results ath Discussion .. •. •. 2]4

Effect of bRnhIin€ on the aphid population .. .. 215

Earwig numbers in the baMs ,. •. 216

NER.AL DISCtSION .. •...... 217

3)MAI .. .. S. I. •• 223

REF1REN ...... •. •, 226

APPE!W]X A. • • , ,. 247

B...... •. • • • • , 252

APPD C. •...... ,. . . ,. .. 270

APPEND] D. .. .. ,. .. .. •. .. .. - 10 -

GENERAL INTRODUCTION

"A struggle for existence inevitably follows from the hii rate at

which all orgenic beings tend to increase ...... there is no exception to

the rule that, if not deatxoy4, the Earth would soon be cowered by the progeny of a single pair ...... battle within battle must ever be

recurring with varying BLiOC 0883 and yet in the long rm the forces are

so nicely balanced that the face of nature remMn uniform for long

periods of time ...... " (Darwin, 1859). Thorodon. jiumuli (Schrank) is the major poet of hops (Thznu1us

1ui,u L.) in England and Europe. Under favourablo conditions the

aphids multiply rapidly and cause severe feeding damage to the hope.

Also, their presence in the cones lowers the value of the crop, due to

cone discolouration by sooty moulds (Cladosix,rium app.) developing in the aphids' honeydew.

aphid has many natural enemies which can exert some control of the population, but before modern insecticides were introduced, crop

losses were often high (Ordish, 1952). However, the ornophoaphorous compounds used from 1950 onwards gave a high degree of aphid control (Darling, 1962). Reliance upon these insecticides was so groat that the

importance of natural oivniee tended to be forgotten.

However, within the past decade the hop aphid baa developed wide..

spread resistance to many commonly-used orgcnophosphorous and carbanate

insecticides (Hi1y, 1970). These difficulties in chemical control have led to a reappraisal. of the part playod by nature]. ennies in the "struggle for existence" of the aphid.

All the major groups of predators (Eagen and van den Bosch, 1968) have boon recorded on hops preying on P. 'M11. and have boon adequately -11-

siminnrised by Campbefl (1973), who also investigad. the effect of

conventional' predators (inainy anihocoricis, coccinellido, syrhids a1 chrysopicls) of the hop aphid.

This work investigalDs the eco1oy of a lees well-known aphid predator, the European earwig, Forfiila auricu3ria L. in coninercia]. hop gard. 'The nain objects of the stIy were :

(i) To evaluate the behaviour and seasonal abundance of the earwig in hop gardens in lent.

(ii) To &etexiine 'ithether the earwig was importrnt predator of the danson-hop aphid. -32-

SECTION I - REVIEW OP THE LITERATURE - 13 -

Introduction

The European earwig, Forficu].a auricu].aria L., has been recogaised as a distinct form of insect life since the middle ages (]!ultxi, 19214.).

The name is descended frcn the .Anglo-Scxon word ecrwicga which means literally "eoa'-creature". In nearly all European languages, the popular ne of the earwig ha the sai meaning. In German, Dutch, Swedish,

Spanish and. Italian, the earwig is known as an earworm. The Gerans also call it "ear-borer", the Danish "ear-twister" and the French and the Portuguese a "pierce-ear". All these names refer to the widespread superstition that earwigs crawl into the ears of sleeping individuals

(Pulton, 1924.). However, there are no grounds to substantiate this belief, except that the earwig will crawl into any crevice far shelter during daytime (Muggeridge, 1927).

Foricula auricularia is the most caiiion of the five species of

Dermaptera found in Eugland (Burr, 1939). It occurs in most types of habitats, especially agricultural land (Beau, 1932) and is ofti abundant in hop gardeme (Theobali, 1896, 1913; Massee, 19Z3; Moreton,

1964.). The earwig is nocturnal (Behura, 1956), and hides during daytime in any available crevice, either above or bolow ground (Jones, 1917;

Worthington, 1926; Crumb, Eide and Bonn, 1%l; G1endeMng, 191ê.7), it occurs in large muiibers in the cracks in wooden poles of hop gardeme

(Theobalsi, 1913).

Most authors regard the earwig as a sporadic pest of various crops, such as orchards (Massoe, 1964.), and field crops (Jomes and Jones,

1964.), althou the omaivorous feeding habits of F. auricula4 (Beau,

1932; Bxlxdley, 1918; Fulton, 1924., 1927; Glendenning, 19.7) may ronaer it harmful or beneficial according to the circumstances of the crop, - ]4-

(Sial, 1958). Ealand (1915) Brind].ey (1918) states that "most garders would assert that t1 earwig is destructive to cultivated plants. Careful observation and experiment, however, diow that it is often carnivorous and devours caterpillars, slugs, snails, etc. its habit of hiding in such flowers as the sunflower and dahlia have earned it an undeserved reputation for evil",

von Schilling (1887) j Crumb, Eide and Bonn, 19Zl, says that "the earwig, because of its mode of life, is extraordinarily nisunder- stood and is often portrayed in a false and contradictory light evon in good books on natural history. It is a very voracious insect and lives by no means exclusively on plant materiel but alao on animals. On apple trees it is decidedly beneficial, and this far outweiia any slight damage the insect may do."

Controversy about the usefulness of the earwig has continued for at least eighty years, and statements are often "as varied as the observers" (Crumb, Eide and Bonn, igi.i). However, it seems that earwigs may be predatory in certain circumstances, depending both upon the type of crop Eu1 the availabilily at suitable prey. - 15

Synonym for Forficula auricuJ.ari Lion. (Alter Lucas (1920)).

auricularia Lizm. 1758 - orficu1 aurici].ria Lion.. 176]. - Forficu]4 auriculoria Steph. 1835 - Forficula neglecta Norshan. 1802 - brficu1a podia &1rshax. 1802 - Forficu1 boreoli3 Steph. 1835 - Forficuia far citata Steph. 1835 - Porficila uricuThria Brunner. 18 - Forfici].a Finot. 1889 - orficu1a Shaw. 1889 - Forficula Burr. 1897 - Forficula Auriculoria Eirby. 1904. - uricu1aria Burr. 1910 - Forfictila Burr. 1911 - Forficu:La Lucas. 1912 - Forficu].a

Brithlqy. 1918 - ForficiAa 1917 - Forficula

Classification systnatio classification of the Europec eoxwig alter von Eeerd.t (i96) Pophari (1965, 1965a) is : ORDEIR ...... Dernaptera StJB0RD .. .• .• Forficu14

SUFWFAMILY .. .. ,• Forfiouloidoa FANTh! .. •. For iculldae .. .. Forficula SPECIES •. ,. ,. Forficulo. auriculria L. - 16 -

The original clzLssificatbn of the Demaptera by Burr (1911) Pophcui (1965a) divided the order into three suborders, the Hxdnerina, Arexenilna, d brficii14n,. Pophom (1961) showed that the Eeninerina hod little In cox3non with the Dermaptera, imd proposed that thoy should have or&tnnl status. Pophua (1965, 1965a) then merged the Arexmiiim oz Porficu].ina into one suborder, giving the Arexenf lna the status of a fcunily. The new classification of the Dermaptera, after Pophan (1965a) proposed four auperfamilies, inolvñirig the Porficulolsloo, which itself contained three families, inclntI(ng the Porficuliclae. family Porficilidae is a uniform oup of insects, including about 900 species within 50 genera (Irrs, 196k.), a1thoui most ore tropical (Burr, 1939). The two donInrmt genera in Europe ore FOrfiCula oni Anecha.u?u (Burr, 1939). In Western Europe, besides P. auricularia. only five species of the family Porficulidae ore fouth (van Reei'dt, 1946)

i) Labia minor L. very rare. (OudervmR, 1921). ii) itprv4a (Chelidura) albipcmi meg. (01trir, 1921). iii) dure]acppthopvt Gie. (Zacher, 1917).

iv) Labiduxa z'incria Poll. (do Bormans ox Krause, igoc).

v) kiechurn binunctala abr. (do Bornona oth Krause, 1900). ftrfictUa tonis. a species closely related to F. icularia. is found in Iuasia (Pesotslcnia, 1927). Earidge ore chnracterised by the fore wings reduced to 'afl teiwi, with large, merbraneoua hind wings, fo]dod in a complex pattern. Thr have unspeciolised biting nouthports, amd l cercii ore modified as forceps (Burr, 1939, 1939a; van Hoerdt, 1946; Irz2a, i96)i.). I

P.S -S

-I I

-'1 - 1.7 -

Distribution The European earwig is widely distributed. Originally a native of Europe (except N. Norway, N. Sweden and Russia), S. GreeT1,1d,

Western Asia ant North Africa (see Fig. i) (van Heerdt, 194.6; Anon,

1957) it has since exterded its distribution by human agency (Pulton,

192l.). L auricularia is now fn1 in Cuba, Brazil, East frica,

Nadagaac (van Heerdt, 1916), the East Indies, Australia and. Japan

(Behura, 1956), ant baa becoma oom'on. arid. widespread in North America (Crumb, Eide and Boim, 1941), end New Zealand, especially the South Island (1'!uggeridge, 1927).

The first recoxd of L puricu,laria in America was at Newport

Rhode Island, in 1.911 (Fulton, 1924); since then the earwig has spread over most of the country, including California (Essig, 1923), ant first reached British Columbia in Canada in 1.916 (alenteririzing, 194.7), ant Toronto region in 1956 (Copeland, 1957). The extensive vertical distribution of Forficula (from 0-1500 rn,) shows the range of habitats which are ooionj.sed (van Heerdt, 1946). It is interesting to note the similarities between the distribution of the main hop growing districts of the world (see map in Thompson,

19'72) and the distribution of F. puricularia. The main hop growing areas are In Europe, N. America, Tasrsn1 a and New Zealand (Thompson, 1.972) and F. auricularia occurs in all. these areas.

Passive spread of F. auricularia by man

Since the earwig hides in any available crevice during daTtime

(worthington, 1926), it is well-adapted for passive transport by man and may be carried long distances on luggage or in vehicles (crumb,

Eide er Bonn, 1941). Barwigs have been fourd on mraeiy trees and -18-

bLabs fran Europe (Jones, 1917), and this pibab]y explains how they reached America and. New Zealand (Iui.tozi, 1921 4.). Brindley (1918)

inveatited the occurrence of '. auricu1arj in the Sciuly Isles

and postulated tlmt man bad introduced earwiga to the islands and,

since the mainland is at least 25 miles away, it was mllre1y that

earwigs could fly that distamoe. 1\übn (19213.) found earwtgs in a

package of daily papers arriving in Portland fran Ontario in Oregon, a distance of over 400 miles,

flight of P. auri cularia

The European earwig baa functional, complex hind wings which az's tucked under the tegn (Burr, 1939a; \i1ton, i921.), but it does not fly readily (Theobald., 1913; Thilton, 1924; Goe, 1925; G1endeming,

1914..'T; Bebura, 1950a). There am few references in the literature to earwig flight, but many of these observations e conflicting.

Theobald (1896) recorded that adult earwigs flew inain]y during the night, especially when the moon was bright. He observed numbers of earwigs flying into his house and attributed this to the attraction of the light. Coflinge (1908) found earwigs flying between 9 and

10.30 p.m. in June and July in Kent. He observed 26 earwigs in flight during three consecutive evn1ngs, end all 'were males. The time of these flights coincides with the maturation of the first generation of adult earwigs, which aees with the observations of Crumb, Eide and

Bonn (1914.1) in Amerioa that most flights were made by recently matured e.

Burr (1939) state a that the earwig flies frequently, and cites

Richter, who on a warm afternoon in September saw 14 . earwigs flying in the s'tm. Sullivan (l9143) found many earwiga in. flight around a 1igit- - 19 -

house lantern at night durixg August in Scotland, and infers that they

were attracted to the light. Crumb, EixIe and Bonn (1941) record that the earwig flies moat reodfly in bright sunshine, moving at least

30 feet and quartering with the wind. These recards show that earwigs fly during both daytime end

nighttime, although since daytime is normally the inactive period for Forficula. it seems probable that f].ight is more frequent during the hours of darkness, but normally goes unnoticed. The records all agree on the fact that flight takes place, especially during early summer. This appears logical, since earwigs are most active when they

first become mature in June or July (BeaU, 1932), aM therefore short dispersal flihgts may enable adult earwigs to colonise new habitats. Initial flight of the closely related species labidura rivaria in

&merica coincided with the maturation of the first generation (Gross

and Spink, 1971).

Dispersion of L auricularia

apart from flight, or passive dispersion by man, earwigs may reach new habitats by dispersal movements over the ground. !nother possibility far dispersion was raised by Morgan (1927), who found that adult earwiga, especially females, were efficient swimmers, and could

be kept floating on the water surface for at least 24 hours without ill-.

effect. Morgan (1927) suested that strean and tributaries were factors in aiding their distribution.

Limited dispersal movements of earwigs can take place, but they are seasonal and occur mainly during early summer (BeaU, 1932a). me distances moved are not great unless environmental conditions are unfavourable (Crumb, Bide and Bonn, 1941). Theoba]d (1926) thought that 20 -

the large numbers of earwigs in a plum orchard in Kit was due to

invasion from rough belts of woodland which surrounded the orchaid. on

two aides.

Stapley (194.9) thought thet earwigs invaded gards from undisturbed land, such as old orchards or hedgerows where they built

up large numbers, while Jones aid Dunning (19 69) recorded that earrigs ate smail holes in sugar beet foliage, but usually the was only noticeable when wasteland, scrub or railway embankmenta adjacent to the field provided reservoirs of earwigs.

Fox-Wilson (1940) exwnined the numbers of earwigs in bands

around fruit trees (apple, plum and pear) in two email orchards sepa-

rated from each other by a f].owei'-bed. The type of ground cover (flowers and horbaceous shrubs) in the vicinity of the fruit trees remained unchanged for the 15 years of the study. During this time,

Fox-Wilson (1940) did not observe any earwig migration to or from this site from other aias, end supported this observation with experiments using markod earwige, from which he concluded that there were several

distinct and separate earwig colonies in the orchard with little or rio

contact with each other.

However, 'ox-Wilson (1940) made his observations on earwig numbers in trap bands in October of each year, when low temperatures decrease earwig activity ('u1ton, l92l.). If the marking experiments of

Fox-Wilson were also carried out in October, the low activity of earwigs at this time may explain why he found little earwig movement between areas of the orchard. Alternatively, the orchard habitat may be stable enough to reduce dispersal movements to a iMmm (Cranib, Bide axI Bonn,

1941). - 21 -

Legner and Davis (1963) did not observe re-infestation of 200 sq.ft. plots in a vegetable garden in Utah, U.S.A. in August, for as many as 26 days after the plots had been treated to kill earirigs. Numbers of earwigs caught in tIE control (untreated) plot also do .- creased during the experimental period, indicating either low earwig mobility, or a general movement of earwigs away from the habitat. BeaU (1932, 1932a) axd Crumb et a]. (19141) made experiments on the value of trapping to remove earwigs froii small areas of land. Beo].1 (1932a) found that the earwig population fell rapidly when trapping was calTied out in spring, when the population consisted of feeble, overwintered adults, and. relatively inactive nymphs of installs I and II. However, in early summer, the population rose again and remained high due to rapid immigration of III and IV mater nymphs and active young adults, which move both over the ground cril by climbing trees and fences (Guppy, 194; i1ton, 19214.). Beau (1932) showed that the climbing ability (i.e. negative geotaxis) of earwig nymphs increased from meters I to IV.

Crumb tl (19141) marked mid released adult earwigs in several experiments. In most cases, the marked individuals moved only small distances, far exmiple, on a lawn, where 75 ft. was tIE maximum distance covered between 19th July and 6th October. However, in another experiment where earwigs were liberated in July inside a racetrack of circumference one-third of a mile, marked earwigs were found all around the track after only three days. Conditions at tIE time were very dry, m1 Ciuinb et a]. (1914.].) state that : experimonts with marked earwigs confirm conclusioma drawn from exmnination of the stomach contents of field-collected

earwigs that, when conditions are favourable, the earwig tends to confine its wanderings to a small area. When

conditions are unfavourable, however, as in the race- track experiment, or when the equilibrium of the popu- ].ation is disturbed, as when a single lot in the

middle of on infested area is trapped, the earwig may

wander extensively".

These results agree with the present investigations, when marked earwigs were released in two hop gardens at different times of the year. Noiinal]y, movement was not extensive, but when one area of the garden was harvested, marked individuals were found in ot1r (non- harvested) ixmrta of the garden as far as 60 m. from thofr liberation point in the harvested elsa. It is not biown whether the moveincit occurs by crawling over the ground or by flying.

proho1ov Male &id fi,t1e earwigs are easily distinguished by the shape of the anal oercii, which are strongly curved in the male, but slitly curved in the female (Crumb, Eide and Bonn, 1914; Glendenning, 1911.7)

(plate 1). The ratio of the sexes vary from year tO year, even in specimer from the sans locality (Brind1j, 1932; Fox-Wilson, i912), - from a roughly 1 : 1 ratio to a male deficiency. Brind1 r (193.2, 1934) found an average of 36.0 aM 37.6 males in the Scilly Isles, Beau

(1932), 11.1.6 % males, Fox-Wilson (1940) 51.0 , Crumb 5t a]. (194.1) 50.8 $, and Behura (1956) 4.9.6 males. Herter (1965) observed a 1 : 1 sex ratio in For±'icula.

Size of the male fceps varies greatly (i1ton, 1924), from about 3.5 mm. to a m41nuin at about 32.25 mm. (Briiñ].ey, 1914.). Work by Bateson. and. Brirdley (1892) on male forceps showed that there were Fig. 2

Life cycle of the EuroDean earwig.

Adults enter Soil, October construct cells

Mating November

December First oviposition

Male e1ected from cell January Maternal egg care

Febuary

March

April Nymphal instars Eggs hatch

11 May II?

Second ovIositIor,

June Nymphal Instars 111 'Ip lvi A I July II Ill

August IV

I September Adults and nymphs aggregate in Crevices above ground - 23 -

PLATE 1. Male (top) and fenale (below) P. auricularia.

/ -24-

two peaks in frequency of forceps of any size, with one peak 3,5 nm. long

('low' form) and another 7 itin. long ('b.igh' farm). Intermediate fms were few. These workers thought thet the 'high' or 'low' form was an inherited characteristic, and several authors including Fox-Wilson (19W)) refer to the 'high' form of male as a distinct variety called forcitat. Crumb, EIe and Bonn (1941) experimented on the inheritance of the male forceps characteristic, but without conclusive results. Howover, Kuhi

(1928), criticized the work of Bateson and Brindley (1892) : Kuhl measured 11,630 sciina arid measured to 0.]. mm., whereas Bateson and

Brin11ey (i. measured 583 male a to approximately 0.5 nun. The results of Ktthl. (1928) showed thet the frequency/forcep size curve was unlmodal; there was a gradual rarge of foroep size from small to large in the population as a *iole. Diakonov (1925) was the first investigator to conclude that difference in forcep size of male earwigs had no genetic origin, but was dtE to external influences, especially the abundance of food during nymphs]. life, conclusions since substantiated by Burr (1939,

1939a).

Life-cycle

The life-cycle of L auricularia has been extensively studiad in

England and inerioa (Briridley, 19)4; Chapman, 1917; Worthington, 1926; Fu].ton, 1924, 1924a; Coo, 1925; Behura, 1950, 1954, 1957; Sin]., 1958; Herter, 1965; &poor and Baijnl, 1967). g. 2 sununarises the life-cycle of this species. Several workers have observed the mating of Forficu1a. but only

Fulton (1924a), Kuhi (1928) and Behura (1956) studied the process in detail. The male earwig locates the female with the antennae, then tin'ts crowd and attempts to place the forceps under the tip of the female's abdomen and. - 25 -

lifts It up, while they are facing in opposite directions. The posterior part of the male abdaen is then orientated so that the ventral surface is continuous with that of the female, the fceps of each sex being extended c].ong the ventral si1e of the others body. Coitus takes place in this position. Normally, male and female earwiga are positioned on opposite sides of narrow crevices, to aid the juxtaposition of their ventral surfaces. Goe (1925) stated that in mating, the male seizes tho female with wide open forceps, but this observation is disputed by Th.ilton

(1927). Various authors give different times of the year when copulation occurs. CImznan (1917) found that pairing occurred during late autwn and early winter, while Worthi.ngton (1926) concluded that pairing was at a maximum in December. Beau (1932) observed pairing in a laboratory culture of earwigs throughout the winter. Sullivan (1943) records mating fran July onwards in the field in Scotland, and Fulton (].924a) found that mating occurred frequently from late summer to winter. Behura (1956) found that they copulated. mainly betwoen igust and September in laboratory culture. However, ho also states that most of the male earwigs were dead. by the end of November, whereas fie]1 observations show that most males survive until early spring (sini, 1958). /ccording to thoste (1957), the male iriago becomes sexually mature between the first oni second month, and the female in about the fifth month after beaming adult. Since the first geiration of earwigs becomes mature about mid-July In England, and individuals from later ovipositions mature about mid-September (Behura, 1956), an extended copulation-period among tho adults wou]d be expected from about November

onwards (uioete, 1957). Because of its worldwide distribution, the lifo-cv1e of Forficula varies frcn country to country, according to the climatic conditions - 26 -

(Sin]., 1958). Bowever, in Bugland and America, adult earwigs pair during late autunui and enter the soil for oviposition and overwintering. The precise period varlee with temperature (Crumb, Eide and Bonn, 1914.1), but, in England, is usually around October and November (Worthington, 1926;

Burr, 1939; Behura, 1956; Sia]., 1958). The female earwig excavates a cell in the soil, d for the most part of the winter, male and female earwigs occupy the cell together

(Guppy, 194.6) although true hibernation does not occur. Adult earwigs are sometines active on the soil surface when the weather is mild (Worthington,

1926). The cell is found normally 'within the top two inches of the soil, often under a stone, or a piece of wood giving overhead cover. Occasionally, a more complex cell is found, consisting of a vertical tunnel 'with a side- chamber sloping upwards in which the eggs are laid (Weyrauch, 1929a; Behura, 1956). In America, this type of tunnel is common (Crumb, Eide w1 Bonn, 194.1).

Oviposition occurs a few months after the female becomes adult, the time being i fliiemoed by climatic conditiona (Herter, 1965). The eggs are deposited between December and. February (Worthington, 1926; Beau, 1932;

Sullivan, 19143; Guppy, 1946; Crumb et a].. 1943.) but occasiorl1y they nay be found as early as November (Behura, 1956) or as late as Nzrch (Brlxxlloy,

19)4). As soon as the eggs are laid, the female becomes pugnacious (Burr,

1939) and expels the male earwig from the nest (milton, 1921.; Worthington,

1926; Behura, 1957) since the male readily eats the eggs (Guppy, 1946).

The female earwig icys two, or sonotines three batches of eggs (üton,

19244 Burr, 1939; Crumb, Eide aid Bonn, 194.1) but the eggs of both batches are fertilised before the first oviposition. Oce mating period was sufficient for a female to subsequently deposit three egg-batches, all of which hatched (Bohura, 1956). 27 -

The numbers of' eggs laid in the first oviposition varies between

30 and 40, a1thoui there i so va.riation between the rewits of diffe-' rent workers. Briniley (1914a) recorded a maan of 23 eggs, while Lucas

(1920) a mean of 25 eggs. Other authors have found a larger number of

eggs, for example, in America, lD-6O (i1ton, 19214.), 30 (Crumb et al.

1911) in Germany 45 (Weyrauch, 1929a), in British Columbia, Canada, 4,1-

57, (BeaU, 1932), in the United Kingiom 48 (worthington, 1926), 38 (Su].livan, 19Z,3) and 40 (Behura, 1956).

Male earwigs remain under stones on the soil surface after being

expelled from the nest (Behura, 1956) but die out during the late winter

and early spring. However, the mortality among the male population

depends upon climatic conditions, since Beal]. (1932) found that moot adult males survived until Nay on the W. coast of Cenada, while in Rhode Island on the E. coast, jones (1917) found that almost all males died, in the more severe winter.

The female earwig displays complex and strong maternal behaviour

patterns onco oviposition has commenced (Weyrauch, 1929a). This maternal

behaviour consists of care of the eggs and repulsing intruders, includl?ig predators. Maternal egg-care was first described by the Swedish entomolo-

gist, Do Geer, in 1773 : Do Geer (, Lucas, 1920) found a female earwig with young nymphs in Juiie ...... "They did not leave her, and even placed themselves

under her body as chiokern under a hen. So insects of this kind

take care, in a way, of their offspring after they are born, and stay near then as if withing to protect them." The eggs are very sisceptible to fungus infection (Burr, l939a) and do not noilly hatch if taken away frc the brooding female (CruriLb,

Eide and Bonn, 19Z4.1; Guppy, 1946; Behura, 1956, 1967). The female 28-

cOnstantly turns each egg with her moutbports, lubricating the eggs and probably removing contaminants such as fuigni spores ('u1ton, 1924., 1924a;

Brindiqy, 1934; Crunb, Elde end Boim, 1914.1) and al8o avoiding parasites and controlling the humidity crnd the eggs (Lhosto, 1957). Coo (1925) and Guppy (194) attempted to hatch eggs separately from the female earwig, but were unsuocossfu]., even what the eggs were packed in sterile cotton in a sterile vial. Behura. (1957) found that eggs removed from the female would only hatch if they were within 2-3 days of hat'Jiing when removed.

Present experlriente, however, (Buxton and 4ndge, 19714.) have iown that cleaning and turning the eggs daily with a fine brush oni sterile water will encourage eggs to hatch without the presence of a female. Whether or not the turning stirnilus is essential to hatching was not determined. If the eggs are scattered, female earwigs will. collect them back into a pile; if the soil becomes unsuitable for egg incubation, for example, if the soil is wet, then the eggs are removed to a safe place (Brindley, 1914; Bera, 1957; Burr, 1939). However, if the female is disturbed too frequently, she may abandon any maternal. care arid eat her eggs (Cruziib et ci. 194.1), Predators are repelled when they near the eggs, the female attacking them with her forceps, 'thich have a aeiring action (Crumb et al. 1914.1). Large carzibids and corabi4 larva have been driven away (Burr, 1939; Puiton, 1924a). 'The female earwig will accept spiders' eggs or globulos of wax and treat them like her own eggs. The requisite conditions are size, rotundity end surface texture. When Weyrauch (l9 29a) roughened the wax egg surface with a pin, they were rejected. Therefore, tactile et4rni 11 appear to be important during the licking process, but chemical at (rn1 11 are also involved, for bad eggs are eventually rejected (Burr, 1939). 29 -

Both enbxyoriio and nymphal early develoent depend upon clii0 conditions, especially temperature (Herter, 1965). Therefore, time of batching varies from year to year, because temperature Varies with the location of the nest and. depth in the soil (Crumb et a].. 1%].), but in England most eggs hatch between March and April (Worthington, 1926;

Behura, 1957). In the hop gardens of S.E. Kent, batching in 1972 and. 1973 took place In April. Incubation aid hatching of the eggs has been fully described 1y

Thilton (l921.) in America, end Bchura (1956) in Scotland. As they natured, the eggs increased in size to a wirnn of about 1.7 x 1.3 mm., aid were semi-translucent with the red eyes of the developed embryo visible. The egg membrane burst in the bead region of the embryo, which immediately struggled free from the membrane. Behura (1956) tbouit that the young earwig nymph ate the egg remin, but Fulton (1921g.) did not observe this.

Workers from De Geer (1773) onwards have recorded that maternal care by the female earwigs ertenis to the young nymphs. The nymphs renAlfl together in the nest until at least instar II, the female often bringing food to them (Behura, 1957; Fulton, 1291i., 1924a; Chapman, 1917; Crumb et a].. l9Zl; Jones aid Dunning, 1969). Recently, the development of mutual "licking behaviour" between young nymphs has been described (Eselen, 1972), appearing about four days after hatching, end involving 'licking' of the abdomen, head. and cercil of other larvae using the inouthparts. Tropho.- ilaxia was not observed. Late instar nymphs (instar III onwards) are more active and tend to leave the nest (BeaU, 1932). However, as soon as another batch of eggs is laid, the female drives out the first batch of nymphs (Behura, 1957). There are four nympha]. Instars in Forficula. the development time of each inatar being directly proportional to temperature (Crumb et al. 1941; -30-

Behura, 1956; Horter, 1965). Instars are distinguished. by changes in the thorax, number of antennal seents, and in the size and shape of the forceps end pygidium (Fulton, 1924). The number of antennal sents in meters I to IV is 8, 10, 1]. end 12 respectively, end 14 in the adult (Behura, 1956). The duration of these instors at approximately 16°C. is ]4, 14, 13, 19 days respectivey (BeaU, 1932), at 18°C. is 13, 10, II, 16 days respectively (Crumb et ci. 1941), md at 25°C. is 7, 9, 8, 13 days respectively (Bohura, 1956). (se authors reared their earwigs on differing diets and hence these results are not strictly comparable). By late spring (April - Nay) most of the adult males are dead, although in Narch many males con be caught on the surface of the ground (smi, 1958). Earwigs ore necropliagous (Crumb et L 1941; Sullivan,

1943) and. young nymphs may oat dead adults (Chapman, 1917). Approxinately one month after the first egg batch has hatched (i.e. Nay - June), many females re-enter the soil for a second oviposition

(Behura, 1956, 1957). At this time, most earwig nymphs from the first oviposition have developed to instara II or III. The number of eggs laid in the second oviposition is usually less than that of the first (Behura, 1956), and Crumb, Bide and Bonn (1941) found that only 15 of females laid a second egg-batch. However, it is also possible that some over'- wintering females laid their first eggs in Nay or June, einco Beau (1932) found females in traps above ground during Nay, when most females were tending their brood in cells in the soil. Beau (1932) dissected 30 female earwigs from traps, and found eggs in all stages of development. These eggs hatch during late June aM early July (Bdiura, 1956). The developmental period of these nymphs is more cciipreased than that of nymphs fron the first oviposition, since temperatures are higher aid food more plentiful (Crumb, Bide and Bonn, 1941). - 3i -

Earwigs fron the first oviposition becone adult in about nid.-July, depending upon the climate. Prori July onwards, adults of this new generation and nynphs of all stages gather in any available crevice, sinoe they are attractsd by the earwig scent (Crumb at al. 1914), arkI show a strong tendency to climb, which increases from nymphs]. instars I to IV (milton, l921f4 van Eeerdt, 1916). Nymphs from the second Oviposition become adults by mid-September (Behura, 1956).

Behaviour

Forficula aux'icularia displays negative phototaxis, positive thino- taxis and negative geotaxis (wigglesworth, 1939). Negative phototaxis is typical of a nocturnal insect; earwigs are disturbed at niit even by the dim light of a hand-torch (Thilton, 19 21a). Observations on marked earirigs in hop gardens at Wye College during the night confirmed that nocturnal behaviour was halted even by torch-light. However, the earwig seems insensitive to red light, since Ncleod, and Chant (1952) observed nocturnal predation by Forficula on aphids, using a red light with a wave- length of about 650 A. A].'though the earwigs' compound eyes detect light readily, they are anti]. with comparatively few facets ('acone' type,

(wiggleeworth, 1939)) and do not form clear linagos (van Heerdt, 191.6).

Weyrauch (1929) thouit that the range of clear vision was no more than

1 cm. distant. However, since earwigs axe negatively phototactic they react more quickly to all st4imiHi in the dark than in a bright light

(Burr, 1939).

Earwig nymphs display stronger negative geotaxis in the later instars (III crid iv), whereas early instars I and II show little tendency to climb (Beau, 1932). Mult earirige and IV instar nymphs climb readily, even to the tops of trees (milton, 1924), and in anch situations may live independently of the ground for long periods. This behaviour persists during the summer months, but during late autuim earwi return to the soil (van Eeerdt, 1946), althoui may become active on the soil surface whenever the temperature exceeds about 40Q• (Guppy, 1946). The tactile stimulus or thignlotaxi9 is very important iii Porfioula (Bun, 1939). The earwiga antennae are covered with artio.ilated hairs (tactile receptors) and serve as tactile organs. Movement is accompanied by continuous palpating of the antennae in all directions, and if one antenna is removed, the remaining one palpates on both sides (Weyrauch, 1929). If placed in a petri-dish, the earwig immediately aligns its body along the glass so as to maintain maximum body contact with the dish

(wigglesworth, 1939). The earwig's hiding places are chosen to satisf'- its negative geotaxis and phototaxis, ani positive thigmotaxis. This behaviour accounts for the strong preference shown for squeezing themselves into small crevices away from the liit, protecting them from predators (Nuggeride, 1927). Hygro- and thermotaxis are less important, since some hiding places exposed to the sun become very hot (33-35°C.), but this temperature does not apparently disturb the earwig (van Heerdt, 1946). Earwigs ore attracted by their own scent and aggregate in suitable crannies during the day in aunmer (\i1ton, 1921g.; Crumb, Elde end Bonn, i911).

Using an olfactometer, Beau (1933) found that Porficula showed a weak orientation to various scents, including liver and apple, but away from, rather than attracted to, the scents, van Heerdt (1946) showed that the olfactory sense of 1orficu) . was weak, end that food was only detected at a distance of about 05 cm. Female earwigs with either eggs or young can orient themselves back to the nest from short distances (Sullivan, 1943). When released at - 33 -

20 or 8 feet (6.2 or 2.4. m.) from the neat, only females from the latter

distance returmed safely, and when released at N., S., E. or V. orientations about 10 feet (3 rn,) from their nests, individual females seldom found their way back, van Heerdt (1946) found that female earwige could occasionally 'home in' on their zest, but rarely left it if not disturbed;

males had no sense of orientation. If earwigs are held firmly by their forceps, dragged backwards over

a piece of paper, and then sudxIenly lifted into the air so that the tarsii

lose contact with the paper, they become immobile for long periods (Weyrauch, 1929). This imnobility or 'akinesie' can be induced by seven other methods, but such stiimilii as draughts or shaking, overcome the effect. Weyrauch

(1929) found that both sexes reacted similarly, and. tained periods of akinesis varying from a few seconds to over an hour. Burr (1939) postu-

lated that the ald.nesis occurred as a counter-react ion against further excitement of a fixed point in the central nervous system, and that the inhibition radiated from the point of origin, involving the whole of the

central nervous system.

Both male and female earwigs use their forceps as defoe or attack organs, male forceps being primarily piercing organs, whereas those of the female are capable of a sharing action. Because the abdomen is so flexible, the forceps can be brought into play in any plane ranging from the horizon-

tal to the vertical (Crumb, Eiile and Bonn, 1941; Behura, 1956). The up- raising of the abdomen and flexing of the forceps is a reflex action; young nymphs having relatively unsclerotised forceps also display this

reflex (Sullivan, 194.3). Thus earwiga can defend themselves from attack by various carabids and carabid larvae (i1ton, 1924a; Burr, 1939), including ?terostichua app. (Crumb, Eide and Bonn, 1941). Earwiga will somatimea attack prey such as blowfly larvae (Fulton, l924a) and adult flies (Goe, 31.

1925) with the forceps, but usually smaller insects such as aphids are eaten using the mouthparts only (Brindley, igis). Occasionafly, the forceps are also used to help fold the wings under the teginina (Crumb et a).. 191i.].).

Feeding habits and economic importance The European earwig is an omnivorous feeder (Brindley, 1918;

\.zlton, 1927; BeaU, 1932; Glendein4itg, 1914.7). Earw'igs have been described as either harmful or beneficial to horticultural and agricultural crops. This controversy has been continuing since about 1887, when von Sdiilling, carrying out feeding taste with P. auricularia. found that caterpillars and pupae of a tortrix moth were eaten. Since then, many workers have commented on the food of the earwig by making feeding tests or emii4iig the stomach contents (Theobail, 1896, 1912, 1913, 1926; Luatner, 19114.;

Muggeridge, 1927; Crumb, Eide ani Bonn, 1914.1; Nassee, 19143; Croxal]. et al.

1951; Sin]., 1958; Asgari, 1966). They all agree that both plant and animal food is eaten, but disagree on the amount and nature of the food.

Eowever, only Schwartz (1908); Lustnor (1914.); Crumb et al (1941); Skubravy (1960) and Asgari (1966) thorouiiy investigated the diet of earwiga. Their results differ, since each author used ea.rwigs from different crop habitats.

Luatner (19)4) j Crumb, Bide and Bonn (1914) extmtined the crop contents of 162 field collected earwigs, and found that the food consisted mainiy of dead plant tissue, sooty fungi, green algae and insects. He thout that the earwig was therefore noithor beneficial nor harmful to

nan. Hever, all his specimens came from apple, pear and peach trees, and Crumb et a]. (1941) criticized the fact that his conclusions were drawn from specialized rather than widely differing habitats. Schwartz - 35 -

(1908) in Asgari (1966) made extensive laboratory feeding experimellt8 and concluded, that vegetable food was preferred to nrd1 food, but ithen slimil- taneously off ered. both were eaten. In an extensive literature review, &iMley (1918) concluded that the universally bad reputation of the earwig among gardeners was founded on tradition and lack of udgement when increasing evideixe showed that the insect was sctimes beneficial. Brindley (1918) stated that "observation at night i particularly needed" to investigate the earwig' a feeding habits • pu.lton (1924) found that the diet consisted normally of green vegetation, although starch and meat were readily taken. Crumb et al (1941) examined, the stomach contents of earwigs which had been confined inside metal barriers where lichens, moss, grass and hid-infoated dandelions were growing. They found that 50 out of 53 earwigs fed upon vegetable and animal mat orial, the main m,imrtl food being aphids. (kily one earwig contained aphids alone in its stomach contents.

The same authors dissected 34.7 specimens during the entire active season of F. auricularia. They showod that, out of 155 adult earwigs, 119 hnd.

fed mostly on vegetable matter, while only 36 had. fed. mainly on animal matter, especially aphids. The proportion of animal matter in the diet of nynrphal earwigs was even less, aiggesting that the adults were cErni- vorous to a greater extent than nymphs.

Skubravy (1960) examined the stomach contents of earwigs from clavor, lucerne, oat, grass and sugar-boot fieJAe over the whole growing season from June to October. He concluded that vegetable matter formed about - 4/5 of the diet, aid. niyIm'1 food. the remainder. Plant food was

composed mainly of dead plant tissue, floral parts, and several species of fungi, especially Alt ernaria ap., ErYsiDhe ap. and St nhvlium sp,, which

the author thought were ingested with the dead plant material. Some aerial

parts, such as leaf romaine, and rust fungi (ionvces sp.) were also eaten. -36-

Skubravy (1960) found that the seasonal avai]ability of aphids within a

crop determined their appearance in the diet, ani that aphids were some-

times dom1n nt in the diet, as for example when the clover and lucerx

fields were harvested and the aphid Acrthosihum onobrych Bayer was

abundant.

The omnivorous habits of the earwig are well-illustrated by the various foods on which various workers have reared earwig colonies

(Table 1). The vegetable food eaten by earwigs is rarely derived from a single plant species (Crumb et a].. 1914.1), and althoui dmnage is sometimes caused to flowers and vegetables, it is small compared with the numbers of earwigs present (Ditnick and Iote, 1934). These authors em4ned the crop contents of earwigs from Oregon and conoloded that the food was mainly composed of lichens and. pollen, (although they do not state the habitat from which their specimens were obtained). There are meny reforezes in the literature to the damage earwiga cause to plants, but in most oases this appears to be exaggerated (Tiilyard, 1925; erid, 1927; Stone,

1934.; Pox-Wilson, 1942).

Crumb, Eide and Bonn (1914.1) stated after a detailed eyptn1rrition of the food habits of the earwig in America that :

"Opinion as to the economic status of the earwig in Europe

is very diverse, but those who have given most attention to

the insect seem, in general, to believe that The importance

of the earwig, both as a pest and as a benefactor, has been

exaggerated, although agreeing that it occasionally does

serious damage to a wide variety of cultivated plants and

likewise is sometimes boneficia].," - 37 -

TABLE 1. Tbe food of earwjs in laboratory cultures

OD A.UTHQR

Potato peelings. Brindley, 19)4.

Dandelion, grass, dead insects. chapman, 1917.

Roast mtitton, imitton suet. Brind].ey, 1918.

Dandelion, cut pieces of insect. .1ton, 1924a.

Raw beef, pork, dead slugs, flies, Goe, 1925. aphids.

Dandelion blossom, meat meal, bone Crumb, Eide and Bonn, 1941. meal, dried pulverized grass.

Boiled beef, liver, breadorumba. BeaU, 1932.

Breadcrumbs, dead. insects. Sullivan, 1943.

Potato, dead insects. Quppy, 1946.

Dandelions, cabbage, potatoes, Behura, 1956. dead flies, spiders.

Dandelion flowers, powdered mouse- Wilson and Wilde, 1971. food, pollen. -38-

edptprv habits Table 2 sumznarises the arthropod prey of F. auricularia which have been recorded in the literature. The list is extrenoiy varied, but of the authors quoted, only .aagari (1966) investigated the quantitative predation in terma of numbers of insecte eaten per day. Most of the other authors mention Forficula as a. predator only from visual observations.

Molagan (1932) conducted a survey of the crthropod predators of the coflembola Sminthurus viri4ia, and found that F. auricularia was the most voracious of any predator tested, including large carabids, staphylinids and spiders. Two female earwigs kept in captivity for 74. days ate 958 Sminthurus. an average of 6.0 per day, while male earwigs ate about 5.7 per day. Mcleo. and Chant (1952), rearing earwigs in Vancouver, British

Columbia, found that adult earwigs readily consumed various species of aphids and scale insects, even when their norma]. food. (lettuce, carrot, meat meal) was present. They calculated tlmt each earwig ate about 8 or 9 evicorvne brassicae aphids per day, althou this is an approximation since detailed feeding studies were not made.

