Effect of Combining Food and Sex Attractants on the Capture of Dacus oleae Flies'

Transcription

1 ENTOMOLOGI HELLENIC 5 (987): 7-33 Effect of Combining Food nd Sex ttrctnts on the Cpture of Dcus olee Flies' G. E. HNIOTKIS nd. VSSILIOU - WITE Institute of Biology, Ntionl Reserch Center «Democritos», P.O. Box 608,53 0 ghi Prskevi, ttiki, Greece BSTRCT Sex pheromonl compounds i.e. the most potent mle ttrctnts, nd mmoni, one of the most potent femle ttrctnts vilble tody for Dcus olee (Gmelin), were combined on the sme trp. This combintion resulted in n overll increse of femle cptures s compred to those of mmoni lone, but decrese of mle cptures s compred to those of pheromone lone. Devitions from this overll effect were observed during certin periods of the yer nd re cused by vrying environmentl nd biologicl fctors which influence insect response to pheromones. Explntions for these results bsed on recent findings concerning the pheromone system of D. olee re presented here. Introduction ttrctnts vilble tody for Dcus olee, effective under field conditions, include: I. Chemicl ttrctnts. ) Food ttrctnts. These include vrious mmoni - relesing compounds, such s queous mmoni solutions, mmonium slts (Bu 933), protein or yest hydrolystes (Orphnidis et l. 958), heterocyclic mines probbly responsible for protein ttrction (Stvrkis 970) nd the fruit voltiles, hexnol, octnl, nonnol nd nonnl (Guerin et l. 983). b) Sex ttrctnts. Femle D. olee flies relese sex pheromone which functions s potent longrnge mle ttrctnt (Hniotkis 98, Delrio et l. 983). This pheromone ws found to be mixture of the following substnces:,7-dioxspiro (5.5) undecne, -pinene, n-nonnl nd ethyl dodecnote t rtio of 3::0.3: (Mzomenos nd Hniotkis 98,985). The first substnce, which is the mjor component of the mixture (Bker et l. 980), hs lso been isolted from mle D. o- lee flies (Mzomenos nd Pomonis 983). Recent studies hve shown tht mle olive fruit flies respond only to the R-(-)- enntiomer of the mjor pheromone component to which they re ttrcted 'Received for publiction June from long distnces, while femles respond only to the S-(+)- enntiomer which functions s n rrestnt nd phrodisic (Hniotkis et l. 986 e). The sme studies hve shown tht femles nd probbly mles relese the mjor pheromone in its rcemic form. II. Visul ttrctnts. The colour yellow with mximum reflectnce between nm (Girolmi nd Cvlloro 973, Prokopy et l. 975, Delrio et l. 979) hs been found to be most ttrctive for D. olee. number of substnces which hve ttrcted D. olee flies in lbortory tests but not in the field hve lso been reported (Delrio 984). Much effort hs been mde during the lst decde towrds the development of n effective trp for D. olee which could be used for monitoring, control, or both. For this purpose ll types of ttrctnts showing field ctivity, nmely food, visul nd sex, were tested individully or in vrious combintions. recent review rticle covers dequtely these subjects (Delrio 984). For monitoring, stisfctory trpping systems re not vilble. Efficiency of trps used for this purpose depends on number of fctors, environmentl nd biologicl, the effects of which re not well known. Relible correltions therefore between trp ctches nd wild popultion densities or fruit infesttion, pplicble to different olive e- cosystems, cnnot be estblished for ny type of

2 8 ENTOMOLOGI HELLENIC Vol. 5. No. (June 987) trp. However, some ppers on such correltions hve been published (Kptos nd Fletcher 983 nd references cited therein). For direct control, there hve been severl ttempts to control the o- live fruit fly by mens of mss trpping. Brief reviews of the subject re included in Hniotkis et l. (986, 986b). In these ttempts vrious trp types bsed on one or more ttrctnts hve been used. It seems tht no definite decision hs been reched yet which is cceptble to ll scientists working in this field s to the best trp type nd ttrctnt or combintion of ttrctnts for this purpose. It ws the im of the present work to field test the sex nd food ttrctnts vilble tody individully nd in combintion under the sme conditions nd evlute the results for the purpose of selecting the best ttrctnt or combintion for use in mss trpping systems. Such