halsall and wratten 1988

8/2/2019 Halsall and Wratten 1988

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Ecological En tomology (1988) 13,293-299

The efficiency of pitfall trappingfor polyphagous predatory Carabidae

NIGEL B .HALSALL and STEPHEN D. WRATTENDepartm ent of Biology, The Un iversity, Southampton

ABSTRACT. 1. The efficiency of pitfall trapping was investigated forseven carabid species, using time-lapse video recording equipm ent, in thelaboratory.2. The effects of differing substrates, trap designs and seasons of collec-tion on the capture rates of the carabids was also investigated.

3. Captu re rate differed significantly between the species studied. T hedifferences in capture rates between the species were unrelated to beetlesize, speed of movem ent and diurnal behaviour.

4. Few differences arose in the capture rates when type of substrate ortrap o r season of capture were changed.

Key words. Pitfall trap , efficiency, carabids, video.

IntroductionPitfall traps have been used extensively to moni-tor the number and activity of surface-activeinvertebrates, especially Coleoptera andAraneida. Catches by these traps depend on thepopulation size, locomotor activity (Mitchell,1963; Greenslade, 1964) and susceptibility ofcapture of the animals. Therefore numberscaught represent only relative numbers of theepigeal fauna present. However, because pitfalltraps are cheap and require little labour theyhave been used as a major sampling method by,for example, workers studying the epigeal faunapresent in cereal fields (Potts & Vickerman,1974; Dunning et al., 1975; Sunderland, 1975;Edwards et al., 1978; Sunderland& Vickerman,1980; Bryan & Wratten, 1984).

The use of pitfall traps to compare speciesactivities relies on the assumption that everyCorrespondence:Mr N. B. HalsaU, Department ofBiology, Building 44,The University, SouthamptonSO9 5NH.

species has the same chance of being captured.However, little if any work has been publishedto investigate this assumption. Related workincludes that of Luff (1975), who demonstratedthe differing efficiencies of several types oftraps; Greenslade (1964) demonstrated thatdifferently-set traps gave differing efficiencies;Obrtel (1971) maximized capture per unit areaby manipulating the numbers of traps; Chiver-ton (1984) demonstrated that the content of thegut affected capture of a carabid species andBaars (1979) found that the use of continuouspitfall sampling could be used as a relativemeasure of the size of carabid populations.

This paper describes the use of laboratorytime-lapse video techniques to evaluate poten-tial differences in efficiency of dry pitfall trap-ping within a range of seven carabid species.Efficiency in this case is defined as the propor-tion of encounters with the edge of the pitfalltrap which result in capture. The data in thispaper compare pitfall trap efficiency betweencarabid species under different experimental

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294 Niger B. Hahall and Stephen D . Wrattenconditions of substrate and trap type. B etween-species comparisons were made, not within-species comparisons between sites, which wasdone by Baars (1979). Tr ap efficiency was alsocompared between carabids caught in th eautumn/winter and those caught in thespring/summer .Although there a re potential p roble ms associ-ated with dry pitfall traps, such as avoidance,predation and aggregation, which may occur inthe field, this work was restricted to the use ofdry pitfall traps to limit the number of compari-sons made.Any substantial differences demonstratedbetween species and between season will haveimplications for the interpretation of past andfutu re field work which uses pitfall trapp ing as asampling method for epigeal fauna.Materialsand MethodsThe carabid species used for the studies repre-sented a range of sizes that commonly occur inarable crops in the south of England. Thesmaller species, with an overall length of lessthan 6 mm (Luff, 1978), included Demetriasatricapillus (L.), Norioph ilus biguttatus (F.) an dTrechus quadrktriatus (Schrank); the medium-su ed species, measuring 8-10 mm (Luff, 1978)included Agonum dorsale (Pont.) and Calathusmelanocephalus (Goeze); and the Iirgestspecies, measuring 12-15 mm included Calarhusfuscipes (Goeze) and Nebria brevicollis (F.). Allof the species were obtained from th e LeckfordEstate , Stockbridge, Hampshire. They were col-lected from field boundaries in October,Novemb er and December using an insect pooter(Southwood, 1978). Gutter traps (Luff, 1978),set in the open fields, were used to collect thebeetles from A pril to July. Eac h tra p consistedof a 2m length of plastic rainwater guttering; thishad a vertical side wall with a slight lip. At eachend a stopend was fitted. At one of the ends anoutlet pipe led vertically down in to a plastic col-lection cup of height 13.5 cm and a diameter of9.7 cm at the top tapering t o 7 cm at the bottom .This cup contained ston es and leaves as a refugefor the captured invertebrates. The beetlescaught in the autumn/winter would be mostlyfrom the new generation of adults ( N . Sother-ton, pers. comm .), whereas th e spring/summercaught ones would be a m ixture of new genera-tion adults and overwintered beetles.