Predators of the broom beetle, Ftivtod.ecta olivace Porster have been investigated by Danpater (1960) and Richards and Waloff (1961). Both authors found that Forficula was among the beetle's predators, and fed on all stages of the beetle. Danpater (1960) showed that approximately 9 of all earwigs tested by the precipitin method for anti-hTytodect4 serum were possible. Moreover, laboratory tests showed that, of about U predators considered, only Forficula and rbbis atoru P. would consume broom beetle larvae as large as instar IV, and adult beetles. Earwigs ate moat beetles at the end of the season (August - September) when the earwigs were most numerous on the broom. However, Dempeter (1960) only recorded earwigs from debisced seed-pods, which offered a convenient - 39 -

TABLE 2. The prey taken by F. auricularia as recorded from the literature,

LEPTh0PTA:

Tortrix viridana. L, von Schil].ing, 1887; Anon, 1922. larvae arid pupae. Lasto9Tesia unebrana Tr. Golubenko, 1969. eggs, larvae, pupae.

Depressaria heracleana deG. Harrison, 1913; Brittain and larvae and pupae. Gooderhani, 1916.

Clvsia ibiueUa (Huebner). larvae.

Polychrosis app. Bernard, 1929; Dobrodeev, 1915. Larvae. Sparaiothis pilleriana (Schiff). larvae ani pupae.

Carpocapsa pomonefla L. Theobald, 19]2; Littler, 1918; larvae aixi pupae. Berlanl, 1929; Crumb et 1. 1941. eggs. Glen, l97l.. adults. White et al. 1969. Pieris brassicae L. Schwartz, 1908; Berland, 1929; eggs, larvae, pupae, adults. Metzner, 1926; B].unck, 19l1,.. Nalacosoma app. Crumb et al, 194]., larvae Dihraea saceharalis F. Negm, 1969. eggs and larvae. Ostrinia nubilaija Hb, Tkalich, 1967. eggs arid larvae. imaethis pariana Clerck. (Heinerohila pariana) Clerck. Minkiewicz, 1925. larvae.

Hvphantri.a textor Harris. 1.sidota ar tta Pack, Crumb et a].. 1914.1. larvae. Trvhaena pronuba L. Lucas, 1920. eggs. Cracilaria svrine11a F. Ber].and, 1929. larvae. COLEOPTER& : Thytodecta olivacea Forster. Dexnpster, 1960; Richards and adults and pupae. Waloff, 1961.

Pterostichua algidus Lee. Crumb et al, 194.1. adults. Cantharis spp. Skuhravy, 1960. larvae.

Levtinotarsus decenilineatus Say. Jolivet, 1950. larvae. Coccinellid larvae. Theobald, 1932. Weevil adults. Skuhravy, 1960.

DIPTERA Cec1.omvia tritici Kirby. Lucas, 1920. larvae.

Leptohv].via poarctata Fall. Dobson, 1961. eggs.

Tipula app, Sullivan, 194.3. eggs and larvae.

Calliphora app. Pu].ton, 1924, 1924a. larvae.

Unnamed adult flies. Goe, 1925; Behura, 1956.

H0(0PTBR& Eulecanium app. and Pulvinaria vii L. Feytaud, 1916. adults. Lecanium corni Bouche. Mcleocl ani Chant, 1952. adults. Lepidosaphes ulmi (I..) Ncleod and Chatit, 1952. adults,

Lecanium ribie L. Lucas, 1920. adults, Aspi.diotus oerriiciosua (Const.) Crumb 194.1. adults.

.Aavidiotus app. }c1eod and Chant, 1952. Perkinstella saccharicida. Lucas, 1920. adult a. Unnamed Jassid adults. S]cultravy, 1960. -41-

hAl*lis idaei van der Goot. von Schil].irig, 1887. Acvrthosioham gDartil Koch, Smith, 1961. Ahis fabae Scop. W aid Banks, 1968. }hprodon humuli (Schxaxik). Eacherich, 1916. iosoma app. .âJ.fieri, 1920. k,hi (ahidu1a) T,omi Deg. Schwartz, 1908; Asgari, 1966. Netovolovhium dirhodum (wik.) Dean, 1974.. !!acrosjphum pvenae (F.)

Brevicorvne brassica p Bouche.

Eriosoma laiiterwn (Hausin). Mcleod aid Ch&mt, 1952. C1avigeris smitbiae Monell. Acvrthosivhuin onobryclils Bayer. Skuhravy, 1960. RY!'NOP2ERA

Divrion app. Sturin, 1942; Dobrodeev, 1915. eggs.

Th'n'med bee larvae. Berland, 1929; Crumb et al. 1941. COLLEMBOL.&

Sminthurus viridis L. Mclagan, 1932 ; .tshraf, 1969. adults. Bourletiplia hortenip (Fitch). Foster, 1970. hiding place for earwigs during the dy. Hi sampling method was therefore

not adequate for the earwig, for larger numbers would probably have been

present in the detritus, cracks in the soil, etc. at the base of each

broom bush. Richards aid Waloff (1961) recorded that Forficula would

prey on broom beetle pupae overw:Intering in the soil.

sgari (1966 ) noticed earwigs inside rolled-up apple leaves in

orchards in Stuttgarb-Eohenheim, Germany, during 1962-1964, usually from

}ay onwards throughout the summer, and found that they were preying upon

the apple aphid, ADhis (athidula) oxi DeG. He made feeding experiments

at 15°, 200 and 25°C. with apple aphids as prey, finding that the mean

number of aphids eaten at 20°C. during instars I, II, III and IV was 2,062,

1,444, 1,838 aid 3,387 respectively. The earwig was a more voracious predator than Chrvsova vu.laris Schneid, Cocciriella sevtemvuzictata L., or

Anthoaoris nemozim L.

Smith (1966) observed that earwigs preyed on the aphid Acvrthosim snnrtii. Koch on broom. Adult earwigs were found to kill about five young

L svartii per day when confined in 7.5 x 2.5 cm. glass tubes with a shoot of broom aid 30-100 first to third instar aphids. In contrast, third instar

Chrvsoa carnep larvae killed about 15 aphids per day under the sane conditions, which is surprising since adult Fbrficula are larger aid heavier than Chrvsona larvae, and might therefore be expected to be more voracious predators, especially as For±icaila nymphs ate more apple aphids than did

Chrvsova vu.lgsris larvae (Asgari, 1966).

In investigations on the active stages of the black bean aphid, bis fabae Scop., on its winter host pxtvmns euronaeua L, Way aid Bwks (1968) recorded that F. auricularia was capable of depleting the aphid population in autumn, but only when aphid populations were m11• -43—

Crumb, Eide and Bonn (1941) showed that earwigs cou]d reduce aphid colonies by planting Aster ap. in several plots surrounded by metal barriers. The asters became infested with aphids, and in those plots into which earwigs had been placed, aphids disappeared even thoui repeated new infestations of aphids were made. Also, European red mites, Paratetranvchus viosus C. and P were eliminated from apple trees in July in plots containing large numbers of earwiga.

Generally, it seema that aphids are the most attractive insect food, and are preferred over vegetable food.

Attack uon Diants

As early as 1896 Theobald recorded sporadic attacks by F. auricularia on foliage. He noticed that in July the leaves of hop plants were eaten in a curious ragged way, usually leaving only the central veins. This 'ragged' appearance of earwig feeding is characteristic (Filton, i921.).

Theobald. (1896) counted as many as 120 earwigs, mainly nymphs, in one hop bill. He states that :

"At n(gbt, one could watch these insects by the aid of a

lantern devouring the foliage with great rapidity, especi-

ally the young tender leaves. As these pests grew the

damage naturally increased, and unch harm was dons to the young plant8."

Since then, various reports of earwig damage to hope have been reported (Theobald, 1913; Nassee, l91h3; Moreton, 1964). However, the damage is sporadic, and usually earwig populations go unnoticed. Both

Theobald (1913) and )Tassee (1943) found that the wooden polework of some hop gardens provided cracks that made ideal sheltering places for large numbers of earwigs. Theobald (1913) was among the first workers to -14-

recommend grease-bend.ing of the poles to exclude earwigs, a technique which has been adopted in exclusion experiments in this study. Theobald (1926) proved that earwigs could occasionally cause severe damage to plum trees by eating out the young buds in April. He states, however, that there was little other food available to the earwigs in the orchard concerned, ani that the d.amage may have been accentuated by the bards of sacking which had been placed around each tree, and which provided hiding places for aurilaria (up to 20 per bath). Theobald (]. g.) noticed similar damage to plum trees all Over Kent, but not usually so marked. Ward. (1969), however, did. not notice foliage or bud damage and. listed P. auricularia as a generally predacious insect on plum trees. There is some evidence that plants providing crevices suitable for earwigs to hide in can sometimes become damaged (see above). Thus, there are several accounts of earwig damage to maize plants, especially the cobs.

Hearle (1929) aM Coyne (1928) record corn ears being damaged by earwigs feeding on the silks. Crumb, Bide and Bonn (igz.i), in Waahingion, found earwiga beneath the husks of maize, The insects were distributed through

fields several acres in extent. Earwigs readily shelter in the crevices between maize leaves and stams, and the leaves sheathing the young cobs.

These crevices are dark and narrow and, therefore, satisfy the earwigs' negative geotaxis, negative phototaxis and positive thigmotaxia. In England,

little damage to maize ha been observed, but elim ination of the aphid

Thonalosiphum padi L. was associated with the presence of earwigs on maize

plants (LL Elamin, Wye College, pet's. comm.). Certain types of flowers, particularly dh1i, and carnations, are

liable to earwig attack (Luatner, 19)4; Fulton, 1921g. (Jleudenxdmg, 191.7;

Crumb, Eide and Bonn, l9Z1). Coo (1925) maintained that earwigs were mMnly carnivorous and entered. flowers such as dahlias only for shelter and. -45-

in search of small insects, but Fulton (1927) maintained that more plant than insect food was taken, and that :

"if they had to depend upon a meat diet, most of then

would starve for there would not be enough insects

which they could capture, or enough dead Rnima].S to support a tenth of them." Earwigs feed on flowers, often in preference to other parts of the plant, probably because certain floral parts such as the stamens and pollen

have a high protein content (Jones, 1917; Mcleod and Chant, 1952 ; Behura,

1956). sku1iravy (1960) and Dimic]c ar Mote (l93l.) also noted that pollen grainp were frequently taken in the earwig's diet.

Various types of soft fruit (pears, apples, plums, peaches) may someti.nies be eaten, especially when ripe (Theobald., 1912; Brindlery, 1918; BeaU, 1932), although usually only when an initial hole in the fruit has

been made by codlirig moth or sawfly larvae (Fox-Wilson, 1942). The damage was considerable in some years in England (Sial, 1958), but usually passed

unnoticed until brown rot, Scierotinia fructi g i, set in around the hole in the fruit. Croxhall et 81 (1951) thought that earwigs were one of the inMn dissninating agents of brown rot from fruit to fruit. They associated earwig damage mainly with grass orchards, and found few earwigs and little damage in arable orchards. In controlled experiments by Crumb, Bide and Bonn (1941), during which earwigs were enclosed inside metal barriers oontain 4 'g blackberry, raspberry, strawberry and gooseberry plants, little damage to fruits was

observed. Moreover, no damage to apple blossom on trees inside the barriers was seen, wd when two isolated branches were sleeve caged to

exclude earwigs, the branches set no more fruit than uncaged ones. The

authors therefore concluded that earwigs do not normally damage sound fruit. -46-

Various types of vegetables have been occasion8l]y damaged by

earwige but, as Diinic]c and Mote (1934.) round, "the damage is usually iafl compared with the hordes of earwigs present," Because the earwig is omnivorous, it will select an alternative

if its favourite food is not readily available (1'uiton, 1924.). Thus, the

number of species of green plants available ae food to earwigs is extensive,

(Behura, 1956), and includes celery, potatoes, marigolds (Giendenx'(ng, l9Z.7),

bean, beet, cabbage, cauliflower, pea (Fulton, 1924.), crucif era, white clover, hol]yhocic, maple (BeaU, 1932), cabbage, french and runner beans,

lettuce, sugar beet (Fox-Wilson, 194.2), and broom (Dempeter, 1960). In many cases, a plant was eaten by earwigs in captivity, when little alterna-

tive food was available. Brindley (1918, 1920) gives a list, of 74. species of plants, including most of the common garden vegetables, flowers, fruits and weeds on which caged earwigs fed on some part of the plant. In an

attempt to clarify the controversy concerng attack by earwiga on vegete-

b].es, Crumb, Bide and Bonn (194.1) sinlulAted field conditions by planting an area to beau, beet, cabbage, celery, corn, cucumber, lettuce, onion, pea,

potato, radish, rhubarb, strawberry and tomato. Then a transverse metal barrier was constructed, dividing the area into two equal plots 45 x 70 feet, surrounded by an earwig-proof wall. 20,000 earwige were liberated into one

plot, while only few were present in the other. They found that all the

plants were eaten to soma extent, especially cabbage, bean, pea and rhubarb,

but as the season advamoed, the plants outgrew most of this injury. Finally, there was little difference between the vegetables in the infested and un-

infested plots. Althoui this was an artificial situation, the density of

earwigs was very high, yet permaneut damage to the plants was small, indicating that most of the damage to vegetables reported would not be serious

enough to reduce crop yield. Jones and Dnnrthig (1969) reported that, - L.7

a1thoui earwigs sometimes ate holes in sugar beet foliage, the dange did not affect crop yield.

Conclusions

Earwigs feed preferentially upon high-prote:In plant parts, such as

stamens and poi].en (Jones, 1917; Mcleod and Chant, 1952; Behura, 1956);

dandelion flowers are especially eaten ( pulton, ).921e. Crumb et al. 1941).

However, Asgari (1966) offered adult earwigs the choice of aphids or apple leaves, carnation or dandelion flowers, and aphids tA phis pomi Deg.) were invariably eaten first.

Experiments at Wye have also shown that hop aphids, Thorodon humuli (Schrank) were preferred to dandelion flowers, although dandelions are a favoured plant food.

Prom these experiments, it appears that earwigs prefer to eat certain food types, such as aphids and floral parts, but if these are not

available they will eat nearly any type of food available in the habitat. Therefore, before stating whether the earwig is beneficial or harmThl to

any particular crop, the fauna of the crop must itself be investigated. In

hop gardens, where aphids (P. humuli) are often available from !r to September, d where clean oniture ensures that little alternative food is

present (Massee, 1963), earwigs may feed all season upon P hunuli. although taking other types of food as well (p. 129).

Thitrv into houses

Besides the reports of damage done to various crops, there are references in the literature to numbers of earwigB entering houses and beoom-

ing a nuisance, although this has never been widespread. Most cases have

occurred in New Zealand and. America, where the earwig was accidentally -48-

introduced into the ecosystQn. Pulton (l92i.) stated that eariga were ma1n1y confined to cities and urban regions in the Oregon area. At night, earwigs crawled over and into houses, taking refuge in clothes, furniture, or any available crevice by day. Polton (1924) reported that a man pulled on a sock one morning which contained three earwigs Dimick and Mote (1934.), also in Oregon, reported that the earwig was not a horticultural pest, but still an occasional nuisance in houses, 25 years after it had been introduced. G1end'r4rg (1914.7) wrote that "the chief objection to the earwig is its habit of invading houses" (in Vancouver, British Columbia). Goe (1925) thought that earwigs only entered houses involuntarily as, for example, when carried in by man inside flowers, but i'ulton (1927) said that earwiga mainly entered houses in search of dark hiding places to pass the daylight hours.

Few references are available about earwigs entering houses in

England. Lucas (1926) recorded a 'swarm' of F. auricularia entering a house in South Croydon in July and August, 1925. Fox-Wilson (1942) quotes a few examples of house invasion, especially on new housing estates, in

England. Occasionally, earirigs become more numerous in an area where man's rubbish provides a food-source (Pox-wilson, Thus, Brindley (l9l1.) found that earwigs swarmed among potato peelings and in old meat tins thrown out by lighthouse keepere on Round Island. (Scilly Isles), and states : "The presence of man has apparently favoured their increase in this spot." However, the reasons behind invasion of houses by earwigs are still obscure. Fox-Wilson (1942) concluded that the stimuli that brought about their invasion of houses appeared purposeless, since they were not directed towards food-fiMlng, mating or oviposition media. He found that most invasions occurred during the period of July - Septnber, which is the period of maturation and peak activity of the first generation of - 4.9 -

F. auricularia (Bean., 1932; Behura, 1956). The invasions m&j therefore represent the outward movement of large numbers of earwige from a focal point, perhaps in response to a dispersal Instinct.

Effect of pesticides upon F. auricularia

Because the earwig sometimes causes damage to crops, pesticides have been occasionally applied to reduce their numbers. Theobald (1913) reported that earwig damage to young hop bines could be reduced by dressing the soil heaviiy with soot, combined with smearing molasses around the base of each bine. However, Theobald. (]. did not obtain good control In a poled hop garden, because the earwige bid inside crevices In the poles and were thus difficult to oontact. Lead arsenate spray was attempted, but seaned to have no effect upon the Insects. Massee (1943) tried derris dust and nicotine sprays against earwigs in a hop garden in Rochester In Jima, but these compounds were ineffective. Lead arsenate was then applied by hop- wa& 1 ng machine, and this reduced the infestation suocessfufly.

The thiginotactic habits of F. auricu3.aria make control by field- spraying difficult, since many of the insects are protected by the crevices in which they hide, and are thus riot contacted by the spray (G1aenth-ng,

194.7). Most attempts at earwig control have been made in merioa to prevent infestation of houses or to try and eradicate earwigs from a large area, such as the Portland earwig c gpaiga of 1923 (Fulton, 1924), end Involved the use of poison baits combined with earwig trapping and removal.

However, several Insecticides are known to kill eaririga, including

T and BEG (a1emevrn4g, 194.7; Stellwaag, 1948; Jones and Jonea, 1964), calcium cyanide (Muggeridge, 1927; DilDick arid Mote, 1934), and dieldrin

(Cox, 1952). Several compounds such as napthalene, parad.icblorbenzene and cyanide dust have been used to kill earwiga hiding in plants or trees -50-.

from a nursery (Mackie, 19314.), but naptimleno aid pard.tohlorcbenzane were ineffective.

HackLe (l93z.) placed earwigs between wire soreens and sprayed contact insecticides on them with an atomised spray. £Liphatio thiocyanates, pyrethrum, derris aid niootine sulphate were used, but only pyrethrum and derris gave more than about 60 mortality. Legaer aid Davis (19 63) found that aidrin, chloxdane, heptachior and dieldrin were effective against earwige in petri-dish tests in which a wooden marker of area 14.1k sq.cm. was dipped in the insecticide aid enclosed with the earwigs in a dish.

Dieldrin had the longest residual effect in these tests, causing about 50 $ mortality up to 521g. hours after treatment at a 'heavy' rate (1.0 lb. a.i./100 gallons), thile heptachlor had little residual value but gave the quickest kill (about 70 mortality after one second's exposure to heptacblor at 1 lb. a.i./].00 gallons). Legaer and Davis (1963) made field experiments using granular formulations of aldrin, chiordane, dieldrin aid heptachlor applied at lb, a.i per acre against earwigs in an irrigated garden in Utah during August. Using 200 sq.ft. (18.6 sq.m.) plots and sampling earwiga by means of Mason-jar traps (Legner and Davis, 1962), similar to pitfall-type traps, they found that heptacblor gave a substantial reduction in earwig population within 12 hours of application, aid after

25 days, field populations of earwigs had been reduced by 950 or more by application of each of the above chemicals. However, the earwig population was not sampled before insecticide application and so the variation in earwig numbers between plots was n1nown. Earwig numbers decreased rapidly in the treated plots from August 3rd (date of application), but after

August 5th, numbers on the control (untreated) plots also decreased, which may have affected the results. Also, the sampling method used probably underestimated the number of earwigs present, since Morris (1965) founl - 51 -

that earwigs were 4,5 times more numerous in 'grooved board' +rape than pitfall-type traps.

Both Muggeridge (1927) and Legaer and Davis (1963) found that earwig nymphs were more susceptible to insecticides than were adult earwigs. Many experiments with poisons incorporated into baits for earwig

control have been made (Muggezl4ge, 1927; i1ton, 1924; Dimic]c ani Note,

1934.; Crumb, Bide and Bairn, 1941). 54 different compounds, ifly salts of fluorine and arsenic, were tested against earwigs by Crumb et al, (1941). The poisons were incorporated in a 'carrier', usually wheat bran, and often an "attractant", such as fish-oil, was added (Pox-Wilson, 1942). The baits are mAjri].y used to control earwigs in or about houses in urban areas

(Dimicic and Note, 1934), the be8t fozw.ila being wheat bran (carrier) 12 lbs., sodium fluosilicate (poison) 1 lb., and fish-oil (attractant) 2 pints. This bait has been ertensively used in America, where large amounts were applied to the city of Portland, Oregon in 1923 in an attempt to eradicate earwigs (i1ton, 1924). However, sodium flun silicate is toxic to mRnnnls and the bait can be lethal to dogs, chickens and cats (Crumb, Bide and Bonn, 1941).

Use of trans The res:ponae of earwigs to stimilii such as light, contact and gravity are satisfied in many types of trap, which catch numbers of earwigs

(Fox-Wilson, 1942). Sizch traps as hay and grass-stuffed pots erected on canes over similar traps laid on the ground, have been used to catch earwigs in gardens for many years (Fulton, 19243 Muggerldge, 1927; Po-Wi1son, 1942;

Crumb sit al. 1941). Baths of sacking material stretched around tree trunks or plant stuns are also used (Theobald, 1912, 1926; Muggeridge, 1927).

Even hollow stems of bamboo or dh1ia either laid on the ground or stood - 52 -

upriit accuzmilate numbers of earwiga (Worthington, 1926; BeaU, 1932; G]dnlng, 194.7; Be1nra, 1956; Sial, 1958). More specialised traps, such as two piecee of grooved board held together by iire clips, have been used by several authors for earwig population studies (chant and Mcleod, 1952;

Crumb, Elde and Bonn, 1941; Morris, 1965). Sial (1958) distributed 6-inch lengths of bamboo cane In apple orchards at Wye College during 1955-1956 to sample the earwig population, while BeaU (1932) used several types of trap, IncliiMng sanld-ng around tree trunks, newspaper bundled up and placed in the fork of a tree, Inverted flower pots filled with grass or newspaper, and. old, dry dahlia or bamboo sections to sample earwigs in British Columbia.

All these types of trap offer d8zic crevices for earwigs to hide. They may be fixed either above or on the ground. Crumb et a]. (1941) found that the number of earwigs cauit in "grooved-board" traps in Washington, U.S.A. increased with the length of tIme the traps were exposed, up to a certain limit. In 20 traps, these authors caught 85 2 earwigs the first week, 4.,450 the third, and 4,485 by the fifth week, ani attributed this to the fact that earwigs were highly gregarious, attracted by earwig odour, and the grooved boards formed satisfactory hiding places for L auricularia.

BeaU (1932a) eTrmmtned the effectiveness of several different types of traps placed In trees and on the ground, in Wev Wesbninster, British

Columbia. Here, tree traps caught approximately five times more earwiga than ground traps. Meleod and Chant (1952) found that traps in trees were three times more effective than traps on the ground. Early in the season nymphal earwigs in instars I and II were abundant in the ground traps, but by mnici-guner III, IV inatar nymphs and adults were more oonmion In traps above the ground (BeaU, 1932). G.lendrn1iig (19z.7) found that the most efficient earwig trap was a sack or paper bundle in the foit of a tree. - 53 -

Several authors have experimented with "baits" or "attmctant&' to increase the catches of traps. Beau (].93 2a) found that beef dripping increased his catch, while the addition of sugar cubes reduced it. Crumb et a]. (1941) tried 590 materials for attractant properties. In thatr experiments they t.ed small waxed paper cups into which was placed a piece of cellulocotton impregnated with the teat substance. The cup was closed by a lid, while two ml1 holes allowed earwigs to enter or leave. The cups were laid horizontally on a grass surface. .sh-oil, honey, sesame oil and capsicun oleo resin were among those substances which caught aigni- ficontly more earwigs than control (untreated) cups. However, when tie same tests were performed using 'grooved-board' earwig traps, more earwigs were taken in the untreated traps. The authors could not explain this result, but quote Bea].l (1933), who found significantly less earw'igs in the aim of an olfactometer where the air was impregnated with liver or apple scent. The oatches in "shelter" earwig traps depends upon earwig activity, which is itself influenced by climatio conditions (Chant an McIeod, 1952).

Legnel' and Davis (1962) thought that shelter traps were inadequate for sampling earwiga on a quantitative basis, since the catch depended upon the degree of mechanical disturbance of the trap, the time of day, wind velocity, and humidity of the air. Legner and Davis (1962) used a modified pitfall trap, consisting of a pint Mason-jar sunk into the ground, with an inverted irax paper cup anchored inside the top of the jar. They termed this a

"no-exit" type of trap. ash-oil, peanut butter and macerated earwigs were used as baits, but peanut butter traps caught about twice as many earwiga as any other type.

xorris (1965) compared the efficiency of Legner traps and grooved- board traps in Newfoundland. The Legner traps were sot in the 50i1 flush with the surface, and protected from rein by a 12 in. x 12 in. board held - 51.-.'

in position by short legs at the four corners. They were either unbaited, or peanut butter, cod oil, molasses, honey, or macerated. earwigs added.

Morris (1965) showed that 'grooved-board.' type traps captured about 4 tines as many?. auri1aria as pitfall traps baited with honey, which was the most effective attraotant tested.. Norris (]. .2j.) used grooved-board traps without attractants during five years study of earwig populations, and recommended the traps f control of earwigs in 11 areas.

During studies on the behaviour of carabids within the hop garden, pitfall traps were used in 1973 but cauit few F. suricularia. while corri- gated. cardboard 'shelter' traps used. at the same tine caught many. Fdward.a

(L97z.) using pitfall traps to study the effect of pesticides upon soil fauna, found that few earwigs were taken in the traps.

Predators and Imsites of the Euro pean exwiR Birds appear to be important earwig predators. Theoba3.d. and McGowan

(1916) found that starlings fed on earwigs throughout the year, especially

during mitunu. Chaffinchee and rooks also ate earwigs, but only in c.n,11

numbers. J1nalysis of pellets of the little ow]. Athena noctua vid.alii

(Bremi) revealed, the presence of large numbers of earwigs fr May to

October, as indicated by the number of earwig anal forceps in the pellets

(Hibbert-Ware, 1937). Other birds recorded as earwig predators include

the house sparrow, skylaiic, thrush (Collinge, 1913), woodpecker, robin,

nuthatch, woodcock (NewsteeLI, igoe), and the hen (Crumb et al. 1941).

Hedgehogs (Muggeridge, 1927) and toaas (Jones, 1917) also feed to some extent upon earwigs. Insects, especially the larger carabids and staphylinids, undoubtedly

r1 11 and. eat earwiga. Crumb et al. (1941) observed that • various carabida inc],ut1n Pterostiolius ap., Carabus ap. and Calasoma sp. attacked earirigs - 55 -

whi confined, although the earwig would often ward off the predators' attack by using its aclerotised. aim]. forceps. Forficula repelled the attack of two tiger beetles, Cicindela spp., in the laboratoxy (Prick, 1957).

Goe (1925) ani Pulton (1924.) recorded species of staphylinid feeding on earwigs.

Two tachinid parasites, Bi gonigMeta seti'pennis (Fall) six'

hacodiueura antiqua (Moig) attack the European earwig, the former parasite being more iniportani (Thompson,, 1928; Crumb t_aL igia.). The effects of both species of taclilnl4 upon earwig populatioms are not usually great.

Thompson (1928) found a miimtiin of 10 $ parasitism by and less 'than 1 by R. antiona, while Chant and Mcleod (1952) found a m1ininn of 12 parasitism by B. setjoennlR in Canada. However, Noleod (1954.) observed high levels of parasitism (from 2-30 $) in British Columbia in 1951, although many of the etinennp pupae were themselves parasitised by a Pteromalid. of the genus Dibrachvs.

Earwigs are perasitised by various woi inclm H rig Filaria loistae

(Brindley, 1918) and 1errni.a subniescsiia (Cobb) (Crumb et al. 1941). Wilson (1971) recorded levels of parasitism by H. subntesos cix' .

miescens from 10 $ to 63 % in Cms3a, and be considered that parasitism by this worm may be a factor in earwig population control. The musoardine

fungus (Netarrizum anisoviiae Sorokin) occasionally infesto earwigs, although the main mortality is cwisod. by the fungus itithom forficulae.

especially in wet, cold. weather (Crumb at al. 19141) Rockwood, 1950). Migratory nymphs (hypopii) of the tyroglyphoid. mite Etstio stoma

v1vort (Oud) may often infect the earwig. They are not true erternal parasites but merely 'riders' upon the insect cuticle. However, their

numbers, especially upon the mouthparts, may be so great as to interfere

with feeding and. cause death by starvation (Behura, 1956a). Fig. 3

aphid. - Life-cycle f dOfl50'°P

month winter hosts summer hosp1 Prunus spp Hops

January Egg in bud axils February

Eggs hatch March (Fundatrk.․) April Spring colonies (Apt....) May

Jun. Summer colonies (Apsee) July

August

teturn migr.nt.s Autumn colonies (Gynop.r.e)

S.ptember

October I Eggs laid

November Eggs Dec.,nb., - 56 -

Life-cycle of the damson-hop aphid, Phorodon bumuli (Sclu'ank)

One of the important characteristics which determines the efficiency of a predator is its degree of aynchron.taation with the aphid population (van en, 1966), aync1ronisation moarLing the timere1ationship between the attack by aphidophagous insects and the aphid population and the life- span of the inlividual aphid. Predators act most often as delayed density- dependent factors (Varley, 1953; Hughes, 1963), but the efficiency of control of prey populations is greatest when predation occurs at the start of aphid population growth (Huasey and Parr, 1963; Varley, Gradwell and. Hassell, 1973). The life-cycle of F. anrioularia has been previously outlined. Earwigs are resident in hop gardens, but before their degree of synchronisation with the hop aphid can be evaluated, it is necessary to describe the life-cycle of orodoz huiuli (Scbrank). overwinters as eggs which are laid in the bud sills of damson, sloe end prtme trees (Prumw app.), especiafl,y Px,mus aminosa L. and P. domestica L, (Moreton, 196l.). These eggs hatch between March and. April, depending on the weather (1aaaee, 1963) eni give rise to apterous viviparous fundatrigenae (Jary, 1936; Theobald, 1900) which produce several generations of apterae on damson foliage (Massee, 1963). The number of fur1atrigenio generations and. the time of appearance of migrantes alatae is determined both by climatic conditions and the oondition of the host plant (Kriz, 1966; Born, 1968) but usually the first alatae leave damson and prune t±'ees and arrive on the auer boat (hops) during late May - early June (Ho]ines, 1955; Gould, 1965). Migration occurs only in dsy].igit when the mean tanperature exceeds 55°F. (32.8°C.) (Anon, 1968).

Fig. 3 summarises the life-cycle of P. huimli. Incoming alatae usually land on the large leaves towards the middle and base of the hop - 57 -

binea and then wa)k to the bine apices (Born, 1968; Anon, 1969). As a reeu].t, alatee cluster in large numbers on the topnet young leaves

(Massee, 1942; Holmes, 1955; Jary, 1965). Zeleny and Hrdy (1969) observed that these leaves were initially heavily colonised by apterse, but the infestation gradually spread down the bine.

Migration from the winter host may extend until mid-August, but is usually over by early July (Darling, 1958j Gould, 1965).

Between 5 aM 13 generations of apterae are produced on the hops during suer, depending upon the weather conditions (wright, 1962w Tsuetkov, 1962). During warm weather, the generation-time may be as short as 10 days

(Nassee, 1963). The apterae normally oolonise the ventral surface of hop leaves (Zobren, 1970; Jary, 1965) and increase in numbers on untreated hope during June, when as many as 1,000 aphids per leaf are found (Ho:imes, 1955).

Their feeding causes chiorotie patches on. the leaf, the 1,mi4 of which eenually becomes brittle and the leaf dies. Leaves also become covered

in honeydew, aphid exuviae and sooty mou].ds, Cladosvorium ap. In severe

cases, untreated bines m be killed, sometimes as early as mid-July (Ordish, 1952; Massee, 1942, 1963; Holmes, 1955; Born, 1968). In field experiments at Vye, untreated hops were defoliated by late July (Campbell and Nave, 1971).

Apteroua also enter the developing cones during August and September (Masses, 1942) where they feed at the base of the braote, causing discolouration and reduction in. size of the cones (Tsuetkov, 1962; Jary, 1965). A].ate gynoparae are produced on the hops in. late August aM often continue into November (Theobald, 1900; Morrison, 1940; Morrison and Thompson, 1955). They fly back to the primary host (Pnmus app.) and produce nymphs which mature as oviparae (Theobald, 1900; Tsuelkov, 1962). Winged males appear on hops about 10 days after the noparae (Theobald, - 58 -

igoo). Males fertilise the oviparao, which thai deposit black, shiny winter eggs in the bud an1 a of damson, blackthorn, aloe, and bufl.aoe trees

(oreton, 1964). Thiring the, initial period of P. huxmili population build—up (June) on the hops, there were few predators apart from F. ricularia and TachvPorus app. (coleoptera : Stapbyl inidae) in hop gardens in 1972 (Campbell, i) and 19'73 (this study). Predators such as anthocorids did. not arrive in numbers until mid or late June. - 59 -

SECTION II - STJDY OF' T BIOLOT OP F. ATJRICULABIL

INFI -60-

POPULATION STUDY OF EARWIG FORFICULA ATL1RICULARIA. L. IN THE

NURSERY GARDEN, 1972

This work forms part of an overall study to evaluate the effoctive- ness of Y. auricu3.aria as a predator of the damson-hop aphid. The earwig

feeds upon both plant and miim'il matter, but is often a voracious predator

upon small insects, especially aphids, although not always recognized as

such because of its nocturnal habits (Brind].ey, 1918; Chant and Mcleod, 1952; Smith, 1966; Way and Banks, 1968).

One of the first requirements in predator evaluation studies is the assessment of predator abundance (van &1en, 1966), aM the fluctuations of predator numbers caused by weather, natural enemies, cultivation techniques, and pesticide applications. The earwig is a gregarious insect in the sunmer months (Burr, 1939;

Fox-Wilson, 1940; Worthington, 1926) anl large numbers gather in bands or sacks placed around plant stems or tree trunks. Few authors have studied

earwig populations in detail, although For-Wilson (1940) counted earwig numbers in trap bands in a mixed fruit orchard, and Sial (1958) attempted

to assess earwig numbers in an orchard using h011Ow canes. Sial (1958) stated that more work was necessary on the value of trapping as a means of

estimating earwig populations.

In the present iork, trap bands were used to estimate earwig numbers

in a ccmnercia1 hop garden of area 2.1 ha. (5.3 acres) from June to Septan- bez'.

Methods The area studied (Pig. 4.) comprised 30 rows of hops, each row of approximately 200 hills. Three corrugated cardboard traps measuring

Flg.4

Young hops and vines

25m

a. rrri i ' I •'II '. I I I I a. L. - . - I I I I I I I I I I I I I I 1 I I I i I I . Ii P I I I .5 Li. '._T I- I I , I I I I I ' I $ Qi)I '_i I L_J o; 40m I L1(7 ) 'S strip 3m S.. (C OOQO 0000 00 Woodland OOO - 62 -

0.2 m. x 0.4. m, (6 in. x 14. in.) were placed about 0.6 m. (2 feet) at random on bines within each row. Earurigs gathered in numbers in these traps because they climbed readily and sought shelter within the traps

(puiton, 1924.; Crumb et al. 194,1). To ml-n(mise edge effects, the outer 25 plants in each row were not sampled. Traps were assessed weeldy. Earwigs were collected in pol.ythene bags, sexed and classified within nympha3. instara I to IV, and total earwig numbers recorded.

After assessment, traps were replaced and ea.rwigs returned to the soil, Pive leaves per bine were selected at random, and aphid numbers on the leaves graded on a log4 system, where 0 = 0 aphids; 1 = 4. aphids; 2 = 16 aphids; 3 = 64. aphids etc. The percentage area of each leaf eaten by earwigs was estimated using a prepared template (hg. 5) as reference. Sometimes it was difficult to distinguish between earwig damage and. that of oapsids (Massee, 1964.), but the 'ragged' appearance of hop leaves

(Fulton, 1924.; Guppy, 194.7) was characteristic of earwig feeding.

Within the trial area, 13 'pole-hills' (bines growing on strings around wooden poles which supported the wirewoit of the garden) and 77 non-. pole-hills were sampled. Pie].d observationa showed that maxy earwigs gathered in cracks which ran the length of most poles.

Two rows of hope were untreated: the other 28 received two soil drenches of ditnefox (0,5 $ solution; 120 ml. per bill), one on June 22nd and another on 2nd August. Eaiirigs were sampled from three traps per row, and numbers within insecticide treated and untreated rows compared.

Results and Discussion Eax mbers

Traps were positioned on 5th June and assessed. one week later, and. at subsequent weekly intervals. Earwig numbers on insecticide treated and

FIG.,5

5' •_•_•%__• / I il ..• • S • '/ J • ''1 . • •/ :_-. 7 . /• •'-, •• -•--. . *

f 7 ••': i;'

0/ O25 —0I 4 cO!

It17 •:T '/z , -' : . :. . / S / I • • /&' /1 %\ q'.• / '-: • '. %'ir' 4 1. '..1.

S _/

Of I 01 10 '-' 10 75C/ - 6 -

untreated rowe were similar intil June 27th, shortly after the first application of dixnefox (Table 3). subsequently, there were more earwigs in the insecticide-free rows, until late August. Numbers of earwigs increa-

sed sharply by June 27th, just after the hops were "earthed-up", i.e. the

soil was banked up around the base of each bine. At the same time, lower leaves of the bines were stripped. These cultural procedures brouit eaz1 wigs in the soil into closer contact with the bines and thus increased the numbers entering traps. This fact could be of importance when considering the manipulation of earwig numbers to increase their effectiveness as damson- hop aphid predators.

TABLE 3. arwi numbers in Dole and non-Dole hills on treated arid un-. treated rows of ho ps. 1972.

Mean number of F. auricularia per trap Sample date dirnefox no dimefoi2 pole bill3 non-pole bill4

12 June 0,6 2,2 1.7 0,6 19 June lie 1.6 5.2 1,2 27 June 39 6.8 11.5 2,8 3 July 3,8 11.8 12.]. 3.1 13 July 7.7 24.5 9.' 8.9 17 July 6,1 10.8 7.5 6,2 25 July 614. 15.7 12.l. 6.0 11. August 15.8 25.2 21.2 15.6 21 August 9.9 16.3 12.5 10.0 31 August 5.5 4113 6,6 52 7 Septenber 5.2 3.9 8.9 4.5 - means ± S.E. 6.1 ± 4.2 11.2 8.1k 9.9 5.1 5.9±4.

mean of 81. traps per sample date 2 II 8 6 a 8 8 I 8 8 "17 3 3 3 4 3 3 77 3 8 II

MEAN NO. APHIDS PER LEAF

-I IP1 I1 S p4-

4- MEAN NO. EARWIGS PER ROW

\. I

Sf.

/ - 66 -

Greater numbers of earwigs were found in trap bands with increasing time intervals between assessments. Crumb et al (19zi) attributed this to

the gregariousness of P. auricularia. ani to the fact that earwigs are

attracted by their own distinctive odour. Thus, the peak of earwig numbers

on August ]4th was probably en artefact, since the traps were not assessed for two weeks previously. Between 13th and. 17th July, earwig numbers

dropped (Table 3). mis drop may have been caused by the heavy rainfall

(53.L rim.) on 16th July. Maximum weekly rainfall for any other week (June

to September 1972) was 27 nm. (data from wye Meteorological station). Probably, sheltering earwigs were literally 'washed out' of the cardboard traps.

Assesnent of earwig numbers in this study was not frequent enough

to record direct changes in numbers trapped with climatic factors. However,

Chant and Mc].eoct (1952) found a significant correlation between earwig numbers in traps (assessed at two day intervals) and mean grass temperature, wind velocity, and an inverse relationship with Relative Humidity at lf.30a.m.

Numbers of F. aucularia decreased from mid-August In both treated and untreated rows of bop. By early September, numbers had fallen to about three and five per trap, respectively. The reasox for this decrease in earwig numbers are unknown, but about mid-August, earwig numbers increased on a plot of maize adjoining the Nurseiy Garden (E.M. Elamin, Wye College, pore. conin.).

More earwige were caught in pole hill traps than non-pole hill traps for most dates (Table 3), but numbers in both types of bill showed the sane general fluctuations. - 67 -

Nvmvhal staRes The inatar distribution of F. auriouleria was recorded at each assesent from June to September. The earwig has two to three oviposition periods during the ser (Behura, 1956), causing phases of occurrence of nyniphal inatars. Fig. 7 shows the distr±bution of instars in the Nursery Garden, 1972. In early Jima, inster fl and III were found, but most individuals reached meter III by mid-June. The change to instar IV occurred in late June - early July in 1972. Adults of the new generation appeared by mid-July. Before this date, male earwigs were absent from the trap bonds. Instar I and II nymphs occurred again in mid-July, probably as a result of a second oviposition period. However, since the climbing ability of young nymphs is low (BeaU, 1932), trap catches probably underestimated their numbers.

