The Population Ecology of an Invasive Social Insect, Vespula Germanica (Hymenoptera: Vesp¡Dae) in South Australia
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The Population Ecology of an Invasive Social Insect, Vespula germanica (Hymenoptera: Vesp¡dae) in South Australia. MRnrn L. Knspen A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy. Environmental Biology School of Earth and Environmental Sciences The University of Adelaide, Adelaide, Australia April 2004 Tnele or GoTTENTS FrcuRE 1NDEx.......... V TABLE lnoex...... X ABSTRACT xil Decl¡nrnoN ......... xlil .. XIV CxapteR 1 : lNTRoDUcnoN............... 1 1.1 PopuLAT|oN DYNAMtcS .............. .1 1 .2 BroLocy oF rNVAStoNs................. .4 1.2.1 Stages of a biological invasion .4 1.2.2 Characteristics of successful invaders.... .5 1.3 SocrAL lrusecrs .b 1.4 INTRoDUCTION TO VESPULA SPP............. .8 1.4.1 Classification .8 1.4.2 Morphology and social organisation of V. germanica...... .9 1.4.3 Determination of sex and caste 11 1.4.4 World distribution of V. germanica and V. vulgaris.......... 11 1.4.5 lntroduction and spread of V. germanica and V. vulgaris 12 1.5 BASIC BIOLOGY AND ECOLOGY OF VESPULA SPP, 15 1.5.1 Nest site selection and preferences......... 15 1.5.2 Life cycle .......... 15 1 .5.3 Colony development................ 17 1 .5.4 Overwintering and po|y9yny ................ 18 L5.5 Foraging.............. 19 1 .6 ANNUAL FLUCTUATIONS IN YESPULA POPU14TIONS,.,,...........,...,, 21 1.7 IMPACT AND CONTROT OT VESPUTA SPP. 23 1.7.1 lmpact on native communities ................. 23 1.7.2 lmpact on humans 23 1.7.3 Chemical and biological control 24 1,8 RESEARCH OBJECTIVES AND THESIS OUTLINE 25 1.8.1 Overall objectives 25 1.8.2 Specific aims...... 25 CHAPTER 2: Nesr SITE PREFERENCES AND SEASONAL COLONY GROWTH OT V. EEN¡øEN,CA IN SOUTH AUSTRALIA. ..........28 2.0 CHAPTER SUMMARY 28 2.1 lNTRoDUcroN ....... 29 Maña L. Kasper - Population ecology of V. Qermanica in South Australia 2.2 MATERIALS AND METNOOS.... 31 2.2.'1 Nest destruction scheme 31 2.2.2 Local councils supporting research 31 2.2.3 Recording of wasp nest sites........... 33 2.2.4 Nest collection.... 34 2.2.4 Nest analysis...... 34 2.2.5 Traffic as an indicator of nest si2e............ 35 2.3 RESU1TS................. 35 2.3.1 Nest sites ........... 35 2.3.2 Seasonal abundance ............... 38 2.3.3 Nest size ..,......... 39 2.3.4 Proportions of small and large cells 43 2.3.5 Colony development................ 43 2.3.6 Sex ratios of brood.......... 44 2.3.7 Eggs per cell 46 2.3.8 Traffic as an indicator of nest size............ 47 2.4 DrscussroN............ 49 2.4.1 Nest sites ........... 49 2.4.2 Seasonal abundance ............... 49 2.4.3 Nest size ............ 51 2.4.4 Large and small cell proportions............. 52 2.4.5 Colony development................ 52 2.4.6 Sex ratios .......... 53 2.4.7 Eggs per cell 54 2.4.8 Traffic as indicator of colony si2e............. Gn¡preR 3: CuruceS IN DAILY AND SEASONAL FORAGING CHARACTERISTICS 3.0 CHAPTER SUMMARY. 3.1 INTRoDUcïoN ......... 3.2 MATERIALS AND METHODS.... 3.2.1 Study area............ 3.2.2 Forager sampling 3.2.3 Experimental design 3.2.4 Changes in resource proportions. 3.2.5 Changes in relative proportions of prey orders 3.2.6 Changes in sucrose concentration ......,........... 3.3 RESU1TS................. 3.3.1 Changes in resource proportions. 