n evlution hs not been reported previously. The visul ttrctnt ws intentionlly not included becuse, for the type of trps used here, it increses mnufcturing nd opertionl costs with only limited contribution to the totl trp ctch (Hniotkis 986) nd t trp densities required for mss trpping it my be detrimentl to the beneficil fun of the olive ecosystem (Neuenschwnder 98). Mterils nd Methods Studies of the reltive ttrctiveness of sex ttrctnt phcromones, mmoni - relesing sources nd combintion of the two were mde during 98 nd 983 in n olive orchrd with medium size trees of mixed vrieties t Prdissos, thens, Greece. Before initition of the min experiment, the effects of the combintion of the two ttctnts on the cptures of D. o- lee were exmined in preliminry test t the sme orchrd. In 98 the trps were sticky poster-bord rectngles (5 x 0cm) of drk yellow colour (Imperil, Vivechrom, thens, Greece) with mximum light reflectnce outside of the preference rnge of D. olee (Prokopy et l. 975) which nevertheless still ttrcts smll number of flies (Hniotkis 986). In 983 trps were sticky plywood rectngles of the sme dimensions but of nturl wood colour, neutrl s fr s D. olee ttrction is concerned (Hniotkis unpublished dt). These trps, when unbited, do not ctch ny flies. The complete blend of the sex pheromone of D. olee (Mzomenos nd Hniotkis 985), t the rtios mentioned bove, ws used t concentrtion of 50 mg/trp, dispensed from ml polyethylene vils (Mzomenos et l. 983). The mjor component of the pheromone blend,,7-dioxspiro (5.5) undecne, kindly supplied by Vioryl, Greece, ws in rcemic form. Pure enntiomers of the mjor pheromone were not vilble in mounts required for this type of test. mmonium bicrbonte slt (0 mg/trp) in polystyrene cups with perforted polyethylene lids ws used s the food ttrctnt during 983. mmonium bicrbonte ws selected becuse it is inexpensive, esy to hndle, nd redily releses mmoni under field conditions for long period, chrcteristics highly desirble for prcticl uses. n queous mmoni solution (5%) in polyethylene vils with perforted lids (5 ml/trp), which ws used during 98, ws replcée by bicrbonte slt becuse the residul ctivity of the mmoni solution is short nd this necessittes refilling of the vils, n opertion which rises the cost in prcticl pplictions. In preliminry experiments, smll number of trps ws plced t spcings of 40 m or more. In the remining experiments, there were rrngements of one trp in every other tree, i.e. pprox. 6 m prt. The ltter trp density ws chosen becuse previous experiments (Hniotkis 98) hd indicted tht it is the most suitble for mss trpping purposes. More specificlly, the proportionl recovery of relesed flies ws not ffected when trp densities were between one trp per two trees nd two trps per tree, but ws significntly lower when lower trp densities were used. Competition between trps, however, is expected to increse s the trp distnce decreses (Delrio et l. 983, Hniotkis 986b). Trps were checked once week nd replced when necessry so tht n dequte clen sticky surfce would be vilble for effective cpture of lnding insects t ll times. Dispensers were not replced in 98; in 983 they were replced once on June 30th. The ctive life of the dispensers used in these tests is expected to be t lest 4 months (Mzomenos et l. 983). The following experimentl designs were used: preliminry experiment 98 (Tble ) block design, experiments 98 (Tble ) block design, experiments 983 (Tble 3) completely rndomized design. The trps in the completely rndomized design were rotted t every check. Numbers of flies cptured on individul trps were subjected to - nlysis of vrince fter logrithmic trnsformtion (x=log(x+l)). Results nd Discussion Tble shows the numbers of D. olee mle nd femle flies cptured on yellow sticky trps bited with pheromone, queous mmoni solution, nd combintion of the two in the 98 experiments. In this experimentl design in which competition between trps ws limited, the combintion of mmoni nd pheromone drsticlly decresed cptures of mles (compred to pheromone lone) nd incresed cptures of femles (compred to mmoni lone). In other words, trps combining pheromone nd mmoni cught fewer mles thn pheromone lone, but more femles thn mmoni lone. The decrese of mle cptures in the combintion trps could be due to either interference of mmoni with pheromone ction, or to n