Distribution of eerwia in the erden Fig. 6A shows the data in the form of mean numbers of earwigs trapped per row of hope, when all dates were pooled. Earwigs were caught in a).]. parts of the garden, but they were more common in the rows nearest the Northern and Southern edges. Variation between the catch in neighbouring rows was high, but fewer earwigs occurred towards the centre of the gs.rden (30-50 m. from N. edge).

Population of P. huniuli. and earwig damage to hop leaves

The aphid population on untreated hops increased steadily until July, when there were about 650 aphids per 1eaf (Pig. 6). Predation by earwigs and other predats was not enough to suppress the aphid population, which caused the untreated hope to become defoliated by early July.

Fig. 7

I V V

- 69 -

TABLE 4. Meen percentage leaf area eaten by earwigs in treated

end imtreated hop rowe, 1972.

Neon % leaf eaten Sampling date Treated1 Untreated!a

]2 June 2,4 6.5

19 June 2è7

27 June 2 8 50

3 July 2.2 40

13 July oig 2,5

17 July 0.7 0.0

25 July 2,2 leo

34 August 1.7 2.0 2lAugust 33. August 7 September

mean of 420 leaves examined/date

a ,, i, I II

Aphid numbers also increased on the treated hops until 27th JUne,

when the first dimefox treatment on 22nd June lowered the population to about four aphids per leaf. Numbers of P. htnuli r€#n,thtod low throughout the simmer (Pig. 6) on treated hops. The mewi percentage of leaf area eaten by P. aurteularia was greatest

ear]y in the season on untreated hops (Table 4), when the leaves were young

arid tender, but by July damage decreased and was not enough to affect growth of the hops.

(ly two rows of untreated hops were sampled for earwiga in 1972. Although differences between earwig numbers in dimefo-free and dimefox

treated rows were found, the sampling area was probably inalequate to mini,- mise earwig mevement between plots, which would tend to reduce these differ- encee. -70-

EARWIG POPULATION STt1DI fli YO HOP GABDE, 1973

The European earwig is often abundant in hop gardens. When present in large numbers, it sometimes &nnages the young leaves (Theobald, 1896;

Masses, 191i3), but m.ain1y feeds on hop aphids (Eacherich, 1916). Several workers have used the earwig's she1ter-seng behaviour to trap than in large numbers. Fulton (192k) used a flower pot filled with excelsior and upturned on a cane, Chant d Moleod. (1952) grooved-boards, BeaU (1932) rolled-up newspaper in trees, Legner end Davis (1963) pint-size jars sunk into the ground, Pew q iantitative population studies have been made, except for the work of BeaU, 1932; Sial, 19611 and Chant and Moleod., 1952. In the present study, strips of cornigated cardboard were wrapped and tied around bios to trap earwigs in two hop gardens, and nunbers assessed from

Ma to September. Attempts were mado to relate pesticide applications and positional effects of trap orientation to numerioal changes in numbers of insects trapped.

abitats sti4ied

(a) Thirsery ôarden.

The hop garden, of area 2.1 ha., is situated on a north to north- westerly slightly sloping terrace near a valley bottom. It is bounded to the north and east by arable and rket garden crops, beyond which sie mixed. deciduous and coniferous woodlands. The western boundary is a small area of mixed woodland (Pig. 4). The two experimental areas were both near the northern boundary of the garden (Pig. 4). The first area was approximately 40 xn. from the western edge, at the bottom of a slight elope and protected frc northerly winds by a cypress hedge approxinately l in. high. The second area was 25 in. -71-

PLATE 2 Grassland along the N. edge of the Nursery Garden in July, with mixed woodland to the west.

i i I

- . .. NIl,

. ______

•L

• I - •- . .1 • - . • , S... •

L I '

,. ,: -c. - ''..' • .- . • ...k- ' ?': . . t---_. . '- ,.• -72-

from the eastern edge at the top of the slope, and was little sheltered

from the north (see Plate 2). The hops were grown in rows extending east and west across the garden. Alternate rows contained poles every 5.5 m. to support the wirewox

trellis. The height of the wirework was approlteiy 1. m. and plants were

strung in the Worcester eyet (Burgess, 1964) with two strings per root- atodc arranged on a north-east-south-west axis. The standard planting

distance was six plants per 5,5 m. within rows and an inter-row spacing of 1.7 rn,, giving approximately 5,000 plants or 10,000 strings per ha. All plants in the garden received frequent aerial fungicide applica-

tions in 1973, and most received one soil application of dimefox (bisd1methrj..

Rmirio fluorophosphine oxide), a systemic aphicide. Weeds were controlled b-

cultivation; aerial insecticides were last used in 1965. The experimental areas were divided into two units, each of 10 plants selected at random. One unit received 120 ml. of 0.5 active ingredient dimefox poured onto the soil at the base of the bines on 11th June,

1973. The plants in the renilnlg unit received no insecticide. Corrugated

cardboard traps measuring 34 in. x 6 in. (0.4. x 0.15 m.) were wrapped around

each bine about 2 feet (0.6 m.) above soil level, nr1, a tots]. of 20 traps in each area. Traps were ern1ned weekly, earwigs collected in bags, counted, and released onto the ground at the base of each bine. Numbers of other

aphid rwedators in the bends were also noted. Three leaves per plant were

chosen randomly at heights of 2, 4. and 6 feet, and eynm1ied for aphids. Thabers of aphids on each leaf were graded on a scale 3. - 6, whore 1 = 4. aphids, 2 = 16 aphids, 3 = 64. aphids; and the mean grade of aphids per

leaf was calculated. The number of predators on the leaves was also

recorded, - 73 -

Resultm

Earwig traps were exnmlned weekly from Key 29th to Septnber 18th,

except for the week of July 17th when records were not token. The hope were harvested in late September. Fig. 8 shows the total numbers of

earwigs (afl. stages) from untreated arid &i.inefox treated rows of hope in

both areas. There were more earwigs from both treatments in the area at the eastern boundary of the garden. There were slight differences in the

numbers of earwigs from treated arid untreated rows in both areas, but these were not significant.

Earwig numbers reaiained low until the assessment of July 10th, when

there was a large increase caused by "earthing-up", i.e. soil was heaped

around the bines, bringl.ng the level of the soil much closer to both traps

and hop bines. This increased the number 0± earwigs entering the traps in

both 1972 and 1973. Differences between munbere of earwigs after kiiefox

was applied on June 11th were smell. Since only one application was made,

differences which occurred later in the summer were probably not due to

toxic effects of the soil-applied insecticide. A peak of about eight and

nine earwigs per trap, in treated end, untreated hope respectively, was

reached on July 24th in the western plot. The peak was duo in part to

traps not being examined the previous week, since more earwigs aooimi1ate when traps are left for long periods (Crumb et ala 1941). Except for a

slight increase In mid-August, numbers then gradually decreased. There were

more earwigs in traps on the untreated, hops for most of this time.

Differences in the eastern area between treated and untreated rows were larger. There was a peak of 21 earwigs per trap (untreated hops) arzi

12 per trap (treated hope) on July 24th, although untreated rows caught more earwigs until mid-August (RIg. e) when numbers slowly decreased in both treatments,

NO. EARW I GS - P';3 0 0 MEAN NO. APHIDS PER LEAF

'0 -75-

Aphid population build-up on untreated hope is usually so rapid that predators alone oannot reduce this increase (Campbell and Neve, 1969). In 1973, aphid numbers increased linearly (Pig. 9) Until early July when the untreated hops wax's severely defoliated. Mobile predators, such as syiphids and coccinellida, were present in the Nursery Garden from the end. of May, end therefore well synchronized with the aphid population., but were not able to reduce the infestation. Numbers of earwigs in both east and west plots were low throuiout the period of aphid population build-up in. JUne (Pig. 8), and predation by earwigs was probably not important at this time. The population of earwiga reached peak numbers two to three weeks after the fall in aphid nunibers on untreated hops. Sone aphid resurgence occurred during August, mM ny on young lateral leaves which grew out after the defoliation of nlRfn bine leaves. Analysis of stc*nach contents of earwigs showed that aphids, aphid eviae and sooty moulds, Cladosoo app. occurred most frequently in the diet during July, August and Septnber. It is probable that earwigs played a part in preventing aphid resurgence on the new lateral growth during August, especially as numbers of other mobile predators were then 1or. Aphids on the leaves increased sliitly in Septber, as gyno- perae started to fly back to Prurius app., the winter boat (Fig. 3), while earwig numbers on the east plot bad. fallen to about six per trap, almost identical to the numbers in the western plot, by Septiiber 18th. On treated hops, aphids increased in. early i\me to reach a peak of about 140 aphids per leaf, but the applications of &tmef ox on June 11th quickly reduced numbers to less than one per leaf by the ezñ of the month (Fig. 9). Some aphid resurgence occurred In July, probably due to the continued influx of migrantes alata over the month. Poliar growth of Nursery Garden hops was not vigorous and the hines and crowns were generally small. Difox was taken up and became effective - 76 -

PLATE 3. Earwig trape.

A. oied a o1vthene ba in ositton to oatch the bsecta.

pjipd IIulI.. ''Ii I

t1Ui iIIJ ic i rc

B. llà*ed male?. auricularia nsIe the trap.

F F

// •,,/ I , f I 1•!)/ -'77-

quickly in 1973 (Fig. 9) despite lack of rainfall iunnediately before or after application (Fig. 15). Dimefox residues maintained aphid numbers at

a low level after the initial reduction in June, aided by predators. Mobile predators, including eaiwiga, occurred in samples throughout the summer, p although by mid-August only earwigs were conmion.

(b) Silks Garden Silks is a 1,1,. ha. hop garden, uniformly level and situated in a valley bottom at a distance of 1.6 1n. S.S.E. from the Nursery Garden site

(Fig. LU). The garden is surrounded on the south, east and west by arable and. pasture fields and on the northern side by farn buildings. The eastern side is protected by a 5 in. tall poplar hedge (Povulus nizra) and on the south and western sides by a 5 in. tel). beech hedge (Faua svlvat:Loa). The northern botaa'y is protected by hop lewing 5 in. high. Weeds ez'e controlled by regular application of herbicides. Hop plants are spaced 2 in. x 2 in. with four strings per plant trained in the Umbrella syst on 5 in. high wire- wo*. String density is the sane as the Nursery Garden (io,oco strings per

1,a.). Every third row of hope contains poles every 6 in to support the wire- woz4c trellis. Si)k Garden was nre representative of a typical hop garden because a "canopy of leaves", i.e. dense foliage growth, developed over the season

(plate i1j, whereas growth was not vigorous in the Nursery and sha4{ng effects were alight. A heavy im1ch of manure and tia* was applied to Silks every three years : as a result the soil surface was covered by a litter layer.

Earwig abundance was studied in three areas, two of which received differing thSeCtiOjde treatments.

A plot 28 in. x )4 in. of hope var. Cobba at the eastern boundary of

the garden (Fig. 2) which received applicatioma of 120 ml. 0.5 0 active

XXIXXXXX1XXXXXI XXX XXXXX1XXXXXXXXXX X X X X)( X X X1X X X X X I X X X )( X XXXXXXXX1XXXXXXXXXX xxx_xxxxx_xxxjxxxxx xxx xx xxxxxxx Xxxx xx xrx—X—X—x--x-1x x x )< X X X X X X X X xix x x x x Ix x X x x x x x x x x x XIXXXXX1XXXXXXXXXXXX xi!x x x lxx x xx xxx xx xx xIIxxxxxIIxxxxxxxxxxxx X1XXXXXXXXXXXXXXXXX x jX XX X x 1 x x xx x X x1< x x x x XI 1X X X X )<'X x x x x x xix x x x xIx x x x x x x x x xix x x x XI 1X XX )< x11x X )( X X>< x 1 x x x x x15 xL xx x)jx c# x x x,x x XXXXXX Grc.ssstrip W U —a--' =t 5

h.dg. Sm high ,If4 _ __ 44 r ) 'I. - 79 -

PLATE 4.

A. The IL edge of Si]ks Garden. showing aas atm at the edge. az beech hedge along the L. side.

B. Cojbe ]g with de fQjie rçwtb, pnd friaIi effects.

ingredient dimefox as a soil drench to the base of each bill on June 26th

and July 20th, and several foliar applications of copper fungicides. Lower

leaves of the bines were roved by bond-stripping. 30 cardboard traps were

placed at random in this plot, using random number tables to select trap

locations. Two plots 14. m. x 7 rn,, one at the north-east corner of the garden (pig. ic), the other towards the centre of the garden, both areas var. Early Bird. 15 traps were placed at random in each of these areas Both plots received applications of dirnefox soil drench on June 27th and

July 24th. Aerial applications of 3upracide (a non-systnio o - p aphicide) were made on 7th and. 14th June. The lower leaves in. both plots were burnt-. off by ground directed sprays of leefex (tar-oil suspension plus potassium

monochioroacetate) on Jine 11th, 26th, and July 23rd. Hops in the corner area received sprays of Dinocap fungicide, while those in. the centre area received applications of Benlate at frequent intervals,

Traps were positioned at random on one of the four strings per plant

available (N.E., N.W., S.E., or S.W. orientations). Traps in all plots

were exsnined weekly from May 21st onwards. Aphid nunbers and percentage

earwig damage were assessed on three leaves per plant as before (p. 72 ),.

iLE 6. Nbers of earwiga from seven. traps at each orientation

Date NJ. N.E. S .W. S.E.

4 June 19 20 31 11

11 June 30 14%3 52 32

18 JUne 73 90 96 78

25 June 150 153 180 192

2 July 89 104% 113 109

TftOanE3j$.E. 72.2 j52.3 82.0±52.3 94.4j 58.1 84,,57l.14. -81-

TAS 7. Xe numbers of earwiga from pole hf]1i (6 re:pe) and non-pole 1i11 (2i. reps) for all dates. Cobbe plot.

Date Pole Non-pole

21 Nay 0.5 1e9 28 Nay 0- 1i3 4 June 1&7 3.0 llJuno 5.8 18 June Bee 134 27 June 23.6 2 July 175 3J0 9 July 3.8.1 32.4 23 July 21.2 20.7 30 July l82 22.6 6 August 9.8 18.0 1.3 August 11.8 13.1 20 August 7.7 7.6

means t S.E. 10.9 7.8 32.1 ± 7.7

Resats Nurabers of eervigs from traps placed on each of the four string orientations In the Cobbe plot were compared by analysis of variance after transfox.ation to the fore log. (x + i) for five snpling dates. The differences were not sigrdricant (Table 6). Th.mibers of earwigs from traps placed on pole and non-pole hills

(Table 7) were conpered by analysis of variance, after trensfoxmatiOfl, for all three plots and all dates, but the differences were not aiguificant.

In 1973, traps on both types of bill were wrapped arouul one string only.

Larger differences in numbers of earwi.gs oocin'red in the Nsery Garden. in

1972, when traps were placed round the pole itself, or on one string.

NO. EARWIGS

'4-

U,,

uI MEAN NO. APHIDS PER LEAF

-a.

I- - 83 -

There were more earwigs at the north-east corner and less at the centre th there were in the Cobbe plot. Population trends in all three areas are shown in . 13..

There was some relation between dimefox applioation8 and decrease in earwig numbers in all three plots, d althoui no control (i.e. insecticide-free) plots were studied for comparison it is probable that dimefox did cause some earwig mortality. ,o applications were made in each plot, and the plots were large enough and far enough apart to ensure that movnent of earwigs between plots was m1n1mL.

In the Cobbe plot, earwig numbers increased to a mrjjç of about

23 per trap on 27th June, but fell to 15 per trap at the next assessment, after the application of dimefox on Jme 26th, and decreased further by July 9th (Pig. ii). There was then a rise to a peak of about 20 earwigs per trap on July 23rd, this peak being partly due to the gap of two wecs since the previous assessment, and probably due to liniigrstion of earwigs from outside the plot. A second application of M1efox was made by hand- dipper on July 20th in the Cobbe plot. No change in earwig numbers was found at the next assessnent, i,e. July 23rd, but since the traps hal not been e1lTed for two yee previously, the large munbers of earwige present may have been sheltered and avoided contact with soil residues of dimefox. There was a small increase in earwig numbers on July 30th and a decrease fro* then onwards to harvest. The population of P. humuli imoreased until the first dimefox treat- men.t was applied, reaching a mrtitun of about 250 per leaf on June 27th and then decreasing to low numbers in mid-August, aided by the second dimefox treatment. The decreaae in aphids was very gradual, however, (Pig. 12) compared 'with the rapid decrease on the grnL1er Nursery Garden hops (Pig. 9), which received only one Mmefox drenth. - 84. -

In the Early Bird plots, earwigs were moat abundant In the north-east

corner than In the oitre plot (Pig. u), althou In both areas, numbers

of earwigs showed similar fluctuations. Decrease in munbers occurred after

both diniefox applioations, on June 26th and July 24th. Traps were assessed

and earwigs released onto the soil on July 23rd, immediately before the

second application of dixmefox was made, Thiø may explain why a decrease in earwig numbers was found at this time in both Early Bird, but not the

Cobbe plots where the second dimefox was applied earlier on July 20th.

Earwig numbers at the edge plot increased rapidly after both dimefox treat- ma'ts, while in the centre recovery was not so rapid, indicating that

ininigration of earwiga from outside the garden probably took place.

Sprays of leefex applied on Jme 11th, 26th and July 23rd, and

applications of &praolde on June 7th aM 14th to the Early Bird hops

could not be related to reductions In numbers of earwigs, althou&i by the third leaf ox treatment there was a brown residue present on some of the cardboard earwig traps. Overall trends In the earwig population wore similar to those of the Cobba plot, with a gradual decrease in numbers over the latter half of kgust, the reasons for which are not ]iown. There was little population build-up of hop aphids on Early Bird hops, owing to the early aerial applications of Supracide (Pig. 12), but the effect of Supracide treatment was short-lived and numbers rapidly increased again to a peak of approximately eiit and three aphids per lea! at the edge and centre plots respectively, helped by the continued {nrtig - ration of migrantes alatae In June (Pig. 13). There were more aphids on edge plants than on centre plants, presumably because inigrantes alatae settled more frequently on the sheltered edge plants (Lewis, 1965).

The first dimefox application on June 27th reduced aphid numbem to virtually zero, which was maintained until harvest.

LOG X+1 NO. ALATES PER WEEK

I '3 LOG X+1 MATES PER WEEK

9'ART 8. Mean numbers of earwiga per trap at differing distances frog the edge, Sfl]cs Garden. (iIeana of 15 asseaønent dates).

Mean number of eanigs per trap at distances shown froi edge

6w. Sm. iOn. 12m. 34n2. ].6m,, 18m. 2Cm, 22ni,, 24w. 26m,

n= 5 2 3 5 2 4 3 3 3 2 16.4. 14.5 12,5 11.1 12.5 9.0 10.3 9.1g. 7.5 6.0 6,5 ± ± ± ± ± ± ± ± ± i ± 15.1 10.1 11.0 7,6 8.8 6.9 6,9 7,5 6,0 6.3 4.9

'Fge effects' in the Cobba plot were analysed by calculating the mean number of earwigs per trap per row of høps, the neaaest row being 6 m. from the eastern boundary of the garden, which gave way to a grass strip

approximately 1. m. wide, a beech hedge, and hehl-M this arable fields.

Subsequent rows were spaced at 2 m, intervals weatwaid into the garden (Table 8). The mean number of earwigs per row were compared by analysis of

variance, but there were no siificant differences, although overall means

showed that traps placed at 6 m. from the edge caught more earw:Lgs than

traps further into the garden. Earwig feeding was recognised. by the characterjsti ragged appearance

of damaged hop leaves (Theobc.ld, 1896, 1913; Massee, 1943). Young, tender leaves were damaged most often, especially those nearest the cardboard trap.

Guppy (194.7) found that earwig feeding was most malted on young plants mesa' to shelter of some kird. The mean percentage of leaf eaten by earwigs did not exceed 2.7 % per leaf in any area of Sl.2ks (Table 9), which did not appear to affect plant growth. Overall means showed that damage was highest In the edge

area of Early Bird bop, but differences probably reflected th. relative PLATE 5. Eanrig feeding damage to hop leaves.

I;;,,, -

d -88-

aburdance of earirigs an1. the availability of alternative food (i.e. aphids) in each area.

TABLE 9. I4ean percentage of leaf area eaten by earwiga, Si]ks Garden 1973. Cobbe plot - mean based on 90 leaves per date.

Early Bird plots - es based on 45 leaves per date.

Ear].y Bird Date Cobb 1ge Centre

0.6 0.1 0 Jime 0.7 0,2. 0,,4. 0,6 1.1g. 0.9 August 1.14. 2.7 1,2 Sept1bei' 0,9

Overall mean 0.8 j 0.3 1q14. + 1.1 0.8 ± 0.5 percentages

TABLE 10. Mean percentages of leaf area eaten by earwigs, Nursery Garden,

1973. (All figures based on 30 leaves per treatment),

West plot East plot Date Untreated rows reated rows Untreated rows Treated rows

May 0.3 0.4. - - Jime OoO 0.0 - - July 0-2 0.8 0.1 Ca6 August 23 2,1,. 14.2 2.3 Septenber 1.6 1.9 2.6 1.2

Overal]. mean percentageS 9 1.3 1.2 j 1.1 1.6 1,9 1.3 1.0

Fig. oc FIG. 16

J I J I A

z In the Nursery Garden there was little leaf damage In east end west plots until late July (Table 10), after which diunoge was more obvious, especially In the east plot where earwige were more abundant. Ci untreated hops damage was confIned almost entirely to the young lateral leaves which grew out after the severe defoliation of mMn bins leaves by unoontrolled aphid populations.

Discussion This stuly has shown that earwig numbers, as reflected by trap catches, were high In two different gardens, but their distribution was not unifoxn and was affected by severe], factors, especially interaction at the edges with other habitats. These 'edge effects occur in many habitat types and azing many insect species, although the factors involved dep1 upon th insects' biolo. Even hily mobile insects such as ooccinellid.s and eyrph.ILIB are often most ab'.nxlant at field edges (Bomboach, 1966; van m1en, 1965), ithile edge effects are marked in species such as Carabidae, which are less mobile (Zatycinina, 1970). Differing types of vegetation along the edge may cwse a variation in edge effect intensity (van en, 1965).

Earwigs wore most abundant In traps near to the east end north edges of Silks Garden, both edges being bounded by a strip of rough grassland varying In width from 5-20 in. Crorall et a] (1951) found that earwiga were more abmdant in graa1ands than In arable orchards. Those suthors attributed this to the cover pruvided by rough grass, end the lack of cultivation in these orchards. Both grasaland and hop garden are, therefore, suitable habitats for the eorwig Earwigs were probably most abundant at the edge

itself merely becanse there, both habitats interacted.

More earwigs were found in traps situated in an eastern area of the Nursery Garden, at the top of a slight north-west slope. Both east end west - 91 -

atudy areas were near the northem boundary of the garden (Pig. i1.), with led to a hedge and garden in the west and a cereal field in the east. The western edge abutted onto mixed woodlands, 'while the eastern edge was adjacent to amble land, but both plots were at least 25 m. and 140 m. distant respectively from these edges. Some of the observed differemee between earwig numbers in east and west plots n have been due to the different habitats near to the northern boundary of each, but interactions with habitats at the west and east edges of the garden were probably not iportant. Probably the main factor involved was the slope running north-west across the garden. Behura (1956) found that steep slopes facing south-west yielded large numbers of earvigs, while BeaU (1932) found earwigs in large numbers only on steep banks, especially if the bank bad a southern exposure.

Both authors associate soil drainage with earwig abundance. Behura (1956) stated that becae earwigs avoid excessive moisture, the natural drainage and drier state of the soil upon steep banks provided conditions more favourable to earwigs. Boa].]. (1932) tounl that a region at the bottom of a drainage basin In Vancouver was lightly infested with earwigs. Soil at the eastern end of the Nursery Garden was better drained than in the western

area at the slope bott. Therefore, although the slope was In a northerly direction it probably accounts for the greater abunlanoe of earwiga in the eastern stndy area•

Earwigs are susceptible to soil applications of many Insecticides,

including dieldrin, ch].ordane and benzene hoxachioride (Legser Davis, 1963). However, no work with organcphosphox'ous compour4a, as for example

d.imefox, has been reported. Dimefox (bisdimethy1 m1iio fluorophosphine oxicte) is a very toxic chemical (scheduled part II by the Agricultural Chemicals

Approve]. Sche), applied as a soil drench to the area of soil around the -92-

base of each hop bins. Any earvigs present in the upper soil layers in thin vicinity would presumably be affected by contact with the insecticide.

Because of its hl# vapour pressure of 0.36 mn. mercury at 20°C. (Martin, 1973), diznefox may also cause mortality by fumigant action, especially

under dry soil conditions. In the western area of the Nursery Garden, where traps were eYPTfft7ed weekly from May 29th onwards, there was no significant deoreaso in earwig numbers foUowig dimefox application to the soil on June 11th, but since numbers were so low in both treatments, differences may have been obscured.

The relatively small size of the treated areas azid the freedom of earwige to migrate from untreated areas may also have reduced any differences.

Traps were not eymn1ned in the eastern area until June 19th, when there was a moan of 0.8 &id 1.9 earwigs par trap from treated arid untreated rows

respectively. Differences between treatments became large in JuLy, but were not significant, and unrelated to the earlier inaectioiile treatment. Weekly

analysis of stomach oontents showed that aphids, aphid oixviae and sooty moulds occurred most frequently in the diet of earwigs from untreated hops in the Nursery. Prom earwigs on the treated hops such stomach contents were scarce, consisting m1-rily of hop tissue, which was not reedily eaten in laboratory tests. Therefore, larger nwnbere of earwigs occurring in the

untreated hops probably reflected the greater availability of preferred

foods there.

In Sflka Garden, earwig numbers decreased in al]. plots after dimofox treatment; unfortunately, untreated plots wore not available for comparison.

4.lthough these results indicate that dimefox causes some earwig mortality, they are inconclusive.

The rapid recovery of earwig numbers after treatment with diinefox, which was most marked in the edge plot, suggests that iiiiml gration of efJrwigS - 95 -

occurred from outside Silks Garden. Beai.l (].932a) compared the catch of

earwigs in plots where they were either destroyed, or released, at each assessment. He found that mi'ation of earwiga from outside areas was so

rapid that there was no reduction in catch in the 'trapped' plots. Mark-

capture recapture experiments near the north edge, Silks Garden, in August,

have shown that the movnent of earwigs within the garden is often extensive, lmt no pronounced movement from or to the edges was detectable. However,

the direction of immigration probably varied with the season; the rapid decline of earwig numbers In all plots, Silks Garden, suggested that earwiga were leaving the garden during August.

NATURAL ENEMI OP P. .LDRICULARI&

Corgated cardboard traps were e rntried for earwigs every week from late May to mid 5eptnber 1973 in Nursery arid Silks Gardens, Wye College.

The occurrence of pupae of the tachinid parasite B. setiDennia. deaths due to funga]. infection, and the esenoe of earwig predators were noted weekly in both sites. Eight earwigs from each garden were dissected each week d infection by menDitbid. worms was assessed. Parasitic worms were lcin&ly identified by Dr. N.J. Harris of the British Museun (Natural History), tachinid edults from field-collected pupae and using Thompson' $ (1928) key, and the fungus itomovthora forfjoulae after the description In Crunb QtOl. (1941).

- 94._

Results The number of earvigs parasitized by B1. setpçm.tp and E. forfiou]..ae was very low in both gardens during 1973 (Table u). Infection by Iner!Eithid worms was also low. Of 136 earwiga emnined from Si]ks Garden, only two were infected, while no worms were found in 128 earwigs from the Nursery Garden. Three tacMnlfl larvae were found during dissection of the earwige from Silks Garden. However, eymntion of traps every wec may have underestimated the percentage parasitism by ta nh4n(ds, the pupae of which may emerge in a few days (Thompson, 1928). The cardboard traps used. in this study tended to absorb and retain moisture after heavy rain. This may have

been conducive to infection by E. forfilae. which is prevalent in wet weather (Crumb et al. 194].).

TABLE 11. Causes of mortality of earwigs, silks Garden (anti Nursery Garden), 1973.

Date No. earwige No. pupae of No. infected by No. of from 30 traps B. setiDennis L forficulae spiders in 30 traps

Nay 80 0 0 0 (ii.) C].) (0) (0)

130].Jime 0 0 0 (ice) (2) (0) (0)

July 2134 2 4. 2 (1138) (2) (0) (0)

August 1259 0 2 9 (1596) (1) (0) (5)

September 351 0 0 11. ('si) (0) (0) (12)

T2.AL9 5125 2 6 15 (3619) (6) (0) (rr)

Overall $ parasitism by B. setiDr'l = 0.04 (0.10 $ ,, I L forficulae 0.32 $ 0.O3 $ -95-

Nbers of the spiders Ainaurobius terrestz'is (Wider) and Narnissa nzuscosa (Clerck) were recorded at each sampling date because they were seen attacking earwig nymphs on several occasions. Bristoire (1958) recorded earwigs among the prey of A. terrestris. Both these spiders were infrequent in the traps and their effects were probably m{rim,1. Sparrows (Passer domesticus L.) were seen feeding on earwigs from curled-up hop leaves in both gardens during August. Eowever, since the earwig is nocturnal and normally hides in inaccessible crevioes during the daytime, predation by diurnal birds is probably minhii

DURATION OF ST.A OF P1. ADRICTJLABIL

Oviposition, hatching, and nymphal develoient were studied in two hop gardens at Wye College in 1973. In. the Thsery Garden, hops were grown in rows with deep furrows between each row. The soil was ploughod several times between January and April to e1lml vte weeds and oondition the soil. Silks Garden was not plouiei1 az4 weeds were controlled by herbicides. When trap bands in the Nursery Garden were e"' 1 ne& in January 1973, inMiily adults and a few IV iriatar earwig nymphs were present. There were more males than females in the sample, probably because many females wore tending eggs in the soil at this time. Earwig nests were only found in the rows of the Nursery Garden. Ploughing operations probably prevented nests being made elsewhere. In Silks Garden, nests were found scattered over the whole area. Females with eggs were first found at the end of Jnrniaiy 1973. Soil sampling was continued at weekly intervals until the end of April, when the eggs began. to hatch.

Fig. 17

I- z w V Fig. 18

I- z r.18a

4I -97-

30 cardboard traps were placed at rdi in a plot of hops, Tar.

Cobbe, in Silks Garden on May ]4th, 1973. 20 traps were placed. at random in untreated hops of different varieties in the Nursery- Garden on Nay 21st.

Traps were emitned weekly, earwigs were counted md sorted into instars. Thstars were iditified by size and by the number of antenral segments, using a hand ].sms. (InstaL, I has 8 segments, instax' II 10, instar III 11, and instar TV 12). The results are summarised in Figs. 17, 18. There were two peaks in numbers of each earwig Instar, indicating two oviposition periods.

Instar I

Traps were first ernmlned on May 21st (Silks) and May 29th (Nursery), when many earwigs had moulted to Instar II. First instar earwigs occurred in small numbers during mid—July, but were never numerous because thay rarely leave the nest before the second mater (Behiu'a, 1957). Moreover, dlrst mater earwigs do not climb as readily an later inatars (Basil, 1932) and theref'e do not readily ascend the hop binea,

Instea' II

Second luster earwigs were at a ,n1imjn on lfth June and 23rd July

(Sims Garden) end 5th Jima d 10th July (Nursery). Deve1opiut of nymphs from the second oviposition was sliitly- faster in the Nursery Garden. mater III

)TAT1Tna numbers on 19th Juno and 10th July (Thxrseiy) wia 16th Jurte and 30th July (Silks) were recorded for this inatar. Peaks were not cleat' cut as third mnstare were found In both gardens from June to August. -98-

Inatar IV

Reached. peak numbers in the Nursery Garden on 3rd July, with another, minor peak at the end of the month. In Si]ks Garden, peaks occurred on 9th

July and 4-August. Again, nymphal delopment was slightly faster in the Nursery Garden. Fourth instars were present from late Jiuie to mid-September, wha recard.s ceased because the hops were harvested.

As earwigs from the first oviposition period matured, the number of

adults increased steacli]y from July onwards (Fig. 18&), There were more females than males in both sites. Adult females and a few males were trapped early in Nay but did. not occur in large numbers again until mid-July, because

by late Nay, most overwintered. males had died, and overwintered females

entered the soil for their second oviposition. The two peaks in numbers of female earwigs thus represent two separate generations of adults,

The slightly faster development of nymphs in the Nursery Garden was possibly caused by some environmental factor. Since both hop gardens were

adequately sheltered from prevailing winds and only 1.6 km. apart, tempera-

ture differences were probably ninIwl. Analyses of stomach contents of earwig nymphs from traps in both gardens showed that hop aphids, aphid exuviae and sooty moulde, Cladosnorium ep. were moat frequent in the diet,

Since the Nursery hops were not treated with insecticide, large ephid.

populations developed, along with much honeydew and sooty taoulda On the leaves. Hops in the Cobbe plot, Silks Garden, were treated for aphids end. thus had less aphids, honeydew or sooty moulds. Until late wuimr, there were less earwigs in the NuXsery than in Silks Garden. This fact, coupled with the eater abmd.ance of food. probably accounts for the slightly faster development of earwig nymphs in the Nursery site. -99-

Trap efficiency varied according to the stage of development of the

earwig population. Pjrst and second installS were collected rarely in the

traps because they do not climb readily (Beau, 1932), and overwintered adults were a].so rare, BeaU (1932) compared the activity of the variouø stages and found that there was a gradual :Increaae in climbing activity

from instar I to ins tar IV, &IUlt earwigs of the new generation were about as active as IV instare, but overwintered adults were less active than II meter nymphs. Since the earwig population consisted entirely of overwinter-

ing adults and young nymphs (instars I and Ii) until mid-June, earvige probably had little effect upon infestations of the hop aphid at this tine. The main impact occurred in Juiy and !ugust when numbers of earwigs were bia in traps In both hop gardens.

PTXMATIO OP THE DISTANCE CLI1 BT EUROPEAN

EARWIG ON HOP BINB2

Later metal's of the European earwig readily climb at niglrt (Beau, 1932), aM xn be easily trapped by- means of corrugated cardboard bande wrapped around plant stems, in this case hop bines, about 0.6 in. from the

Earwiga can be voracious aphid predators (iTc1eod and Chant, 1952;

Asgari, 1966) aM have been shon to feed on the hop-damson aphid, Fnorodon (cbrank), the major pest of hope (Esoherich, 1916). However, it was not known to what heiit earwigs climb hop bines, althou BeaU (1932) aM Mcieod and Chant (. cauit many earwi.gs in traps placed 5 feet

(1.5 n.) above ground. 100—

PLATE 6. Corrugated cardboard traps placed about 6 feet (1.8 m.) )i!i on a bins.

_; c _, - .:

PLATE 7. Pitfall trap in the soil at the base of a hop bins. I-' i7/ q•

,'. ,_. I,'.. • !

- : - 10]. -

Certai.n species of cocc:Inellid predators feed at different heights on corn plants (Ewert arid Clang, 1966) • Hop binee grow very rapidiy and may reach about 16 feet (5 in.) in height by late June, about four months after starting to grow. Nigrantes alatae of the hop aphM are most iminerous on the topnost leaves (I4aasee, 1963; Anøn, 1969), wbfl.e developing apterae move down the plants as their numbers on the upper leaves increase (Zelar and Hrdy, 1969).

In this experiment, cardboard traps were placed at various levels On hop bines to determine to what height various earwig instars olimb and, therefore, whether the effects of earwig predation woul]. be limited to certain areas of the plants.

Metbod The experiment was made in Si]ks Garden, Wye College,during 1973. Standardised trap baths of corrugated cardboard measuring ]4 in. x 6 in.

(o. in. x 0.2 m.) were used throughout the experiment. Traps were placed at three levels on the hop bines, i.e. 2 feet (0.6 in.), 6 feet (1.9 in.) arid

10 feet (34 m.), referred to subsequently as bottom, middle and top traps respectively (Plate 6). There were four treatments, each of three replicates, involving a total of 24. traps, plaoed in a rathoie block desiga in two uniform rows of hops, var• Gobbe, at the eastern end of Si1]s Garden. The four treatments were designed to show both the numbers of earvigs climbing to the top of hop bines and the influence of traps at lower levels upon catches in the top traps.

(a) Traps placed at 2, 6 and 10 feet.

(b) Traps placed at 2 and 10 feet.

(o) Traps placed at 6 and 10 feet. (a) Traps placed at 10 feet on],y. - 102 0

w p r-I Lt o N I 0 0 rI ri ri C3 CJ CJ 4, 0 0 r4 t\ IA LA D %O i-I LA •1 LA I 0 0 0 0 0 N ri 0 0 rI 0 0 0 0 0 0 r-4 0 0 0 0 0 0 '-I Fl I 0 4, 0 0 0 0 AZ LA LA 0' 0' N w

I•oI

4, o rI -* - LA a ri

vp-I

g i1 o AZ r4 0 0 a) ri IA 0 0 0 0

o 0 0 0 0 '-I 0 0 0 0 0 0 ri c'J I LA

•8 o

a) I \ 0 0 0 N IA i-I 0 0 0 0 0 N N N CO a) 0) a) CO 0' . ., S S S S S S S S. 5 - 103

The experiment was assessed weekly from June 34th to September 6th

1973. A step]aider was used. to reach the topmost traps and care was taken to avoid damage to adjacent hop bines when moving the ladder. After removing and counting the earvigs from the traps, they were then released close to the base of each bine.

Results

Table 32 shows the numbers of each earwig instar found in traps placed at 2, 6 or 10 feet on bines, and. the totals for each trap. Few second instar earwiga were taken in traps at any height, but traps at 2 feet caught most Individuals. More earwige of instars III and IV were found in the higher traps, but the lowest trap still caught more of these Instaz's. Adult earwigs were the moat active, more occurring in traps at 10 feet than at either 6 or 2 feet. Pew earwigs occurred in the middle traps until early June and few in the top traps until mid-July, again showing the reduced. climbing ability of early earwig instore. Numbers of earwigs reaching the top traps increased steadily in all treatments during July (Table 13), due mainly to the increasing number of active new generation adult earwigs.

More earwigs were caught from bines on which traps were placed. at all three heights, or at 2 and 10 feet, than from bines on which traps were placed. at

6 and. 10 feet or 10 feet alone (Table 14). Analysis of the mean number of earwigs caught In traps at 10 feet for each treatment showed that traps at

10 feet only on the blne caught most individuals. When traps were placed. at all three heights, the number of earwigs In the top traps decreased

(Table 14). Traps placed in the middle region of the bins, i.e. 6 feet, caused a reduction In numbers of earwiga reaching the top traps. - 104. -

TABLE 13. Total numbers of earwige in traps placed at 10 feet, treatments

pooled. (32 replicates per date).

Date Total number of earvigs

34 June C

23. Juno 0

28 June 2

5 July 23

32 July 24.9

26 July 62

2 August 105

9 August 157

16 August 130

23 August 73

30 August 60

6 Septmiber 46

PABTJ 14. Overall mean numbers of earwigs per trap, and mean numbers in

traps at 10 feet fur each treatment. (Mean of 12 sampling dates

and three replicates per treatment.

Traps placed at 2,6andl0ft. 2aMlOft. 6ond3Dft. lOft. onlY

Overall mean number of earid.gs per 22.5 ± 8.5 21.4± 7.7 10.7±4.8 7.5±4.3 trap.

Overall mean number of 5,8 5.3. 3.7 3.1 7.5 earvigain 5.1 ± 4.3 ± 4.3 10 ft. trap. - 105 -

Discussion

Beau (1932' and }Icleod and Chant (1952) found that traps around

trees, about 5 feet above ground, caught more earwigs than traps placed on

the ground. This at3y has confix!ned the climbing ability of the later

instara, which occurred in shelter traps on hop bines at all heights up to about 10 feet, although most individuals occurred in traps only 2 feet frcm the ground. Earwigs are nocturnal insects, actively climbing bushes or

trees and feeding during the night, but hiding In crevices by day (Crumb

, i9Zl). In most situations, such as a tree, bush or hop bins, there are few aerial h(M places and most individuals desoerd to the ground at dawn

to fInd a suitable crevice (ilton, 1924). However, in a few cases earwige

shelter In rolled up leaves (Smith, 1966) or tuer crevices in tree bait (Noleod and Chant, 1952) and may live independently of the ground. Cardboard traps placed at three heights on hop binee provided ideal sheltering places for eax'wigs, and although the extent of earwig movnait at night between bins and ground, and on the bino itself is not known, it is probable that providing the traps were not disturbed, large numbers of earwigs would rnn.&n

on the binea, feeding at night and shelterIng above ground during the day.

Thus, positioning of traps on the binea would ensure a resident earwIg popt-

lation and mrjjil so predation of the hop aphid at all locations on the bine. Earwigs will midoubtediy climb higher than 10 feet, the highest location of

traps in this st3y, since Pulton (19214.) a earwigs reach the terminal branches of trees.

However, since young earwigs do not roedi]y climb (BeaU, 1932), there

is probably little predation by earwigs upon the hop aphid on leaves higher

than a few feet before late June, ithen the majority of nymphs roach instar

III. This fact, coupled with the large increase In population of P. humuli

on untreated hope in June, indicates that en early application of a systnio - 106 -

aph.tcide at the beginning of June would be necessazy to maintain aphiilB at

a low level until predators became effective.

