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Release and recovery of theintroduced wasp parasitoid,Sphecophaga vesparumvesparum (Curtis) (Hymenoptera:Ichneumonidae) in New ZealandB.J. Donovan a , H. Moller b , G.M. Plunkett b , P.E.C. Read a

& J.A.V. Tilley ba Entomology Division, Department of Scientific andIndustrial Research , Canterbury Agriculture and ScienceCentre , Private Bag, Christchurch , New Zealandb Ecology Division, Department of Scientific and IndustrialResearch , Private Bag, Nelson , New ZealandPublished online: 09 Feb 2012.

To cite this article: B.J. Donovan , H. Moller , G.M. Plunkett , P.E.C. Read & J.A.V. Tilley(1989) Release and recovery of the introduced wasp parasitoid, Sphecophaga vesparumvesparum (Curtis) (Hymenoptera: Ichneumonidae) in New Zealand, New Zealand Journal ofZoology, 16:3, 355-364, DOI: 10.1080/03014223.1989.10422900

To link to this article: http://dx.doi.org/10.1080/03014223.1989.10422900

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New Zealand Journal ojZoology, 1989, Vol. 16: 355-364 0301-4223/89/1603-0355-$2.50/0 © Crown Copyright 1989

355

Release and recovery of the introduced wasp parasitoid, Sphecophaga vesparum vesparum (Curtis) (Hymenoptera: Ichneumonidae) in New Zealand

B. J. OONOV AN* H.MOLLERt G. M. PLUNKETTt P. E. C. READ* J. A. v. TILLEyt *Entomology Division

Department of Scientific and Industrial Research Canterbury Agriculture and Science Centre Private Bag, Christchurch, New Zealand

tEcology Division Department of Scientific and Industrial Research Private Bag, Nelson, New Zealand

Abstract The introduced European wasp parasit-oid Sphecophaga vesparum vesparum (Curtis) was r~ed in the laboratory at DSIR Lincoln then distributed in the South Island and at one location in the North Island, from 1985 to 1987.

In early November 1986, one yellow parasitoid cocoon was recovered from an overwintered nest of the German wasp, Vespula germanica (p.), in sub-urban Christchurch. Before that recovery about 197 female parasitoids had emerged from release boxes in the area, and 41 wasp nests had been collected. There have been no other recoveries in this area, de-spite the emergence of about 1585 parasitoids from released cocoons and the collection of a further 385 wasp nests. . .

Systematic searches for andexammatton of wasp nests from 17 sites in the north and west of the South Island recovered rapidly multiplying parasitoid pop-ulations from 2 out of 42 nests of the common wasp, Vespula vulgaris (L.) at Pelorus Bridge, 42 Ian ~t of Nelson. The nests were 33 m and 625 m away 10 separate directions from different parasitoid release boxes. From the three parasitoid release boxes in the area, 266 adult parasitoids had emerged.

Received 11 May 1989; accepted 19 July 1989

When poisoned on 5 May 1988, the two para-sitised wasp nests contained 471 and 1034 parasitoid stages, respectively. At least 1491 wasps had been killed by the parasitoid. The completion of all propa-gation stages of the parasitoid life cycle at Pelorus Bridge suggests that the environment of the area is favourable for the parasitoid. Because parasitoids had multiplied in and dispersed from the two common wasp nests, and the likelihood of the .exis~e~ce of other attacked nests in the area seems high, It 18 con-sidered that the parasitoid has probably established at Pelorus Bridge. The potential for a rapid increase in parasitoid numbers appears to be very good.

Keywords Wasp; parasitoid; Sphecophaga vesparum vesparum (Curtis); Vespula germanica (p.); German wasp; Vespula vulgaris (L.), common wasp; recovery

INTRODUCTION The adventive German wasp Vespula germanica (p.), and common wasp V. vulgaris (L.), occur throughout most of New Zealand and in some areas reach very high densities. A wide range of human activities are affected: people are directly and personally caused pain and fear by stings (one person has died), tourists avoid and leave infested areas, honey bee colonies may be damaged and destroyed (Clapperton et al. 1989), systemati.c silvicult~ operations are interrupted, and hortIcultural fruIts damaged. The natural environment is being severely disrupted by direct attacks on native insects, removal of honeydew in beech forests, and adverse flow-on effects on some native birds (Moller et al. 1988b; Moller & Tilley 1989).