3 HNIOTKIS ND VSSILIOU-WITE: FOOD ND SEX TRPS FOR DCUS OLEE 9 increse of femle numbers in the vicinity of the trp in response to the S-(+)- enntiomer of the mjor pheromone (rrestnt). Such n increse hs ctully been observed (Hniotkis et l Zervs 987). The nturlly - produced pheromone of these femles would compete with the pheromone dispenser on the trp, thus reducing its effectiveness. negtive correltion of pheromone TBLE. Numbers of Dcus olee flies cptured per trp per week on yellow sticky trps bited with pheromone (Ph). queous mmoni solution 5% (), nd Ph+ dispensers. Mens of three replictes. Preliminry experiment. Prdissos. thens. 98. Men no. of flies cptured b> f Ph Ph + Dte mles femles mles femles mles femles Oct. 7 Oct b 3.0 c 6. b 44.3 c 38.7 d 63.0 d 7.0 c 67. e 94.7 f 8. f Source of vrition d.i. nlysis of Vi incc S.S. M.S. F-cle. F-rec. (p=0.05) Blocks Sex Tretments Dtes Tret, χ Sex Sex χ Dtes Tret, χ Dtes Tret, χ Dtes χ Sex Residul Totl ( 'Mens followed by sme letters re not significntly différent. Duncn's Multiple Rnge Test. p=0.05. TBLE. Numbers of Dcus olee flies cptured per trp per week on yellow sticky trps bited with pheromone (Ph), queous mmoni solution 5% (), nd Ph + dispensers. Prdissos. thens, 98. Dte Oct. 6 Nov. Nov. 0 Nov. 7 Nov. 4 Dec. 8 Dec. Dec. 30 mles Ph Men no. of flies cptured by* femles mles femles mles 7.7 b.7 b 6.0 b 0.8 b.3 b.5 be.8 b 3. c 8.7 c.8 c 8.5 c 5.0 c.5 c. c 0.5 be 5.7 d 7.0 d 7.4 d 9.3 d 3.7 c.8 b 0.5 be 43.8 c 47.3 e 34.7 e 6. d 8.5 d d 0.7 c Ph + femles 80.0 f 4.8 f 6.0 f 37. de 6.3 d 3.9 b 3.6 d 0.7 c Source of vrition Blocks Sex Tretments Dtes Tret, χ Sex Sex χ Dtes Tret, χ Dtes Tret, χ Dtes χ Sex Residul Totl d.i. 5 7 : nlysis of Vrince S.S. M.S. F-clc. F-rcq. (p=0.05) "For ech dte, men ctches of mle nd femle flies followed by the sme letter re not significntly different. Duncn's Multiple Rnge Test. p=0.05.

4 30 ENTOMOLOGI HELLENIC Vol. 5, No. (June 987) trp efficiency with insect popultion density hs lso been observed on certin occsions in D. o- Oe (Hniotkis unpublished dt). The increse of femle cptures in the combintion trps could lso be the result of femle popultion increse - round the pheromone sources. Trps with pheromones lone do not ctch femles becuse the femle rrestnt does not function s femle ttrctnt s well. The smll number of femles cught by these trps re ttrcted by their yellow colour. Insect popultion densities nd therefore trp ctches vry significntly with the dte of observtion. Tble shows the results for 98 nd Tble 3 for 983. In generl the results of Tbles nd 3 gree with those of Tble. However, if we exmine more closely Tble 3 in prticulr, which covers the entire period of the yer during which the in- TBLE 3. Numbers of Dcus olee flies cptured per trp per week on nturl color plywood sticky trps bited with pheromone (Ph), mmonium bicrbonte slt (), nd Ph+ dispensers. Mens of 6 replictes, Prdissos. thens Dte Mr. 9 pr. 5 pr. 4 pr. 9 pr. 6 My 3 My My 6 My 3 June 5 June 30 July 7 July 4 July July 8 ug. 4 ug. ug. 8 ug. 4 ug. 3 Sep. 8 Sep.5 Sep. Sep.9 Oct. 6 Oct. 3 Oct. 0 Oct. 7 Nov. 3 Nov. 0 Nov. 6 mles I'll femles 0.5 h. b 0.8 b 0. b 0. b 0. b e 0. b 0. b 0.5 b.8 b.0 b. b. b 0.7 b 0. b 0.8 b 0. Men no. of flieset iptured b) mles 0.8 b 3.8 c 9.9 c 0.9 c 4.5 c 3. c. c 0.3 c 0. c 0. c c.3 c.3 c 0.7 c 0.5 c.0 c 0. b.8 c. c.8 c 4.8 c 3.0 c 4. c c.8. b femles 0.5 b d.7 b. d. c.8 c.0 c. d 0. b 0. b 0.8 c 0. b 3.4 c 0.7 d 6.6 d 6. d.3 cd 6. d 3.7 c c. b mles 7.7 c 0.7 d 5.3 e 4. e e.9 c. d 0.9 d 0.7 d 0.3 c c 6.0 e 3.3 e. d.3 d.0 c.6 d.0 c 3.4 c 3.7 e 9.8 c 5. cd 8.8 e 8.3 e c 5.3 c 4.8 d.5 b Ph+ femles 7.5 c 4.5 e c.0 d 0.4 c 0. c.5 d 0.7 d. d 0.7 c.5 d.3.0 d.7 d 3.8 c.3 f 6.3 d 4.8 c 3.5 c.8 f c 4.8 c 6.7 e.7 c Source of vrition Replictes Sex Tretments Dtes Tret, χ Sex Sex χ Dtes Tret, χ Dtes Tret, χ Dtes χ Sex Residul Totl d.i. 5 I ( nlysis of Vrince S.S. M.S F-rec F-clc. (p=0.05) (Kl "For ech dte, men ctches of mle nd femle flies followed by the sme letter re not significntly different, Duncn's Multiple Rnge Test. p=0.05.