EFFECT OP EXAMINATION FBDQThINC! UPON NUMBERS OF

E.ARW]C8 !PAj IN TRAPS

Earwigs invariably shelter in the daytime in any available crevioe.

Uptuxned. flower pots filled with straw and placed on a cane are ooxinon1y

used to trap large numbers of earwigs from gai'd (Jonee Joee, 1964.). Another type of "shelter trap" was used to study earwig numbers in the hop garden. The trap consisted of a strip of corrugated cardboard wrapped

around the hop bins, 2 feet (0,6 ni.) above soil level. Numbers of earwigs in the traps were affected by several factors, including (i) changes in actual earwig numbers (population changes), (ii) changes in earwig activity

and (iii) changes in trap efficiency. Field investigations in 1972 suggested that trap efficiency varied with the frequency that traps were examined.

Traps were usually assessed weekly, but a group left for two weeks accumu-

lated more earwigs. The aim of this experiment was to aho y what effect the

time Interval between assessments had upon earwig numbers in the traps.

Methods Standard corrugated bands were wrapped around hop bines in a plot of hops, var. Early Bird, in two areas of Silks Garden, Wye College.

(a) At the N. edge, adjo14 n a wide strip of rough graasl. (b) In the centre of a uniform stand of hops. There were three treatments in both areas, (i) traps examined at 3-.day

intervals (ii) at 5-day intervals, and (iii) at 1-.day Intervals, oonsisting

- 107 -

of five replicates per treatment. Traps wore laid out In a randomized block design, one traps per hop plant at a density of one trap per 2 n

tor opening the traps earwigs were recovered In a bag and counted.

Thr were then released onto the ground at the base of each plant. Due to

insecticide treatment the infestation of hop aphid, Phorodon hiimuli (Schronlc)

was low during the experiment (28th Ju]y to 25th August). During this time

the 3-day traps were emnivied nine times, the 5-day traps five times and

the 7-day traps four times.

T.BLE 15, Mean numbers of L auricularla per trap when assessed at

different time intervals.

'oqeacy of assesemnt Mean no. of earwigs per trap 3 days 5 days 7 days

E.lge S.E. 52.0 j 25.5 109.0 51.5 103.0 j 61.0*

Centre S.E. 24.5 ± 101,8 37,8 19.]. 315 ± 12.1

No. traps eniiied 45 25 20

Means underscored by the same line are not significantly different. ( p , 0.05)

* (p=o,o)

Results

Table 15 shows the numbers of earwigs from five traps per treatment

at the edge and centre of the garden. Numbers of earwiga from each treat-

menlV'date wore transfoid to the form log (x + comparea by analysis

of variance. There were aiguificantly more ( p 0,05) earwigs oaut in

traps assessed at 5 or 7 than at 3-day intervals at the edge of the hop -108-

garden. There was no signi-ficant difference between the numbers taken from

traps assessed at 5 or 7-day intervals. There were no sigriPicant differ- enoes between numbers from traps assessed at 3, 5 or 7-day intervals at the centre of the garden. There were more earwigs at the edge than the centre, regardless of the time interval between assessments.

Disousion

The edge effect shown in the experiment occurs in both N. and E. edges of Silks Garden, where the edges Interact with another habitat.

"Mae effects" are co among many inseot species and from many typos of habitat (e.g. van en, 1965; Zatymi, 1970). mis may be caused by several factors, as for example shelter at the edges (Taylor, 1962), or the presence of uncultivated larri (van Emien, 1965). The explanation for this observed edge effect is not known, but it is probably important since the impact of earwiga upon the edge plants and the aphids upon these plants will be greater than upon correspomling plants at the centre.

The number of earwiga per treatment varied at oach assessment, probably due to changes in earwig activity. The activity of earwiga, ]ike many

other insects, is affected by climatio conditions (Chant and )lcleod, 1952).

The earwig's speed of movement increases linearly with increase In tempera..

ture (van Heerdt, 1945), and temperature is probably the main climatic factor affecting earwig activity. Therefore, fluctuations In numbers of -

earwiga between assessments were probably caused by ohsmges in the weather. This experiment has shown that the time interval between ex1-tion

of the traps has a asilced influence upon the number of Insects caught. The

total number per trap increased as the time Interval was extended up to about five days. There was no significant difference between the numbers

caught from traps at 5 or 7-day Intervals. )Iu r earwigs which asoeth hop -109-

bines at night end then shelter in a trap imist rmM there f3r long periods of time, living independently of the ground and obti1n1ng all their food from the hop plant. Analysis of sttnsh contents of earid.gs removed fr these traps baa shown that their food is composed almost entirely of organisms associated with the hop, end hop tissue.

TD(ATION OF TEE ABUNDANCE OF SOJ ARTRROP IN SILKS GARD, tflTG PITFALL TRAPS

During a study of the effectiveness of the European earwig, Forfloula

auriculeria L. as a predator of the damson-hop aphid, Thorodon 1uli (Sobrank), soil predators were excluded from certain hop bine in 1972.

Before treatment d.ifferences could be attributed to earwig predation, it was

necessary to know what other insects, especially Coleoptera, were present

in the soil, their relative abundance and whether they were of az importance as aphid predators. Pitfall traps have been widely used to sample soil

artbropoda, especially Coleoptera (Southwood, 1966), and although their

catch is influenced by many factors (Brigge, 1961; Greanslade, 1964.) tb

nevertheless provide useful informatian.

}!ethod Perspex jars (9 cm. high, 6,5 o.m, diameter) were sunk into the

ground with their rime level with the soil surf ace in Silks Garden, Wye College. Pour replicates were placed at the eastern edge of the garden

next to a grass strip approximately 5 in. wide, and four towards the centre of the plot. The traps were situated close to the crown of each hop bins

(Plate 7) and were therefore partially shaded by foliage. These effects

were more pronounced at the centre of the plot than at the edge (Plate 14). - 110 -

The inner surface of each trap was eared with 'fluon' (an aqueous suspension of po:1,ytetra±'iuoroethane) to prevent ineocts from escaping. The traps were ers ithed approxin'te1y every three days from Juno 18th to Septe- mber 12th, 1973. Carabida were removed with a 'pooter' (Southwood end

Leston, 1959) to avoid continued soil disturbance. - Carabids wore Hndly identified by P. T oud, ath arachnids by D, Norman of the British )bse (Natural History).

Results Six oomnon species of Carabidae were caught in the traps. The most abuthant at both the edge ath centre of the plot were Nebria brevicoflis F. aui Pterostichus melanaria (in), wbiie om dorsale (Pont), Noticthoiiis maiustris (Duft), L substriatus (Waterhouse), L biittatus F., Thec1 anaLristriatus (Schrank) w Harralua aeneus P., occurred in smaller znmibera (Table 16).

Stapby].inids were rarely caught in the pitfall traps; smong the species recorded were 1nçprl (Oliver), Tsctnua rufices (DoG.), oaeaius cz'u&itus (oi) ath Stanhvlinus atei' (Gravenhurst). TaclxvDOD.W app. were the only 000n stap 11'it1 in the hop garden, but wore not caught in the pitfall traps. They were fouth in cardboard baths placed aroux4 the bine, and on hop leaves. Species of staphylinids caught included Jrnorum P., P. obtusus L. and L. chrvsomeliuuq L. Other beetles occasionally found on leaves or in baths were flRorcha (1a), L lutes (1), C.thçris livada I. (Cantbaridae), ani Rhi- chilus atrioa-Dilhias L. (Carabiñae), Ear,rigs, Pox!fioula auricularia L. occurred in the pitfalls from June to September. Two species of spider, maurobiva terreatris (Wider),

1,7 ,DiBsa niaoq (Clerok), and one species of Harv-eaan, Thalangium ocilio L., were found infrequently in both pitfall traps and. cardboard baths. The - 111 -

red ant, vrmica rubxa L. was omiion in the pitfall traps, especially in

those at the edge, Numbers of carabid species at the edge an1 centre of the plot wore

compared by a t-test. There was little difference between catches of cars-

bids in each area. Eaidgs and red ants were more abundant at the edge,

although differences were not slgnffjcant (t 2,265 and 1.392 respectively).

Pee&tnR habits of the aDecieS identified

Nebria brevicollis. the most cmmin corabid in the traps is strictly carnivorous, feeding 'n"dxily on oollsmbola, spiders and m' 1 arthropoda

(Davies, 1953). Eteroatichus (= 'eronia) melanaria feeds on both plant and

nnimt4l food on the soil surface CDavies, 1953). It has been recorded feeding on strawberries (Brigga, 1961) and other beetles (Mitchell, 1963). P. melanaria was the largest carabid collected during this sty. In laboratory tests, earwigs were readily eaten when confined with this beetle.

Hop aphids were also taken, but since the mouthperts of P. molanaria are massive the prey taken would normally be larger than aphids. It is probable

that this beetle does not climb, but is active only on the soil surfaoe

(Dempater, 1967), eating large prey, as for emnple, slugs (stephenson, 1965).

Aonum dorsale may be a predator (Davies, 1953) but its diet is not oomnple

tely laiown. Notiotholus spp. are completely carnivorous, feeding on Rm,%1l

arthropods, coliembola and mites (Davies, 1953). echua auadristriatua feeds on many tpes of inaecta, inc1utii Pieris raDae larvae (Denpeter,

1969), cabbage root fly eggs (coaker and Wi111mi, 1963), oollembola, mites and small beetles (Mitchell, i963a). This beetle can climb bruesel out plants (Denpeter, 1967); whether or not it will climb hop blues and feed on

is not yet laiovn. Harnalus aeneu feeds mainly on vegetable matter

(Davies, 1953) but has been reoorded preying on cabbage root fly eggs (Coaker and Williams, 1963) and Piers ra,aa caterpillars (Denpeter, 1967). —112—

NU' ,-ic.J o4 1A4

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Spiders are known to prey upon apW.ds (Hagen and van den Bosch, 1968; Shiga, 1966) but they were not numerous either in the pitfall traps or In aerial samples. Staphy linids were rarely cauit in pitfall traps and the species taken were al]. general predators. i1y 'achvorua sp, and a few

Quedius cruentus were seen on the hops; they may have taken some aphids.

Dicker (19414.) recorded imnature T. hvnorum preying on strawberry aphids, but the usual diet is probably mites and small collGnbola, Mult canthaz!4a are predatory and will feed voraciously on aphids. Way and Banks (1968) found that Cazitharids were important predators of the black bean aphid on

its winter host, Euolwmun europaeus L., especially in hedgerow habitats. They also recorded R. atricacillus and P. hvnnoruiq from aphid-infested bushes. Three species of Cantharid were found in small numbers on hops, but only during late June and early July, while R. atrtcaDillua and Tachv . 000n (Table 17). All these beetles fly readily -oi,is species were more and were found equally on hops from which soil fauna was excinded by banding,

and on those which were not banded.

Harvestmen feed mMrily upon n{m1 matter, but fungi, seeds and psi-' lets of vegetable matter have been recorded among their crop contents (savory, 1964). They scavenge or prey on such as woodlioe, milli- pedes and mites (cloudsley-mompson, 1958). sankey (194.9) observed Thalariium oDillo L. preying upon P. hwuuli In hop gardens at night.

DiscussioU Pitfall trap catches are influenced by the density of the population being sampled and the activity of individuals (Southwood, 1966). The activity of Carabidae is influenced by tsmperature and food supply (Brigga,

1961), the general habitat surrot mMng the trap and. the amount of moisture in the soil (Mitchell, 1963). The trap's efficieney varies from species to

- 1]4 -

species (those active during the day seem to avoid capture (Greenslade,

1g6l)), from habitat to habitat, and according to the precise location of the trap. Therefore, the results of this study may not indicate the true

abundance of each carabid species recorded. However, comparisons between the catch at the edge and in the centre of the hop garden are valid. There

was a dense litter layer of dead leaves and the straw imiloh applied to tho

hops every year in Si]ics Garden, which may have reduced insect mobility and caused the smaller species as, for example, Notionholus sp, to be under-

estimated, especially as they are diurnal beetles (Greenalade, 1964) and may

hence see and avoid the traps. However, the traps enabled the m'th' doin1mt

species of Coleoptera present in the hop garden to be caught id identified.

There were six main species of carabid in the garden. AU ware pradacious,

but their predatory activity was mMnly confined to the soil surface and so

they were probably of little importance as hop aphid predators, although Trechus auadristriatua may have climbed the binea.

TABLE 17. Numbers of non-specific predators found by weekly exmn1notion

of 30 traps and 90 hop leaves (May 21st - September 17th), Silks Garden.

Date StaphyliM dae Cantharidae Carabidae achvDoxvs Quedius Iizovbilus atricavillue

May 0 0 0 0 June 4 1 1 1 July 5 3 4 0 August 2 0 0 3 Septber 7 0 0 8

18 4- 5 -115-

Staphylinid.a, especially Tac1iorua spp., probably fed on hop aphids. The pitfall traps were inadequate to szunple active, free-flying staphylin4ds, an! weekly ermiriation of trap banda an! hop leaves have unIerestiiated their nuubers. Of the other insects recorded, many were predatory, inc1iiMrlg the phalangid a1tum oi4io L. Sankey (19z.9) recorded P.. ovilio preying on hop aphids. Bialangida are also ready climbers (Savory, isSi). They were found in trap bda at 6 and 10 feet above ground level in Silks Garden, but were not numerous enoui to significantly affect the aphid population. Earwigs were one of the most abundant izvertebrates in the pitfall traps, especially at the edge of the garden. However, the strong thino- tactic and negative geotactio behaviour of this insect (weyrauoh, 1929) caused their numbers to be imierestlinated by pitfall catches, since greater n,.mi,bera of earwigs were recorded in cardboard traps on the hop bines about 2 feet from the ground.

DISPEEION OP DTJLT ERWI( ON THE SOU SURP4C, A.ND flii- GAIO! flITO THE S.âME'LING EWFICIBNC! OP CORRUGA C.BDBO.ABD

When stu1ying earwig populatione using corrugated cardboard traps placed around the base of hop bines, earwig numbers decreased during August and Septnber in 1972 and 1973. Darpeter (1960), atwlylng earwtgs as one of the predators of broom beetle, rtodecta olivacea.. also observed this decline In the population, which may be accounted for by 1imite rmovaient of earwige out of an unfavourable area. - 116 -

Beau (1932) found that ].imited movement of late inetar and adult earwigs to or from a email area would occur readily, a1thoui the fiM(ns of Crumb at el (1941) indicate that appreciable distamoes are not moved unless the earwig population equilibrium .a disturbed or environmental conditions become adverse.

The aim of these experiments was to use mait.4 Individuals to detect earwig movement, or earwig emigration, Into or out of the hop garden in summer, and to calculate the sampling efficiency of the traps used in samp- lirg earwig nbers in relation to the habitat in two different hop gardens.

Narkiria methods

Prol 4m4 nary experiments were made in the laboratory to determine the most suitable type of markers Fluorescent powder mixed with gum arabio glue

(Nacdonaid, 1960) did not last for more than two days. Fluorescent powders alone lasted better, but needed complicated ultra-violet equipnent to detect the particles. The two most suitable markers, capable of being detected at riigbt using a torch, were found to be 1limilnlum paint (xuxdoch, 1963) aM fluorescent wel paint ("safe-spot"). Trials were made by applying these paints with or without abrasion of the cuticle, but the persistence of marker was not increased by abrasion. None of the paints used caused earwig mortality.

roer1ment . Nursery Garden, September 1972.

200 adult earwiga were collected from the field and marked 'with a

RmCL]. spot of red. nail varnish on the mesothorax. The varnish was applied thinly, as thick spots were shown to flake off soon after being applied.

Earwiga were released in mid-afternoon on September 2nd In the centre of a square of 36 hop bines, occupying 50 sq.in. at the N. garden edge. - 117 -

eriment 2. Nursery Garden, June 1973. 19 adult earwigs were anaesthetieed. with 003 aM each maited with a i1 spot of al__1 {m paint on the mesothorex. Laboratorbred stock had to be used., as few adult earvigs were present in the fiejil in mid-June. Traps made from corrugated. cardboard ]4 in. x 6 in. were placed about 2 feet

(o6 in.) above grouth on hop hines aM strings on Jv.no 20th, at the rate of one per hi].].. The trapped area formed a rectangle 10 in. x 5 in. at the N. edge of the garden (Plate 2), contAining 36 hop binee, Therefore, trap density was 36/50, or 0,72 traps per ii?.

Marked earwigs were released In the centre of the plot on Juno 30th. A few individual earwigs left in the laboratory- rnained alive, showing that the paint did. not apparently affect tham. Nursery Garden hope were grown in raised rows, where the soil was heaped to about 8 in. above the furrows. Weeds were cleared by plugting aM hoeing, ireed]d.11ers were not used. The experimental hops were not treated. with insecticide, so the population of hop aphids during the experiment, June 30th to Jui 11th, was large. At each sampling occasion, earwigs were collected. from the traps Into large bags. Malted aM unmarked irdividuale were counted and the earviga released on the soil at the base of each bins. Samples wore taken at appro.. itely two-day- intervals after the initial release of marked Inaects.

roeriment 3 Silks Gerdan, August 1973. The trial area, on the N. perimeter, was a rectangle 16 n. x 18 m. of area 288 sq.m. (Fig. 10). Traps were placed. on each alternate hop bine and a total of 41 traps at a density of 0.]1. traps per ni2 • were used..

300 adult earwigs, malted as before, were released in the centre of the plot on August 15th, 1973. Release was made during the day to ml'1Mse

o 0 0 O 0 0

o 0 \ 0• 0 0 oW o 0 CO X 0) 00010CD0O00h a. o o o 001 oo oC ooW

0 0 0 0 OI o o 0 0 0 0 CD

o O 0 0 0. o 0

o 0 0. o ow 0 o o 0 o o ow opj o Cl) o opjo oW o o

O%IXCDO o o XoGi 0 0 a 0 0 0 0 OPJ o

0 00 Cl) 0 o oo o a a 0

0 co S o o 0

0 0 0 - 119 -

ubsequit niovnent (Soutiiwood, 1966). The soil surface In i]ka Garden was virtually flat an]. wiploughed, with a deep surface litter layer. Weeds were el1minstecl by Paraquat spraying and nunibers of hop aphids were kept

low by soil treatments of dimefox and aerial applications of supracide.

The differences in the habitats between Si3ka and Nursery Garden were expected to alter the efficiency of traps and the mcveinent of earwigs in each site. &rwigs were counted as before, every alternate 1ay from August 16th to 29th, 1973.

roei'ient 1 Si]ks Gardon, Septnber 1973.

aps were placed on the three )'fllg nearest to the N. edge for 15

rows. In addition, 27 traps were plaoed. on canes at 2 m • intervals on the

grassland strip adjo1fllTle the northern edge of the hop garden (Plate 5), to follow dispersion from the garden into the grassland strip. 200 earwigs marked with fluorescent esafe_SpOtø paint were released at the mid-point of

the trial (Pig. 19) on August 31st. The hope wore harvested on SepteTnber 4th and only three readings were taken.

Marked earwigs were observed the night following their release, using a hand torch which picked out the maited insects at distances of up to 3 feet. The light tended to arrest their activity and, therefore, continuous obsei. vationa could not be made.

çilta Field studies in 1973 showed that earwig mortality caused by predators and parasites was low in both gardens. Probably the main error in these experinenta was due to enigration of marked earvigs outside the area, The tine taken to assess each trap imposed limits upon the size of the trapped -120-

I I

0 N I

0 I 4. U-' N

I cc ik I ci

'.0 I IC' .I p I p N tr. It' P r4 U-' IC N N

P N '—I It' a' N

M• '4.':1 I-I

I 'S 1 8 N '-I

.4.3 0

cr i . . o •o . .cO l. '-I DO - 121

area, a1thoui thia problen was partly overcome by reduoir trap density in Silks Garden.

a) bers found at intervals after release Table 18 shows the numbers of earvigs found after release in three experiments. Their numbers fluctuated daily, probably due to o].imatio variations which affect the number of earirigs found in shelter traps (Chant and Mcleod, 1952; Levier and Davis, 1962).

b) Rates of die].acnent Since the traps were equally spaced in each experiment, distances of each trap from the central release point could be found. Rates of displaoe- ment were calculated using Clark's (1962) method. For each day after release the root mean square of distances travelled by marked earwiga (D) was calculated. using the formula : D = (d)2 where d = distance of each trap from release point

N and N = total number of marked insects captured..

TABLE 19. Average displacement distances of marked. P. auricularia. expressed as root moan squares (m) at atiocessive intervals

after release.

Site & date Time in days from release of release 1 2 4. 6 9 11 34

- 29,72 2,45 3.51 4,00 4,80 3,60 2.74. 3J2

30.6.73 - 992 11.09 10.34. 9.41 7.87 - Silk 15.8 .73 21.13 17.64. 17.39 19.62 18.65 - 15.67 Silks 31.8, 19.35 22.34. 15.4.3 - - - - -122—

Table 19 shows the average diaplaonent distances of ked earirigs

for the fow experinnts. Mter wi initial increase, the disp1acneflt distances changed littlee In the Nursery Garden m iiw dispersal occurred

between the fourth and sixth day after release, while in the first experiment

in Silks Garden, the greatest dispersal occurred on the firøt day after release.

Distances covered were unich higher in both experiments in Silks,

probably because of the flat soil surface as compared with the rows and furrows of the Nursery Garden. Pig. 19 shows the locations at which marked. earwigs were recovered

in the Nursery and Silks sites, 1973. Recaptures in &periment 2 (Nursery

Garden) were most frequent In the two rows of hops adjoining the release

point (marked I on the plan). Total captures In the four quadrants were N.Y. 5, N.E. 14, S.W. 53, S.E. 46 ( 1 2 = 3.70; N.3.). 1ore maiiced. earwigs were caught in the area S of the release point than N, of it (actual numbers

99:19), showing that marked individuals did not generally move towards the N. perimeter of the garden (approximately 15 m. from the release point). Mean distance moved two days after release was approximately 10 m., although

the 1im distance recorded. was approximately 20 m for three earwigs found in a trap outside the trial area two weeks after the last assessent,

On July 27th (27 days after release) there were still 18 marked earwige in

the trial area. In Silka Garden, recaptures were not as concentrated near to the release point (Pig. 19). Total captures in the four quedrants were N.Y. 17,

N.E. 19, S.V. 7, S.E. 17 ( x = 1.27; NS). More recaptures were made

In the N. sector (nearest the edge) than in the S. sector (ratio 41:27) but this did not prove that movement was directed towards the edge of the garden.

Mean distance moved two days after release was approximately 18 m. (Table 19), - 123 -

although one female was found approximately 26 m. from the release point five days after release, and one male at 36 in. 12 days after release, in traps Outside the trial area.

Traps placed in the grassland strip in the second erperiment in Silks Garden are not shown, because no marked earwiga were found there. )Soat recaptures were close to the release point. Because the trial area did. not extend beyond three hills into the garden, many marked earwigs presumably dispersed Outside the area and were lost. However, this trial was desied to show movnts of earwigs from the hop garden towards the grassland edge.

No such movements were found. No marked, and few inimci*ed earwige were taken in traps placed at 2 ii?. intervals on the grassland (Table 20). Most earwigs were caught within 2 m. from the hop garden edge.

T.BLB 20. Numbers of earvigs taken in cardboard traps approximately 2 feet

above ground in a grassland strip adjoining the N. perimeter of

Silica (27 traps assessed at 1, 2 and 1. days after release of marked insects.)

Distance of trap Row number from edge (ia.) 18 19 20 21 22 23 24 25 26

2 8 24 10 15 2 5 26 5 1

1. 2 1 0 1 1 2 0 5 4

6 0 0 0 0 0 3 1 0 1.

Mean distances travelled were caloui.ated. as 1.1 in./day (range 1.5 -

0.9 m.) (3,7 feet/day) in Nursery Garden, end 3,9 m./day (range 7.2 - 2,4 m.)

(3.2.8 feet/day) in Silks Garden. - 124. -

Tran efficiez 'om the number of marked insect s caught on each sampling date after release (Table 18), calculations of the percentage of individuals recovered

(i.e. the efficiency of trapping) were made. Nean percentage recovery from traps In the Nursery Garden was 11.6 (range 6,7 - 18.7 $), where traps were spaced at a density of 0.72 per square metre. In Silks Garden, where trapping density was O]4 per square metre, mean recovery was 39 $ (range 17 - 53 %). Trap density corrections were made, giving a mean recovery of

3,9 x 0.7g. or 19.7 $ in Silks. However, because the experiment in the 0.14 Nursery Garden was clone in June and in Silks in August, these figures are not strictly comparable, because earwig activity affects the nunber entering traps, an. activity itself is affected by the weather (Chant and Neleod, 1952) which may alter from month to month.

Absolute monulatign eatmatee

Absolute population estimates were In&Le usi ng the formula of Lincoln

(1930) Southwood (i966), 'where it is assumed that the ratio of marked recaptured insects to the total number of marked insects originally released is the same as the ratio of the total number of insects (marked ama. unmarked)

in the sample to the total insect population. These estimates are liable to errors, the main one being loss of marked earwigs outsijie the trial area, which was probably greatest In the

Nursery results where plot size was limited. i) Nursery Garden, 1972. Septaiber. Plot size 50 d. Population estimate

1206.3 ± 202,l.

(standard error)

ii)Nursery Garden, 1973. June. Plot size 50 . Population estimate

489.2 j39.9 - 125 -

Lii) Silks Garden, 1973. Axgiist. Plot size 288 in2 • Population estimate

5154.6 1451.2

Absolute estimates are i) Nursery Garden, &eptber, 1972, approxi-. niately 200,400/ha. (81, 1140/acre). ii) Nursery Garden, Jme 1973, approxi- niately 97,860/ha. (39,600/acre). iii) Silks Garden, August 1973, approximately 179,300/ha. (72,440/acre).

The experimental area of hops, var. Early Bird, in Silks Garden, was harvested on Septnber 14.th, but the rn,4mi er of the garden Mial nod intact until September 15th. Catches of earwigs in pitfall traps placed due south of the Early Bird area increased immediately after that area was harvested

One male yelloip-marked earwig previously recorded on August 318t, was tak in the pitfall traps on Septnber 10th. This individual had ooverod approzi-. mately 50 in. from its point of release.

Discussion

Working in the U.S.A., Crumb, Eide and Bonn (1941) released marked earwigs in several habitats, incluMng a dry grass race-track, a lawn and a paved aUey. General].y, traps near to the release point cau&it most maited insects. W'thinun distance travelled was about 75 feet (23 rn.), except in the dry grass race-track where distances of up to i/ mile were covered, owing possibly to the unfavourable environment where little food was present.

These workers concluded that the earwig normally confines its movements to a small area, except when conditions are uxifavourable or when the equilibrium of the population is disturbed, whi the earwig may wander extensively. The present work has confirmed these cqnolusions. Many marked earwigs occurred in traps close to the release point, but large distances were covered when the plot of Early Bird hops was harvested. Probably, the disturbance caused by harvesting caused many earwigs to move out of the area; movement was - 126

probably random since orientated migration had not been prevfrusly shown in experiments with marked earwigs.

The European eand.g rarely flies (Fulton, 1921k.), a1thoui several authors give conflicting reports as to the minnn flight-period. Crumb •

(;Qg. saw most flights on briit, sunny days, while Collinge (igoe) observed flight on warm, dark nights. However, the main method of dispersal is probably by movement on the soil surface.

The speed of dispersal and the distance moved depends partly on the ground contours. Distances covered in the Nursery Garden were much lower than in Silks Garden where the ground was flat. BeaU (1932, 1932a) and. Crb et a]. (.]. .) found that earwig trapping and removal did not eliminirite earwigs from plots of land unless practised on a large scale, because otherwise immigration of earwigs from surrounding areas was rapid.

During field studies in 1973, earwig numbers in three plota decreased immediately after treatment of the hope with a soil-applied insecticide

(dimefox), but numbers recovered quickly In one plot close to the perimeter of the garden, suggesting that rapid immigration from outlying areas was taking place.

knigration of earwigs from the garden was thought to occur in late summer and autuii, to account for the gradual decrease in nnbers fomI in traps at this time In the years 1972 - 1973. No orientated movement has been shown by these marking experiments and it is probable that earwigs dispersed in random dfrectiorE, as Clark (1962) found with grasshopper's. Several factors may contribute to the hop garden becoming a less favourable habitat in aut, inclutli mg the lack of hop aphid prey, lack of young hop leaves, and abecisgion of most leaves up to about 6 feet from ground level. - 127

T FOOD OF EABWIGS IN HOP GARDE

me European earwig is an o!mivorous insect ('ulton, 1921.). Specim'ns

collected within a short distance of one another n383r show etrl]d.ng differences

in stomach contents (Crumb et Sla 194,1). Many authors have reached dferent conclusions about the type of preferred food of earwigs (Schwarts, 1908; Ncleod and Chant, 1952; Goe, 1925), but differences may be explMned on the basis of food availability in each habitat studied. The earwig eats many kinds of plant material when available (Brirxlley, 1918), incliiMng hop tissue on occasions (Theobald, 1896; Massee, 1914.3), and ninny types of insect, including oodling moth pupae (White, 1969), caterpillars (Borland, 1929), Col].embola (Mclagan, 1932) and broom beetles (Richards and. Wa.off, 1961). Soft-bodied insects such as aphids are especially eaten (Mcleod and Chant,

1952; Smith, 1966; Asgari, 1966; Way and Banks, 1968). ETm4riing the stomach contents of an insect is one of the simplest and most direct methods of detexn1lng its food. Earwig stomach contents have been studied by Luetner (1911 4.); Mmiok and Note (1934); Crumb et al

(19l1) and Skuhravy (1960). They all used earwige from different habitats. These authors ooncluled that both vegetable and. srn11 food (especially aphids) were taken, but that vegetable food was more important. ilthouga F.. a icularia was first recorded by Eacherich (1916) feeding on the damson-hop aphid, Thorodon Iumu1i (Schrank), other workers (Theobail,

1896, 1913; Nassee, 1943) have also recorded earvigs feeding on hop leaves. In thia study, earwig stomach contents from two hop gardens were eramined. weekly f 14 weeks to determine to what extent earwigs fed upon during the sLmner -128-

Xethocls

An average of eight earwigs per week were removed from both Nursery and Si)ka Gardens, Wye College, between Nay and September 1973. Early in the season different nynph&. Ins tax's were diasected later, mdxi1y adults of both sexes were used, Earwigs were taken from insecticide-free rows and occasionally treated rows of hops Iii the Nursery Garden, and from treated rows only in silks Garden, Earwigs were killed in a cyanide kill 4..jar, embedded in wax, dissected wider water, the crop removed and contezite teased out in a drop of water on a slide. The contents were then examined in water.

(x 10 az x 40 mr€n1fication). 10 microscopic fields (x ic) were examined per replicate and the contents noted. When analysing stomach contents, soft-bodied insects such as aphids may be missed, since they are cuic1c1y digested and, therefore, may not show up in the ermi ruition (McNillan and Healy, 1971). Therefore, before field earwigs were analysed, experiments were made to determine the length of time that P. humu]i rfne were detectable in the crop of F. auricularia. Earwlgs were starved for 48 hours to clear the crop of contents, and then allowed to feed. on pieces of hop leaf infested with P. humuli for 30 minutes.

Crop contents were then examined at various intervals, from 2 - ?0 hours after feeding, and the presence of aphids in the crop was determined. It was found that even at laboratory temperatures (a. 20°c.) aphid r1n* were detectable for up to 20 hours. Daipeter (1960) found that eggs of the broom beetle, Phv-todecta olivac (Forster) were detectable in the gut of an eox'i,jg for 27 - 30 hours after the meal, although be used the precipitin test. Theref9re, earwigs were rved from the field each wec at approxj.. mately 10 a.in, knowing that aphids fed upon the previous night would be detectable. - 129 -

The frequency of occurrence of different foods in the earwig's diet was classified by Sktthravy's (1960) method, i.e. :-

0 = not present

+ = present only occasionally in the diet

= present in of individuals examined

+4-1- = present in of individuals eynnth*d = present in + of individuals examined

-1-H-H- present in all :irxdlviduala examined

Although not all gut contents could be accurately identified, aphid remains were easily detected (flate 8). Hop tissue was diaosed by the presence of numerous transparent hooks or setae on the epidermis (Gross, igoo). Many hop tissue bits in this study had only single books, which are usually found high up on stem and bine leaves of the hop (Gross, .

Other constituents of the diet such as sooty moulds, C1ndosDori1. species, were identified by comparing the appearance of stomach contents with materials

scraped off hop leaves in the field (Plate 8).

Results

Table 2]. summarises the analysis of stomach contents of earwigs fran

the Nursery Garden, April to September, 1973. Out of 91g. earwigs dissected

only 9 had empty stomachs. The stomach contents analysis may be divided into different phases,

refleoting the availability of different foods in each phase.

Early in the season before slates of P bimili had. arrived, food

consisted mMy of green a3.g, Pleurococcus species, and various types of

fungi and funga]. spores. Dissectioxis showed that Pleurococcus rnM

occurred a]iaost entirely in earwigs taken from traps on pole-h(1Th (i.e.

hines growing in association with the wooden poles which support the wire

— 131 —

framework of the hop garden.). Pleurococcus was abundant on these poles

and occurred lii the diet of earwigs from pole-hi 'is sporadically throughout

the suniner. The alga was rare in the diet of earwigs from non-pole hills.

BeaU (1932) found. that Pleurococcus sf53 CQfl in earwigs in. Vancouver,

British Co].umbia.

Enong the types of fungi identified were hLternaria ap., Trichoden

sp. and rvsithe sp., the first two being con fungi in Boil or decaying vegetation and the latter probably the powdery mildew of hops. Sku.hravy (196o) found spores of Alternaria and Fxvsinhe in crops of earwigs from various typea of cultivated fields.

Hop tissue was also present in. the diet, especially during early s11nner when the majority of earwigs dissected were young nymphs of instara II or III. Pield observations and laboratory tests showed that young leaves

were preferred to older leaves and that most damage occurred on leaves

adjacent to corrugated cardboard traps at tho base of the st, in which large nunibers of earwigs sheltered. Hop aphids first colonised the hops on Nay 28th in. 1973 and large populations of apterae soon built up in the Nursery Garden. However, aphids did not occur in. stomach contents until June 19th, probably because the

inactive juster II earwig nymphs do not climb readily (Beall, 1932) and would,

therefore, not encounter many aphids which Initially coloniso the young

leaves at bine apices, i.e. about 1,. — 5 feet above soil level (Massee, 1963). Aphid rnRins were found in. all individuals dissected from 19th June onwards until harvest, although aphids were scarce on untreated hops after mid-July.

Sooty moulds, CladosDorium ap., became prevalent on the leaves in 1973 owing to the copious secretion of honedew provided by the aphids. Cladosnorium sp. and aphids forxid an important part of the earwigs' diet fro the remiMor of the summer. It seema probable that earwiga grazed over - 132 -

PLATE 8. Earwig stomach cortents.

A. ADhid ax1 undentffi art1UOOd

.4,

B. C1adosDorizn soores an4 hthae frazneuts.

- - , I,- :9

...,1,

- ,., .

- 133 -

PLATE 8. (Contd.)

C. Ho tissue aI aphid bits.

p. - e

D. ezai4 mass of Cladosporiizi hy-phae.

4 *

A. y b — 134 -.

the dorsal and ventral leaf surfaces, feeding indiscriminately upon sooty moulda, aphids and aphid eruviae. Large quantities of sooty moulds were eati during July, so that the crops of earwiga were filled with spores and hypbae of this fungus, intermingled with aphid remains. Other arthropods found were mites (infrequent), coliembola (frequent) ani other renaii iiiich could not definitely be identified, although sone rmMns were probably that of earwigs, since the earwig is often necz'ophagoua

(Crumb et al. 1941). Coflembola, particularly ktanobrva ltifasciata Tullberg, were abundant both in the earwig bands and in cracks in the poles. Coil anbola rnl were identified by franenta of setae, furculae, mouthparts or antennae (I*tttcheil, 1963; Poster, 1970). In laboratozy tests, earwigs confined in glass tubes fed voraciously upon this collanbolan. The results of stomach oontents analysis of earwigs fran Silks hop garden showed 1mi1' food constituents (Table 22), although hop apbiis appeared earlier in the diet (June ith) in earwigs from this garden and were found in all individuals until harvest (September 12th). from a total of 102 earwiga examined, 12 had empty stomachs. Applications of dimefox on

June 26th and July 20th ensured a steady reduction in numbers of live aphids during July, and the aphid population was el(m1nted by early .A:uguat. Daad aphids aocumulated in large numbers on the dorsal surfaoe of the leaves an! the earirigs, therefore, must have fed m.cinly upon dead aphids from July onwards, indicating the possibility of earwig poisoning through food-ohi1n toxicity (Bi.nns, 1971). Sooty moulds, Cladosoorium sp., were a,moi g the food constituents from late June onwards, but the amount of thia fungus in the cropa was never as great as in eaririga fran the Nursery Garden, probably because the lack of hneydew meant that CladosDorium growth was restricted in Silks Garden.

-136-

Discussion

This study has shown that the diet of the European earwig in hop gardens is composed Of both funga5. and. insect mattei the fungus boin available as food indirectly through aphid population build-up and honeydew secretion. Live aphids, aphid exxviae and deed aphids are all eaten by

earwigs. The earwig does little harm to the hop although small amounts, particularly of young leaves, are eaten early in June, but this is far out- weighed by their beneficial effect of aphid predation. The result8 show that a fairly wide range of plant and nn1inr1 matter is taken, but the mono-

cultural habitat of the hop garden ensures that the hop, inclmHug orgm1iFms

associated with it, are the only abundant types of food.

The omnivorous habits of the earwig (1rulton, 1924.; alendei'niig, l9z.7) might be advantageous to a predator, since it can exist on alternative foods

when aphid prey is scarce (Forbes, 1883). Slcuhravy (1960) dissected earwigs from various types of cultivated fields, 1nol'ing oat, sugar beet, clover and lucerne, and found that aphids

were the main type of insect food, particularly at certain times of the year. Generally, plant food formed about 80 of the diet, but the seasonal availability of aphids imist affect this result. Other insect prey identified by Skuhravy ,) were jassids, curculionids and thysanoptera. Earwig movements are usually restr,ioted to a limited rouge, unless

their population equilibrium is disturbed (Crumb etl. 1914), which probably accounts for the frequency of Pleurococcus algae in crops of earwigs from pole-hills where the algae grew freely, and its rarity in earwiga from non- pole hills, even though both types of hill were as little as 4. m. apart.

The Collanbolan's ld-thly identified by . Peter Lawrence of the Department of Entomology, British !4.iseum (Natural History). - I37 -

URvEI OF EARWIG .ABIJND.ANCE IN S .E. K21T

Earwigs were connon in two hop gardens at Wye College in 1972-1974, w together with Anthocorids were the amln predators of in

1971-1972 (Campbell, 1973). It was not known, however, whether earwig abundenee was localised within hop gardens at Wye. The stzIy was, therefore, ext1ed to eTalnine earwig numbers in several hop gardens in S.E. Kent.

Kethod.s

Gardens within a 20.-mile radius were selected in areas N.W., S.E. and SW. of Wye (see Table 23). 20 standard earwig traps were placed in each garden on ].3th-]4th June. The traps were only sampled at monthly intervals, i.e• early July and. early August. The total earwig catch, numbers infected by mngus (ntpmopthora forficulae) or tachinids (Bjccinj- chaeta setiDermis were recorded. Any other predators in the bands were noted and numbers of aphids counted on 20 leaves (five from each of four bjnes) chosen at random at heights up to 6 feet. Samples of top soil were taken from each garden and soil classes identified.

