Australian Journal of Entomology

(2002)

41

, 306–309

Colony structure and nest characteristics of European wasps,

Vespula germanica

(F.) (Hymenoptera: Vespidae), in Victoria, Australia

Darren Ward, Patrick Honan and Greg Lefoe*

Keith Turnbull Research Institute, Department of Natural Resources and Environment, PO Box 48, Frankston, Vic. 3199, Australia.

Abstract

European wasps,

Vespula germanica

, are common across southern and south-eastern Australia and havea negative impact upon urban areas, primary industries, and natural ecosystems. Aspects of colonystructure and nest characteristics are examined for nests located in the ground and collected from urbanand rural sites in Victoria during two summer–autumn field seasons (1996 and 2001). On average, nestswere located 28 cm beneath the surface (range 5–58 cm). The average number of combs in the nest andthe total area of the nests increased from early February to late May. In addition, the proportion of cellsused to produce workers and different life stages (larvae, pupae) also varied throughout the season;being consistent with studies from New Zealand. No differences in colony structure or nest character-istics were detected between urban and rural nests.

Key words

European wasps, invasive species, nests, seasonal variation,

Vespula germanica

.

INTRODUCTION

The European wasp,

Vespula germanica

(F.) (Hymenoptera:Vespidae), is native to Europe, North Africa and temperateAsia, but has successfully invaded parts of North and SouthAmerica, New Zealand and Australia (Spradbery & Maywald1992). In years of high abundance, European wasps becomea serious pest in urban areas, stinging and annoying largenumbers of people (Levick

et al

. 1997).

Vespula

wasps arealso pests of stone fruit, grape, and beekeeping industries(Clapperton

et al

. 1989; Thomas 1993; Darby

et al

. 1998),and have a negative impact on natural ecosystems (Toft &Rees 1998; Beggs & Rees 1999).

European wasps usually nest underground in holes dug inthe soil, but nests may be found amongst stacked materials,in compost, tree trunks, or hedges. Many nests are found inwalls or roof spaces of buildings in urban areas (Moller

et al

.1991b; Donovan

et al

. 1992). Queens begin constructing nestsin spring. The first batch of adult worker wasps emerges totake over the work of enlarging the nest and feeding thelarvae, leaving the queen to continue egg-laying (Spradbery1973). There is continuous enlargement of the nest duringsummer, to a point in late summer/early autumn when severalhundred queens and drones are reared. These usually departfrom the nest in autumn and take part in mating flights(Spradbery 1973). The queens seek winter shelter to hiber-nate, the males die off, and the remaining occupants usuallydie, leaving the nest empty. Occasionally, new queens andsome workers remain in the nest over the winter period,

building the nest up to an extremely large size in thefollowing summer.

Seasonal changes in colony structure and nest character-istics of European wasps have been described in detail forNew Zealand (Fordham

et al

. 1991; Moller

et al

. 1991a;Donovan

et al

. 1992). However, there is little comparablepublished information available from Australia. Comparisonsof nests between New Zealand and Europe have provedvaluable for New Zealand researchers, assisting in the devel-opment of control methods, and in understanding the inva-sive biology of wasps (Fordham

et al

. 1991; Moller

et al

.1991a). For example, New Zealand nests are much largerthan nests from Europe, and overwintering nests occurmuch more frequently in New Zealand (Fordham

et al

. 1991;Harris 1996). In Australia, Crosland (1991) has shown theimportance of comparative research when he found that aslightly longer wasp-activity season exists in warmer parts ofAustralia (Sydney) compared with cooler parts (Melbourne,Hobart), as measured by the number of nests destroyed permonth.

The aim of this paper is to document some aspects ofthe colony structure and nest characteristics of Europeanwasps in Australia, and to make comparisons between nestsin Australia and overseas. In particular, differences in urbanand rural nests, and the seasonal changes in nests, areexamined.

MATERIALS AND METHODS

Nests were collected in the summer and autumn periods of1996 and 2001, having been brought to our attention bymembers of the public, park rangers and local council

*Author to whom correspondence should be addressed (email:greg.lefoe@nre.vic.gov.au).