5 HNIOTKIS ND VSSILIOU-WITE: FOOD ND SEX TRPS FOR DCUS OLEE 3 TBLE 4. Men numbers of Dcus olee flies cptured per trp per week on sticky trps bited with pheromone (Ph). mmoni-relesing dispensers (), nd Ph+ for periods during which insect response to trps vries due to differences in environmentl or biologicl fctors (criticl fctors). No. of flies cptured by* Period Oct.6-Nov Nov. 8-Dec mles 77.6 d 3.4 Ph femles b mles 7.7 c. b femles 33. b 4. mles Ph + femles 35. b 40.8 b Criticl fctor* * Mr. 9-pr. 9, 983 pr. 0-My 6, 983 My 7-June 30, 983 July -July. 983 July-Oct. 3, 983 Oct. 4-Nov. 7, b c 0.4 d 0.3 e 0.0 c 0. c 0.4 e 0.6 d 3.9 be.5 c 0. b.6 b.9 d 3.5 be. c.0 d 0.0 c.4 b.5 d 3. c d 7.0 b.9 cd 0.6 e 5.5. b 5.7 b 3.5 c 5.4 b "For ny prticulr time period, mens followed by sme letter re not significntly different. Duncn's Multiple Rnge Test. p=0.05. ""Criticl fctor: = low tempertures. = full insect ctivity, 3 = sexul inctivity, 4 = reduced sex ctivity. sect is ctive, we cn mke the following observtions (summrized in Tble 4). With regrd to cpture of mles by mmoni, pheromone nd the combintion, the following periods cn be distinguished: ) The cold periods (Nov. 8 - Dec. 30, 98. Mr. 9 - pr. 9 nd Oct. 4 - Nov. 7, 983), during which mting - ctivity nd therefore insect response to pheromone ws restricted by low fternoon tempertures. mmoni s food ttrctnt is ttrctive throughout the dy. During these periods n dditive or slight synergistic effect of sex nd food ttrctnts ws observed in the combintion trps. The limited interference between sex (long-rnge ctivity) nd food (short-rnge ctivity) ttrctnts due to restricted pheromone effectiveness could be the reson for these results, b) The period of no sexul ctivity of the insect (My 7 - June 30, 983), which coincided with the lck of mture fruit in the orchrd. During this period mles do not respond to pheromones. s ws expected, the results - greed with those of the previous cse nd could be ttributed to the sme reson, c) The period of prtil sexul ctivity (July - July, 983), during which the results of the combintion of the two ttrctnts ppered but were not yet significnt. d) The period of insect reproductive ctivity (Oct. 6 - Nov. 7,98, pr. 0 - My 6 nd July - Oct ), when results greed with those of Tble. Differences in trp ctches between the vrious trps were not s pronounced s in Tble i", proööty crue ft; ote mcrirjstrf Cry cxmrpvrcrciim llowed in this experimentl design. periods of insect reproductive inctivity or reduced ctivity. Probbly femles, like mles, do not respond to pheromones during such periods. The effect of cool fternoons which ws observed in the cse of cpture of mles did not occur in the cse of femles. The fct tht femles responded to rrestnt pheromone throughout the dy s opposed to mle response to the sex pheromone during fternoon hours only cn very well explin this difference (Hniotkis et l. 986). Simultion models indicted tht combintion of sex nd food ttrctnts on the sme trp is the most efficient system of those tested here for mss trpping (Krndinos nd Hniotkis unpublished dt). This is understndble since in ddition to mles, lrge number of femles, i.e. the dmging sex, is lso removed. On the bsis of the - bove findings, it is likely tht trps using only the pheromonl enntiomer which functions s mle ttrctnt will ttrct more mles thn those bited with the rcemic mixture, since in the former cse competing femles will not ggregte in the - re of the trp. Such n ttrctnt my be more suitble for monitoring purposes. cknowledgment We would like to thnk Miss C. Siili, gronomist. nd E. Kpros, lb technicin, for technicl ssistnce, nd Drs. P. I. Kltsikis nd G.. Tsim for their help in the sttisticl nlysis of dt. With regrd to femles, the combintion of pheromone nd mmoni resulted in n increse of cpture of femles s compred to the cpture by mmoni trps throughout the yer, except in the References Bker, R., R. Herbert. P.E. Howse, O.T. Jones, W. Frnckc nd W. Rcith Identifiction nd synthesis of the mjor sex pheromone of the olive fly (Dcus olee).