Results axiI Discussion

Table 23 sunimarisea some general data on all seven hop gardens studied. In the table, P foliar spray and S.D. = soil drench of insecti- aide. All the sprays used were organophosphorous compounds except Lannate

(xetlicsnyl), which was a carbamate. Leefex (Taroil plus sodium monochioroacetate) was used to burn off the lower 1-2 feet of vegetative growth on the bines in all gardens. All the gardens used the m4n1ru1 cultivation technique; the oonstant passage of tractor wheels caused soil compaction in a].]. cases. Soil types varied from a sathy loam to a clay soil, but _ 1.38-

S o . r4 * :1i .cI ,.. . S • N i 00 Hi d Li 1m

p • S • • S • S S • H • p• •H • 0 0 II q4 4'OO 4) 0 0

Pi .-I44 il.

l4 Et I o 0) 0)

• S S I

io j r.b •)• •

0 0 P4 0)'j 111 oo 0 • • r1. •r4 P1 r4'd • 43 I-4 c3' i i4II $4 I

4) hi • 'C' h 1. 'h

Jill U U hil p4 - 139 -

organic 're was used as a top dressing throughout. The percentage infection of P. auricularia by ftmgus and by tacbir'tdR was very low ovrel1 (Table 214.), but varied between different gardens • The highest percentage infection by tnopthora forficulae 0) occurred in Oushmere, Pour Vents and Nash Court. Since infection by the fmga is only successful when the air is moist (ioo 0 R,E.), microclimate effects (such as dense foliage growth) probably caused the fungus to be more prevalent in these gardens. hids were scaroo In all gardens by early July (Table 214,) due to the heavy insecticide treatments aid, therefore, there were few specific aphid predators In the bands or on the 20 leaves examIned per garden. Mult anthocorids aid henerobids occurred in small numbers in the auri-ey, but

syrphid and coocinellid larvae were rare. Rbizothiius atricaDiilus (Core. om in the bends. -bidoe) and Tachvoorus hvonori (Staphylln{dae) were

Earwige occurred in all gardens examined, but were only coion in three of then, i.e. Nash Court, China Farm and Pour Vents (Table 214.). The distribution of earwigs is limited by climate (van Reerdt, 1946), but as all the gardens were within a ,w1i area of the coimtry, climatic differences between then were 11. The three main taotom controlling earwig abun&3ance in hop gardens are probably : i) pe and frequency of insecticide sprays. Soil drenches of eystenio insecticides, which have been shown to be hily toxic to F aurloulari( in ].aboratozy tests (Section iii), were used. in only two gardens (Table 23), but earwigs were ooin in both. Highest numbers (about 30 per bard) were found at Four Vents, where only toiler sprays were used, and about 24. per band were fount! at China Penn, which hat! the heaviest insecticide dosage

of any garden. Deed eanriga and earwigs dying in spasms were found In early July at Gushinere shortly after a toiler spray of Lamate, but otherwise

00 00 hr

00 00 II

"-I U 00 c'J0 I II

r4 0 00 cJcsJ 4

00 ci I U 'ii g

I ow 00 I

43 cs1 U-., .c'.J 0 I c%J I's'— d

I 43 iL I 1-

43 PIP143 I0 J 411,4 ii - 141

there was no obvious relationship between numbers of earwigs and insecticide use' ii)Eal)itats surrounding the hop garden. Stapley (1949) considered that earwige were normally insects of undisturbed waste or grasal1. Jones and Dunning (1969) found that earwi.gs were moat con in sugar beet when the orop edges wore next to grass or sci,abland. The surroundings of each hop

garden (Table 23) may have influenced earwig numbers, but more detailed study is needed to clarify this aspect.

iii)Soil type. Iost oonmeroial hop growers do not plough their gardens

and use contact herbicides such as Paraquat for weed control (the m1Mnl

cultivation tecimique). Depending upon the soil type, this technique may cause some coxirpaction of the soil and also affect its dr"inage. Earwigs overwinter successfully in 10 soil, but few survive in heavy clay or sandy soils (Crumb et al, 1941). Viability of earwig eggs is decreased,

and infection of nymxrpha and adults by fungus is increased in badly drained soil (Boa].1, 1932; Bebum, 1956). Therefore, the type of soil in a garden may be important in earwig survival. Of the four garder where earwigs

were scarce, three (i.e. Cusluners, Sheephurat Farm, Haffenden Farm - see

Table 23) hal clay or c].a-1oam soils. However, earwigs were also scarce at Sheerland. House which had a lo soil suitable for earwig breeding.

)in1m1 cultivation techniques do cause s compaction of the upper

soil layers, but this is probably not as haxmfu]. to the breeding of Z.

auricu1a.rj as cultivation by plough, which destroys earwig eggs end young in the ground (Croxall, Coliingwood end J0nHri, 1951). - 142

SECTION III - T TOUCITY OP DPDX TO P1D AND LLBOR.ATORY

POPULATIO OF P. AURICULARIA -143-

LABORATORY w]tt

Most of the work published on the effects of soil-applied pesticides

on non-target organisms concerns the persistent organoch].orine pesticides,

the uses of which have now been restricted (see reviews by )iwards, 1970,

1970a). Comparatively little work has been done with organophosphorous insecticides (Critchley, i972) and mosl inacrofai.ma investigations have

involved carabid beetles (iwar1s, Thompson aixi Benyon, 1967; Griffiths, Raw

and Lofty, 1967; k1wards, Thompson and Lofty, 1967; Critchley, 1972a).

The insecticide diniefox (bisdimotbyP' mino fluorophosphine oxide) was

first introduced for use on hops in 1953 under the nams Terra4sytam (Martin,

1973). Dimefox solution (0.5 $) is watered onto the base of each bine, taken up systemically and gives control of the damson-hop aphid, Phorodon wm4j (Sobranic) (Noreton, 1964). During studies on predation by earwige on the damson-hop aphid in

1973, numbers of earwigs decreased following applications of dimefox to the soil. Laboratoiy studies were clone to determine the toxicity of variot concentrations of dimefox to F. puricularia in different types of soil.

Meth

Soil was dug from the surface 4-5 an. layers of Si]ks and Nurse:ry hop gardens, Vye College, in Jazivaxy 1974. The soil was sieved to remove large stones (> 10 mm.), spread onto blotting paper sheets and air dried.

Smafl. atones (2-10 mm.) were removed by a sieve (no. 10 mesh). Moisture content of the soil was estimated by weigii-1rg five 25 . samples, heating the samples at 105°C. for 24 hours, then reweigh.ing. The percentage moisture content CM) of air-dried soil was then calculated as follows :-

H = loss in ireiit at 3fJ!5°C. x 100 weight of oven dry soil -114-

A mean value of 1! for both soil types was calculated. For Silks Garden thin was 10.6 ± 2.8 and for Nursery soil 3.7 1.2 . Samples of soil from several locations over both hop gardens were removed and the soil pH estimated by the method of Madge and Sharxna (1969).

The mean soil pH of Nursery Garden soil (4. samples) was 7.80 ± 02, and pH of Silks soil (9 samples) was 7.5 ± 0.7. The distribution of particle sizes from a bulked sample for both soil types was determined by the Bouyouoos hydrometer method, while soil organic matter was determined by the method, of Waikley and Black ( Nadge and

Sharina, 1969). Dimef ox was obtained as Terrasytam (a 50 $ v/v solution contM11lg

17 % tris (d1metIyis4m1no) phosphine oxide and aciiradan). A 0.5 % solution was made up in distilled water and used in all experiments. Dimefox solution at pH 6 has a half-life of about two years (Ripper, 1952, Hassell,

1969). Earwigs used in laboratory tests were taken from corrugated cardboard traps placed about 2 feet (0.6 ru.) above grouzxl in Silks Garden. The Insects were lightly anaesthetised with CO2 , counted, sexed and placed In a large plastic box lined with fluon (P.T.F.ES suspension) to prevent them escaping. They were fed regularly on a mixture of lettuce leaves, dandelions and hop leaves infested with hop aphids.

Tests were done by weighing a sample of soil, adding distilled water to give a standardised moisture content, and miring thoroughly. Moisture content of soil can affect the toxicity of soil insecticides (Cr1tc11ey,

1972 Iwards, l97Oap Harris, l96.) and was stanilardised at 20 $ of air- dried soil. Subeamplea of 100 n. were weighed In pol,ythene bags and then transferred to clear perspex boxes (10 cm. x 10 cm. x 7 cci.), with perforated

lids. Mean uncompacted depth of soil samples was 15.6 3.2 =1. — 145 —

All tests were made at 16 ± 3°C., with a photoperiod of 16 hours. Jo •0 Light intensity at the bench level was fron ee5- — e lumens/sq.ft. The photoperiod. was standardised. at 16 hours because the hours of d.arkness determine the activity of nocturnal insects such as Forftcula and therefore the extent of their contact with soil insecticide residues (Critc]iley, 1972, 1972a).

Dimefox solution was added to each container to give the required concentration in parts per million of active ingredient in the soil. Since.

d.imefox is applied in the field as a soil drench, rates were also calculated as ng. active ingredient per sq.cm. of soil surface.

Pour to six earwigs per container, and three to four replicates per treatment were used in the experiments. Earwigs were introduced immediately

after adding the toxicant to the soil. Tliue/mortalities were recorded and

toxicity measured as the time (hours) for 50 $ 1cm (LT 50) at 16°C. The test insects were prmnl "ed. at frequent intervals and moribund individuals

which could not right theinse].ves when overturned, or dead insects, were

counted. Stellwaag (1948) faumd that moribund earwigs never recovered and

used. inactivity as his criterion for mortality when assessing the action of

DDT and BHC on F. auricularia.

)orta1itie among the controls were corrected by using Abbotta

correction (Kealey, 1952) and Ii1 50's were found by the probit method. of

Blisø (1935).

Results

Initial tests using a range of concentrations of dimefox showed that

male earwiga died In concentrations frun 32 p. upwards. }Iales were used in

most tests since they were dor'i?innt among field-collected. specimens in

January and February, 1974. 146 -

The first experiment was desiied to ahoy whether there was & difference between the sexes of auricularia in their reaction to dimefox, aisce Critchle7 (1972) found that female carabids of several spocie weze

more resistant to thionazin (a syatnic organophosphoroua compound) in the soil than malee.

22 female and 22 male earwiga were anaeathetised with CO3 and

weighed on an Oertling balance (sensitivity 0.01 mg.). Yiean female and.

male weights were 65.9 j 11,5 mg and. 54..6 ± 9.14. mg. respectively (differ-.

ences significant at p = o.oi) (Table 25).

TABLE 25 • Analysis of variance of male and female earwig weights (mg.)

Source d4. 5,8, m.s. F. Treatments 1 1401.2 1401.2 ]2,73** Residual 42 4622.9 110.7 Totai. 43 6024..].

(*. p=o.oi)

TABLE 26. Analysis of soil composition, organic matter content and pH

Silks Nursery COmDOaitiOn () Coarse a 19.5 15.3 e sand 24.1 25.7 Silt 34114. 36,3 Clay 10,2 12.8 Noisture 10.6 3.7 Qanio matter an. 9arbon content () Organic matter 13.1 5.3 Carbon 7.14. 3.0 pH 7.5 .j 0.7 7.8 j 0.2 - 11.7 -

The experiment was set up on February 12th, ut1iig four replicates per' treatmit and six earwigs per container in a randomised block design. Dimof ox was • edded to all replicates (except controls) to give 128 pmi., or 0.07 mg. ai. per cm? • of soil. Table 27 ahows the results. Differences between

LT 50 values for both sexes were not significant, but female earwigs took longer to succnnb to the pesticide. This difference was possibly correlated with their significantly heavier weight.

TiBLE 27. Toxicity of dimefox to male and female eaririga

Sex Dimefox LT 50 (h) 95 $ confidence (parta/].C) ±S.E. limita (Ii)

m 128 193.0 ± 23.0 170.5 and 215.5 f. 128 223.0 ± 67.0 I 190.3 aM 255.7

m1 = male &'aciceted. means not significantly different. f. = female (P> 0.05)

Diinefox is a volatile insecticide vapour with a pressure of 0.31 . mm. Hg. at 25°C. (Martin, i973). Because it is more volatile than related compounds, such as Sobradan, and is 500 times more volatile than Parathion

(Lloyd and Tweddle, 1964.), it cannot be used as a spray (Noreton, 1964).

The fumigant action of diinef ox from treated soil was shown by Bennett (19!4.9) using cabbage aphids, Brevicor'yne brassioae. and David aul Gardiner (1951) using *nhis fbna on bean plants. Bennett (].g4.9) also found that concentrations of dimefox as low as 50 ug showed fumigant action in petri dish tests with flwtodecta vttellinae. the brassy willow beetle. F;g.20

Apparatus for tasting fumigant activity of dimafox

I 'cm - — top -

13cm -a -148-

Modified lib. Eflner jars with the inner lid roved and gauze

stretched over the metal outer 1d were used to assess the fumigant action

of dimefor against earvigs. Square pieces of gauze (15 cm. x 15 cm.) were inserted inside the lid and. pushed dawn to make a cavity into which the

oaxwigs were placed (Fig. 20). The containers were of diameter 7 an. and height 13 an. giving a soil surface area of 40 cm? • and mean soil depth of

25.6 The distance between soil surface and gauze was standardised at about 65 . This apparatus gave a 'false floor' enabling earsigs to be suspended at fixed distances above treated soil, with &tmef ox residues free

to volatilise out into the surro mtR1rg air. A 1i11 apparatus was used by Harris and Lichtenatein (1961), although their containers were made from

galvanised iron and their test insects were bald. 1.5 in. (3.75 cm.) above

treated soil. Harris and Lichtenstein (2Q.. found that the relative hinnidity and rate of air flaw over the containers, soil tmnperature and moisture all affected volatilisation rates; therefore, these factors were standardised. in the test.

Concentrations of dimefox of 32 ppn. (O.C4 mg./on?.), 64 ppn. (o.00

ng./cm?.), ]28 pn. (0.16 rng./cm?.) and 256 ppm, (0,32 m&,/cm2 .) were applied to 100 ga. amounts of soil, with three replicates per treatment and four earwiga (male) per replicate, on February 18th, 1974. Table 28 aurises the results of this experiment. Earvigs were killed by Mmefox vapour at all concentrations, but they died faster at the 256 ppm, rate, while 32 ppm, took about 180 hours to k(11 50 of test earwige.

All the caged controls reiaitiad alive. These I/l' 50 values are not strictly comparable with LT 50's from experiments with perspex cages, where earwigs were in contact with treated soil, because of both the different method of exposure and the reduced soil surface area in the Eflxer jars.

- ]49 -

TABLE 28. Toxicity of ditnefox vapour

Dime!ox soil concentration LT 50 (bra.) ± S.E. 950 confidence (bra.) (part) limits

32 (o.oz.mg,/can2.) 178.3 .j 21.9 164.0 and 192.6

614 (o.o8 ) 165.7 ± 21.9 151.4 and 180.0

128(0.16 " W ) 92.3±214.6 76.2 aM 108.4.

256(0.32 ) 84.0 ± 15.8 787 and 893

Investigations by Getzin and Chapman (1969), Harris (1964., 1964a) and F1wards (1970, 1970a) showed that the type of soil to which a pesticide was applied influenced the toxicity and persistence of pesticide residues.

Differences shown between the soil pH, organic matter content and particle analysis of Si:ucs and Nursery soils (Table 26) indicated that these differ-

ences could affect the soil toxicity of dime!ox. 100 ga. samples of each soil type were put into perspex containers and treated with 64., 128, 256, 512 or 1024. ppm, of dime! ox, using three

replicates per treatment and four male earwigs per replicate. Table 29

shows the results of this test. Earwigs were killed, faster at all concentrations of diniefox on the Nursery soil, although the mortality rate increased on both types of soil as the amount of dimefox increased.

The main factors affecting the toxicity of systemic pesticides in

soils are organic matter content, clay and mineral content, soil pH aM

soil moisture content (Harris, 1964). Of these factors, soil organic matter content is the most important, since it determines the degree to which most pesticides are adsorbed onto soil particles (Ge'tziu and. Chapman, 1959;

Fiwards, 1970a). Bu]iced samples of soil from Si]]cs Garden oontaixd unith

higher proportions of organic matter and. carbon than did Nursery Garden soil

- 150 -

(Table 26); thIs probebly exp1air the decreased toxicity using S1]lca

soil, where the dmef ox was probably adsorbed and thus rendered less effeo- tive to a greater extent.

TABLE 29. Toxicity of dinfox in two types of soil

Dnefoz concentration LT 50 (bra.) 95 confidence (parte/1CP & mg./cm2 . soil) ± S.E. liiits (bra,) Silks Nursery Silks Nursery

286,7 265.7 254..0 241.2 61. (0.04.) ± and and 50.]. 37,6 319.4. 290,2

240.6 105.0 225,5 77.2 128 (o.crj) ± i and and 38,5 42,5 265,7 3.32.8

79.3 50,3 64.,0 38.1 256 (o.ii.) ± and aml 23,4 18.6 9Z..6 62.5

280 19.0 19.9 15.3 512 (o.28) and and

12.]. 5,6 361 22.7

1.6.3 11.7 a.o 6.4 1024. (o.io) and

8,1 9.0 21,6 3.7.0

Discussion This pre1lminry stiz3y has shown that d.iinefox at a range of concen- tratioz will ]CLI]. earwigs by contact and. fumigant action in the soil. However1 there are several factors to be considered when assessing the possible action of diefox on F. auric'.ilaria in the 4ield. Diinefox is

noxmafly applied twice, once in late June when apterous colonies of P. h'Tnuli have become established, and again in mid- to late July if control is - 151

ineffective, or if inigrantes alatae have continued to colonies the hops (Masgee, 1963; )!oretozi, 1969).

During June, most earwigs are nymphs of the new geration in inatara

II Or Itt, although some overwintered fsmales are still alive and may incubate a second lot of eggs in chambers about 2 In. (5 an.) deep in the soil (Beliura, 1956, 1957). Nymphal earirigs are more susceptible to poisons than adults (Muggeri4ge, 1927; Crumb pt al. 191e].; Leer and DavIs, 1963) anl although nymphs were not available when these laboratory tests were made, it is possible that nymphs succumb to lower doses of dimefox than do adults, Sampling the soil upper layers by rsmoval of detritus within 1 u?. quadrants showed that many earwigs were present in the vicinity of hop bines in summer 1973. These earwigs would be either wetted by the soil drench of dimefox (120 n].) applied to the soil at the base of each plant, or contact soil residues, or be exposed to dimefox vapour. Neaaurmnents in the field showed that the average area occupied by hop bine crowns was about 400?. (Dicker, 1971). Application of dimefox is normally made to this area at the rate of 0,28 g. or 0,56 g. a.i, per bins in 120 ml, water (nery, 1954., 1956; Kriz and TR4mIr, 1962; Laws and Darling, 1958). If application is made to a greater area, then uptake of diinefox is not as effective (Mcker, i9ii). .e1& application gives a deposit of 0.70 - 0.40 mg. ai. per an2 . of soil. This rate is higher than the mn.r1 concentration of dinefox in laboratory teata (0.4. mg. a. 1./on?. soil), which gave 50 $ mortality of earwigs between 1]. and 3 boura after application. The high field concentration of dimef ox within a small area means that earwige, especially nymphs, would almost certainly be killed. ri,igs and other predatory soil fauna, such as Carabids, harvestmen aid spiders, which were common in pitfall traps in Silks aerden in 1973, may be affected by dimef ox vapour even outside the drenched area, but the degree - 152 -

of volatilisation will dep on several factors. Harris and Lichtenstein

(1961) found that a1fflcant amoun1s of phorate and aidrin. were lost from the soil by vapour loss, which was initially M, but decreased after one day to a constant rate, which varied with soil type. However dinefox vapour is still present in the air 5 feet (1.5 m.) above hop binee, even three days after field application (Lloyd and Tireddle, l961). Burt, Bardner end Etherislge (1965) found that phorste and disulfoton

could diffuse through dry soil and reach plant roots, where sysio uptake occurred. Burt at al (1965) attributed this movement within the soil to the volatility of these conpounda. However, the yapour pressure of phorate is

only 23 x ].0ian. Hg, and of disulfoton is 30 x i0 mm. Hg at 25°C.

(Martin, 1973). while di.mefox has a vapour pressure of 0.324. n. Hg at 25°C. and is therefore even more likely to diffuse through the soil pores and contact insects (Davit and Gard.iner, 1951). The amount of moisture in the soil during dimefox application also

affects the degree of volatilisation because d.imefox is water-soluble

(Arthur and Caebla, 1958; HasseU, 1969) and enters into solution In the water-film around soil particles In moist soil, when release of vapour is probably mi-Mm'l• Dense oover crops, such as cabbage decrease the rate of volatilisation of organophosphorous compounds from soils, probably becaiiae

the crop reduces air flow over, end increases relative hTn1dity above the

soil (Lichtenatein, )uel]er end Sohu].i, 1962).

Although a fairly dense growth of lateral shoots develops around the

base of hop biiies, these laterals are usually hand-removed during the sr

(Darlirg, 1961) and therefore cover effects on dimefox volatilisation are

probably Volatilisation of diinefox would thus be expected to be

greatest in dry soil ininediately after application, but if the soil remained dry then dlmefox may later be bound tightly to the organic 1 clay fractions of the soil (warc1s, 1970a) and decrease volatilisation. - 153 -

Therefore, from these factors an initial high kill of earvigs both

In and aron the treatec areas would probably occur, with vaporisation of dimefox only s1ge1ficant if the soil was dry at the time of application. Rarwige inigratirig into the hop gaxden from outside areas would probably not be affected by soil residues of dime!ox, since orficu1a

auricularia does not burrow readily even In moist soil. and would thus not contact dimefox in solution around soil particles, and in dry soil the toxicant would be gradually adsorbed by the organic matter fraction of the soil, which is high in Silks Garden. Moreover, organophoephate residues decrease through volatilisation 10 times faster from surface soil application

than when incorporated into the soil (Lichtenstein et a].. 1962), and must also decrease through take up by plant roots, since dixnefax is selectively

absorbed from solution (David, 1952; Arthur and Caaida, 1958), and also

through leaching, adsorption on soil particles and run-off of surface water (iwarda, ].970a). e].d trials using dimefox as a soil drench estab].ihed that the optimum amount of drench per bine was 120 ml (4. fluid ozs.) (nery, 1956) and since then many workers have used this method (Darling and Derbyshire, 1956, 1957; Carden, 1956; Laws and Darling, 1958; Darling et al. 1958;

Nassee, 1963; Hrdy, 1970; Kriz and TdTn4r, 1962). Dimefox in granular or capsule form has also been tried (&iery, 1956; Darling and Derbyshire, 1957).

Both gelatin capsules and pellets buried In the soil gave as good. a control

of as a soil drench, but took longer to be takm. up by the plant ai become effective. However, this type of formulation would be ideal for reducing toxic effects on non target soil organi such as earwigs. Although dimefox, acting systanically, avoids contact action on baeficial foliage-inhabiting inseota, such as anthocorids, 000cinellids and syrphids and is therefore an 'ecologically selective' pesticide (Ripper, - 1511.-

Creenslacle mid Hartley, 1951), its fie]4 effects upon predators and parasites have not been adequately Investigated, and therefore deserve further aty.

Dimefox is taken up by plants' roots from the water film around soil particles, and is thought to travel ,nMriiy In the xylem since it is water- soluble, but sparingly lipid-soluble (Bennett, l9Z9; Hassell, 1969). The experiments of Arthur and Oasida (1958) showed that &imefox was resistant to hydroysisl and persisted for long periods in. plant tissue, but nay be oxyd.ised by plants to an active cholinesterase inhibitor which is probably the bydroxyniethyl derivative or the anino oxide (HasBeU, 1969). Laws and Darling (1958) studied the uptake of diinefox by hops when

a:pp].ied at 0.5 g. a.i. in 120 ml. water per bill, by analysing leaves from various heihgts on the bIns at intervals following treatment. They showed

that 1 days after treatment the levels of dimefox in leaves from 3 feet

(0.9 m.) and 8 feet (2.1. m.) above grown were 2.5 ppm. mid 3.2 ppm.

respectively, and that these levels persisted for up to 58 days after treat-

inent. David (1952) showed that bean aphids, Aiibis fabse Soop. acc1.1Tm1ated radioactive P, labelled dimefox which was applied to bean plants. Noreover, David and Cardiner (1951) arid David (1952) found that there was little ices

of active dimef ox when passing from plants to aphids feeding on the vascular flow of treated plants. Hop aphids killed by diinefox in the field may, therefore, contain concentrations of the unchanged or oiydised active anti- cbo].itiesterase toxicaut, and predators consuming these aphids may be at risk. Bennett (l9.9) mid David (1952) also showed that dimefox vapour was given off by leaves of plants treated systmnically, i.e. by dipping their

roots In dimef ox solution. The leavee were toxic to brassy willow beetle,

&qct&jttelJ4.pg arid the aphids Lnhis fabae and Brevicorvae brassioae1

either on the plant or removed and placed in a petri-dish with the test insect. Therefore, predators active on hop foliage soon after an initial - 155 -

application of dimefox may be exposed to toxic vapours in the difThsion of six' from hop leaves. Vapours of thionazin, dneton-e-metbyl and meth]. from leaves of treated plants cw.ised 100 % mortality of the spider mite predator wtoseiu1iis rsinilis (Bums, 1971).

Pood-chA(n toxicity is well-established for several systnio pesticides, incltIing systox (imed, Newsom, kiereon and Roussel, 1954), echradan

(imied, 1955), thionazin and methoirl (Birme, 1971), but other pesticides, inolvil-ng phorate, dimethoate and monazon, wore not toxio to xithocoris nemonmi or A. confusus when the anthocorids were fed with treated aphids (Eiliott, 1970). Some predators appear to be resistant to toxic materials when contaoted via prey, such as aphids, thioh have been killed by the toxioant (Ripper et a].. 1951). Thus, syrphid larvae were susceptible to systox-killed aphids, but chrysopid larvae were practica1]y inmiune (&bxnec! etaL l951.). Work upon the food-chain toxicity effect of dimef ox has not yet been reported. It appears that predators, such as earwigs, are at risk in several ways from the pesticide :

i) By contact with dimefox residues and vapours In. the soil. ji) By erposure to toxic vapours from hop leaves, or by eating portioma

of hop leaves after treatment. iii) By eating poisoned aphids. — 156 -

EARWIG POPULATIONS WITHIN ENCL AID UIIENCLOSED

AREAS OP A HOP GA1i

A stndy in Si]ks Garden in 1973 showed that numbers of L auricularia in cardboard bands decreased atter dimefox application to the soil. Un- treated areas were not available for comparison and, therefore, definite conclusions could not be mede. Little or no crop is obtained from insectb- dde-free hops in moat years, due to P. huxnili damage (Massee, l963

Morrison and Thompson, 1955) and therefore it is uneconomic to use large areas of untreated hops, The present experiment attempts to overcome these difficulties by enclosing earwig populations within ail1 areas by polythene barriers. Even if untreated and treated areas of hops are available, the plots must be large enough and far enough apart to ensure that movnent ef mobile insects such as P. auriculari p does not reduce differences in insect numbers caused by the insectioije treatment. Using small enclosed areas, interplot movement is prevented, and it is possible to demonstrate the effects of insocti- aide use within the areas (Coaker, 1965; Edwards ot ci. 1970).

Materials and Nethod.ø

The experiment site was towards the E. side of the Cobbs plot, Si3ks Garden (see Pig 10). Groups of four hills within rows (barriers could not be placed across the rows because of access for tractors) were either eno closed within po]..ythene barriers or left unenclosed, in a randomised block design of three replicates per treatment. Polythene barriers were 36 inches wide and about 66 feet (20 in.) long. The barriers were buried 12 inches deep in the soil. The upper 24. inches was supported by eight 1 inch square wooden stakes placed at 8 feet (2,4. in,) intervals. The po]ytheno was - 157 -

PLATE 9. Polythene barriers.

A.. Barriers around. grous of four bines in June. Silica Gard.

..- -,-.

'1 *s."

B. Close-un of barrier. - 158 -

securely stapled to the stakes and irml11g repairs conducted when necesealy

(see Plate 9). Earwigs were sampled by standard cardboard traps placed on one string per bill within each block. Barriers and traps were positioned on Juno 10th. The traps wore sampled weekly from June 14th to Soptunber 2nd; earwigs wore released onto the ground at the baao of each trap. All the bills of the plot were treated with diuiefox (0.56 g. a.i. in 120 nil, per bill) on Juno

17th, and with cytrolane (0.5 g. a. i, in 120 ni. per hill) on June 29th.

Resuita end Discussion Since sprays of Leefex used to "burn off" the lower foliage growth of hops could not roach the birie enclosed by a polytheno barrier, the growth of laterals at ground level was extensive. To reduce any microclimate effects, those laterals were cut by hand and. ronovod at re€ular Intervola.

Compared with the 1973 results (pig. ii), applications of pesticides to the soil in 1971g. caused little change in numbers of earw&gs in the traps

(Table 38). Untreated controls could not be used in the plot in 197k because of interference with other experiments. The general trend of the earwig population both in and outside barriers in i97l. was sir4lar to the tr in 1972 amI 1973 (see PIgs. 8, ii), when barriers were not used. Earwig numbers increased in June and July, reached a peak in early August, and then decreasod (Pig. 21), This increase in earwig population was due to the increasing number of nymphs and adults from the two or three successive oviposition perioda of the European earwig (Behura, 1956), and the increased climbing ability of older nymphs (Bean.,

1932) causing more of th to climb the bines.

Earvigs were more rnnroua in traps outside the barriers until late

August. A1thoui the differences were not siiificant (Table 38), they

No. earwigs per trap - 160 -

PA1T 38. Mean ntb f F. auricularia per trap1 and mean percentage

of adults in the catch from enclosed ani unenclosed binee.

enclosure No enclosure Date Polythene Mean no. earid.gs adult Mean no. eanrigs adult u1. June 6.2 ± 2.1g. 0 7.5 2,8 0 24 June2 7.2 j 2,9 0 8.8 ± 3,2 0 2 July 10,3 ± 1.8 0 36.2 2.7 0

8 July 11.5 1.4 3 13.7 , 3.3 2

22 July 12.3 ± 5,6 63 29.2 34.9 24 29 July ± 5.8 53 34,0 6.5 20

5 August 30.1 .j 5.7 39 43.7 8.2 23 12 August 21.7 .j 4.1 36 26.8 7,0 28 19 August 32.6±4,2 46 17.8 1.8 39

26 August 17.5 ,j 2.3 54 17.4j 4.7 14.9

2 Septnber 11.0 ± 3.5 61 7.1 ± 1.8 51g.

Mean of 12 traps per treatment/date.

2 D:imefox applied on 17th Juno, cytrolane on 29th June.

Means underscored by a line are not aigufficant].y different ( p > 0.05)

were greatest in late July to early August (see Pig, 21). If it is assumed that the po3ythone barriers reduced or prevented movnent of earwiga either out of or into the barrier areas, then the differences between earwig rniinbera inside and outside the barriers was probably due to the imnlgration of active nymphs from the edges, or from other areas of the garden. This view is supported by the consistently higher percentage of adults in the catch inside the barriers, especial].y during July (Table 38). - 161 -

The rapid decrease in numbers of earwigs in the traps during late

August, also observed in 1972 aM 1973, was difficult to exp1n. It is possible that earwigs moved out of the plot, either to other parts of the garden or to grassland or other crops at the edges but, if so, the barriers must have been ineffective since earwig numbers also decreased inside the enclosed areas. A reduction in earwig activity would affect the climbing of hop bines end therefore numbers in the traps, but would be caused by low temperatures, which are unlikely in August. Noreover, earwiga were active right through to mid-October during a study of their daily abuMance im

1973, and were found by wr and Barilca (1968) in iormus bushes as late as

November. - 162 -

VAP0tfl TOXICIT! oi' DflX TO F. jqoi

When predators eat aph.b on insecticide-treated plants, food-hjdn toxicity may- occur (Elliott, 1970). Small syrphid and ooccinellid larvae

feeding on systemically killed aphids can acquire enough demeton to d11

themselves, but large larvae, adult coccinollids and larvae of rvsoDa app.

are less susceptible (Abmet%, Newsom, nerson and Rouseel, 1951i). Aphids killed systemically by phorate, dimetboate or menazon are not toxic to nymph8 of Anthocoris nemortnn or A. cfuus (Ealiott, 1970), and aphids killed by contact action idth elcatln (thiaieton) are toxic to cooclnellid.s, but aphids killed systemically are not (Zeleny, 1965). Almed (1965) found that aphids killed systemically or by contact action with sobradan were

t.c to syrphid larvae but not to coccimellid adults and larvae, whereas aphids killed by contact action with syatox were very tcxio to 000cinellidn but of low toxicity when killed systemically.

Therefore, the toxicity of an insecticide to a predator depends not

only upon the species of Insect but also the method at application and the

pesticide concerned. Dimefox (bid mothy1mn1 ri fluorophoaphine oxide) persists for up to eight weeks in treated hop plants (aiery, 1956), probably

In the unchanged state or' as the active hydroxymethyl derivative (Hassell,

1969) and occurs In systemically killed aph1ii (David, 1952; David en!

Gerdiner, 1951). This experiment was designed to show whether hop aphids, Thorodon hrmili (Sc1rank) killed systemically by dimefox wore toxic to nymphs and

adults Qf P. auiicularia. Dlmefox is an extremely volatile Insecticide

(Arthur and Casida, 1958) and vapoua'a of the compourd are given off frc leaves of systemically-treated plants, which may kill insects merely sitting

On the foliage (David, 1952). Therefore, a further experiment was dome to - 163 -

PLA!L'E 10. Po1ythie furinel5 used to collect poisoned P. humi1i.

PLATE II. Clip cages at two heiits on the bine. -164.-

investigate the toxicity of dizxetox to P. ricu1ax'ia exposed Ofl leaves of treated hop hines.

a) Foedoba1n toxicity

Dimefox was applied to a plot of hops, var. Cobba 2 in Silica Garden, Wyo College, on June 17th, 1974., as 120 mi. of O.5 a.i. solution P° x' hill (0.28 g. a.i. pox' bin). On June 18th, polythene fumnels (diametex' 20 on.) with their st attached to flat-bottomed glass tubes (5 x 2 cm.) were positioned under the leaves to collect poisoned aphids (Bee Plate io). This apparatus was 8liwfljn' to the device used by Elliott (1970) to collect aphids killed by phorate. The funnels were placed at a standard heiit on the bine of about 1 ni,, since the level of dimefar within treated leaves depends on their heiit on the bine (Laws and Darling, 1958).

Aphids were removed from the field at intervals, and. stored at 4.°C. for a 1mi, Of two days before use. Two feeding rates with IV instar and male P. auricularia were used : approximately 10 aM 50 aphids per day,

(actual numbers were approximate since dead aphids clumped together and were difficult to count accurate,y). Aphids were placed on an untreated leaf

inside Buffacker-type cages (Thffao1cer, l918) and kept at 20 ± 3°C., 16 hour photoperiod and lit intensity at bench level of 280 )nAYlR per sq.ft. Wads of blotting paper within each cage were periodically moistened to maintain

100 RJ. .ve replicates of each treatment, and five controls fed heat-

killed aphids plus five unfed. controls were set up on 25th June. .Aphids

were replenished and mortality recorded every day.

aphids wore collected 6, 8 and 10 days after diniefox treatment. jjte1y after the dimefox application no rain fell for eight days (until. June 25th), whIch may have reduced systemio uptake. Aphid numbers on

experimental bines increased from June 18th - 25th (see 1. 26). ?rcin - 165 -

25th - 30th June rain fell every day (see Fig. 16), but the diinefox was still ineffective, perhaps due to resistance of htunuJi. to the compound. Therefore, on 29th June a half-strength application of cytrolane

(inephosfolan) or 2-(diethorphosiny11 mino).4.uiethy1i, 3-ditbiolane was made to the base of each hill which reduced aphid numbers by July 2nd (Pig.

26). Dead aphids were collected at one, five and eight day intervals after cytrolane treatment.

The feeding experiment was continued for 14 days. At the low rate

(io aphids per day) four male but no XV mater earvigs died. No deaths were recorded at the high rate of feeding (50 aphids per day). No controls and only one standard control had died by the end of the experiment. These results indicate that dinefox or cytrolane-killed aphids caused little toxicity when fed to P. auricularia. i) Vavour toxjcity

Previous experiments (see p. 149) had shown that dimefox vapour was toxio to adult earwigs placed 6.5 cm. above treated soil, Large clip-cages (diameter 6.5 cm.) were placed over hop leaves on June 17th, 1974, the day of dimefox treatment. The cages were placed at heights of 0.5 m. and 1 in. from soil level. One adult male or IV instar earwig (five replicates of each) was placed In each cage, which was than fastened with 'lassotape' and secured to the main bine with wire (see Plate u). Five control cages were set up on untreated plants nearby. Hop aphids, oroiju1 (• were present on all, leaves at the start of the exporlinent After one week the cages were examined for dead earwigs, but all replicates, including the controls, were alive. The insects were removed to the ].aboratoiy and observed for a further four days, but no mortality occurred. -166-

Dimefox is translooated upiraids by the hop bize after soil app3io-

ation (Laws arid Darling, 1958) aM probably oxdiec1 within the plant to

a toxic derivative (Arthi.r and Casida, 1958), which causes rapid death of

brassy willow beetle, teca ]4aa. enclosed with systemically

treated leaves cOntAllllflg 0.6 ng. of dlmefox (Bennett, 194.9). Moreover,

dimefox residues (approximately 0.03 mg/cu.m. of air) are present 5 feet (1.5 rn.) above the ground in hop gardens three days after treatment (Lloyd

arid Tweddle, l96l.). &iuit '. auiularia used in the clip-cage tests were, therefore, in contact with dimefox or dimefox metabolites during their seven days exposure, but since there was no mortality it is probable that climefox treated foliage has little effect on predators such as eareigs in the field.

The feeding experiment contirnied for 14 days, which was probably long enough to detect axw food-chain toxicity with since Elliott (1970) found that .AntboenriR 'nn nymphs acquired detectable amounts of 35 3— labelled phorate after only 10 days feeding on poisoned aphids. Elliott

(1o. .) found little mortality of A. nnorurn nymphs even after feeding poisoned aphids for 25 days. The dead P. hinm]j collected from the field presumably contained traces of dimefox or cytrolane, but it is possible that during the 2-day intervals between collections the toxicant became inactivated. Moreover, because take-up of these systemic compounds from the soil is gradual and affected by such factors as soil moisture and temperature, the residues of toxicant within regions of one plant, and between plants, may Vary,

Further studies on food-chain toxicity of either compound sbou]d be done in the ].aboratoxy, using the cut-tap root technique (David mmd Garcljner, 1951; Elliott aM Way, 1968) whioh enables plants to absorb a measured dose of a systemic insecticide quickly and completely. - 167 -

It is probable that P.. aur'iou1ari is not normally as susceptible as other predators to food—chain toxicity, since aphids fm only a part of the earwig' a diet (Skuiravy, 1960). Other dietary cciuponents .n earwige fran hop gardens, such as Pleurococcus algae ath sooty moulda, are not likely to be oontsimin ted by pesticides. - 168 -

SECTION IV - T EFECTIV3 OF F. AtJRICULABIA. IN REDUCI1

P. HtJTtJLI PQPULATIO1 ON ROlL 169 -

IBORATORY EXPERD

FEEDING flENj IT 20°C.

The European earwig, Forficula auricularia L. is a oonmon, ivoroua besot (i1tou, l921.) which readily feeds upon aphids (way and Banks, 1968).

The present work foi pert of an Investigation on the effectiveness

of earwigs as predators of the damson-hop aphid in hop gardens. (e of the major factors influencing predator effectiveness is the voracity of the predator (van en, 1966), which is affected by the number of prey consumed. In this stedy earwigs were confined individually In perspex cages and fed solely with damson-hop aphids to determine the number of aphids consumed during dovelopneut. Other earwigs were fed on lettuce, so that the effect of different foods upon d velopment could be evaluated.

)Iathods

Earwig nymphs were taicon at birth and roared individually in modified Euffacker cages (Huffacker, i%8), similar to those used by 1erson (1962)

in his experiments with Anthocoria species. Cages were made by aandwicbing a perspex petri dish base (B) (diameter 9 cm.) between two tope (A, c). & hole, 5 cm. in diameter, was made in B and lined with sponge rubber mlring

an arena for the earwigs. The cage floor was lined with moist blotting paper, and the two units of the cage bei1 together with elastic bandø. The top U) had a 6 cm. diameter hole covered by 'Terylene' mesh fabric, which allowed free circulation of air in the cages. Pieces of corrugated cardboard

(5 x 3 cm.) were plaoed on the floor in each cage to provide shelter for the eazwigs. Batches of cages were placed in trays which were lined with sponge rubber and kept moist to ensure high humidity iii the cages. The earwiga - 170 -

were kept at a photoperiod of 16 hours, a light intensity of 280 luinena/eq.ft. aM a temperature of 20 ± 2°C.

A known number of apterous nymphs of L. 1niuli were transferred from culture plants to pieces of hop leaf in the arena of each cage, using a camel- hair brush. Equal numbers of instars I - III of P. huili were provided as food for each earwig. The Cages were ermhied daily and the aphids rer14fliTIg counted, using a tally counter. 'esh aphids were then introduced so that excess aphids were always present, Every third day the leaf pieces were removed nnd the percentage of leaf area eaten by earwigs noted. 12 earwig nymphs were used in the experiment, A further 12 replicates fed on lettuce tissue (var. Density) were used. Small portions of inner heart leaves were out and placed in the arena every 48 hours. The leaf portions were weighed on an Oertling balance (sensitivity 0.01 mg,) before and after feeding. The loss in fresh weight was corrected for the fresh weight loss of identical leaf portions in control cages (i,e. without earwigs), at each assessment, end expressed as weight loss (mg.) per 48 hours. Rxcess food was always present. Earwig nymphs were removed from the cages and weighed Immediately after each ecdysia.

Results Of the 12 nymphs fed on aphids, eight were reared. to maturity. (kily a m l1 quantity of hop leaf was eaten by the nymphs. Table 31 ahows the mean number of aphids eaten by each nymphal stage. The mean number of aphids eaten per day increased from inataa' I to instar IV; most aphids were eaten in the final instar, which was also the longest. The feeding experiment was continued for about nine days using new'y matured adults. Female earwigs ate more aphids per day but differences were not significant. Although adult females were heavier' than males, differences were not BigT'4ficaflt (Table 32).