Nest characteristics of European wasps

307

officers. Nests were located, and either removed alive ortreated with insecticidal powder and removed several dayslater. Only annual nests were studied (not large overwinter-ing nests that have survived more than one season). Nestswere collected from urban areas (Brighton, Heathmont) ofMelbourne, Victoria, and surrounding rural areas (LysterfieldLake Park within eastern suburbs of the city; Yarra Valley45 km NE of the city; the Mornington Peninsula 60 km SE ofthe city; Eildon/Alexandra 150 km NE of the city; and fromWilsons Promontory National Park 250 km SE of the city).Nests were not collected from buildings because they weretoo time-consuming to remove from these sites.

In 1996 the number of discrete layers of comb were counted,and the width and length of each comb were measured andsummed, giving the total area of a nest. In a selected 30-cm

2

section of each comb in the nest, the number of worker(small) cells, queen (large) cells, and the number of cellscontaining larvae, capped pupal cells and empty cells (includ-ing those with eggs) were counted (see Fordham

et al

. 1991).In 2001, measurements were made on the length of the nestentrance tunnel and the distance of the nest beneath thesurface. Statistical tests were performed using Systat 7.0(Systat Software Asia Pacific, Bangalore, India).

RESULTS

A total of 116 European wasp nests were collected (77 from1996 (31 from rural sites, 46 from urban sites); 39 from 2001,(all from rural sites)). Nests were obtained from mid-summerthrough to late-autumn (Fig. 1). The average length (

±

SE) ofthe entrance tunnel was 33.9 cm (

±

2.8 cm, range 2–76 cm,

n

= 31) and the average (

±

SE) distance of the nest beneaththe surface was 28.0 cm (

±

2.4 cm, range 5–58 cm,

n

= 31).The average number of combs per nest increased linearly

from February to May (

r

2

= 0.80,

P

< 0.01,

n

= 66; Fig. 2).No difference (

t

= 0.61, d.f. = 68,

P

= 0.54) in the average(

±

SE) number of combs per nest was found between rural(9.9

±

0.5, range 4–15,

n

= 30) and urban nests (9.5

±

0.6,range 3–18,

n

= 40). The average area of nests also increasedfrom February to June (

r

2

= 0.81,

P

< 0.01,

n

= 66; Fig. 3).Again, no difference (

t

= 0.56, d.f. = 68,

P

= 0.58) for the

average (

±

SE) total area of nests was found between rural(3526 cm

2

±

270 cm

2

, range 471–6442 cm

2

,

n

= 30) andurban nests (3281 cm

2

±

339 cm

2

, range 387–8847 cm

2

,

n

= 40).The number of cells used to produce workers in the nest

(as a percentage of the total number of cells) decreased fromFebruary to June (

r

2

= 0.94,

P

< 0.001,

n

= 69; Fig. 4), butparticularly from late March. The earliest queen cells wererecorded from nests was 22 March (53 nests examined).Larval and pupal cells decreased from early to late season(

r

2

= –0.88,

P

= 0.063;

r

2

= –0.52

P

< 0.28, respectively),whereas empty cells increased (

r

2

= 0.81,

P

= 0.10; Fig. 5).

Fig. 1.

Number of nests collected each month (

n

= 116) for (

�

)1996 and (

�

) 2001.

Fig. 3.

Average total area (

±

SE) of nests for early and lateperiods of each month in 1996:

y

= 744.6

x

– 151.37,

x

= day ofthe year. Early is defined as from ‘the start of month to mid-dateof month’, late is defined as from ‘the mid-date to the end of themonth’.

Fig. 2.

Average number of combs (

±

SE) in a nest for early andlate periods of each month in 1996:

y

= 1.224

x

+ 3.756,

x

= dayof the year. Early is defined as from ‘the start of month to mid-date of month’, late is defined as from ‘the mid-date to the endof the month’.

308

D Ward

et al

.

The proportions of cell types did not vary between urban andrural nests (

χ

2

= 1.20, d.f. = 2,

P

= 0.55).