6 3 ENTOMOLOGI HELLENIC Vol. 5, No. (June 987) J.C.S. Chem. D. 06:5-53. Bu. G Esperimenti del 93 con sostnze ttrttive per l mosc delle olive. nn. R. st. Sup. gr. Portici. Ser. 3,6: Delrio, G Biotechnicl methods for olive pest control. Proc. Internt. Joint Meeting, CEC/FO/IOBC on Integrted Control in Olive Groves. Pis, Itly, pril 3-6, 984, p Delrio, G., S. Ortu nd R. Prot Fttori che influenzno Γ ttrzione di Dcus olee Gmelin e Certìtis cpitt Wied. lle trppole chemio e cromotropiche. Redi 6:9-55. Delrio, G.,.P. Economopoulos. P.V. Economopoulos, G.E. Hniotkis nd R. Prot Comprtive studies on food, sex nd visul ttrctnts for the olive fruit fly. Proc. Internt. Symp. of CEC/IOBC on Fruit Flics of Economic Importnce. thens, Greece, Nov. 6-9, 98: Girolmi, V. nd R. Cvlloro Metodi cromotropiche per indgine di popolzione degli dulti di Dcus o- lee Gmel. Note ed ppunti Sper. Entomol. gr. Perugi 4: 3-9. Guerin. P.M., B. Ktsoynnos, G. Delrio, U. Remundnd E.F. Boiler Fruit fly electrontennogrm nd behvior responses to some generlly occurring fruit voltiles. Proc. Intern. Symp. of CEC/IOBCon Fruit Flics of Economic Importnce. thens, Greece. Nov :48-5. Hniotkis, G.E. 98. Field evlution of the nturl femle pheromone of Dcus olee (Gmelin). Envir. Entomol. 0(6): Hniotkis, G.E Effect of size, color, nd height of pheromone bited sticky trps on cptures of Dcus o- lee flies. Entomologi Hellenic 4:55-6. Hniotkis, G.E. 986b. Experiments towrd disrupting phcromonl communiction in Dcus olec. Proc. Intern. Conference of IOBC/WPRS on «Mting disruption: Behvior of moths nd molecules», Neustdt. W. Germny. 8- Sept. 986 (in press). Hniotkis. G.E.. M. Kozyrkis nd I. Hrdkis pplictions of pheromones for the control of the olive fruit fly. Proc. Intern. Conference on Integrted Plnt Protection. Budpest, Hungry, July 4-9, 983, 4:67-7. Hniotkis, G.E., M. Kozyrkis nd C. Bontsos Control of the olive fruit fly, Dcus olee Gmelin by mss trpping: Pilot scle fesibility study. Z. ngew. Entomol. 0: Hniotkis. G.E., M. Kozyrkis nd K. Bontsos. 986b. re - wide mngement of the olive fruit fly by feeding ttrctnts nd sex pheromones. Proc. nd Intern. Sympos. on Fruit Flies, Colymbri, Crete, Greece. 6- Sept. 986: Hniotkis. G.E.. W. Frncke, K. Mori, H. Redlich nd Y. Schurig. 986c. Sex specific ctivity of R-(-)- nd S-(+ )-,7-dioxspiro (5.5) undecne. the mjor pheromone of Dcus olee. J. Chem. Ecol. (6): Kptos. E.T. ndb.s. Fletcher Estblishment of e- conomic injury levels for olive infersttion by Dcus o- leein Corfu. Entomologi Hellenic : Mzomenos. B.E. nd G.E. Hniotkis. 