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I '.0 N 0 U S if cQ 0 P - IL

S -4. - '.O -4. 0 I S , S E

4, 1itI ii I i.rI - 173 -

The fresh weight of aphids consumed by the earwig nymphs was caloi- lated by Russell's (1970) method, as follows1 50 apterous of each instar I to III were weigheti on a torsion b1moe (sensitivity 0.0(2 mg.) and the average weight of an aphid fouM. Then the mean number of aphids consumed in each instar was multiplied by the mean fresh weight of an aphid to give the fresh weight of aphids eaten. The total weight of aphids eaten during development was 65.5 mg. (Table 32); this compares with a moan of 63.0 mg for &1aLia bintmptptp L. reared on several aphid species (Black- mail, 1967), Growth rate indices (JMereon, 1962) were calculated for male ai femc].e earwiga from the formula :

Growth rate iodex = weight of unfed &.ult days to maturity after adjusting male weights by 1.2 to be equivalent to female weights. conversion ratios (Pewkes, 1960) were calculated from the fozmla: C,R. = m. wciht gained by the nredator ing. food eaten during development

Male end. female weights were combined in the results, which g&ve a C.R. of 0,1,,321 for F. auriculoria. This conversion ratio compares with the value of 0.22].]. obtained from the data of Campbell (1973) for &ntiocor1s nemo at 20°C. using P. humuli as prey, although the different moisture contents of the two predators will alter the values obtained (Russell, igio). Table 33 shows the mean fresh weights of lettuce tissue eaten by Forficula nymphs in each stadium. The figures are corrected for weight loss of controls, which was approxinate]y O3 mg. per mg. lettuce tissue per 48 hours (mean of 50 weighings).

1mpba]. mortality was lower with lettuce than when apM wore given as food. Growth rate indices (G.R,I.) calculated as before were similar for individuals fed on both typos of food, but the conversion ratio (Pewkea, - 174. -

1960) for oarvigB fed on lettuoo was zmith lower, ii4ioating that the nutri- tional value of lettuce was low.

T.ABL 33. Mean fresh weight of lettuce tissue eaten and nymphal developnent of earwiga at 20 2°C.

No. Instar Mean weight Weight tissue Duration of stage used (mg.) eaten per stthii.n or observation or day (mg.) (days)

12 1 2.3 ± 0.6 27.9 .± 6.3 110 10 2 3.9 , 0,6 140.1 25,3 10.5

10 3 7.7 ^ 20 235.2 •j 125

10 1. 18.4. 2.4. 505.14. .± 51.5 16.3

1. Adult 33.6 ± 7.6 41.3 3.7 5.6 fnale 6 Adult 273 ± 3.4. 37.2 j 8,7 4.0

However, earwigs fed on lettuoe were heavier at maturity than thoao fed oni,y on hop aphids (Table 32).

Causes of death during the experimerrt were not always obvious. Most of the nymphs which died during rearing were in instar I. These nymphs died through being trapped in condensation or aphid honeydew, or did not auoceasfu].ly undergo ecdysia to instar II.

Discussion The European earwig is not a specific predator and iU eat a iride range of prey (Crumb ek al. 19l1). Among the species of aphid recorded as prey are Athis fabao Scop. (Way and Banks, 1968), ThoIop.1mn1]i, (Scbranlc) (Eschsrioh, 1916), Aovrthoeinnn snartli Koch (Smith, 1966), .inhis (ath.tdula) - 175 -

naxi D.GLAsgari, 1966), and ioso 1xiiezwi (Hauson) (I,c3.eo1 c Chant• 1952). However, the ntber of aphids eaten by a predator depends upon the size of the aphid and its activity (Dixon, 1973), although in the cages active aphids could still not avoid the predator.

In this study, III instar, IV instar and adult earwiga ate an average of 46, 89 and 122 per dbr, respectively. Smith (1966) found that earwig nymphs of inatar III ate 6.2, and adult earwigs an average of 52

Acvrthosinhuni snartli pei day, while Moleod and Chant (1952) calculated that caged adult earwigs ate about eight or nine Brevioorvne bric* per day.

However, 4. soartii is a large aphid which in pert]y explain the much lower feeding rates obtained by Smith (]. Q.). Also, Smith's (1966) experiments were done In cages outdoors, with a mean temperature probably less than

20°C. Since no controlled feeding study was done, the date given by Hc].eod and Chant (1952) are therefore approximate and probably i.mderestimates of the numbers of aphids eaten. Asgarl. (1966) investignted the feeding rates of auricularia. at three temperatures, 15°, 20° and 25°C., using Anbia

(a!tdJlth) Domi DoG, as prey. Developuent was fastest at 25°C., but least aphids were eaten at thia temperature. The feeding rates obtained by Aagari

(1966) were much higher than those in the present study. At 20°C., earwigs

of inatars I, II, II and IV ate an average of 166, 140, 168 and. 200 £. ni. per day, respectively.

Present obsorvatics suggest that young earwig nymphs ate large

adult aphids when these were present, but preferred yoiger apterous aphids.

Mult earwigs and late instor nymphs showed no suth preference. Dempater

(1960) found that adult earwigs would eat adults and larvae of all stages

of the brown beetle, Thvtodecta olivnoea. which is much larger in size than

the hop aphid. Other predators such as Anthocoris would riot take beetle larvae which were larger thmi instor III. - 176 -

The duration of earwig nynzphal stages in this study agree closely with those of Asgari (102, .QJj.), who foui at 20°C. mean deve].opiient times

of 12, 10, 11 ath 17 days appxoxiinateiy for inatars I, II, III aM IV

respectively. The results also agree with those of Cxumb et3. (19z L) aM Behura (1956), although these authors used dandelion flowers and riot apb.iIs or lettuce as food,.

PREDATOR/PREY EFWTS AT 20°C.

Sinpiffied. systs of predator and prey ucder laboratory conditiome

may help to explain the processes followed in natural (field) conditiome (Hodek et aL 1972). These systeme use controlled &vironxnente, where the effects of physical factors, such as tnperature, relative humidity, or

lihgt may be investigated. In the present atMy, earwiga wore introduced to caged plants oontair- ingbiown numbers of hop aphids arid the effects upon aphid population follo-

wed.

!ethoda

Hop plants, vat. Bullion, were grown from rootatocka in 7 in1 diameter pots using John Innes No. 2 compost in the glaashouae. Plants of

approrIm te1y siinii.ar size (about 12 in. (0.3 m.) high) aul about 30 days o3ñ. were transferred. to a growth room at a tarperatui'e of 200 2°C., photo-

period. 16 hours and R.H. 30 - 40 . Light Intensity at the bench surface

was 280 1um per aq.ft. Plants wore repotted into square containers of

si1e 32 in. (0.3 .) and depth i . in. (o.i in.). •Perspex insect oontaixiers of diameter 8 in. (0.2 in.) and. height hi, ifl. (0.36 in.) Wore strengtbend at - 177 -

top and bottom 'with flexible perspex stripe and coated 'with a 'fluon' layer (P.T.F.E. aqueous suspension), giving a non-toxic barrier which prevented insect escape. Cages were placed over each plant and pressed down until

about 1 tn. below soil level and the soil Inside the cage firmed down to make a seal. The number of leave. on each plant were ootmted at the begf rrn1ig of

the experiment and then each plant was infested with 25 adult apterous

P. 1rmn1i and a close-meshed fabric top put on the cages, All plants were watered dai]y.

knh1t samn]in meth.

Two control plants and six experimental plants, arranged randomly on the bench, were used. Three leaves were taken, one from the bottdin, middle wid apex of each plant.

1phit numbers were counted visually with the aid of a. tally counter, leaf areas determined, with a photo-electric planimeter and the mean densi of aphids per 100 cm2 • calculated for each plant/date. Any earwig damage to the leaves was also noted. Absolute aphid popilation estimates were made by nniltiplying the mean numbers of aphid per loaf by the total number of leaves on each plant, and then the number of adult earidga (both sexes) introduced to give a known aphid : earwig ratio. Experiments were made using 150 : 1, .300 : 1, azx 400 : 1 aphid : earwig ratios, all at 200 j 2°C. At the end of each experiment, cages were removed and the number of earwigs counted so that estimates could be made of any experimental error caused by escape of predators,

Results and. Discussion

Table 34. shows the mean (log x + i) dei11ty of aphids per 100 om2. leaf for control and experimental plants at an aphid/earwig ratio of 150 : 1. - 178 -

TABLE 3Zj.. Mean log (x + i) numlers of per 100 cz2 ied. Controls and prey/predator ratios of 150 : 1

Days after Controls 150 : 1 infestation

10 1.98 2.48

2• 30 2.77

16 2,52 2,25

18 2,92 1.4.7

20 3.OZj. 0.99

22 3.53 0.85

Mean of 6 leaves per date (controls), 18 leaves per date (experimental) * Predators introduced on Day il'..

Eax'wigs were introduced on Day ]4 and quickly reduced aphid numbers to about 006 per cm2 • loaf by Day 22 (Fig. 22). analysis of stomach contents of earwigs removed from the cages on Day 22 showed aphid remains in a].]. five

individuals crammed. Little leaf damage by earwiga was observed, except a few small holes eaten in the young leaves at the apex of one plant.

Table 35 gives a statistical analysis of an experiment when earwigs were introduced to aphid-infested plants at the ratios of 1 : 300 and 1 : 400 aphids on Day 15. By Day 17, there were eign4ficant]y fewer (P = o,o5) aphids on the 1 : 300 replicates. Differences between controls aM 2. : 400 rep1i- catea were first sigeificant (P = o.o5) on Day 21, Earwig predation reduced aphid muitera, compared with the controls at both ratios (ig. 22) but to a sigrd-ficant]y lower level ( p = 0.05 - o.oi) on plants at the ratio 1 : 300 (except for Days 24 aM 26). At the end of the experiment there were approximately 13, 1.7 aM 0.8 aphids/cm2 . on control, 1 : 400 and 1 : 300 plants, respectively. - 179 -

¶ABLE 35. Mean log (x + i) density of P. humuii per 100 ied. Contro].a az prey/predator ratios of 300 aM 400 : 1

Days after Contro]±S.E. 300:1jS.E. infestation 400:1±S.L

]Jf 2,62±0.03 2;lj.7± 03]. 2,64±0.18

15 2.44.j O. 16 2,38±0.32 2.48jO.]2 16 2,62 ± 0.15 2,53 ± 0.26 2,37 j 040

17 2.72 j 0.38* 2.52 0.17$ 2,19 0,70 18 2.96±0.I2 - - - 19 - 2.58±0.33 2.02j0.1O 20 3.07 0.6L.** 2.61 0.25* 2.10 j 0.34.

21 347± 0.17** 2.54j0.27* 1.94±0.28 22 3.13 j 0.20*' 2,48 ± 0.30* 1.82 0.22 23 3.16 ± 0.64*' 2,58 0.36' 1.73 0.45

24 3.20 0.51*' 2.39 0.45 1.95 ± 0.15

25 3.05 0.57'** 2q39 O36** i61. ± 0.95 26 3.16 ± 0.16*" 2,22 0.31 . 1.77 ± 0.21g.

28 340 038** 2,22 9.35* 1.57 0.33

+ Predators Introduced on Day 15 to all plants. Mean of 6 leaves/date (controls); 9 leaves/date (3x) : 1); 15 leaves/date (100:i). Means uMoracored. by the aáné line are not sig'1fioant]y different (, 0.05). (* p = o.o5 ** p = o.oi - p = o.00i). Data for Ds 18 aM 19 not analysed..

Analysis of atcinach contents showed. biii rnfnq in al]. of four

earwige erniithed. Also present were ruilm of a Coflembolan speciea, which

was mmerous in the soil in which the plants vaxe growing and may have acted

as en alternative food source. l4clagan (1932) found that 7 auricularia

was a voracious feeder upon the Collembolan .nthurns virid.1s L.

LOG X-4-1 APHIDS PER OO SQ CM LEAF - _

I,,

S 4 LOG Xe1 APHIDS PER 100 SQ.CM LEAF

I I

- 181

At the end of each periinent the cages were renoved and oil earwigs

searched for and found. Earwiga can squeeze into the nallost of crevices

(Wiggleaworth, 1939) and therefore so were unavoidably lost from caged plants (Table 36).

TABLE 36. Comparison of the number of earwiga rnaining in cages at the beginning on end of one experimont (15th - 30th Nay, 1973)

Plant No. No earwiga placed in cages to make 3. $ 400 ratio OrigincUy At harvest Missing

3 37 35 2

4. 14.9 48 1

5 16 16 0

6 21 20 1

7 27 25 2

8 15 11 14.

9 39 39 0

10 23 22 1

In the first experiment, readings were discontinued after 20 days when the aphid population on the control plants was still increasing. How- ever, in the second erperimit aphid numbers on the controls increased in a

lm41rii' rnaer for about 20 days but then levelled off (Fig. 22), with snll fluctuations.

In the field, P liumuli normally multiplies rapidly on untreated. hope until the population density of aphids rises well above the carrying capacity of the plants (Nzissee, 1963). Then the quality of food suddenly declines, with wilting of the leaves or even defoliation, £md aphid numbers suddenly - _

and rapidly decline to a very low level, as Messenger and Force (1963) observed with the aphid Thexioavhis inaculata (Buckton), and termed a pop- latian WCrsah. Therefore, population curves of in the field normally increase rapidly and then decline (see Campbell, 1973), this study

(p. 67). Se]!—regulation of aphid population is poorly developed in L.. and vagrantes ].atae are not produced as a result of crowding

(ZoIren, 1970).

In contrast, are the aigmoidal growth curves obtained with nersicae Suizer (Ui3,yett, 1953) ai m±z. aphids on potatoes (Shanda and

Simpson, 1959). These aphids are probably similar to Anbis fabae Soop., which becomes legs fecund as aphid colonies become more overcrowded (Way and

Banks, 1967; Dixon, 1973). Tnmkf and Weeks (1968), using a predator/prey sys ten involving the aphid Mvzus oersioae SuJ.z., found that aphid nwnbei'B on the control plants increased rapidly after about 10 days, and thereafter fluctuated within fairly narrow limits in a similar manner to .,J3IjI ° control plants in the second experiment (Table 35). The observed population growth curve of on control plants was not as would be expected from field data. To teat the repeatability Of the results, a firther experiment was carried out a year later in 14pril 1974, using four untreated plants and trking six to nine loaves per sample. How— over, the plants used were not repotted into the square plastic containers as used in the predator experiments. Table 37 shows the population growth of 1. himvli in this experiment.

Pig. 23 compares the 1ogthmio slopes of the lines of control plants from the three separate experiments. The slope of the lines of log (x + 1) aphids/l00 cm. against time were compared by regression analysis. The elope value or increase in log numbers of aphids with unit time for experi-

i&it 1 was 0.125 ± 0.014., for experiment 2 was 0.051 0.011, aM for

- 183 -

experiment 3 was 0.078 j 0.019. These values agree closely, except in the

ease of experiment 1, where readings were not taken after 22 days.

TABLE 37. P. hunruli population developnent at 200± 1°C, April 1914.

Daya since No. leaves Mean aphids Log (x + i) apbid.s/

infestation in sample per i? leaf 100 en? leaf ± S,E.

9 9 0.31 ± 0,38 1.50

Li. 7 0.91 j 0.65 1.96

13 9 1.87 j 1.8]. 2,27

15 9 208 ± 1.07 2,32

17 9 2,73 ± 1.51 2.44.

19 8 5.69 ± 4.33 2.76

21 8 10.87 8.00 3.04

23 8 17.37 j 9.61 3,21g.

25 6 21.58 . 6.54. 3.33

27 6 12.10 ± 7,32 3.08

30 6 10.80 6.0]. 3.04

Differences between the population trend projected under field condi-

tions and in the laboratory experiments (Fig. 23) may have beon duo to the

environmental conditions or, more likely, the Fmtll size of the hop plants

uaed, which may have limited the rate of increase in the population, since

the quality of an aphid's host plant is a major factor influencing aphid

population developnent (Kennedy and stroyan, 1965).

The experimental method used was subject to several limitations:

i) Because the cages end hop plants were emnll, only a few leaves per plant

could be removed at each assessment. Also, the experiments could not be - :1.84. -

continued for long periods because constant leaf reval would cause the plants' physiological condition to deteriorate. ii) Occasionally, aphid-infested leaves became pressed against the cage wall and large numbers of aphids then developed in these predator protected sites. iil) Even with a 'Fluon' barrier, some earwigs nevertheless escaped from the cages.

Control of aphid populations (in the sense of Niine, 1959) was achieved at all predator/prey ratios using F.. aur1culaia. however, even at the lowest ratio of 1 : 150, aphids were not completely el1mited. Observations at night using a red li&it which did not disturb the osririgs' nocturnal activity, showed that earwigs readily fed on any aphid which they came across, but at low aphid densities not all the aphids were found and eaten.

Scopes (1969) also found that control of h(vzus ersicae by the chrysopid C. carnea was inefficient at low prey denaities. he obtained control of the aphid using third inatar' predator larvae at a ratio of 1 : 200 at 21°C., but predator effectiveness is effected by the innate capacity for increase of an aphid species (IIessenger and Force, 1963) and. the host plant (Trmikf and Weeks, 1968) and, therefore, results are not strictly comparable. Earwig feeding damage on hop leaves was only noticed at low aphid densities (the 150 : 1 ratio experiment) and only then on young leaves, indicating that hop aphids are preferred as food. This conclusion has been borne out by laboratory preference studies and eYi'Lrution of otomath contents of earwigs from the field.

The experimental method is suitable for eYnmfn1vg the influence of several factors upon the effectiveme es of earwig predation. Since earwigs are nocttn'nal predators their period of activity depends upon the duration of darksess. The effect of this factor could be investigated using ortifi- cicUy lengthened photoperioda. Tnperaturo is a major deterninnnt of both - 185 -

the number of prey consumed ax the efficiency of predation (Sundby, 1966;

Hodek et al. 1965). The effect of tnperature upon total aphid consumption by F.. auricu].aria has been studied by Asgari (i966) who fonth that more aphids were eaten at 15°C. than at 20°C. during the nymphal earwig stages,

However, no effectiveness studies with nymphs]. or adult earwigs uairg an artificial laboratory system slmilar to that of Kodek et 4 (1965) have been previously reported. This type of study is valuable when the tren towards more and more artificial, ecologically simplified agro-ecosystems, which can be adjusted n a similar way to laboratory systems, is considered (Kennedy, 1968). - 196 -

PID

CLUSION OP EARWICS BY SE-BALING HOP BI1ES, 1972.

ie of the most conmon methods in predator evaluation studies is the

exclusion technique (Smith ar de Bach, 192; van en, 19?2). In this

study earwiga were excluded from hop bines by a coating of fruit tree grease

(Stiotite) applied to the top and bottom of the bine. The effect of this

treatment was assessed by chocking the hop aphid populations on greased and ungreased blues.

It was hoped that the grease banding of certain binea would exclude

all crawling soil fauna, inclvdlng earwigs, from those binea. Earvigs have been 1aawn to fly on rare occasions, although reports in the literature are both scarce and conflicting. Collinge (1906) reported that Porficula

auricularia flies on dark, warm nights in inid-suimner, thile Crumb et ci

(19i4,1) stated that fliit occurs most readily on warm, sunny days. Crumb

et si (i. gj,) saw as xnaxr as 20 earwigs in flight at the same tine.

However, for the purpose of this experiment it was assumed that no sigr1ri

cant predation of the damson-hop aphid would occur due to earwigs flying

onto grease-banded. bines.

(ethods

In this trial, pole hills and non-pole hi lie were taken as separate

treatments. There were often more earwigs in traps on pole hills tnMr1y

duo to the cracks and crevices in the wooden poles which shelter earwigs.

There were eight treatments each of four replicates in the trial, Involving

pole and. non-pole hillø from which earwigs were either excluded or allowed

access, and situated either in an insecticide free row of ho:pe or in another

receiving commercial applioatima of insecticide. The insecticide used. was - 187 -

Terrasytam' (dlinefox) applied on 22nd Jui and again on 2nd August as a

soil drench (120 ni.. of 0.5 a.i. solution) at the base of each hill.

Stiotite grease was applied on 7th June at the base of each bLue

and string, at the top of each string end on the wirework adjacent to the bine in the case of non-pole hills. The sane points were greased for pole bills, but In addition a layer of fine cardboard impregnated on both sides with Stiotite was wrapped tightly around the pole and secured with wire. Standard corrugated cardboard traps were put on each bins appr- mate]y 0.6 m. (2 ft.) above the ground. Earwigs accumulated in these bands and their numbers were checked every week.

Aphid numbers on the blues were assessed by esnnin1ri leaves at all heights at random, to give a total of 15 leaves per bine per week. Numbers were assessed visualiy on a log4 scale, i.e. 0 = 0 aphids, 1 = 1-4 aphids, 2 4-l6 aphids, 3 = 16-6k. aphids etc, This method of estimation of aphid numbers was oheoked ani found to give results accurate within jlO % or the true grade.

The grease bands were checked weekly and any that seemed to be losing efficiency wore renewed. The presence of other predators, mainly coccinellida, anth000rIIs and syrphida, on the blues was recorded. The adults of all these predators fly readily and generally oviposit on the leaves and stems of the blue Itself. These predators were connon on both banded and unbanded. blues.

Any differences In aphid populations on these bines was, therefore, di to the exclusion of earwigs and possibly other predatory soil fa'w.

Results Earwig numbers At the start of the experiment on 22nd June, 1972, earidgs were relatively scarce on both untreated and insecticide treated bLues. At this -188-

time the first generation of oarwigs bad. not matured., the trap catches being made up largely of III and IV mater flmpbs (]9g. 7), Table 38 shows that mean earwig numbers gradually ircreased over the ser, reached a peak about early Au€ust and then decreased, The reasons for this decline are not understood.. It sens imj1jy that earwigs were entering the soil for hibernation at this early date. More earwige occurred on pole bills than on non-pole hills over the whole season in untreated ath insecticide treated zows. The bRnMng treatment did not affect the numbers of earvigs trapped on pole hills, but did seen to reduce the numbers taken on non-pole hills.

fThcts of the handiER treatment on athi& numbers Ci) Untreated bines. Aphid populations on all troatments were similar until early Ju2y, when the numbers of aphids on banded and unbanded. binos began to diverge. Cki bathed pole hills, aphid numbers increased to a peak of about 2,000 aphids per leaf by mid-July (Table 39). Where earwi,gs were allowed aocess, however, aphid numbers deoreased slightly during the sane period. Pg. 24. shows the develojment of aphid populations on banded and unbathed pole hills. Similar trends in aphid numbers occurred on non-pole hills but the differences between banded and unbanded biries was not so great. This may be due to the fact that there were 1es earwige caught in cardboard traps on non-pole bills during the sier. However, regardless of experimental treatments, P. ]iumu.li numbers on insecticide free hines became so high by late July in 1972 that the hops were severely defoliated. Although some regromrth of laterals occurred later on, little or no crop was obtained from these hops, showing that without any insecticides, predators alone cannot nonnally control P. humuli.

MEAN NO. APHIDS PER LEAF

U" 2 Fig. 25

4 dimefox + K

- 190 -

N 0 0 W a LA 0 S S S S S S S H H LA N LA K\ N

0 0 r-I p(\ H s- 4-4- H I

0 H N X) N W .O LA - I ::I

p4 LA N N %Ø N CX) LA LA I

LA LA i' CX) a I'\ 0 0 H W 0 0 I 'I

S.. NWS 0 t'\ H H N LA 4- LA 0 H

'I o P

i-I i-I N N

a'•S P o

,c - 0\ 0 ,-I LA CX) -* i-I 4j N 0) I(\ H 1 N N +1'-

'0 W N N N N CO CX) 0i 0' a S S S S S S S S S S S N LA i-I 0 4-N 0 H i-I N H N N 1i - -

TABLE 39. Mean grade (mean of 60 leaves/treatment) of P. hwnuli numbers per leaf on untreated and dimefox treated hopa*

tkitxeated Treated. Date P Pb Np Npb Mean P Pb Np Npb Mean

me 24 2,2 1.9 2.2 2.8 2,0 3.0 2.0 2.5 2.1. 14 June 34 3,3 2,1 2.6 3.]. 3.5 3.0 35 3.0 3.3 22 June 4.2 4.1 3.3 3.5 4.]. 4.0 4.0 4.0 4.0 4,0 30 June 4,4. 4.3 3,7 4,3 4.5 0,0 2,5 1.5 2,5 1.6 6 Julzy 3,4. 4,5 3.7 3.6 37 1,2 0,9 0,3 0,5 0.7 13 July 3.2 5,2 4.5 5.0 4.5 1.0 1.2 0.2 0.9 0.8 17 July 3.1 5.6 4.0 5.7 4.4. 0.3 0.5 0.1 0.]. 0.3 25 July 3.5 4.1 3.9 5.0 4.1 1.1 1.4 0.4 1.0 1.0 U August 0.9 0.4 0.9 2,0 1.5 0.1 0.4 0.0 0.0 0.1 20 August 0.6 0.2 0.4 1,9 0.8 0,2 04. 0.0 0.0 0.].

Means 2.9 3,4 2.8 3.6 - 1.3 1.7 1.2 1.5

S P = Pole hi11 Pb = Banded. pole bill; Np Non-pole bill; Npb = Banded non-pole bill.

(ii) Insecticide treated hines Two applications of dimefox were made over the sunier (see Pig. 6), mintR11i1ng aphid populations at such a low level that little difference between banded and unbathed blnes occurred. Aphid numbers were starting to recover before the second insecticide application (Table 39). If this had not been applied, natural e'emies alone may have been able to keep the aphids under control and prevent any major increase in population. Natural ennies of çirodi humuJ (Sclwan]c) can sometimes affect this degree of - 192 -

control once the population baa been reduced by an early application of a

systemic insecticide (campbell, 1973).

Discussion

Theobald (1913) was the first to reoonm the banding of hop binea

to exclude eaririga. He stated that molasses put around the bins would prevent earwigs climbing up, for "these insects have wings, but rarely use then and

so are prevented from getting to the bines." The bending grease (Stiotite) used in this study was almost onp1ete1y effective in exo1ui1-ng earwigs. Pole hills were sometimes diffioult to cover with the grease because of cracks in the wood. These were filled up using a thin blade to push the grease in. Pollard (1969) used the same compound to exclude ground fauna from brussel sprouts during an evaluation of the effeot of ground predators on populations of the cabbage aphid, Brevioorvne bzassicae.

Theobald. (1913) noticed that wooden poles in the hop garden tended to attract large numbers of eanigs, which sheltered in crevices in the poles. The present study has confirmed that pole hills act as aregation centres for F. auricularia in the hop garden. As a result aphid populations on the binea adjacent to a pole were affected by earwig predation to a greater extent than aphids on non-pole bines.

Predation of P. hiii I by earwigs and other predators in this study was not sufficient to give economic control of P. 1i'irn'li on insecticide free bines, but control in the broad ecological sense of van ien (1972), i.e. any reduction In aphid numbers, was achieved. Earwig predation only became important in mid-sumner as their numbers increased, the first generation matured. Since the aphid population on untreated hope had 'crashed' by the end of July, the effect of earwigs could not be estimated In late mr aut.min. Several authors have noted earwigs preying on aphids In late simmer 193

or early autumn. Way and Banks (1968) found that F, aurleularia was one of the few predators that could deplete Athia fabae Koch. mmthers in autumn, thout only when aphid populations were small. Smith (1966) recorded Z. auricuisria Inside debisceci seed pods Of broom feeding on aphids Acvrthosi- vhum snertii (Koch) from August Onwards. Due to the two insecticide treatmerrba, aphid populations on treated hops were too low to observe any effect of predation. The effect of earwig predation would best be studied using only one application of dimefox early in the season. van ken (1972) called attention to the predatory habits of various groups inclutling the Dermaptera, which merited Thither investigation. This experimental work provides a clear demonstration that F,. atWicularia L. can be an important predator of the hop aphid.

T.B OF SLEEVE CAThS TO CLUDE APKTh PREDATORS, 1973

Increasing insecticide resistance of the hop aphid (Dicker, 1971) has stimni ated a re-appraisal of the role of natural enemies. The role of specific hop aphid predators, especially Anthocoridae, have been alrey studied (Campbell, 1973). However, non-specific predators, especially the European earwig, Forficula auricul3 L., are abimdant in hop gardens and are also important predators of P. hunj. Sleeve cages have several limitations in the study of natural enøxy effectiveness, for example, they may cause changes in the plant's microclimate (Yi.eschner, 1958), or prevent prey dispersal (Pollard, l969 Way and Banks, 1958). Tho hop plant in particular is difficult to cage satisfactorily - 194. -

without disturbing the aphid population, since heights of up to 20 feet are involvei. Ground fauna may be excluded more easily than foliage-inhabiting predators, by the use of mechanical or chemical barriers (Nuggeridge, 1927;

Pollard, 1969; Kiritani az4 Dempeter, 1973). In the present atixly, large sleeve cages were used to exclude predators from whole binea and. ti4eatxnents desied to show the relative importance of specffio and non-specific predators, especially earwigs.

Methods The experiments were made in Silks Garden, Wye College, on hop variety

Cobbe, In a plot 28 m x ]4 m. at the eastorn boundary of the garden (Pig. 3.0).

c].uzion caos

Each predator exclusion cage was 2.5 ia. long (before fitting and sealing) x 0.5 m. diameter, with four steel hoops 0.56 m, apart within each cage (campbell, 1973). Samples were collected through three closeable slits in each cage. Bines were kept in the middle of each cage by cross-bracing strings fastened to the hoops and to the bines' support string.

A fine terylene net with 400 meshes per cn?. was used; this mesh reduced the light intensity by about one-third. Hoops were made from 2.5 nnn. diameter galvanised. steel wire, the ends being joized by nylon-covered electrical wire connectors. This framework was fitted around the binee wi braced to the support string 1 - 2 weeks before the netting material was fitted.. Netting was placed over the bines after cutting the supporting strix and secured. to the hops by ribbon, Control cages were also used by leaving the ends unsealed, excess material at the end being gathered and tied to the adjacent steel rings. . Thus, access for predators was restricted to the unsealed ends of the open (control) cages. Plate 3.2 shows exclusion and control cages over the bines after the rest of the hop garden was 195 -

PLATE 12. o1uaion cages.

A. Onen end. control cage B. Double seal and stictite barrier at eud of a comvlete exclusion case.

L- 1! 'at

C. Cares In tb hoD RaideD. In Seotiber atter barvestinR.

w 11

•t - - 196 -

harvested. Cages were fitted. during July, well after the peak of aphid

(mm4ation to the hop garden. &cluaion cages were tied tightly at top az

bottom and fruit-tree bRnding grease smeared on the wires and support strings

above the cages, and on a 0.1 m. wide band of ali linl,thlm foil wrapped tightly

around individual bines below the lower seal of each cage. This tecbniqu

virtua].ly excluded earirigs and other climbing predators from entering the

cages.

There were four treatments, each replicated four times :

A) Complete exclusion cage.

B) Partial exclusion cage. Cages open to admit flying predators, but earwigs

excluded by bRMlng top wires and bottom wires with grease.

c) Control (open) cage. Cages open and ground arthropoda riot excluded,

D) unoaged strings.

Pour adjaoerrt bines at the plot centre were chosen arid treatments .Ar-D

applied at random to one string, giving four treatments per bine. Before the

exclusion cages were put on, bines were searched (July 22xd) and all natural

enemies removed by hand. Cages were put over the bines on July 23rd. Thicaged

strings were studied to determine whether caging had arty effect upon the aphid

population. Samples of lateral leaves (five per cage) were taken at random from the full length of bines each week from July 26th to September 20th.

From August 15th onwards, a sample of 20 cones per week was taken from each cage in addition to leaf samples. Samples were removed to the laboratory in polythene bags and stored at 5°C. until ready for assessment. Sample leaves were heated for one hour at 45°C. and aphid and mobile natural enemies removed by flotation (Muir, 1967). Where estimated aphid nunbers were greater than 1,000, sub-samples were taken, but for mmibers below 1,000 direct counts were made using a low power binocular microscope. Numbers, stage end species of predator were noted. iLl los! areas were measured with - 191 -

a photo-electric pl meter. After August 16th, 10 cones per treatae/ replicate were stripped arid aphids and predators ooimted. Samples of 20 cones per treatment were weighed on an Oertling balance (sensitivity 1 xng.) arid mean fresh weights calculated. Axiy feeding damage on leaves or cones by earwigs was noted, Earwiga were sampled by fitting cardboard bands to 30 randomly salected strings (but not to strings in the exclusion cage tndy) within the Cobba plot.

The hops were scheduled to receive only 1e diinefox application in late June to reduce the initial aphid population build-up and to allow predators to prevent aphid resurgence, 120 ml. of 1 active ingredient was poured onto the base of each bine on June 26th. Unfortunately, its effect was extremely patchy and some blnes remained heavily infested, probably due to the dry weather during July (Fig. 15) which prevented uptake of toxicant, and vigorous crown growth of the bines making complete coverage with the pesticide difficult (Emery, 1954.). Consequently, &thief ox was again applied on July 20th. This aecond treatment was very effective and. rapidly decreased aphid mmbera to nearly zero by mid-August, The caged binea were artificially infested with aphids on hop pieces from laboratory culture on August

20th and 23rd. These aphids survived and multiplied In the cages.

Results Hand removal of predators before putting on exclusion cages was

incomplete; efficiency of removal varied with predator type. Relatively

inactive syrphid and coccinellid larvae were easy to find and remove, but active anth000rids occurring on strings, leaves and petioles were riot

(Pollard, 1969), and small numbers were removed each week from the exclusion

cages (Table 40). Similar difficulties were experienced by Sailor (1966) and Milne (1971) during their exclusion cage studies,

- 198 -

TABIE 4C). Total numbers of natural enemies of P. himn1i on leaves and In

cones1 between 26th July and 20th Septnber, 1973, (Exclusion cage ety).

Closed Open Bathed Open No cage cage cage cage

.Axrthocoridae: unidentified 24 22 31 17

Syrphidae: 0L balteatus 0 2 14.

Hnerobidae: L. buni1lYn1a 0 3 0 6

Chl7sopidae: C. carnea 0 0 1 0 Staphylinidae: T. hviuiorum 0 3. 0 0

Parasite 'mtiiiinlea': Athidiva ap. 0 3 2 3.3

0thers 0 3. 3 3

160 leaves and 50 cones/treatment examined.

* Rhizothilua atricapiflus L. (carabidae); a1ar1Rium opi1i L.(Phalangidae)

However, by mid-August the scarcity of aphid prey had. caused most of the specific edators, especia].]- anthocorids, to disperse and few antho-

corids were n'esezit when the cages were re-infested. with P. hwnuli. Earwigs were common throuiout this period and were noticed in the open cages, hiding In folds of fabric at the top and bott of the cages Other aphid predators found in cages during August and Septnber were the carabid r&izophilus

atricavi1] I., the staphyll 4'l Tachvvorus hvpnorcm F. and the harvestman

it ppilio L, but they were not abundant. - 199 -

It was not possible to excle all earwigs from the cages. $m11

numbers were found in grease-banded cages Ofl two sa3flp].:thg occasions, probably having crossed from adjacent hines whose laterals touched the cage. Earwigs were numerous in July and early August ( pig, u) after whici numbers In the traps decreased. As a result of the second dimefox treatment (Table 4]), numbers of P. }1U1TflI1( in leaf samples decreased to virtually zero. After re-infestation on August 20th aM 23rd, however, aphids increased in all

treatments and were first found in cone samples on August 30th. The mean

log (x + i) numbers of aphids per 100 cm?. leaf in each treatment were

compared by analys of variance far most dates In 1973 (Table 42). Differ-

ences were not significant until the final assessment of September 20th when there were significantly more ( p = 0,05) aphids in the complete exclusion cages. Differences between open control and open banded cages were not sign ificant, although there were consistently more aphids where earwl.ga were exch4ed. There was no significant difference between numbers

of aphids on imcaged and control caged strings. Cone fresh weights were analysed for all dates. The results were varied, probably due to moisture loss during storage, but indicated that cones from open cages and uncaged strings tended to be heavier than cones from closed cages. Differences between numbers of aphids in the cones were not significant until the final assessment, when there were significantly more (p = 0.01-0.001) In cones of closed cages and open banded cages (Table

43). Aphid population In the cones eho*ed silTdlar trends to those on the

leaves (Pig. 25) and aphid numbers were increasing in cones of all treatments on the final sampling date (September 20th). However, this was not a normal

situation, since the plants bad been artificially infested with P. humuli

late in the season (August). -200—

TABLE 41. Total numbers of P1. humuli counted on samples of leaves and in

hop 00fl08 (Exclusion cage siy), during 1973.

Sample Olosed. cage Date Open banded Open No cage - cage cage

26 July leaf 1062 1395 1723 1318

2 August leaf 59 33 58 20

9 August leaf 3 0 9 2

16 August leaf 1 0 1 0

cone 0 0 0 0

30 August leaf 14 9 1. 6

cone 7 11- 3

6 September leaf 78 46 19

cone 90 97 11

13 September leaf no 67 34 36

cone 106 43

20 September leaf 637 185 29 28

cone 235 '315 30

20 lateral leaves and 10 hop cones per treatment/date. (-. = not counted)

TABLE 42. Mean log (x + i) aphids per 100 on?. leaf area durLng the

exclusion cage study, 1973 (nan of four replicates).

Date Closed. Open banded Control caged cage cage cage

26 July 2.182 2.061 2.180 2.053 2 August 0.695 0.562 0.712 0.115 9 August 0.1014. 0.0 0.228 0057 16 August 0.0 0.0 0.0 0.0 30 August 0.123 0.318 0.196 0.255 6 September 1.009 0.870 0.526 0.4.96 13 September 1.223 1.020 0.732 0.677 20 Septüber 1.932* 1.382 0.584 —

Means underscored by the same line are not s 1 gn(ficant].y different. (P>o.05)

** P = 0.0]. (Data for 6 September not analysed).

- 201 -

TLE 43. }Sean fresh weight of oories in g. (mean of 20 cones/date) and mean P. humii11 mbers (iog x + i) per cone (mean of 10 oones/ date) during 1973.

Closed Open banded Open Uncaged cage cage cage

16 August Fresh Weight 0.263 0.2614. 0.213 0.380 P. bumuli 0.0 0.0 0.0 0.

30 August Fresh Weight 0.351 0.355 0.505* 0.551 P. huixiuli 0.230 0.1146 0.111i. - 6 September Fresh Weight 0.269 0.428** 0.261k. 0.479*** P. buntili 1.000 1.029 0.322 - 13 September Fresh Weight 0.11.37 0.1421 0.586* 0.577* p. hinrtuli 1.065 1.068 0.7Z1.

20 September Fresh Weight 0 .381 0.14.98*

P. humul 1.393** 1.512*** 0.602

Means underscored by the same line are not siguificantly different from the controls (i.e. open cases). (p> 0.05) • P = 0.05; ** P = 0.01; *** P = 0.001

The return migrants to Prunus spp. (gynoparae) are normally formed in September and. October (Masses, 1963). For the last two sampling dates (13th and 20th September) the mean percentage of alatoid nymphs in the cones of each treabient determined. was 7 % aM 36 respective3,y. Therefore, emigre- tion of noparae contributed to some decline in aphid populations on open- caged, compared. with closed-caged hines. Eowever, differences between

aphid. populations on open baziled and. open cages are not affected. by emiigra- tion and reflect earwig predation in the latter treatment. When the eperiment was harvested on September 21st aM cages removed, as many as 20 earwigs were found in each open cage. -202-

Discuson

This study has shown that aphid numbers were higher on bines from which earwigs were excluded. Differences between numbers of aphids in both leaf and cone samples from grease-banded and unbanded. bLues were consistent, but only statistically significant for cone samples. Bowever, by using a second difox treatment and artificially infesting the binee, conditions in the experiment were not representative of norms]. field conditions. Aphids in the cones are better protected from predators than aphiRs on the leaves, although anthocorids, the most important specific aphid predator, are efficient at searching for prey (Anderson, 1962) and readi]y penetrate the cones. Earwigs climb readily (Boa).1, 193 2; Nuggericlge, 1927) and feed upon P. hinli on the leaves (Escherlch, 1916). In laboratory tests using fully expanded cones, earwigs would sometins enter the cone structure, feeding on aphids and occasionally eating small holes in the petals. They probably do enter cones in the field since they are strongly thigTnotactio

(Weyrauch, 1929) and are often found sheltering in flowers such as dh1i

(1'ulin, igZii.), Earwigs were the most important predator of P. h,imuli in this stiy, but the lack of aphid prey in the plot at the beginning of the experiment meant that other aphid predators, especially anthocorids, were scarce and did not contribute much to P. htmxuli predation In the cages. As a result, there was no sigr-lfioant difference between aphid numbers In leaf cone ssnples from the open banded and completely closed cages. Earwig predation alone was not enough to prevent an increase in ap?iiAa on leaves an! cones, but on the last sampling occasion aphid numb are had decreased and there was a moan of only three aphids per cone at the end of the experiment, compared with 31 and 23 In banded and complete exclusion cages, respectively. - 203 -

HAND RF240V.L OF APHID PREDATORS FROM INDIVfl)U.AL LEAP PAIRS

There is little direct evidence of the effect of predators on numbers of their prey (Pollard, 1969). The use of cages to exclude• predators (Smith and de Bach, 1942) also affeote microclimate and probably the dispersal of prey species. The technique of band removal does not have these limitations and is one of the simplest and most effective methods (H1e]c et al. 1972).

Its mMn disadvantage is the time and labour involved In locating and removing predators from whole plants (Lenhner, 1956). In this study, predators were removed fran selected pairs of individual leaves which were tagged for easy recogeition and so easily searched for predators.

Methods

The plot of hops, var. Cobba., used. in the experiment was situated on the eastern side of Silks Garden, Wye College. 10 hills were selected, five at the eastern plot edge about 5 in. from a beech hedge and grassland strip, and five towards the centre of the garden, at least 22 in, from the edge. There were four treabnents, each replicated 10 times. i) Control - Al]. predators and parasites allowed access to the leaf pairs.