DISCUSSION

Seasonal trends in the number of combs per nest, the area ofthe nest, the proportion of worker cells and the proportions ofdifferent life stages corresponded well with previous researchin New Zealand. Fordham

et al

. (1991) and Donovan

et al

.(1992) have shown that, although considerable variationexists, the number of combs per nest and the area of a nestincreases throughout the wasp-activity season. In New

Zealand, Fordham

et al

. (1991) found an average of11 combs per nest (maximum of 15) in late March to earlyMay, corresponding well with our data (Fig. 2). Furthermore,Fordham

et al

. (1991) found the average total area of nestsin late March to early May was 3460 cm

2

(maximum of7080 cm

2

), similar to our data (Fig. 3). European wasp nestsin New Zealand are considerably larger than nests in England(Fordham

et al

. 1991); this is also true for Australian nests.The proportion of workers’ cells decreases rapidly after

mid-March, and is associated with a dramatic increase in theproduction of reproductive cells. Fordham

et al

. (1991) andDonovan

et al

. (1992) have described these trends in greaterdetail for New Zealand nests. Moller

et al

. (1991a) found that50% of nests had initiated queen cell development by earlyMarch, slightly earlier than we found. This difference islikely to be a result of environmental differences betweenNew Zealand and Australia, and probably the much largernumber of nests collected by Moller

et al

. (1991a). Theproportion of cells devoted to different life stages is also verysimilar to that found in New Zealand (Fordham

et al

. 1991).Larval cells remain generally constant at about 20%, with aslight decrease as the season progresses. Pupal cells decreaseover the season from about 35% to 25%, and the proportionof empty cells increases from around 40% to 60% at the endof the season. Fordham

et al

. (1991) shows a slightly largerdecrease in the proportion of pupal cells (40% to 20%), butthe proportions of other life stages are similar to those thatwe found. Fordham

et al

. (1991) use these data, when thenumber of empty cells increase and the number of pupalcells decrease, to support the view that nests achieve theirmaximum numbers in mid/late April.

In our study, we found no differences between urban andrural nests. However, differences between urban and ruralnests have been described previously. In urban areas, 30% ofnests are located in buildings, but in rural or forested areasclose to 100% of nests are in the ground (Moller

et al

.1991b). Fordham

et al

. (1991) found urban nests producedmore workers and reproductives, and had more combs thannests in rural settings. However, Moller

et al

. (1991b) did notfind any difference in the number of wasps entering andleaving the nest (wasp traffic; an index of colony size) fornests located in the ground, roofs of buildings or the walls ofbuildings.

To our knowledge, there is no comparable information forthe length of entrance tunnels and the distance of the nestbeneath the surface for

V. germanica

in Australia or NewZealand. However, Donovan (1984) found tunnel entrancelengths and the distance of nests beneath the surface rangedfrom 10 to 35 cm for six English wasp nests,

Vespulavulgaris

(L.), in New Zealand.Basic information on European wasps (e.g., diet, density,

extent of invasiveness in natural ecosystems, impact onprimary industries) is still lacking in Australia; although itis likely that the impact of European wasps will continue tobe felt, if not intensify. For example, European wasps areexpected to continue to spread, particularly into northernAustralia (Spradbery & Maywald 1992). There is also little

Fig. 4.

Average number (

±

SE) of worker cells as a percentageof the total number of cells (worker and queen) in nests for earlyand late periods of each month in 1996:

y

= –6.906

x

+ 111.26,

x

= day of the year. Early is defined as from ‘the start of monthto mid-date of month’, late is defined as from ‘the mid-date tothe end of the month’.

Fig. 5.

Average number (

±

SE) of (a) empty cells or those witheggs (

y

= 5.808

x

+ 37.415), (b) pupal cells (

y

= –1.860

x +33.971) and (c) larval cells (y = –3.948x + 28.614) as a percent-age of the total number of cells in nests for each month in 1996;x = day of the year.

Nest characteristics of European wasps 309

information on the impact of European wasps in naturalecosystems from Australia; although Matthews et al. (2000)and Bashford (2001) have recently updated the distributionof Vespula wasps in Tasmania and discussed their potentialimpact on native calliphorids (Diptera). However, the extentof penetration by European wasps into other Australiannatural ecosystems, and their impact, need to be investigatedfurther.

ACKNOWLEDGEMENTS

This project was funded by the Grape and Wine Researchand Development Corporation (GWRDC), and the VictorianDepartment of Natural Resources and Environment (DNRE).

Many thanks to Jacqui Brooks (DNRE) for assisting in thecollection and measurement of nests during 1996, the vine-yards and all members of the public for allowing access totheir properties to collect nests, and to Margaret Stanley(Landcare Research, Auckland, New Zealand) for reading anearlier version of this manuscript.

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Accepted for publication 13 May 2002.