The beetles were maintained in polystyreneboxes in a culture room. The boxes measured17.5X 11.6x6.0cmandwerefil ledtoadepthof2cm with soil obtained from the field site. Refugesmade from broken clay plant pots were placedon the soil surface. The culture room was m ain-tained at 16 h light/24 h with a mean tempera-ture of 15C and a 2C range. The beetles werefed every 3 days with second, third and fourthinstar pea aphids (Acyrthosiphon p ku m (Har-ris)) which had been cultured on broad beanVicia faba (L.) cv. The Sutton. The mediumsized to larger species were given twenty ap hidsper be etle, the smaller species were given ten .A 0 . 5 X 0 . 5 ~ 0 . 1 8 aren a containing four pit-fall traps positioned in a silver sand or soil (asused in the boxes) substrate was used for thework. Sand was initially chosen as a substratesince this contrasted with the colour of thebeetles, providing a clear video image. It alsocreated a homogeneous surface giving thebeetles unimpeded movement. Because thissubstrate is unnatural the initial experimentswere repeated using a soil substrate. It wasnecessary to create contrast between thecarabids and the substrate in this case by mark-ing each b eetle with a spo t of white enamel painton its right elytron .The hardboard walls of the arena werecovered with polythene which was coated withan aqueous suspension of PTFE (poly-tetrafluoroethylene). This coating preventedescape by the beetles. White polystyrene cups, 8cm deep with a diameter of 8 cm at the toptapering to a diam eter of 4.7 cm at t h e bottom,were used as traps. The se were positioned in asquare formation in the arena, with each cupbeing opposite the mid-point of a wall. Theoutermo st point of each pitfall was 11.3cm fromthe nearest wall. The cups were set such thattheir rims were level with t he su bstrat e surface.The substrate used for the experiment wasplaced to a depth of 1 cm in the bottom of eachtrap to enable the beetles to bury themselves.Refuges made from broken clay plant pots wereplaced at the four com ers of the arena and at thebottom of each trap.Th e experimental are na was situated in a plantgrowth room. This was maintained und er condi-tions as described for the culture room aboveexcept that the light intensity was approximately80,pE m-* s-' and the relative humidity variedfrom 60% to 70% rather than the 25p E m - 2s-'


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Pitfall traps and carabid beetles 295pitfalls were set such that their lips were sub-merged approximately 1 cm below the sand sur-face. This experiment was camed out in anattempt to maximize the trap efficiency. (4)Experiment 4. A s 1 , but spring/summer-caughtanimals were used.Data w ere obtained from t he video tapes dur-ing playback in the 12 h time-lapse mode. Th efrequency and nature of th e encoun ters with thepitfall trap edges were recorded. Encounterswith the trap edge resulted either in captur e oravoidance/escape. Several categories of avoi-dance were noted (see Results). The speed ofmovement of each species was obtained by trac-ing the path of an individual with a permanentmarker pen on an ace tate sheet overlaying themonitor screen. The paths were traced from thepoint at which the beetle left the wall or refugeuntil it encountered a trap, refuge or wall. Themean speed of movement was calculated fromten tracks for each species in each experiment.Th e proportion of encounters resulting in c a pture and no capture were calculated for eachspecies. A G-test (Sokal & Rohlf, 1981) wasused to evaluate whether there was overallheterogeneity of the numbers capturedln ot cap-tured between the species for each experiment.Pair-wise G-tests, incorporating the Williamscorrection factor (Sokal & Rohlf, 1981), wereused to compare the trap efficiency (numberscapturedlnot captured) for each species fromone experiment to the next. This test was alsoused to evaluate the differences between eachspecies within each experiment.A t-test was used to com pare the mean speedsof movement between th e experiments.The mean fresh weight of each species wasrecorded after 48 h of starvation. The beetlesused for the experiments w ere weighed in groupsof te n; the balance w as sensitive to O.OOO1 g.