2) Ground fauna excluded. by grease-banding leaf petioles, but specific

predators not removed.

3) Ground fauna excluded and. specific predators hand removed. i1.) Soil fama not excluded, but specific predators removed by hand. Ce treatment was allocated at random to one leaf pair per string, giving four treatments per 1II in a randomized. block design. Leaf pairs of similar age, size and height on the bins (about eye level - 1.6 n,) were selected, fi narked with tags. - 20L. -

Non-pole hills were used throughout. A binItng grease was applied to strips of silver paper to avoid possible phytotoxicity and the paper i.rapped tightly around leaf petiolee to exclude climbing predators. Predators, parasitized aphids and aphids killed by the fungus

tomontbo& were removed by hand every other day, using fine forceps.

The experiment was repeated during different stages In aphid pOpu.. lation developnent, from June 6th to 27th, when the influx of alate aphids to the hops continued aid apterous aphids multiplied rapidly, aid from

July 30th to August 5th, when migration of slates had ceased.

Dimefox was applied as 120 rn]., of 0.5 $ active ingredient solution poured onto the base of the binee. Only one application, on June 26th, had been planned, but this gave inadequate control aid therefore another application was made on July 20th. After the second treatment aphid numbers fell rapidly aid at the end of the second experiment leaf pairs were artificially infested with hop aphids. Leaves were harvested at the end of each experiment aixi aphids washed from the leaves after being killed by heating for one hour at 45°C. (Muir,

1967). Aphids were then counted over a 1 cm. grid pattern using a binocular microscope. Treatment leaves were bulked and counted by an optical planimeter. Traps of corrugated cardboaxd were placed at random on one bine of each hill to sample the earwig population in the plot.

Results periment 1, June 6th-27th, 1973 : Mean leaf heights (,j s.B.) were 164.1 10.2 on. at the edge and

165.0 7.2 cm. at the centre. Many more slate aphids were found on banded leaves than on unbanded. leaves (Table Differences were sie'ifioant ( p = o.o5..o.ol) at the edge

205 -

for all datea, but at the centre differences were only aiificant on Ji

13th (see Table 46). ilate aphids often wander from leaf to leaf on their

host plant after a migratory flight (Johnson, 1958). A3.ates of P humuli

land mainly on the old leaves low down on the bims and later cLimb up to the younger leaves (Anon, 1969). The grease-band prevented this behaviour

and caused a build—up of alate aphids on the banded leaves. Obviously, the number of apterous offspring would thus be increased and so each week from June 6th, all alates on leaves of treatments 2 and 3 were rsmoved with forceps. Numbers of alates were higher at the edge, probably due to the sheltering effect of a 6 m high beech hedge (Lewis, 1966).

TABLE 44. The total number of alate on five leaf pairs per treatment at the ed and centre, Cobba plot.

Date CENTRE Trt.I 1rt.2 Trtj Trt.4. Trt.l T'rt.2 Trt.3 Trt.4.

6June 7 62 85 3 2 18 21 9

l3June 10 114. 104. 4. 2 30 26 6

2OJune 3 57 20 14. 6 17 20 3

27Jurte 3 29 12 5 9 15 1]. 3

TO1'AL 23 262 221 26 19 80 78 23.

There were few specific predators in Silks Garden during the first experiment (Table 45), equally distributed at edge and centre. The fungus, Entonoothora killed a few alate aphids, and parasites CADbidius sp.) appeared

towards the end of Jtme but parasitism was never greater than 3. %. Earwigs

were the only comon predator in the hop garden during this time (Table 4.7).

-206-

Hand removal of predators was not completeiy efficient since young syrphid

larvae and nrmphs of .Antiiocoris sp. were difficult to detect.

TABLE 45 Natural enemies of P. bumu3.i removed from treatments 3 and 4 at the edge and centre of the Cobbe plot, between June 6th and

June 27th.

EDGE CE

Anthocoridae 3. 2

Syrphidae 4. 2 Coocinefllfl ae 1 Hemerobidae 2 1 Staphyl In4 &ae 2 0

Parasite 'munxnie& 9 9

Entoxnopthora 3.0 5

TABLE 46. Mean log (x + 1) numbers of P. huinuli alates per leaf at tbe edge and centre of the Cobbe plot1.

Date EDGE CENTRE Trti Tx-t.4 Trt.2 Trt.3 Trt1 Prt.4 Trt,2 Trt.3

6 June 0.38 0.20 l.13** L26** 0.15 0.15 0.66 0.72 ± ± ± ± ±• ± ± 0.21 0.23 0.54 0.38 0.27 0.20 055 0.8Z4. 0.1513 June 0.4.7 0.26 138** 134.** 038 0.850* 0.86*0 ± ±. ± ± ± ± 0.15 0.18 0.56 0.24 0.22 0.29 0.16 0.4.3 20 June 0.23 0.58 1.09** 0.70* 0.31. 0.20 0.61. 0.61 ± ± ± ± ± 0.16 0.35 0.56 0.21 0.28 0.23 0,26 0.38 02Q27 June 0.35b 0.83** 0.53b* 0.4.5 0.21 0.60 0.5]. ± ± ±. ± ± ± ± ± 0,27 0.25 0,22 0.18 0.13 0.16 0.29 0.39 Means of five leaf pairs/treatment. Means underscored by the same line or subtended by the same letter are not siificant1y different. (p , 0.05) * P = 0.05; ** P = 0.01; 0*0 P = 0.00]. - 207 -

TBL 4.7. Barwig numbers in five traps at the edge and centre of the

CC'Obe plot (6th June to 12th Septenber, 1973).

Date

June 127 212

July 305 93 I

A31gust 396 167

Septenber 37 36

TOTAL5 865 508

The rperiiuent was harvested on June 27th anl mean density of aphidR per CE3 • leaf calculated (Table 4B) Apterous aphids were more numerous at the edge of the garden, probably reflecting the initial greater abundance of inigrantes alatae at this site. The treatments involving banded leaves bad signi icantiy more ( p = o.oi) aphids than unbanded leaves in both sites.

TABL48. !4eanlog(x+].) numbers ofP._htnnu.1.ipl00 cd'. leaf atthe

edge and centre. Harvested June 27th (mean of 3.0 leaves per

treatment).

freatment i • Controls 2.15 ± 3.42 2,00 ± 1.63

2. Bathed 2.54± 1.56** 245 j 1.42**

3. Bathed and band renoved 2.14.3 1.92CC 2.27 j l.23$ 1. Hand renoved. 22]. j 1.76 2.03 j 1.60

Bracketed means are not significantly different. ( p , 0.05) ** p0.Oi 208-

owever, since bathing caused alates to accimiulate on the leaves, differences may not be due entirely to the exclusion of climbing predators. In both sites the banded leaves from which predators were removed had fewer aphids, probably because constant emlntion of these leaves disturbed the aphid population. Adult apterous P. hni'mili are especially prone to 'drop oft' the host leaf when disturbed. Compared with the controls, aphids were more numerous on leaves from ithich predators had been removed, but differences were not aierftficant and reflected the scarcity of speoifio predators during

June.

Fxperiment 2, July 30th - September 5th:

The same bines were used as for the previous experiment. The mean leaf heiit (j S.E.) was 189.0 ± 15.7 on. at the edge and 181.2 ± 12.5 on. at the centre. Because the influx of slates had ceased by this time, it was assumed that treatment differences between bathed and mbandod loaves would reflect only the activity of climbing predators, especially earwigs. The experiment was set up on July 30th. ])uring early August many of the lower leaves of the hines were subject to yellowing and die-back, because growth was only vigorous in the upper bine regiome where cones were being formed. By August 15th few available leaves were left on the bines below about 2 m. and the experiment was then abandoned.

Records of predators removed from the leaves were kept (Table 14.9). Predators were abundant at the start of experiment 2, but scarce by August 15th when the second dimefor treatment had reduced the aphid infestation.

Aiith000rids were the most abundant specific aphid predator but their removal was only partly successful. On the unbathed leaves anthocorids were free to wander, drop from above, or fly onto the leaf (adults) and were found during each eT1 tion. Because thr fly readily adult mithocorids occurred on

-209—

banded leaves where they oviposited, giving rise to young nymphs which were

difficult to detect. Nymphs also reached banded leaves when laterals or adjacent leaves were blown across, forming a bridge.

TABLE li.9. Total number of natural ennies of rnoved from leaves

of treatments 3 and 4., July 30th - August 15th. (40 leaves/date).

EDGE CTRE

.Anthocoridae 20]. 168

Syrphidae 1 1 Coocinellidae 2 0

Hnerobidae 14. 1 Chrysopidae 3 0 Parasite 'mummies' 16 11

An attnpt was made to continue the experiment on binea on the perimeter of the plot which did not suffer from die-back of lower leaves, probably because they were not shaded,. New leaf pairs were selected and treatments applied at random to nine replicates on kgust 29th. Pieces of

aphid-infested leaves (from a laboratory culture) were placed on the experi-

mental leaves on August 29th anl 31st. Unfortunately, the whole garden was scheduled for harvest on Septnber 6th so the experiment only ran for nine days and was harvested on Septenber 5th.. Predators other than earwigs were

scarce at this time. Only two adult anthocorids were recorded from treatment

leaves. reabnents were compared by analysis of variance after transfoi'tm-

ation to the log (x + 1) form (Table so), There was no i gnlficant diff'ei'-

enoe between treatments I and 4. or treabnent8 2 ai4 3, which was expected

since specifio aphid predators were scarce. The banded leaves (2 and 3) had. - 210 -

a1ificant1y more (p = o.o5-o.ol) aphids than inibathed ones (1 and 4.), indicating that climbing predators, of which earwigs were the moat abintant, had. a sifficant effect upon aphid numbers. However, it is poasible that aphids placed on the experimental leaves wandered an to other leaves and tbLt the b1t process caused artificially high numbers on treatments 2 and 3 by confining them on each leaf.

TABLE 50. Mean log (x + i) numbers of P. humuli per 100 czi. leaf,

experiment3, harvested September 5th. (Mean of 14. leaves paz' treatment).

Treatment No. apbid/'lOO cm2 . S.E.

I • Controls 0.56 0.15

2, Bed 1.16 j 0.54.*

3, Bathed and hand removed 1.24. ± 0,4.5**

4, Hand removed 0.81±0.40

Bracketed means are not si'1fioazitly different. ( p , 0.05)

* P=0.05;** P=0.01

Discussion

Several authors have followed the interaction of aphid predators and their prey on individual tagged leaves of plants (Pollard, 1969; van en,

1963). However, aphids like Brevicorvne braesioae L. were used, which foii small ooloniea and enable frequent counts of numbers to be made in the field. The hop aphid, Thorpdqn 1iumu1 (Sebrank) proliferates very rapidly on the leaves and field counts axe therefore impractical (Muir, 1967). Hand— removal of predators from whole hop binos would be impractical since the plant m reach 20 ft. high and each leaf would have to be exemined. Using - 2U -

single leaf pairs overcomes these difficulties, but it appears that teanents such as grease ba1ing confine alate axñ apterous aphids in too small a nit area of plant. Pollard (1969) banded whole sprout plants, and Wi and ariIcs

(1968) individual Euon.vmus branches to exclude soil fauna, but no work with small plant units such as leaf pairs has been previously reported.

BM1 ng of leaves caused siificantly hiaer nunbers of aphids to develop, but in the first experiment it was difficult to di.stinguieh between the effects of soil fauna predation and the effect of oonf 1 g alate to the banded leaves. The soil fauxa of the hop garden includes several species which probably take aphids, including Trechus Quadristriatua Schrank

(Carabidae) and the harvestman Thalanun o'ilio. but earwigs were the most abundant species. Therefore, most of the observed aphid predation by soil fauna can be attributed to the earwig. However, during June there were few adult earwigs present end the majority of the population was composed of young nymphs which do not c]iEb as much as later instars (Beau, 1932). It is probable that few nymphs climbed as hii as the experimental leaves

(approximately 1.61. m.) before late June. Numbers of specific predators, such as anthocorida, were also low at this time1 Therefore, population develoanent of P. humuli was little affected by predators during the first experiment In June.

Anthocorida and late Instar earwiga were abundant during the second experiment in July, but because the leaf pairs were lost, unfortunately, results on the comparative effect of these two predators are not available.

Earwigs were still present in the garden in late August when new plants were selected, and treatment differences at this time were probably due to earwig predation. - 212 -

ENC0URAQ c EARWIG PREDATION ON P. HMULI

In 1973 it was found that earwigs would gather In cardboard bands placed arow hop binee at hei#ts of up to 10 feet (3 rn,) above ground. Moreover, the number of earwige within such traps increased if thy were left miisturbed for long periods (Crumb, Eide d Bonn, 1941).

In this experiment, bands were put at Intervals on the whole 1gth

of hop bines, hopefully to build up large numbers of P. aurlcularim in the bands and thus increase earwig predation on P. humuli.

Methods

The experimental site in 1974. was the Cobba plot, Silks Garden (see

ig 10). Treatments were allotted to one string per bill In a randornieed

block design, of four replicates, using four bills towds the B. edge of

the plot.

Treatment Ci) Staniard cariboard traps (6) placed at 0.8 m. intervals up

the blue. Positioned May 29th.

Treatment (ii) No traps.

The site was treated with dimefox (120 ml. of 0.5 al. solu.on on

the base of each blne) on June 17th. The application failed to reduce

numbers of P. bm1i (see Fig. 26) and cytro].ene was applied on June 29th

(0.5 g. ai In 120 ml. solution per bill).

Aphids were enp1ecI by removing five leaves at raMo from the full

length of each bine using a tripod ladder. A total of 20 leaves per treat-

menildate were reved at weekly intervals from June 1 4.th to July 30th.

Leaves were heated at 45°C., then dead aphids washed off and counted on a

1 cmn. grid under a binocular microscope uir, 1967). Leaf areas were

estimated by comparison with prepared templates. -21.3-

PLLTB 13. Si]ks Gard, June 19714.. Cardboard trape placed at lntorvala along the blue. - 214 -

Results crd Discussion Aphid density increased in early June (Table 51) on both treatments.

Lfter the drench of dinef ox on June 17th aphid numbers actually increased in 1974. Thfortunato1y, the application of cytro].ane which fol].oved on

June 29th reduced ,hid numbers to nearly zero by the end of July (Pig. 26) and differences between treatniite in the experiment could riot be shown.

These results do, however, point to the difficulties involved in attenting to obtain a 'medium' level of aphid infestation. Campbell (1973) used. climefox successfully in 1971 and 1972 to reduce, but not e1im4iate, P. humul.i numbers, and found that in aoe cases predators would then contain the resurging aphid. population.

TABLE 51. Log (x + i) meam numbers of P humuli per 100 aI. loaf during

the 1974 study.

Sampling date Banded Control

June 2.Zi1 0.24 2.34±0.25

11 June 2.65 0.26 2.41 j 0.28

18 June2 2.87±0.22 2.66±0.19

25 June 3.0k. j 0.19 3.00 j 0.21 2 Ju1y 2.63± 0.28 2.28j0.22 9 July 2.11 0.36 1.69 0.10

23 July 0.76 j 0.11 0.61 j 0.17

30 July 0.00 0.00

Mean of 20 leaves per treatment/date. 2 Dimefox applied. on June 17th. Cytrolane applied on June 29th. Means underscored by the sie 1ix e not significantly different (, 0.05)

LOG X+1 APHIDS PER 100 SQ.CM. LEAF

9 (N 216 -

It is possible that at Wye has now developed resistanoo to difox, although the poor control given in 1971i. may have been due to lack of rain before and after application (Fig. 16), since dimefox is only effective when the soil is moist (Dio]cer, i g m.), Cytrolane aens to be too effective an aphicide for use in predator evaluation experiniexxta. Perhaps other systios such as diinethoate, which is less persistent in plant tissues (Nartin, 1973), would be more effective in these experiments. Regardless of aphid po*i1ations, the technique used in this experiment was euooessfu]. in encouraging numbers of F. auricu.laria onto the bines. Traps were removed on August 1st after having been in place for 613. days.

Mean ntbers of earwigs were 67±12, 36 19, 17±5, 6±1, U 3

7 ± 2 per trap at heights of 0.8 m., 1.6 rn,, 2.13. rn., 3.2 m., 14..0 Ui. Rz

48 m. respectively. Although earwig numbers decreased higher up the bines, this large population on one string indicates that predation upon P. hunuli would probably be increased by the use of cardboard bands. Whether or not this technique would have any commercial use in an integrated systen for

P. humuli oontrol would depend l nly upon the labour involved in its use. .217-

GENflUL DISCUSSION

This thesis foins part of an overall stwly at Wye Coflego, to

Investigate an integrated1 syaten of control of the dazns-hop apbid,

oçop inrjS (Sc1rank). The 1n reason for tho Integrated control approach was the difficulties In insecticide control oxperienced by so growers due to increasing aphid resistance, particularly in Sontborn

England (Gould, 1965; Baryanovita and Muir, 1969).

Cio of the first requirements for tho introduction of a pest mancge- ment schne is the identification, study and evaluation of the pest's natural ennioe (Botho, 1963). In this woit, the role of orficul auricularia L. In the predation of L bunuli under ooercial hop garden conditions has been studied. Campbell (1973) showed that an initial application of an insecticide was necessary to ohedc aphid population build-up, otherwise predators were

Inadequate to control aphid numbers. Predators (4ity anthocorids and earwige) could inrilntoin the resurging aphid population at a low level when the effects of insecticide treatment eventually wore off. Oer-effoctive aphid control in the years 1973 and 1974. meant that the quantitative 00Th- tribution by earwigs to overall predation of could not be found.

Stomach contents analyses fromi June to Saptambor showed that aphids were eaten, among other foods, by earwigs. A rmVI ammmt of damage to the hops was caused by earwigs In the years 1972 - 1974, but this was mainly confined to yowig loaves. Thus, earwiga did more good than harm in the hop gaxdan

Integrated control means 0A post monagamont syaten that, in tho contort of 'the associated eriviroamant and the population 4ynamics of the post species, utilisos all suitable techniques and methods In as compatible a tnmner as possible Wi& maintains the pest populations at levels belov those causing eoonainio injury. (Anon, l96). - 218 -

During the three years, earwigs were the only predator that was numerous in June when slates of P. hmu1 I co1onfed the bines. Other predators, such as anth000rids, did not appear until early July. However, because the earwig population in June consisted mainly of young stages which tended to rc,Mn on the grounj or only on the lower regions of the bine, the amount of predation on 1JJ was ineiIficacrt during this period. Maximum predation occurred during July and. August when earwigs wore most numerous and readily climbed the bines.

Croxall, Collingwoocl and Jnk-t (1951) found that earwigs were numerous in grass orchards, but scarce in arable orchards. They attributed the latter fact to the frequent tractor cultivations which destroyed the eggs and young of F. aricuipz'ia in spring and early sv'r. A population att*iy in the Nursexy Garden in 1972 showed that earwig nests only occurred in the rows of hops and not in the furrows, which were frequently cultivated.

It was of interest to note the oorrelatian between "earthing-up" the and an increase in numbers of earwigs in the traps in both years 1972-197y, but as the technique of m1ithn1 cultivation uI ng herbicides to control weeds is now standard ceroial practice, the correlation is not important.

N1nIir,1 cultivations may favour the increase of P. auricularia by not disturbing their eggs and young stages in the soil, but evidence frxi a fie]1 survey suggested that soil oaupaction as a result of tractor passage occurred in varying degrees depv1Thg upon the soil type, and could adver- sely affect earwig numbers. However, mIn(InAl cultivation spares the dormant stages of other aphid predators, such as syrphid pupae, which are destroyed by p1oudzig (Way, )kudie and Galley, 1969). Earwigs were found to be most numerous along the edges of both

Si]ks and Nursery Gardens in population studies from 1972-1974. Both gardens were surrounded by stripe of graas1, and earwig nests and young -219--

were coon under stones and in the soil of these areas. The earwig popu- latiori in all three years increased in June, with a peak about mid-August, and. thai slowly declined. Possibly, movements of earwigs between the edges and hop garden might account for this decline in numbers. Repeated maticing experimeuta were unable to confirm this hypothesis, but there was evidence from the results of a po].ythene barrier experiment in 1974. that such movement occurred. Moreover, in Septther 1972, in the Nursery Garden, as earwig numbers began to decrease, they increased in an adjo 1ii1- plot of maize infested by cereal aphids (E.N. E1inin, unpublished data). Therefore, populations of P. auricularia. cannot be considered as static entities, but respond to habitat changes, especially lack of preferred food, and are able to move long distances on occasions (Crumb et al. 194,1). (ie of the major fac-tors affecting the efficiency of natural enemies in an integrated programme is the type of chnico1 used for pest control and. its time of application (Mordzhanyan and Ust'yon, 1965; Smith and. van den Bosch, 1967). .e1d experiments in 1973 suggested that soil applications of dimefox reduced the numbers of earwige caught per trap, but this was not found after toiler sprays of supracide. Sinoe earwi.gs normally hide during the day under stones and debris on the soil surface, or in soil cavities (Sial, 1958), foliar-applied sprays probably have little effect upon them, although they may contact pesticide residues when climbing binee at night. In laboratory experiments, earwiga were ld.11ed by concentrations of dimefox in the soil at only one-tenth that of field rates (See Section iii); however, only adults were used in these tests. As most of the earwig population consists of young nymphs when dimefox is normally applied

(June - July), it is also necessary to evaluate the toxicity of dimefox to these stages. Nymphs of L auriculari are more susceptible to inorganic poisons than adults (Muggeridge, 1927). In a further field experiment lit -220-

1972i., earwig numbers were not reduced after soil treabnent with dimefox and cytrolane; hence, definite conclusions could not be made

The range of insectid.des used for oontrol of P. humuli ani their frequency of application, varied iong the growers surveyed in 1974. 1om the period 30th May to 12th August, one grower obtained aphid control with

one 80i1 drench and two foliar sprays, while another used one aol.?. drench aM. six foliar sprays. Even allowing for variations in the numbers of

inigrantes alatae arriving in different hop gardens, seven treatments by the latter grower is surely too many. However, economic injury levels have not been established for P. humuli on hops. If the levels of aphid infestation which could be tolerated early in the season without loss of yield wore known, then the number of sprays could probably be reduced by correct

timing and choice of compound. This would reduce aelection pressure On the

moat resistant iridividwils in the aphid population, and obviously save the grovers money. Both Zobren (1970) and Compbell (1973) ooriMdered that natural enemies of P. liumuli could maintain low aphid numbers after an insecticide treatment bad initially reduced the aphid population. However, the appearance

of predators in large enough numbers was uncertain, which ]±nited the co1ner-. cialiise of the method. Both authors did not appear to consider the possible impact of 'resident' predators such as earwigs, which were numerous in Si]ka and Nursery Gardens during the three years of this study. In 1974, attempts were made to increase earwig predation upon hutnuli by placing 'shelter' baths along the length of bines. Lack of aphids meant that the effect of this treatment could not be found, although the llMinturbed bands attracted large numbers of earwigs. The bnM(ne technique might prove useful in a coirmiercia]. integrated control system, depending upon the cost of suitable traps, the labour involved in fitting them to the bines, and the possible - 221 -

interference with niac ne-pi*l-ng of the hop cones (LA. Neve, pers. conn.)

Bands also provide shelter for predators such as anthocorids SAl thus lover their mortality (Anderson, 1962a).

The abundance of predators such as anthocorids and syrphids is influ- enoed by the type of vegetation in the vicinity of a hop garden (Bombosoh,

1966; Ze].eny and Hriy, 1969). These predators were more oonmion in the Nuaery Garden, which was surrounded by belts of mixed woodland to the north and west, than in Silks Garden which was more open, in 1973. (see Appendix c). It may be possible to cultivate certain non-crop plants along the garden edges as a source of aphids, and thus act as a means of enriching both predator and parasite fauna within the garden (Stazy, l96i.). The oul$i- vation of various flowering weeds would be uri11rely to form a reservoir of alternate hosts for P. huznuli. since the damson-hop aphid is host-specitio (Taran, 1971).

Zobren (1970) advocated the breeding and, release of selected aphid ennies In large numbers to control P !xumuli. Although earwlgs eat .arge numbers of aphIds they would probably be of little use as an in'mdative control measure, as umny of then would probably r4n in the area even after the aphids had been rnoved and, being omnivorous, would then attack nearby plants or hop bines.

Apart from the observations of Eacherich (1916), the beneficia. role of the European earwig in hop gardens has been neglected, probably because the insect is unobtrusive and active only by night. Diaing the field suvey, four out of seven growers thought that earwigs damaged the hops, and the

others wore uncertain. This stndy baa shown that earvigs are useful insects;

such information might eventually prove useful to hop growers.

As Asgari (1966) stated ".ccording to the results of these experiments, one is not justified to desigeate Forficuj.a auricularia L. as -222-

izuiffererit or harul to our cultivated plants. For the good which theae

im4 do In aphis years outweighs by far the damage which they can eventualiy produce on our p].axits."1

"Nach den Resultaten dieser Thitersuchungon ist man nicht berechtigt, Forficula auricularia auf tmseren Kulturpflanzen ala Ii1Ifferent odor ger ala schMlich u bezeichnen. Doim der Nutzen, don diese Tiere in Blattlausjahren bringen, flberwiegt den Schaden ureitaus, den ale eventuell auf unsoren Pflanzen anrichter K.8nnten." - 223 -

STJARY OF RTJLTS

The biology of F. auricularia was studied in two connercia3. hop

gardens at Wye College in Kent.

2urserv Garden : (a) Barwigs occurred in traps throughout the garden, but were nre COfl at the N. and. S. edges, end ure were found at the B. end of the garden

then the V. end, when a slope ran Ej—W., which was attributed to effects of soil drRfruge.

(b) In 1972 and 1973 numbers of earwigs in the traps Increased when the garden was "earthed-up", i.e. banks of soil were pushed up on each side of the binea to a height of about 2 feet. (o) Nymphs]. develomnt was slmIlr In both years. Two oviposition periods were identified, nymphs from the first oviposition becoming adult about

mid-July, and those from the second oviposition about Septenber. (ci) Damage to hop leaves by earwigs was mjnjy confined to young leaves, but the overall level of damage was low in both years.

Silica GaxIen : (a) Again, earwigs were found throughout the eastern half of the garden, but the highest numbers occurred in traps near the B. edge and grass strip. The nean catch of earwigs per trap decreased quickly within

10 m. of the edge and was fairly stable further into the garden. (b) Nymphs]. developnent was slower here than in the Nursery Garden. This

was attributed to the greater availability of preferred foods in the

latter. - 224. -

(d) Parasitin of earwigs by taohiriids and infection by EntomoPt1 pra fungus

was less than iØ in 1973.

(e) Earwigs climbed as high as 5 in. up hop bines, but the climbing ability

of early nymphal meters was low. Later inatars ani adults climbed

freely ani m jjni numbers of earcIga in traps above 6 feet (1,8 in,,) occurred in August.

(f) Traps en4nod at intervals of two days cauit less earwigs than traps left for five or seven day intervals,

(g) Naxiced earwigs dispersed slowly from a central release point, bit the

population was hot erogenous with respect to dispersal. Moan distance

moved in two days was about 18 in. in Silks, but only 10 in. in the Nursery Garden. (Ii) The traps sampled approximately 20 % of the earwig population in Si3ks aM about 12 $ in the Nursery.

(i) Aphids (p. humuli), green algae (Pleurococcus sp.), fungi (especially

Clalosporium ap.) and hop tissue wore the main items of diet of earwigs in both hop gardens.

A field survey showed tbt earwigs were abundant in some hop garda

in S.E. Kent end rare in othem, but the study was not detailed enouØi to identify the factors affecting earwig abundance in hop gardens.

Observations were made on the effects of the organophospborow

insecticide dimefox on earwigs in field and laboratory experiments. (a) In 1972 aM 1973 more earwigs were caught in insecticide-free areas then in dimefox treated areas of the Nursery Garden. (b) Nt.unbers of earwigs caught decreased in most areas of Silks Garden after diinefox application to the soil in 1973. -225w

cations of dimefox and Cytxolane to Si]ks Garden.

(d) Diinefox-killed aphids were fed to nymphs and adults of P. auriculaz'ia for 14 days, with no adverse effects.

(e) Concentrations of dlmefox in soil as low as 64 ppn., and concentrations of dimefox vapour as low as 32 ppn. caused 50 % mortality of test ear-

wigs within 10 days.

The effect of predation by earwigs upon populations both in the field and laboratory was investigated.

(a) Hop aphids were a suitable food source during nymphal development of the earwig,

(b) I, II, III an1 Iv earwig lusters ate an average of 18, 30, 46 and 89 P. .1x'rt1i. per day, respectively, at 20°C.

(o) When adult earvigs were Introduced to P humuli infested hop plants in a constant environment room at 20° 2°C., control of the aphid was obtained, at prey : predator ratios of 150 : 1 and 300 1, but not at 400 : 3. ratios.

(d) In 1972 when earwigs were excluded from insecticide-free binea by banding grease, there were more than on similar blues to which earwigs were allowed access, but eventually over-population by

aphids caused the collapse of all the blues.

(e) When cages were placed on blues in 1973, over-application of ditnefox reduced numbers to zero, but after artificial re-infestation aphids were most numerous on the leaves and heavily infested the cones

of blues fitted with complete predator exclusion cages.

(f) When earwigs were excluded from cages, aphid numbers in leaf and cone senpies were hiier than when earwiga were allowed access. - 226 -

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Artificial incubation of eggs of the co mon earwig, ForficuJ-a aixricularip L.

The female earwig is well-known for the maternal care with which she

looks after her eggs. The eggs are laid in a chamber at various depths in

the soil. Within the chamber, the female usually orients herself with the forceps towaxds the chamber opening (PlateAl). The female spends a great deal of time liciring and gently turning

over the eggs, which are laid in a cluster at the lower and of the chamber

(Briruey, 1914; Crumb, Eido and Bonn, 1%l; Behura, 1957). This behaviour' begina shortly after oviposition and continues until the eggs hatch. This behaviour is not understood although attempts have been made to

explain its purpose (wort1ington, 19 26; Behure, 1957). When the eggs are removed from the brooding female they invariably go mou].dy and fail to hatch

(Goe, 1925).

This work attempts to artificially incubate and hatch earwig eggs by

simulating the '].iclr(ng behaviour' of the female earwig.

Methods

Female earwigs were collected from the field during November 1972

and kept at a temperature of about 20°C. in a large p].aatic container. The

earwigs were fed on lettuce leavea, potato peelings and hop leaves infested with the damson-hop aphid, orodp pmu (Schrank). A layer of sterilised

soil (John mnnes Compost), two inches deep, was provided far excavating breeding chambers. The earwigs started laying eggs in mid-December and first

inatar nymphs hatched from early in. January. -248—

PLATE Al. Female earwig in soil chamber, Silks Garden, April.

b_ _- - - .g.- .M , - ' ' .' .- U"

im A2. Earwig eggs.

L. Eggs cleaned daily; still B. tjncleaiied eggs coyered in fungal viable. irairth. -249-

New],y-laid eggs were found by regularly inspecting the breeding chambers. The attendant female was first removed, than the eggs removed from the neat using a fine, moistened camel-hair brush. The eggs from one nest were divided into batches and placed on moistened filter-paper disIc. The disks were placed on a layer of unaterilised. soil over a wadding of moist cotton wool in. small covered perapex containers, th keeping the air in. the chamber saturate!. The first batch of eggs received no treatment. In a second batch the linkl-ng behaviour of the female earwig was simulated by regularly oleai- ing end rolling each egg on the filter-paper with a moistened camel-hair brush. The olei(ng process was repeated daily until the eggs hatched. A third. egg-batch was enclosed with the mother earwig in order to determine the hatching period with eggs receiving maternal care. Unfortunately, disturbing the female earwig caused her to eat all the eggs, an. observation also noted by Bethra (1957).

Results Table Al switnarises the results. On each occasion, the untreated eggs becamed infected with mould and failed to hatch. However, a significant number of eggs that were cleaned daily hatched successfully. Slightly over half the total number of eggs batched; the average incubation time for artificially incubated eggs was 16 (range 11-22) days. The eggs were taken from the first oviposition period of the earwig, which is 1cown to have a second and sometimes a third oviposition period in Britain (Behura, 1956). It is not Icown whether eggs taken from later oviposftiona are likely to be more viable.

- 250 -

TABLE Al. Percentage hatch and incubation tine of eggs of F. auricularia

reared artificially at about 20°C.

No. No. Incubation Replicate Treatment eggs eggs hatch Starting Hatching time used hatched. date date (da's)

cleaned 10 40 ll.12o'72 2.1.73 22 1 unc].eaued 10 0 o 11.12.72 -

cleaned 34 8 57 4.1.73 22.1.73 18 2 unoleaned 16 0 o 4.1.73 -

cleaned 32 8 66 27.1.73 7.2.73 3.]. 3 uncleaned 12 0 0 27,1.73

cleaned 22 11 50 3.6.2.73 2.3.73 111. 14. uncleaned 19 0 0 16.273

Discussion

Behura (1957) attempted to incubate the eggs of the ooion earwig, Forficula auricu],az'ja L., artificially but the eggs failed to hatch unless they were remod from the mother only 2-3 daya before batn-1vg. Crb (i941) stated that eggs failed to hatch without the presence of the female, probably because it was necessary for then to be kept in a moist situation, yet free fran mould. These authors describe the maternal care of the eggs, which Included 'licking, turning as is dora by a hen, and frequent shifting

of their position'. According to Lhoste (1957) the instinct of the female in oaring for her eggs has the dual purpose of avoiding parasites and controlling the hiunidity around the eggs. Porficula tonic. a species of earwig

closely related to F. auricularia but found in the U.S.S.R., was also shown

to exhibit maternal care (Peaot Rc iA, 1927). This wodcer observed that the female took each egg In her niouthparts and covered it with a liquE. Eggs - 251 -

that were not 'polished' in this ma, ner were dull in appearance, clung together and became covered in mould. Goe (1925) attempted to hatt 48 eggs of L. auricularia. but after nearly a month none of the eggs hod hatched.

Goe (1925) conc1ted that the presence of a fnale earwig was necessary for egg-hatMiig. Worthington (1926) also arrived at a sinilar ooncluaion.

The present wolic appears to be the first successful. attempt to hatch eggs without the female earwig's maternal care. Clemrt ng ath moistnlg the eggs simulated the nattnal attentions of the female earwig. The eggs wore moved to a different position each day, dislodging f'mga]. spores iditch were oontRndnsting the outer egg skin and shifting the eggs' centre of gravity, both of which may be prerequisite factors fqr hatching. Uncleaned eggs quiokly became covered by fungal hypbae which penetrated the egg-shell and destroyed the oontents (Plate A2). These observations also indicate that the female earwig does not secrete a protective covering around her eggs, as suggested by Pesotskaia

(1927), but merely removes ai oont 1 i* ite upon the surface of the eggs aid also keeps them moist. Rolling the eggs during the o1e process may be a factor which induces batohing, but since it is impossible to clean the eggs without moving them the separate effects of these two factors cenxot be distinguished. - 252 -

APPE!WX B

Relative humidity reactions of the European earwig,

Forficula aurioularia L,

The response of an Insect to the range of relative hiir1-Mties enoowi- tereci in its environmit can be very important in determining its behaviours

Chant anti woleoti (1952) found an inverse relationship between the numbers of earwigs occurring in wooden traps and the relative humidity of the air at i.3O a,m. Earwigs do not settle in contact with moist surfaces and the effect of moisture appears to be stiimilatox7 or kinetic (weyrauoh, 1929). Although several authors have investigated the relative humidity response of earwigs in alternative ohambers, the results are confusing (van

Heerdt, 1946; Perttimen, 1952). The present work attempts to investigate further the earwig's reactions to relative humidity.

Methods

A culture of Forficula auricularia was kept in the laboratory In a large plastic box at a temperature of 20° ± 3°C. Earwigs were fed on lettuce and dried meat; the soil in the cage was moistened daily. Relative humidity in the cage varied from about 90 % just above the soil surface to about 40% at the cage top. Earwigs were removed and plaoed in small perspex oontdners lined with moist filter paper (100 % R.H.) and kept In darkness for approximately one hour before each experiment.

The alternative RJ. chamber1 (Gunn and Kennedy, 1936) was 200 mm, in diameter &zi 36 mm. deep, consisting of upper and lower chambers separated

ObtMn'thle from Griffin and George Ltd. - 253

by a fine nylon gauge f1oo of mesh size 10/inm2. The lover chamber (:12 i'm. deep) was divided into four equal aenents by 8 xmn high perspex partitions.

The upper chamber (16 nmi. deep) located on the lover chamber via a flange

5 mm. deep. The flange gripped the gauze floor and beI it taub, maldng an airtight seal inside the chinber.

Solutions of sodium hydroxide (140 ml.) calculated to give the required relative himil dity (Iladge, 1961) were put into each of the four segments of the chai'iber, and a piece of cobalt thiocyanate paper (i x 0.5 cm,,) placed on the gauze floor over each segment to iM{cate the hum1tity (Solomon, 1957). The apparatus was left to equilibrate for 30 minutes before introducing the insects into it.

Earwigs were introduced through a circular bole in the middle of each chamber which was then sealed by a cover slip coated with Vaseline.

Five earwigs per chamber and. three replicates of each hnm{M ty comparison, plus a control chamber oontainirig water in all segments, were used in each experiment.

All experiments were carried out In darkness, by covering the chambers with a black cloth during the daytime, or at night, when the chambers were

il11ntted solely by a red lamp, to which earvigs are insensitive (Ncleod and Chant, 1952). 10 readings were taken at five minute intervals. The Insects were redistributed after each reading by tapping sharply on the chamber, Half

way through each experiment, each chamber was rotated through 1800 to lessen

the influence of any external st4m 11i1 (Kennedy, 1937). The following range of four relative humidities () was tested with adult male and female earwiga

at 20° ± 3°C. 10 20 30 140

30 40 50 60 - 251g.

506070 eo 60 70 80 90 10 20 80 90

In addition, adult earwigs were tested with the choices of 100/20 and

l00/0 0 R.H. in the chambers under various conditions.

Results

(a)Response to humidity ranges. Table BI summarises the response of male and fcniA earwiga to a range of relative humidities. The figures represent actual position records of the number of earwigs In each senent of the chamber. Both sexes showed

a trend to ri-n in the drier range of humidity, showing that the earwigs could detect differences in humidity in the order of 10 %. The dry prefer-

ence was most marked wbi the range 10 20 80 90 humidity was offered,

giving a humiHty difference of about 60 $ in the chamber. (b)Responses to two huznid.ity choices only. Both male and female earwigs were tested with the choice of 100/50

and l00/0 $ R.H. to determine whether any difference existed between their humidity reactions. The reaction index (R) for each experiment was calculated

from the formula :

R = 100 (w - D) where W = no, position records on t1te moist N (100% R,H. side of the chamber.

D = no. records on the dry side.

N = Total no. observations.

Therefore, a positive R indicates a moist preference and a negative R value

indicates a dry preferelEe (Gunri and Corny, 1938).

Table a.mmiariaea the results. Adult earvigs showed a strong preference for the driest side of the chamber. Pna1es gave a slightly

- 255 -

i-I i-I i4 • rI 0 0 0 U) U) S S -• S • S o 0 0 0 Z z

pC 0 t-. rl C•.J GD 0 a 0 '-4S I j '-I' CJ• CJS

I 0i o GD c\I

tL S o r,, .-i c U) P4' . S S S S S o o z 0 Z z

,-t 0 0 C I\ S 4I 0

II I - 256 -

stronger reaction than males, but the differences were R?nIill • The intensity

of the dry reaction was greater when earwigs were given a choice of 100/20

R.H. than when given 10/O R.H. at 20 0 j 3°C. These experiments were done with earwigs in January 1973 and 1974., and a dry preference was ehoi at both these times

TABLE . Mean reaction indices (means of four experiments) for male and.

female earwlga at 20° ± 3°C., January 1973.

Male Total no• Female Total no. R.H. choice R position R position ______S.E. records SE. records

100/0 -51 15.4. 537 -.58 ± 15.5 456

100/20 -55 16.3 526 -68±18.3 18

Controls + 0.7 153 - 8.3 161 (Range + 17 (Range -18 to -23) to + 8)

Those results agree closely with those of Perttunen (1952) wIio found a dry preference among earwigs from a laboratory culture when tested in the suDnner (August). However, van Heerdt (1946) found that well-fed, undessi- cated earwiga showed no humidity preference, but when dessicatod a strong moist preference was shown. Moreover, Perttunen (. found a preference for the moist aide of the alternative chamber when earwigs were tested in January. He explains these results by considering the change In the earwigs' habits.

During the sur, most Mult earwigs remM above ground but in autuini, they enter the soil to hibernate and lay eggs; the humidity of the soil is high, thus accounting for the change iii preferred humidity from dry - 257 -

to moist. However, Perttunen (.. .) stated that these results need. confirmation with earwigs taken directly for experiment from their burrOwS in the soil in winter.

In January, 1973, earid.ga were obtained from the soil of the Nursery Garden, Wye College and used for testing their humidity preference. The earwigs were kept in pots outdoors until needed.. Experiments wore carried out at laboratory tnperature (200 and In a refrigerator at 8° j 1 00. The results are shown in Table B3. The field earwigs showed a strong dry preference when tested. at 8°C., but this became much weaker when tested at 20°C. No preference was shown for the moist side of the chamber. Further experiments showed that both field. and. laboratory earwigs

gcve a moist reaction if previously dessicateci for 12 hours at 2500. over calcium chloride, as Perttunen (1952) and. van Heerd.t (i9z6) also found.. (R value of + 8]. j 13.0 obtained),

For comparison with the reactions given by mixed field adults hi

January 1973, adults from the laboratory culture were tested In Jinuary l97l. (Table BZf). Again a dry preference was shown, the reaction to 200

being greater than 50 % alternative humidities.

