BIOLOGY OF EUROPEAN EARWIG FORFICULL ATJRICtJL.ARIA. L. WIlE REFERENCE TO ] PR).ATORY ACTrnTi ON DAON-HOP APHID PEORON HUTtJLI (sciiax).. BY 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 distri- bution 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. 1f 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 -.6- 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