and a relative humidity of 5 0 4 0% in the cultureroom. A Licor Inc. (U.S.A.) LI-IBSB quan-tum/radiometer/photometer fitted with a quan-tum sensor was used to measure the lightintensity. A Gluck thermohydrograph was usedto monitor the temperature and humidity.Ten individuals of each of the medium-sizedto larger carabid species and fifteen of each ofthe smaller species were used. All beetles werestarved for 24 h before the experiment in orderto enhance foraging activity. The beetles wereintroduced into the arena at 17.00 hours 2 hbefore the start of the experiment during whichperiod polystyrene cups, identical to those usedfor the traps, were inverted and placed over thetraps in order to prevent prem ature capture. Theinverted cups were removed after the 2 h periodand subsequ ent activity was monitored over a 24h period using time-lapse video equipment andeither VHS or U -matic cassette recorders set inthe 24 h time-lapse record mode. The equip me ntconsisted of a National WV 1800B Vidiconmonochrome video camera with a Fujinon CF125C, 1 2.5 mm F 1.4 ens; a Melford D01-17 highresolution monochrome monitor; an NE C 9507U-m atic time-lapse video cassette recorder withtime date generator and a Panasonic NV-8050VHS video cassette recorder. The NEC videocassette recorder was used only in the firstexperiment for A .dorsale, T.quadrktiatus an dN .brevicollis. After this time the Panasonicrecorder was used, because of its better imagequality during play-back.Some illumination was necessary in the darkperiod to enable the camera to produce animage. This was provided by two 60 W redtungsten bulbs positioned 60cm from t he surfaceof the arena. These created a light intensity ofapproximately 3 p E m- 2 s- at the subs trate sur-face. Griffiths (1983) demonstrated that A.dor-sale could not perceive red light from this sourceso it was assumed that the species used behavedin the red light as they would in the dark. Thecamera was positioned 100 cm from the sub-strate surface. This gave a field view of45x59 cm.Pitfall trap efficiency was evaluated for eachspecies under the following conditions: (1)Experiment 1.Silver sand was used as th e substr-ate . Autumn -winter caught animals were used.(2 ) Experiment 2. Soil was used. Animals as 1.(3) Experiment 3. Sand and spring/summer-caught animals were used. Also the plastic cup

R e s u bInitial reviewing of each 24 h tap e revealed tha tN.b i g u f f a mwas almost exclusively active dur-ing the day. A.dorsale, C.melanocephalus,D.ahicapillus and N .brevicollis were almostexclusively nocturnal and C.fuscipes andT.quadristriatus were active throughout th e dayand night.The results given in Fig. 1 represent the cap-ture efficiency (I), avoidance behaviours (11)


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2% Niger B. Hahall and Stephen D . Wratten

EXPERIMENT 1 W I N T E R S A N D -LIPPED TRAP

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EXPERIMENT 3 SUMMER SAND-LIPLESS TRA P

EXPERIMENT 2 WINTER SOIL-- LlPPEDTRAP

EXPERIMENT4 SUMMER S A N D -T LIPPEOTRAP

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FIG. . Behaviour of carabids in a pitfall-trap arena. T he capture efficiency (proportion capture ( toproportion non-capture ( 0 ) )I) ; avoidance behaviour (proportion investigate and skirt (.)/skirt ($$) toproportion investigate then retreat ( 0 ) )11); and speed of movement (given with 95% confidence limits)(111). Sample sizes are given above each column in observations of Types I and 11. Key to species:C.f.=C alath us fuscipes; N.br.=N ebria brevicollis; N.b.=Notiophilus bigunarus; C.m.=Calarhusmelanocephalus; T.q.=Trechus quadrirtriatus; A.d.=Agonum dorsale; D.a.=Dem errias atricapillus.