3.3.2 Changes in prey orders 3.3.3 Changes in sucrose concentration .................. Maña L. Kasper - Population ecology of V. qermanica in South Australia il 3.4 DrscussroN............ 73 3.4.1 Overall resource proportions 73 3.4.2 Daily changes in resource proportions 74 3.4.3 Seasonal changes in relative resource proportions 75 3.4.4 Seasonal changes in prey 77 3.4.5 Changes in sucrose concentration ......................... 78 CHapreR 4r FAcroRs TNFLUENcING DATLY FoRAGtNG AcrlvlrY 79 4.0 CnnprER SUMMARY. 79 4.1 INTRoDUCTION 79 4.2 MnrrnIALS AND METHODS.... 82 4.2.1 Data collection .............. 82 4.2.2 Modelling factors influencing foraging 83 4.2.3 Summary of daily activity pattern 84 4.3 RESU1TS................. 85 4.3.1 Effect of rain............. 86 4.3.2 Effect of light 87 4.3.3 Effect of temperature ............. 88 4.3.4 Effect of humidity 89 4.3.5 Modelling factors influencing wasp activity................. 89 4.3.6 Daily foraging activity pattern........ 90 4.3.6 Changes in incoming vs. outgoing traffic.......... 91 4.4 DrscussroN............ 92 4.4.1 Daily activity pattern 92 4.4.2 Envuonmental influences on wasp activity 93 4.4.3 EfÍect of rain 94 4.4.4 Effect of light 95 4.4.5 Effect of temperature ............... 96 CInpTeR 5: DIET oT V. eenmnN,cA AND PREY OVERLAP WITH A NATIVE PAPER WASP POL,SIES HUMtLtS.... 99 5.0 CHAPTER SUMMARY. .99 5.1 lNTRoDUcroN......... .99 5.2 MATERIALS AND METHODS,,,. 103 5.2.1 Prey collection and visual identification........ '103 5.2.2 Prey identification by nucleotide sequencing 103 5.2.3 Phylogenetic analysis 105 5.2.4 Complete prey inventories 106 5.2.5 Prey overlap values 106 5.3 RESU1TS................. 107 5.3.1 Morphologically identified prey ........... 107 Maña L. Kasper - Population ecology of V. qermanica in South Australia ilt 5.3.2 Nucleotide identified prey inventories 108 5.3.3 Complete prey inventories ol Vespula and Polrsúes....... 114 5.3.4 Prey overlap 114 5.4 DrscussroN.............. 114 5.4.1 Diets of Vespula germanica and Polrsfes humi\is........... 114 5.4.2 The use of nucleotide sequencing for prey identification 115 5.4.3 Extent of overlap between V. germanica and P. humilis 118 CHAPTER 6: PopuurION DYNAMICS 'l'19 6.0 CHAPTER suMMARy.. .........119 6.1 lNTRoDUcroN.......... ........119 6.2 MATERTALS AND METHoDS.... ................122 6.2.1 Study area and wasp density data......... ........122 6.2.2 \Nealher data ...........124 6.2.3 Time series analysis ...................124 6.2.4 Population model .....125 6.2.5 Forecasts............ .....126 6.3 RESU1TS................. ..........126 6.3.1 Time series analysis ..................127 6.3.2 Factors affecting density....... ......128 6.3.3 Modeltesting....... .....131 6.4 DrscussroN............ ..........132 6.4.1 Nest densities and fluctuations............ ..........132 6.4.2 Modelling annual fluctuations ..... '133 G¡lnpren 7: GeneRnl DtscusstoN. ............... 138 7.1 OurcoMES............... ........138 7.2 PRoBLEMS ENCoUNTERED........... .........142 7.3 FUTURE RESEARCH ..,.,,,.,.,143 APPENDIX 1: NEsTs USED FoR SEASONAL COLONY GROWTH PATTERNS ..,.,.,.,.,...,.,,.,144 AppENDtx 2: HraeRr¡eiloN rN V. eenua¡,trca QUEENS ........147 A2.1 BAcKcRoUND .................147 A2.2 MATERTALS AND METHoDS .................147 42.3 Resu1rs............... .........148 A2.4 DrscussroN.......... ..........149 Apperuolx 3: Detnrteo Ltsr oF V. cERMANtcA pREy........... .................. 