98. multicomponent femle sex pheromone of Dcus olee (Gmelin). Isoltion nd biossy. J. Chem. Ecol. 7(): Mzomenos. B.E. ndg. J. Pomonis Mle olive fruit fly pheromone: Isoltion, identifiction nd lb biossys. Proc. Intern. Sympos. of CEC/IOBC on Fruit Flies of Economic Importnce. thens, Greece, Nov. 6-9, 98: Mzomenos, B.E. nd G.E. Hniotkis Mle olive fruit fly ttrction to the synthetic sex pheromone components in lbortory nd field tests. J. Chem. Ecol. : Mzomenos, B.E., G.E. Hniotkis. I. Spnkis,. Ionnou nd M. Kozyrkis Field evlution of olive fruit fly pheromone trps with vrious dispensers nd concentrtions. Proc. Internt. Symp. of CEC/IOBCon Fruit Flies of Economic Importnce. thens, Greece, Nov. 6-9, 98: Neuenschwnder, P. 98. Beneficil insects cught by yellow trps used in mss trpping of the olive fly, Dcus o- Icc. Entomol. Exp. ppi. 3: Orphnidis. P.S., R.K. Dnielidou, P.S. lexopoulou,.. Tskmkis nd G.B. Krynnis Recherches expérimentles sur l'ttrctivite exerce pr certines substnces proteinees sur le Dcus dulte de Γ olive. nn. Inst. Phytopthol. Bcnki (N.S.) : Prokopy, R.J.,.P. Economopoulos nd M.W. McFdden ttrction of wild nd lbortory - cultured Dcus olee flies to smll rectngles of different hues, shdes nd tints. Entomol. Exp. ppi. 8:4-5. Stvrkis, G.N ttrctnts for Dcus olee: the probble inborn ssocition of heterocyclic mines in locting the food. nn. Inst. Phytopthol. Benki (N.S.) 9: Zervs, G Significnt increse of Dcus olee trpping using sex nd food ttrctnts seprtely in the sme tree. Proc. Intern. Symposium. EEC/IOBC, Fruit Flies of Economic Importnce. Rome, Itly, pril 987 (in press). KEY WORDS: Dcus olee, Olive fruit fly. Sex pheromones, Sex ttrctnts, Food ttrctnts, Trps

7 HNIOTKIS ND VSSILIOU-WITE: FOOD ND SEX TRPS FOR DCUS OLEE 33 Επίδραση Συνδυασμού Προσελκυστικών Φύλου και Τροφής στην Ίδια Παγίδα στις Συλλήψεις Εντόμων Δάκου Γ.Ε. ΧΑΝΙΩΤΑΚΗΣ και Α. ΒΑΣΙΛΕΙΟΥ-WITE Ινστιτούτο Βιολογίας, Ε.Κ.Ε.Φ.Ε. «Δημόκριτος», Τ.Θ. 608, 530 Αγία Παρασκευή, Αττική ΠΕΡΙΛΗΨΗ Προσελκυστικά φύλου, τα πιο ισχυρά προσελκυστικά για τα αρσενικά έντομα του δάκου της ε λιάς, και αμμωνία, ένα από τα πιο ισχυρά προσελκυστικά για τα θηλυκά του ίδιου εντόμου που έ χομε στη διάθεση μας σήμερα, συνδυάστηκαν στην ίδια παγίδα. Ο συνδυασμός αυτός είχε σαν α ποτέλεσμα την κατά μέσο όρο αύξηση των συλλήψεων θηλυκών εντόμων, σε σύγκριση με τις συλλήψεις των παγίδων αμμωνίας, αλλά τη μείωση των συλλήψεων αρσενικών, σε σύγκριση με τις συλλήψεις των παγίδων προσελκυστικών φύλου. Αποκλίσεις από το αποτέλεσμα αυτό παρατηρήθηκαν κατά τη διάρκεια ορισμένων περιόδων του έτους οι οποίες οφείλονται στην επικράτηση διαφορετικών φυσικών και βιολογικών παραγόντων που επηρεάζουν τη δράση των προσελκυστικών φύλου. Με βάση πρόσφατες πληροφορίες που αφορούν τη λειτουργία του συστήματος χημικής επικοινωνίας των δύο φύλων του δάκου δίδονται εξηγήσεις για τα αποτελέσματα αυτά.