TABLE B3. The humidity preference of orficula adu3.ts removed from the

sol]. in J-rniaz'y, 1973 and tested at 200 and 8°C. (mean of four experiments).

RH. choice )lean reaction Index Total no. Temperature S.E. position records

10% -15 8.2 518 20° 3°C. 100/20 -69j12.0 515 8° j 1°C. Controls -6.8 (Range -31 to + 6) 214.7 - 258 -

T.BLE Blê.. Mean reaction imIioes of mixed laboratory &bilt earviga (mean

of six experiments per hiidity oboioe) at 200 j 300.

Total no. E4H. choice Mean R S.E. position reoozd.s

100/50 -56 , 7,5 9U

100/20 -64.±9.l 918

Oontrola -0.25 (Range -24. to + ic) 307

The experiments o Perttunen (1952) were done in the light, The effect of daylight upon the humidity reaction of laboratory earwigs was therefore investigated (Table B5). After an initial period of great activity after being placed In the cages, the earidgs became less active and were difficult to redistribute after readings, when the light intensity was from 50 - 100 ft. candles. Compared with the reaction given in dar1ess (Tables B4., B5), the mean reaction indices (mean of six experiments) was decreased.

TABLE B5. The effect of daylight (50 - 100 ft. candles) upon the humidity

response of adult earwigs (means of six experiments).

Total no. BJ. choice Mean R j S .E. position records

ioo/5o -35.3 ± 3.8 878

100/20 -48.7 8.8 901

Controls + 6.3 (Range + 22 to -7) 264.

Perttimen (1952) did not state the temperature used during his

experiments. Previous wo& (Table B3) with field earwiga had shown that — 259 —

removal frc a law temperature (ca. 8°C.) to a higi temperature (20°c.)

ciaed a iriarked. decrease in the intensity of the dry reaction. Laboratory

earwigs giving a strong dry reaction were placed outdoors in Jminr1ry 19714.

for one wec, and then tested in the alternative chbez' at 8° 1°C. aM

200 ± 3°C. (Table B6). ter each experiment, earwige were returned to

cages and placed outdoors. Mean air temperatures during this period (11th —

18th January, 19714.) were 10.7°C. -him, 5.2°C. min4i (Records fron Wye Meteorological Station).

TABLE B6. The effect of preconditioning laboratory earwigs at ].ow tempex'-

atures (5° — u°c.) upon their reaction to htmuid.ity at 8° and

20°C. (mean of four experiments).

Total no.

R.H. choice Mean R ± S,E. position Temperature records

00(1 iOo/5o 54± 5,2 844 J 'I

0011 100/20 -55 ± 8.7 817 -' Ide 100/50 +19 j 10,]. 618 20°C,

100/20 -95.7 598 20°C.

Controls + i (Range -15 669 to + ia)

Preconditioning at these fluctuating outside temperatures did not

affeot the dry response given at 8°C. (Table B6), but at 20°C., the wet

side of the chamber was preferred. when the choice of 100/50 % RJ. was

given, ami with 100/20 % RJ. the dry preference waa weak. Therefore, preconditioning at low temperatures tended to reduce the dry response when the earwiga were subsequently tested at a higher temperature. - 260 -

Discussion The results showed that adult earirigs of both sexes normally prefer the d..?ier of each pair of humidities. This dry preference is not unusual; for exauple, nymphs and adults of Locusta irdzratoria. (Kennedy, 1937), adults of Blatta pr1entali (Gunn end Coaway, 1938), adults of six species of 4bo1ivm (Roth and Willis, 1950) antI nymphs of two species of grasshopper (Riegert, 1959) reacted similarly. van Heerdt (194.6) showed that the optimum conditions for the survival

of Forfiiila auricularia adults are between 75 and 90 % R.H. Thus, the

low humidity preferred by the earwige is not optimal for survival. Kennedy

(1937) found that the low humidities preferred by adult locusts were not

optimal for deve1oent or breeding. Behura (1956) recorded that adult

earwiga avoided soil which was excessively moist. As a result, he found

that south-west facing slope a yie]ded large numbers of oarwigs because the

natural dr4iiiige of the soil provided favourable conditions for breeding.

Excessive moisture will damage eggs of the earwig (Burr, 1939) and reduce

the survival of adult oerwigs over-wintering In the soil (Crumb et al 194.1).

The earwig is strong]y photonegative (Pox-Wilson, 1942) and thi

reacts more quickly to all stimulii when left In darkness (Burr, 1939). The

effect of ].ight In reducing the intensity of the humidity reaction (Thble B5)

was, therefore, expected. Perttunen (1952) conducted his experiinits in daylight, which probably reduced the activity of his insects and caused a decreased hnrifdity reaction. van Heerd.t (1946) stated that the humidity to 'which earwigs had been previously subjected was important in determining their humidity reactions.

However, Perttunen (1952) obtained a strong dry prefererxe with adult earwigs kept previously in dry and moist conditions during the ainner. In the present woxc, the Insects were always kept in saturated. air for at least an — 261

hour before each experiment. Normally, preconditioning at high humidities subsequently causes insects, for exemple the huinen louse IedICULUS. to avoid low humidities (wigg].esworth, 1941), but laboratory earwiga gave a fairly constant dry reaction even after an hour of preconditioning at 100

R.H.

However, the pre sent work has shown that temperature preconditionitig has a strong effect upon the humidity reaction (Table B6). i!ter conditioning at a mean temperature of 8°C. and 100 0 R.H. and then giving the earwigs a choice 9f l00J 0 0 ILL at 200 ±3°C., they chose the moist side of the chainbei

The variation in R.H. between solutions of NaoH prepared for use at 20°C. but also used at 8°C. is very small (Nadge, 1961), therefore, the humidity in the chambers at 20° and. 8°C. varied only s].ight:1y. However the saturation deficit of the air increases with increase in temperature

(Table B?) (PenmAn, 1955) and it is possible that the eaxwigs xnit respond to changes in saturation deficiency rather thai R.H. Cloudsley'-Thompson (1956) found that woodlice responded to the saturation deficiency of the air rather than RH. and correlated this observation with the fact that woodlioe lacked an epicuticular wax layer w1, therefore, their rate of water-loss was proportional to the saturation deficiency of the air. However, insects auth as earwigs possess an epicuticular wax layer end their vat er_loss during short exposure periods is negligible below 35°C., regardless of the saturation deficiency of the atmosphere (Clouds1ey-mcmpson, 1960). Platt, Collins and litherspocci (1957) foumd that the response of edult boDho].es quadrimaculatus Say to R.H. was independent of temperature; thesame R.H.(70 $) waspreferredatbothl5° and 32°C. P1att.etal(l. .) conclIed. that the mosquitoes were sensitive only to R.H. and not saturation deficit, which increases with an increase in temperature.

-262-

T.ABLE B?. Values fox' the saturation deficits (nun. Hg.) (from Pelmai., 1955) at 8° d 20°C.

air saturation deficit (nmi. Hg.) at Temperature (°c.) 20$ R.H. 50 R.H.

8°C. 653 407 20°C. ]4.014. 8.78

savoIy (1934) observed that the spliler Zilla-x-notata went consistently to the moister emi of a box kept at 500., but to the drier side when the temperature was 20°C. or more. This appears to be due to a real reversal of

direction of the humidity reaction, depdent upon temperature (Gunn

Cosway, 1938), since spiders possess en epioutloiilar wax layer and do not, therefore, lose moisture at a rate proportional to the saturation deficiency of the air.

In still air, the rate of diffusion of water vapour increases as the

temperature increases (wlgglesworth, 1939). Therefore, at a given saturation deficiency, evaporation is greater at hia temperatures than at low (wiggles-

worth, ]. This may explain why the R.H. preference of adult earwigs chgod. on removal from 8° to 20°C, The preference then shown for the moist

(lao $ R.H.) side of the chamber may have reduced the evaporation rate which

was increased by the sudden rise in temperature, although total watex'-loss was probably negligible in these shorb-term experiments.

Since Perttmen (1952) did. riot state his experimental temperatures, the moist preferoe which he observed. may have been due in part to a

temperature-linked. response. - 263 -

Mechanisms of the Relative Humidity response in adult earwigs

The behavioural mechaz1-ng which lead to humidity responses have been analysed for several insects, including Mvrzha-l8-guttata (Pulliainen, l961.), sitoi1us granariu. (Barlow and Perttunen, 1966), Orvzaeohilus sur1namensi

(Arbogast and Carthon, 1971) and Rhtzoertba doniinioa (Perttunen, 1973), but work upon the mechanism of the humidity response of the earwig has not previously been reported. These mechanisms were ana),ysed in terms of simple miin1 behaviour iii the present study.

Methods 10 adult earwigs were placed in containers lined with moist filter paper and kept in darkness for one hour before starting each experiment. The alternative chamber used has been previously described. Relative

Humidities were obtained, by using dilutions of NaoH (Hedge, 1961) aM distilled. water used to obtain 100 % RH. All experiments were carried out with choices of 100/30 % RH. at 20° ± 300., and in darkness. Observations were made by a red light to which earwigs are insensitive (Mcleod and Chant, 1952). Single earwigs were introduced through a small hole in the centre of the lid.

after the humiiiity in the chamber had stabilised, and the insectta course

was followed for 10 minutes. The track was obtained. by marking on a paper the same size as the arena (Barlow and Perttmen, 1966) with a fibretip pen. 10 male earwigs, yielding a total of 1,791. cm. of track were tested., aud

32 fsmale earwigs, yielding a total of 2,365 cm. of track. This was consi-

dered sufficient for analysis of the response mechanism. Arbogast and

Carthon (1971) used 1,310.5 cm. of track in their analysis of Dzaophilw

sujnsmensis larvae. Tracks were also obtained. of six indjvjdus1 in

control chambers (i.e. where the R.H. was 100 $ throughout) which gave a further 1,3141 cm. of track. - 264 -

In analysing the tracks, the following cr1. tens were determined :

i) Number of turns at the boundary. An area extending 10 (found by Relative Humidity measurement using Cobalt thiocyanate paper (Solomon, 1957)) on either side of the line dividing the moist and dry sides of the cbamber,was considered the boundary zone between the two hn1iitiea.

If an earwig entered the zone from the drier side and then turned so as to re-enter the drier side, a turn was recorded for the dry aide. Thrna

were recorded for the moist side in a si ynI 1 ar ''ner,

ii)The distance travelled by individual earwigs in 10 minutes was found. from the track record using a map measure. iii)The total time inactive. Any time exceeding 10 seconds during which an earwig showed. no forward movement was considered an inactive period, whether or not the insect showed some other foim of movement, such as climbing. The inactive time and. total time spent in dry, wet and

boundary zones was recorded.

iv)The average speed (cm. per second) was calculated by dividing the distance travelled on wet and dry sides of the chamber by the active

time (in seconds).

v) The number of turns inside each segment of the chamber, involving at least a 90° change of direction and not caused by the walls of the chamber, were counted for wet end dry areas.

Results and Discussion

All individuals were active when first placed in the chamber, but

later their activity decreased, althoui a few individuals remained active

throughout the 10-minute period. During Inactive periods, earwigs frequently

tried to climb the chamber wall, but ixost of the inactive time was spent in

cleaning movements. Activity consisted mMr'ly of movement along the pen..

Fig. Bi

1000/. R.H. - 266 -

meter, but occasiom1ly an earwig would move about the middle of the

øhamber.

Pig. Bi shows a typical 10-minute track record. Table B8 shows the

analysis of all tracks. Fnale earwigs were more aot:Eve than males, giving a greater mean distance travelled in 10 minutes, and were inactive for

shorter periods, but the differences were not significant. The large

standard errors for mean distances travelled by both sexes show the wide range of response given by different individuals in the chamber. Turns at the boundary were more frequent when moving from the drier

to the moister side t]iau vice versa (Table Be), in both sexes. The diffex- enoes were sigrrifjcaxit ( p o.00i) indicating that high (ico R.H.) 1nmidi-

ties were avoided.

Most earwigs moved in a U-turn through 1800 and did. not stop at the boundary, although sometimes the insect walked some distance along the

boundary before turning back to the dry side. This reaction was definitely

a directed, i.e tactic, reaction ('raenke]. and Gunn, 1961), but was difficult to classify. Perttmen (1973) investigated the hiimliiity reactions of Rhizopertha dominica . (coleoptera : Bostrychi.dae). He found an avoidance

reaction at the dry/moist chamber boundary, but In this case the beetles made slight lateral turns to left and right as the humidity boundary was

approached. Hence, Perttunen (1973) attributes this reaction as a klinotaxis. In this atndy, earwigs were not seen to successively compare tho humidity

by nal1 lateral turns. However, WigLesworth (1939) stated that kil-notaxis may also Involve movements of the whole body so that stiiml'tion is compared

successively on two sides. Earwigs in the experiments behExv'ed as if there was an invisible barrier between dry and moist sides of the chamber, turning back to the dry side either on the midline itself or a short distance before it, and only exceptionally entering the molat side. If the reaction involved - 267 -

TVBLE B8, Analysis of the behaviour of 1. euricularia adults in the

alternative R,H. chamber1.

Male Pna1e Controls (3m., 3f.)

No. insects 10 12 6

Tot1tack 1,794. 2,365 1,341 -

Mean distance l79.4Oj 197.05j 223.7± moved (cm.) ±,8.E. 78.3 9Z79 68.75 D Jj, ***5.20 2.49 ***4,83 ± 3.13 0,3 Mean no. V turns at boundary V 0,70 0.82 0.58+1.06 0,5 D Mean no. 1.60±1.51] 2.00±1.54 1 3!80±1!941 random turns V 1 50 1,06 225 2q26 J 3.30 3,oij D 3,28 j 1.97 1.51 119 300 j 2.38 Mean time inactive V 138 ± 2,17 1,86 j 1.72 2,83 ± 2 0Z1. (minutes) By 053 0.93. 0,35 ± 0,48 0.50 0.81 D 7,55 1.05 6.89 ± 3,24 1..41 2,42 Mean time apentin V 2408 .j 1.07 2,71 ± 3,20 5.19 j 2.41

D 0,81 ± 0,4.9 0,65 . 0.29 1.56 1.19 V 1.C2±0.0 1,09±0.46 1,03±0.50

D represents the drier si4e (30% RH.) and V the moist side (100% R.H.) of the chamber. By = Boundary. Bracketed means or means underscored by the same line are not eigrift- cantly different (i'> 0.05).

(Ml. p=o,00i). - 268 -

in this process is tioughtof as successive oompariaona of humidity in time by the whole body of F. auricularia then the mechanism concerned is probably a klinotactio one. In the controls (without any humidity gradient), retreats from the boundary were very rare (Table B8) and the distances travelled, times inactive and speed of locomotion in the two halves of the chamber were very similar. Mean speeds (czn./aec.) were higher in the controls than when alternate humidities were used, probably because of the unifozn high

(icc % R.H.) throughout the chamber. Eantigs made a similar munber of random turns within both dry and moist eenents of the chamber; the differences were not sigsificant for both sexes. Therefore, I '*I-'esia (Praenkel and (hum, i96i) was probably not involved in the reaction to Relative Humidity. In male earwigs a greater part of the inactive time was spent on the drier side (Table B8) and in both sexes the speed of movement was greater in the moist side. Therefore, or+ ho eI nesis (wigglesworth, 1939) involving viationin both activity and speed was involved in the earwigs' humidity responses.

Experiments to find the location of the bygroreceptors were not carried out. However, We3rrauoh (1929) stated that the chief site of humidity detection was the ventral abdoTnin1 L surface in Forficu.a. while van Heerdt

(19z6) and Perttunen (1952) found by antennectony that the antemne were not used to detect RH, van Heerdt (i%6) showed that the remova]. of the inaxillazy paips abolished the hi'm{&ty response. In this study earirlga often turned immediately they crossed the d-wet boundary, when only the heed was in the region of high hu midity. Therefore, the R.H. sensors postulated by Weyrauch (1929) are probably incorrect. In the alternative chamber the earwigs spent most of their inactive time clesm-I-ng the ens]. ceroii and ventral abdo,nI 1 surface with their bind legs. The curvatne - 269 -

of the body daring this prooess suggests that an area on the ventral abdolnl?lsil surface is responding to the huTniM ty be].ov. Thus, the mMri factors involved In the humidity response of Porficla are a r11notactio reaction at the boundaiy of high and low R.H., causing the high R.L to be avoided, and an ortholctnetic reaction In which more time is spent on the dry side, coupled with a reduced speed of movement. - 270 -

AI?fNJJ C

Sampling inethod for predators of the damson-hop aphid,

Phorodon huma1 i (Schrsnk)

During the study of earwig abundance using cardboard traps, it was

found that the main groups of other aphid predators, as for awple antbo-

corids, ooccinel]ida, occurred in the traps, sometimes in large numbers. The effectiveness of earwig predation upon the hop aphid was being studied,

ar4 since a predator cannot be considered without incl uding its importance in relation to other types of predator, numbers and types of these predators

were recorded from traps during summer 1973. Leaf sampling was also carried out. Three leaves per hop plant were exandned, at 6, 14. and 2 feet front the ground. Leaves were chosen at random and the grade of hop aphids and predator numbers noted.

The two sampling methods differed in the numbers of predators, including earwigs, recorded.. The two methods were compared and an attampt made

to explain fluctuations in predator numbers and to correlate these numbers with aphid. abundance on untreated and insecticide-treated hops. Two areas

were studied : Silks Garden and Thirseiy Garden, Wys College.

Samplin methods

(a) Corrugated cardboard baths.

Bands were wrapped arouM the hop bine approximately 2 feet (0.6 si.) above soil level. Many earwiga were caught sheltering in the ba. Other predators were also found, but their numbers fluctuated over the su.

The bands were used by these predators for ecdysis, pupation, or as a shelter when aphids were scaroe. - 27]. -

(b) Leaf samplesa Earwigs were not found by the 3-leaf samp].i.ng method. The earwig, being a noctuna]. insect, seeks shelter by day. Thus, none were found by leaf examination, although earwigs were seen at right on the leaf under- sides feeding on hop aphids. As aphid numbers increased, large numbers of other predators, especially anthocorid.s, were found on the leaves.

Silks Ua Garden Predators were sampled by the 3-leaf method and from trap bands in two plots : (a) An area of hops, var. Cobba, which received two dimefox applications on June 26th and July 20th as a soil drench to control hop aphids. (b) n area of hops, var, Early Bird, which received several feller applications of supride (an organophosphorous aphicide) a, in addition, two dixnefox soil drenches. Table Cl shows the monthly total numbers of predators (excluding earwigs) found in the Cobbe plot on 17 sampling occasions. Alate hop aphids were first reoorrded on 25th May and apterae were present in leaf samples taken on 28th May. Numbers of aphids continued to rise until June 27th when the dimefox became effective and then decreased gradually. The second application of d.imef ox on July 17th decreased aphids to less than one per leaf by early August, aided by the action of predators which reached a peak during July. Fig. Cl shows the rise in munbers of predators, other than earwigs, from leaf samples. The peak of predator numbers on the leaves occurred approximately three weeks after aphid numbers reached their maximum. This indicates a partial lack of synchrony between the hop aphid and its predators, which is normal since most entomophagous insects act as delayed density depent mortality factors (Var].ey, 1953; Hughes, 1963). me

- 272 -

E rIO 00.- l NN N N N' O\ 0 '-. .-

S __•% - P1 P 00.- - '-.0 LC \ N rl W 0 I-I'-.

0r0 r4r1 I i-IN

__ -.- -. __% 00 riO OiN LC0 NW .-. ' '.0'-

40 I-IP

I ri1- 00 C'Jr-I NN 4-t - .4o - ..D LC' O ri o'o o N

00%__ 00- 'DN. 00.- 00.- WC'J

0 I '-I ri ' -., % __ 00 04 .4a NO 00 rII4' I I ri ri ri .1-I -.. . 0 0 0 t)

I(0 I Ir 1' I I-I I 273 -

peak in predator numbers from bands was reached about five weeks after the peak in aphid numbers. The data show that predato:rs inc"eased in late June to early July, but their prey became exhausted owing both to predation and the effect of diinefox. Numbers of predators on leaves then greatly decreased while in the bands numbers continued to increase, probably because m predators left the leaves and. sheltered in trap banda. Within two weeks their numbers fell as adult predators dispersed from the hop garden.

Earwigs, Forficula a.uriculeria L. were the only predator present in any numbers in the hop garden when hop aphids arrived at the end of May.

Mobile predators such as .Aiithocox'id ap. were slow to arrive, their numbers starting to increase in early July. Table (2 shows the numbers of predators from band end leaf samples in the Early Bird plot of hops. Aphid populations did not increase after 11th June owing to frequent foliar applications of supracide. Aphid numbers rose briefly in late June with further immigration of iriigrantea alatae, but the application of dimefox on June 26th combined with the effect of supracide sprays to reduce this peak. Pew predators were found in this plot throughout the summer, owing to the lack of aphids. Earwigs were the most abundent predator throughout the season; anthocorids were most coimou of the other predators.

erv Garden

Trap bamis and leaf samples were taken from completely untreated and treated rows of hops in two areas :

(a) n area at the 1. edge of the garden, near the bottom of a slope

r?mnir'€ V.. and N. (b)An area at the E. edge, near the top of the slope. - 274 -

TABLE C2. Total numbers of predators from 30 traps ed 90 leaves, over 11.4 samplixg dates. Early Bird. plot, 1973.

Species Trap bands Leaves

Eandga 5,131 0 Anthocoridae 19 2 Coocinel]idae 1 0 Syrphidae 0 2 Hemerobidae 2 0 chrysopidae 1 1

Tachvorus ap. 14. 1 Parasite 'mummies' 0 1 Cecidoeyidae 0 0 Others 7 1

The numbers of predators found in 10 traps from untreated. ath treated hops in areas (a) arid. (b) were combined in the results, as were the leaf samples. Table 03 shows the total number of predators from 20 traps and. 60 loaves in the untreated area. Aphid numbers increased from the arrival of nmigrantes alatae on May 28th (Pig. 13) until early July. Aphids were classified on a scale 1 - 6, as previously used. GO leaves were examined in this way am5. the mean grade per leaf was oa3.eulated for each sampling date. By mid-July the hops were semi-defoliated because of the huge aphid population. )lain-.bine leaves re!nMir4g became cz'a&ed, dry aM coated with aphid exuviae and honeydew. Simultaneously, the numbers of aphids decreased as their food supply became exhausted. By the eM of July there was an average of less than one aphid per leaf on untreated hops (see PIg. 9). Later (early Septnber) there was some aphid resurgence, mainly on new

TOTAL PRETORS C 10's)

MEAN NO. APHIDS PER LEAF Fig. C2

w 0

4 6 TOTAL PREDATORS ClOb

Ca A w

MEAN NO. APHIDS PER LEAF - 276 -

0 It\ .__% -... C3O-' WO C' cJ I -'

cg o UO cJO WO 00.- .-. c •- c'j ' . II •

P1 _ o 00 NO c'JO 00

I l) .- '-.-

D . ' 00 00 M)cJ 00 NO c'Jc'JU-'.--, S MI

o 1 00'-' * '-L\ 00 UH 0

i-40 00 I .-. -

0 I q, I

F_I 03 - 00i-. 1 i8H-I'--- ci H o iI o I o I

! ' r-IO LC\O NO ao - LC\-' -- pC.- - w U) H lI I I 0:11

U) - 277 -

].aterai. growth which appeared after the defoliat±on of nmln bine leaves.

The first predators were recorded In leaf samples in early June, about two

weeks after the arrival of migrantes alatee on hops In the Nursery Gardi.

They continued to increase with the increase of aphids from June to early

July. Pig. c2 shows that the synchronisation (van 1966; McDonald

ani Cheng, 1970) of predators with aphid population developnent was closer in the Nursery Garden than in Si)ks Garden. A peak in predators (from leaf

samples) was recorded about the same time as the peak of aphid numbers. The total number of predators other than earwigs was higher in the Nursery than Silks Garden (Tables Cl, 03). The Nursery Garden was surrounded by rough woodland at the W. edge,

with a woodl near to and along the length of the N. edge. Bomboach (1966) has shown that numbers of the coion predators, such as syrphids and antho-

corids, were highest In woodland areas in early spring. Later, predators increased in cultivated areas near woodland as aphid populations on the

crop Increased. Zeleny and Urdy (1969) concluded that greater numbers of hop-aphid predators were found In hop gardens which were close to trees, bushes and herbaceous vegetation. Therefore, it seems probable that the proxImity of belts of woodland to the Nursery Garden, together with the

large aphid population on untreated hops, were responsible for greater numbers

of mobile predators. Trap catches of predators increased slowly through June, then changed

from 115 (July 10th) to 9iO per 20 traps (July 214.th). This sudden peak

ocourred two weeks after the decline in numbers of aphids (Pig. (2). A s1 1 ' peek was obtained from the Cobbe plot, Silks Garden, and was

caused by predators, especially anthocorida, sheltering in the bands when aphids were scarce. Predator numbers remained very high in the bands for

two weeks and then fell quickly, because predators dispersed from the hop - 278 -

garden. A inaYini'm of about 4.7 mobile predators (excluding earvigs) per trap iras recorded. Earwl.ga, Forficula auricularia L. and .Antb000rid app. were the moat ocimon predators in the Nursery Garden. Other tpea (cocci-

nellfds, syrphids) were also oonnon and were more oomnon here than in Silks

Gardai. A species of Amhidoletes (Diptera: Cecidridae) was found in leaf samples from the Nursery but not from Silks Garden. The only predators

present when the first influx of alate hop aphids occurred. were earwigs and.

rachvDoz app. (Coleoptera: StaphylinicIae). Species of Tachvorus have

been reported preying on aphida of strawberries (Dicker, 194 1i.) and lettuce root aphid. (Dunn, 1960). Table Cl4. gives the total numbers of predators from bath and, leaf samples from insecticide treated hops. Those hops had one application of

the syetanio organophosphoroua aphicide dimefox applied as a soil drench on June 11th.

Aphid numbers reached a mrjniii. of about 40 per leaf in early June, thai decreased rapidly as the dimefox took effect (Fig. C3). The aphid population fluctuated slightly over July but ranained less than one aphid

per leaf until harvest. Pow predators were recorded from leaf samples

because of the early decline in aphid numbers. However, most of the common

species, including earwigs, were present. Trap bath catches rn4ied on

a par with leaf samples until the end of June, when they increased.. Again, most of this increase was probably due to predators sheltering in the baths

because aphid numbers were so low. The sudden peek in trap bath catches

on July 31st (Fig. C3) was unrelated to any resurgence of the aphid popu-

lation. Possibly, mobile predators 'spilled. over' at this time from the adjo1n4n untreated hop rows on which large aphid populations had previouSly developed.

- 279 -

TLBLS C4.. Total numbers of predators from 20 trap bands and 60 leaves,

in treated rows of hops on 16 sanpling dates. Tharsery Garden,

1973. No. of predators fr Species of predator Bands Leaves

Earwigs, Porfiai].a auricularia 1,658 0

Cocoinelliclae 37 6

Syrphidae if 34

.Anth000ridae 2 7

Neuroptera:

Henerobidae 16 0

Chrysopidae 8 8

Paohvpox ap. 36 0

Parasite 'mummies' 0 0

Cecidoiiidae 0 0

Others 22 0

Discussion

Numbers of hop aphids on each leaf were classified by a grading

systn in the field. Similar systems were used by Ripper (191i4) and Greavee

and Venablea (1950) for cabbage aphid, and by Banks (1954.) for bean aphid. The grading systi enabled a large rnnnber of leaves (at least 60 per s&-

ling date) to be emnired, and also e1 ml ated the necessity of renving

large numbers of leaves. Numbers of apterous P. humuli on leaves of un-

treated hops increased greatly from early June onwards.

It was not possible to make a visual count of the total ntnnber of

aphids on each leaf. Even had such counts been made, they would probably

have been inaccurate. Church end Strickland (1954) found that when there - 2& -

were more than 200 aphids present, visual counts tended to under-estimate by about half the actual number, and more with heavily infested plants.

Since accurate aphid numbers were not essential in this study, the

grading systam was used in preference to methodi involving renoval of leaves

for counts of aphids, since it enabled a greater number of samples to be

counted during the time available. In the field, the syatam of grading

proved to be quick and reliable. All records were taken by the same indi-

vid.ual to reduce possible errors, although Banks 195li.) found no significant

variation between the classification of aphids de by separate observers.

Trials in the laboratory ahowel that aphid numbers on a hop leaf were graded

on the scale 1 - 6 with a T-hmm of 10 % error. Moreover, the large numbers

of leaves which wore graded in the field enabled a representative estimato

of the maan numbers of aphids per leaf to be made.

Leaf samples may be considered to be "dual purpose" samples, since

both aphids and. predators were counted during sampling. Lord. (1968) has

suggested that the most important criterion for such "dual purpose" samples

is "that the sampling unit be one oomnOn to both predator and prey species

and encompass representative proportiox of the habitat of each". Sampling

on hop leaves did not detect all aphid predators. Th. coumon predators

(anthocorids, lacewinga etc.) 'were found, but nocturnal predators, such as

earwiga, (Forficu].a auricularia. L.), harvesthien and various Coleoptera

tTachvDorua apr.) were not. Moreover, it is probable that leaf sampling

for Inthocoril app. was not efficient. Anth000rida occur on ta ani

stinga of the hop and may often r1 inactive there for long periods

(Elton, 1927). The immature stages of brown (Henerobid ap.) am green

lacewings (Cbrvsota ap.) were rare in leaf samples but ctr from trap

bands. Again, these active predators search all areas of the hop bines and

may be missed by Just examining leaves. - 281 -

Trap bands were found to be vexy ueful in detecting predators In conjunction with leaf samples. All those types of predators, especially earwigs which were not found during leaf sampling, were collected in the bathe. The bands, therefore, enb1ei the whole spectrum of hop aphid predators to be identified. They provided a place of shelter for many species, being used by anthocorids for ecdysis, syrphids and coccineUlda for pupation, and by earwigs and immature lacewing larvae for shelter. Mobile predators occurred in trap bands for many weeks after din- appearing from the leaves and were often found in baths when aphid numbers were low. Bands probably gave some protection to predators from foliar sprays and soil drenches of insecticide. - 282 -

Prey choice by the European earwig

Laboratory feeding tests showed that F. iricu1ari Could be reared

from birth solely on a diet of using aphid instars I - III. However, it was not 1aown how efficient earLy earwig instars were at

capturing IV ins tar and adult aphids, or how effective az defence reaction

by P. huvu.li would be. Encounters between predator and aphid are mIn1y determined, by their relative sizes (Dixon, 1973). Several workers have

studied predator/prey reactions, using coccinel].ida (Dixon, 1958, 1959, 1970; Banks, 1957), chrysopida (Pie sobner, 1950), and other small predators.

Generally, young predators only killed youmg aphids. Predators which do this allow mature aphids to continue reproduction and so reduce their regu- latory effect upon the aphid populat ion (Dixon, 1970). Earwigs are relatively large and. voracious predators compared to coccinel].ids and ebrysopids (Asgari, 1966). The interactions of different earwig and aphid inatara were studied in the laboratory to determine the efficiency of prey capture, defence reactions of P. htm"1i and choice of prey by earwigs.

1ateri.a1s and Methods Observations on the capture of prey by earwiga were made in perspex chambers with a central arena, used previously in feeding experiments. Experiments were made at a constant temperature of 16° ± 3°C. and a photoperiod of 15 hours. The 'day' fell between midnight and 9 a.m. This procedure enabled observations on the (nocturnal) earwigs to be made during daytime, by red light, to whioh they are insensitive. - 283 -

Earwigs were collected as da-o1d inatar I nymphs from the field on

25th April 19724., placed individually In glass tubes (6 x 2.5 om.) and fed with hop ap1-idi. Individuals were starved for 24. hours before each experi- nient. 20 of instars III, IV or adult were placed on a freshly

cut hop leaf in the arena end allowed to insert their stylets. An earwig was then introduced, into the arena and observations on each individua3. made for 15 mi.nutss with a binocular microscope. When an earwig touched an aphid, this behaviour was considered as an "encounter" (Dixon, 1959). The following

criteria were found :

i) Time spent active in the chamber.

ii)Time inactive.

iii)Total number of encounters in 15 minutes. iv)Outcome of each encounter.

v) Time taken to eat each prey. vi) Tota3. time taken handling and eating prey per 15 minutes.

The tI available for searching for prey was calculated by subtracting vi) from i). Percentage efficiency of each earwig mater in capturing prey

was calculated as : mean number of camtures mean number of encounters. If an aphid avoided an earwig, the method of avoidance was noted. Two

methods of avoidance were observed : (i) 'Wring' - a drop of oily ].icjuicl

appeared at the top of one, or usually both siphunculi, and the ome nearest

the point of contact siung over and touched the head of the earwig, where

it solidified rapidly, often on the mouthparts. 'Wrthg' may immebilise

a predator for a short time and allow the aphid to escape (Dixon, 1955).

(ii) SometImes an aphid withdrew its stylets from the leaf and walked out of

the earwig's path. This was called away". - 284. -

The experiments were done with earvigs of instar I, II, IV and adults; instar III nymphs were unfortwiately not available. Aphid instare

UI, IV and adult were used as prey to represent small, medium and large aphids (see Table 1)2), 20 aphids of an lnstar were used in these tests

In later experiments, 10 aphids of lusters III, IV and adult were p].aoed

simultaneously in the arena and the prey choice from a mixes aphid population

recorded.

Results and Discussion Table Dl sunmarises the results of the observation. First and

second instar earwigs were inefficient at catehing aphids any larger than instar III, but fourth lusters and adult earwigs were efficient predators

and caught over 80 % of' all aphids encountered. Inatars IV and female

earwigs wore more successful than males, Since all the adult earwigs were

taken from the field in February 1974., they were about one year old when tested, Beau (1932) found that luster IV nyiirphs wore more active thni

overwinterel male earwigs which usually die out by Nay (Behura, 1956). This may explain the lowered figures for the efficiency of prey capture by males.

The mean numbers of enoountera with aphids during 15 minutes was lowest In instar I and II earwigs and increased in IV instara and adults.

This may reflect an increase in efficiency in search for prey, for the mean active time and time available for searching was about the same in ci]. instora (Table Dl).

Table suznmarisea the relative weights and lengths of predator and aphid and Table D3 gives the ratio by which the earwig was larger than the aphid. F. auricularia increased in size and weight in each instar a this was associated with a decrease in the mean time taken to eat one prey.

Adult female earwigs ate aphids of all inatars most quick1y, while IV instars

285

43 - 0 N I-I

N i-I H' pr' ci 0 4 w

0 H' 0 r4 H H' I I 00 N g

42 a K 0 H • • S -. 0 I1 r1

H' 0 0o - I 431 r4 tH' r4 H t 8 0 0 S I-I

42 —* 0 rI N N '-4 • 1 -' v '.0 N $1 I csJ N '.0 • ) 0 Ci e i '. H' I 4'! '.0 H' H' N I H N -* K 0 43 . .-i o m '.0 C4 H'

.11 0I 0 r4 1w r4 S S S . .,. w• K\ C'4 H

'.0 0 0 i-I 0. I-I N • 0i it i-I • • I-I '.0 V csJ N N r-4 H I f-4 . K\ i-I 43 '.0 N • LA • s • - I 'o

: —* 'a csj N H' Lr% ,-4 LA co

—* CO 1-4 It' • S S N

0 0

r14$ 0 p4p.4.• •

- 286 -

were faster than males. However, even instar I earirigs ate their prey vnioh faate than other predators, e.g. ooccfziellids.

TABLE 1)2. The fresh weights and body-length of F. suricuj.aria and P. humuli. Earwig instars Aphid instars I II IV Male Pei1e III IV .Athilt

No. individuals used 34 10 10 10 10 ]4 14. 16

Mean weiit 2.37 4.20 16.71 43.00 54.10 0.08 0.15 0.21k. (mg) ± + ± ± ± ± ± 0.30 0.53 1.27 3.33 11.53 0.02 0,07 0.07 Mean body 4.50 5.97 11.04. ]4.90 15.30 0.94. 1.1.3 1.40 length ± ± ± ± ± ± ± 0.38 0.50 0.63 0,70 1.82 0.06 0.].1 0.09

Banks (1957) found that large IV instar Cocod.zeila.7-iunctpta larvae took about fair nthnites to consume an aphid of about the same size as an adult while an natar IV earwig took about half a mlinite (Table

Dl). Adult Anth000ris remoi took 13 l r'utea to eat a fii'st imetar DrenanoeiD1nm D].atanoides (sycamore aphid) (Dixon and RusseU, 1972).

TABLE D3. The ratio of body length (nun.) of predator and prey (from above

data).

Aphid Earwig instar inatar I II IV Male Pnale

III 4..8 : 1 6.4. : 1 11.7 : 1 15.9 : 1 1L3 : 1

IV 4.0:1 5.3:1 9.8:1 13.2:1 13,5:1 Adult 3.2:1 4,3:1 7.9:1 10.7:1 11.0:1 - 287 -

The percentage of encounters when the predator was waxed increased

with the size of the aphid. Adult aphids were most efficient at wr4g,

but only with earwig inatars I and U Larger earwigs were rarely success-

fully waxed (Table Dl), since the aphid prey was engulfed and quickly eaten,

Aphids rarely walked away from IV instar or adult earwigs without being caught.

has long, flexible siphunouli (Theobald, 1926). On most occasinna young earwigs were waxed when they attacked the aphid from behind, but sometimes the siphunculi flexed round and waxed an earwig which was

• attacIr g the aphid at the middle or head end. Dixi (1958) also notioed

this mobility of the siphunculi with the nettle aphid, ioroloDhium evansii

(meobalci). When waxed, I or II instar earwigs usually backed away from

the aphid end then spent a variable amount of time oleimi ng the oily wax

fran their mouthparls, using the forelimbs and mandiblee. In two casee, after suocesafully atta dng an adult aphid, instar I earwigs' mouthparts became stuck with the waxy secretion from their prey, but both individuals eventually cleaned thnselves

When an aphid of any instar waxed an earwig, or even if wax was secreted as the aphid was being eaten, other hop aphids in the area witMrew

their styleta from the leaf end moved off. Probably, this was a reaction

to en alarm pheromone in the siphuncular secretion, for example trans-B-

farnesens, which was identified as active for six species of aphid (Bowers, Nault, Webb and Dutlçy, 1972).

Dixon (1973) classified aphids within two min treixia in the evolu-

inn of their behaviour in relation to enanien : (i) Speoiee which depI upon their activity to avoid an approaohing enexi, by jumping off the leaf

or yllcliig away, e.g. sp1pmplatanoiIes (Schr.) - the sycamore aphid.

(2) Species which are generally inactive and form large compact colonies. - 2 -

These species have long, flexible siphunculi and are often efficient at wtrg a predator.

P. 1iu1i belongs to the second class of aphids. Aphids rarely wa3ked away from even the smallest earwigs (Table Dl), it1ou inatar I earwigs are still about 3.2 times as large as adult aphids (Table D3).

Most unsuccessful encounters were when the predator left a prey after apparently detecting it. This behaviour was highest in luster I end II earwigs, but about 5-10 of aphids were rejected even by later lusters. III luster aphids were rejected least by I and II luster earwigs, probably because the size ratio was greatest with the small aphids. When earwigs were placed in the srsma with 30 aphids, 10 of each luster III, IV end adult, the total number of encounters (five individuals recorded. for 75 minutes) increased. from luster I to a1ult earwigs (Table

D4.). Approximately equal mnnbers of nm1l and large aphids were encountered by all the earwigs tested.. Therefore, young earwigs do not 'choose' Rmaller

aphids, but they are most successful in their encounters with these aphids

and so mostly smell aphids are eaten. Bla rkin i (1967) observed the behaviour of individual first luster CocizieUa'-7-wnotata larvae and concinded that, although small aphids were captured most often, the larvae would attrpt to capture aphids of all sizes.

Only about 10 % of earwigs of lusters I and II were successful in

capturing adult L hunuli (Table 14). These teats may underestimate the hop aphids' capacity to escape since in the field hop aphids, especially apterous adults, readily drop off the leaf w'rien disturbed. This escape

mech1 n was not possible under the artificial conditions of the tests

and, therefore, adult aphids may have been captured more readily.

Instar IV and adult earwiga were very successful in capturing luster III and. IV aphids. They encountered. similar nbers of adult - 289 -

• I LL N 0

N • -* W

:; j

0 0 0 S p S I fl.

U.1 U.1 L( I bI . H - 290

but wore slightly lees aucceseThi in capturing then.

These results imlicate that under field oonditiona, young earirigs of instars I and II would probab] not be very successful in capturing apHts, except cim.11 P. bi1i. and adult aphids wauld be free to continue repro- ducing, However, other faotore effect the efficiency of earwig predation upon P. itCLi. such as the height to which young earwigs climb the hop binea. Earwig nymphs of meters I and II do not ueual],y climb actively and so probably do not contact higher up the bins. Nevertheless, they will eat some apl:iids on the lower hines and also aphids which have fallen to the ground. Older earwig nymphs appear in early or mid-June and these nymphs will eat aphids of any instai'.