151 REFERENGES .............152 Marta L. Kasper - Population ecology of V. qermanica in South Australia IV F¡cune lruoex Figure 1.1: The four factors determining population size. Arrows pointing towards the population indicate an increase, while arrows pointing away indicate a decline in numbers..'1 Figure I .2: Density dependent and density independent factors influencing births and deaths in a population (modified from Gutierrez 1996). .................3 Figure 1.3: Phylogeny of the Vespoidea showing the position of Vespula germanica (modified from Carpenter 1982 and Carpenter 1991). .. .....................9 Figure 1.4: The distinguishing dorsal metasomal marks of (a) Vespula vulgaris and (b and c) Vespula germanica (from Akre et al. 198'1), and lateral pronotal markings of (d) Vespu/a vulgaris and (e,f,g) Vespula germanica (from Clapperton ef a/. 1989b). ...........10 Figure 1.5: The native (shaded) and introduced (black)world distribution of Vespula germanica (modified from Greene 1991). The Ascension lsland population is marked with an arrow..12 Figure 1.6: The current (black) and potential (shaded) distribution of V.germanica in South Australia. The potential distribution is as predicted by ecoclimatic matching by Spradbery and Maywald (1992). ..............14 Figure 1.7: The life cycle of Vespula spp. ........... .............16 Figure 1.8: Summary of prey items captured by Vespula germanica in three introduced habitats: New Zealand (black), Australia (white) and Argentina (grey). Data was obtained from three studies in New Zealand (Harris 1991;Harris and Oliver 1993; Harris'1996), one study in Australia (Madden 1981), and one study in Argentina (Sackmann et al.2OOO). Dala from the three New Zealand studies was summarised by site and by study. Error bars represent standard error of mean.......... .......................20 Fig. 2.1: Map showing the relative sizes and positions of the twenty Adelaide metropolitan councils: Adelaide City Council (ACC), Adelaide Hills (AH), Burnside (BU), Campbelltown (CA), Charles Sturt (CH), Gawler (GA), Holdfast Bay (HB), Marion (MA), Mitcham (Ml), Mt Barker (MB), Norwood, Payneham and St Peters (NPSP), Onkaparinga (ON), Prospect (PR), Port Adelaide Enfield (PAE), Playford (PL), Salisbury (SA), Tea Tree Gully (TT), Unley (UN), Walkerville (WA), and West Torrens (WT). ......... ..................32 Fig.2.2: Proportions ol V. germanica nests found above ground (grey), below ground (black) and inside artificial structures (white) during (a) 1999/2000, and (b) 2000/2001 wasp season. Data is compiled from locations of nests destroyed by councils (see text). ...........36 Fig. 2.3: Proportions of V. germanrca nests found above ground (grey), below ground (black) and inside artificial structures (white) during (a) 1999i2000, and (b) 2000/2001 wasp season. Each pie represents a different council region. Council codes are as follows: AH = Adelaide Hills, Ml = Mitcham, PL = Playford, PR = Prospect, TT = Tea Tree Gully, UN = Unley, and WT = West Torrens. ................37 Fig.2.4: Regression of percent of nests found (a) below ground and (b) in artificial structures on human population density. Mean nest data were used for each council region. ............37 Maña L. Kasper - Population ecology of V. qermanica in South Australia Fig. 2.5: Monthly frequencies of nests destroyed by '1 1 of the 20 metropolitan Adelaide councils pooled for the 1994195-1995-96 and '1997/98-2000101wasp seasons.