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Pitfall traps and carabid beetles 297were recorded (Fig. 1). In the first, carabidsapproached the edge of the trap, lowered theirbodies into the mouth of it and hung on withtheir hind legs; this will be term ed investigatefrom now on . Within a few seconds they re-treated. In the second type of avoidancebehaviour the carabids approached t he edge andskirted aroun d it without any lowering into th etrap. A number of the individuals that skirtedalso investigated, so this behaviour wastherefore added as a subca tegor y of skirting.D.atricapillus, the species least pron e to captur e, avoided being caught mainly by employingthe skirting behaviour. C.melanocephalusevaded the traps mainly due to its investigateand retreat behaviour. For the other speciesneither of the avoidance behaviours predomi-nated. There appeared to be no relationshipbetween the capture rate and the type of avoi-dance behaviour.NO orrelation between the mean fresh weightof each species and its captu re rate was obta ined .All of the species studied mo ved significantlyfaster in experiment 4 (that is the experimentusing spring/summer-caught carabids for whichspeed was measured) than they did in experi-ment 1 (autumn/winter-caught carabids)(P


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Pitfall traps and carabid beetles 299Bryan,K.M.& Wratten,S.D. (1984)Theresponsesofpolyphagous predators to prey spatial hetero-geneity; aggregation by carabid and staphylinidbeetles to their cereal aphid prey. EcologicalEntomology, 9, 251-259.Chiverton, P.A. (1984) Pitfall trap catches of thecarabid beetle Pterostichus melanarius,in relationto gut contents and prey densities, in insecticidetreated and untreated spring barley. EntomologiaExperimentalis et Applica ta, 36,23-30.Coombes, D.S. (1987) Factors limiting the effective-ness of Demetrias atricapillus (L.) (Coleoptera:Carabidae) as a predator of cereal aphids. Ph.D.thesis, University of Southampton.Dunning, R.A., Baker, A.N. & Windley,R.F. (1975)Carabids in sugar beet crops and their possible role

as aphid predators. Annals ofApplied B iology, 80,125-128.van der Drift, J . (1951) Analysis of the animal com-munity of a beech forest floor. Tijdrchrift vorEnfomologie,94, 1-168.Edwards, C.A., Parsons, N., George, K.S. &Heilbroon, T. (1978) Carabids as predators ofcereal aphids. Annual Report of RothamstedExperimental Station for 1977, p. 101.Gilbert,0 . 1956)The natural historiesof four speciesof Calathus (Coleoptera: Carabidae) livingon anddunes in Anglesey, North Wales. Oikos, 7 , 2 2 4 7 .Greenslade, P.J.M. (1964) Pitfall trapping as amethod for studying populations of Carabidae(Coleoptera). Journal ofAn imal E cology, 33,301-310.Griffiths, E. (1983)The feeding ecology of the carabidbeetle Agonum dorsale in cereal crops. Ph.D.thesis, University of Southampton.Lindroth, C.H. (1974) Handboo ks for the Identifica-tion of British Insects, 4 ( 2) , 1 4 8 .Luff, M.L. (1975) Some features influencing the effi-ciency of pitfall traps. Oecologia (Berlin), 19,345-357.

Luff, M.L. (1978) Die1 activity patterns of some fieldCarabidae. Ecological Entomo logy, 3 , 5 3 4 2 .Mitchell, B. (1963) Ecology of two carabid beetles.Bembidion lampros (Herbst) and Trechusquodrisiriatus (Schrank). I. Life cycles and feedingbehaviour. Journal of Animal Ecology, 32, 289-299.Obrtei, R. (1971)Number of pitfall traps in relation tothe structure of the catch of soil surface Coleop-tera. Acta Entomologica Bohemoslavaca, 68,3oQ-309.Penney, M.M. (1966)Studieson certain aspectsof theecology of Nebria brevicollis (F.) (Coleoptera,Carabidae). Journal of Animal Ecology, 35, 505-512.Potts, G.R. & Vickerman, G.P. (1974) Studieson hecereal ecosystem. Advances in EcologiculResearch, 8, 107-197.Sokal, R.R. & Rohlf, F.J. (1981) Biometry, 2nd edn.Freeman, New York.Southwood, T.R.E. (1978) Ecological Methodr withParticular Reference to the Study of Insect Popula-tions, 2nd edn, pp. 236-237. Chapman and Hail,London.Stork, N.E. (1980) A scanning electron microscopestudy of tarsal adhesive setae in the Coleoptera.Journal of the Linnean Society, 68, 173-306.Sunderland, K.D. (1975) The diet of some predatoryarthropods in cereal crops. Journal of AppliedSunderland, K.D. & Vickerman, G.P. (1980) Aphidfeeding by some polyphagous predators in relation

to aphid density in cereal fields.Journal ofAppliedEcology, 17,389-396.Thiele, H.U. (1977) Carabid Beetles in their Environ-ments. Springer, Berlin.

Ecology, 12,507-515.

Accepted 5 December 1987

halsall and wratten 1988

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