Wasps can become enormously abundant in some habitats. For example, in one area of beech forest (N othojagus spp.) studied by Moller et al. in 1988, a year in which wasps were much less abundant than in some other years, there were 46 wasp nests/ha (Moller et al. 1988a). A contributing reason for the high populations reached by wasps in New Zealand

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may be the complete lack of arthropod enemies in nests with adult wasps present (Donovan & Read 1987). This prompted the introduction in 1979 of the EuropeanSphecophagavesparumvesparum(Curtis), an ichneumonid parasitoid of social wasps, for attempted biological control of both vespid species (Donovan & Read 1987). Although field nests of both species of wasp were attacked following direct release of S. v. vesparum into and around nests, re-covery could not be claimed because the parasitoids had not themselves sought out and entered the nests. There are no data from the home range of the parasitoid in the Northem Hemisphere on parasitoid dispersion distances and subsequent level of attack on wasp nests.

Here we report on the release of S. v. vesparum in the South Island and one site in the North Island, and its recovery from one nest in Christchurch, Canterbury and two nests at Pelorus Bridge, Marlborough.

Parasitoid life cycle Donovan & Read (1987) outlined the life cycle of the parasitoid, but more data are presented here to allow interpretation of our field results. Female parasitoids oviposit primarily into cells in which wasp pupation has most recently occurred. In the laboratory, eggs were sometimes found in in-completely sealed cells containing larvae which were closing their cells, and in sealed cells containing wasp prepupae. When preferred hosts were in short supply, eggs were also found on later pupal stages. Parasitoid larvae fed upon the host gaster, and within a few days the host was killed.

Two types of parasitoid cocoon were produced. The most common were "yellow" or"overwintering" cocoons. These filled the basal third to half of a cell and were whitish when firstfonned, but soon became yellowish or reddish brown. They were very hard and composed of several layers of material. Adults emerged from 10-12 days to4 years after oviposition, were male or female, and flew strongly when released outdoors.

The second type of cocoon was about one quarter the size of a yellow cocoon, and was white, fragile, and composed of only a single thin layer of material. They were usually fonnedagainst the side of the cell near its base, and produced only brachypterous females, which emerged 10-11 daysafteroviposition. These oviposited soon after emergence, and progeny consisted of both brachypterous and winged females which emerged within 10-12 days of oviposition,

New Zealand Journal of Zoology, 1989, Vol. 16

and yellow, overwintering cocoons. Further details will be presented elsewhere (Donovan, unpubl. data).

During wasp nest founding in spring/early summer, it is assumed that winged females that emerge from overwintering cocoons seek out and enter wasp nests. Mating is not a prerequisite to oviposition. Resulting progeny in the nest 10-12 days after oviposition may be brachypterous and/or winged females, and/or yellow, overwintering cocoons. The brachypterous females can fly weakly at best, but most cannot fly when given the opportunity in the rearing room. It is assumed that they do not attempt to leave the nest; instead, they stay and rapidly oviposit into wasp cells. Winged females are assumed to leave the nest to seek out and attack other nests.

Brachyptery in female S. v. vesparum appears to be a mechanism through which the species maximises its reproduction when hosts are abundant Winged females presumably are a means by which the species disperses to other nests. Thus, the progeny of one female entering a nest can, during one season, con-ceivably destroy much if not all the nest, disperse to other nests, and leave descendants that will emerge and attack nests in each of the following four seasons.

METHODS

Parasitoid releases and flight of winged adults Releases directly into wasp nests. Donovan & Read (1987) outlined the release of S. v. vesparum directly into seven nests of V. vulgaris and six nests of V. germanica in Canterbury from 4 March to 26 April 1985. A total of 10 winged females, 66 brachypterous females, and an unknown number of immatures in comb were placed either between combs or into the cavity surrounding nests. It is unlikely that any of the released winged females left the nests at that time, because of the restrictive method of release, but flight cannot be discounted. Examination of nests in winter after the cessation of wasp activity, showed that nine nests had been attacked, and that at least four winged adults had emerged from yellow cocoons that had fonned in one nest. Presumably these adults had left that nest. Releases in and around Christchurch in spring 1985 and 1986. At DSIR Lincoln, from December 1984 to July 1985, 13 consecutive generations of S. v. vesparum were propagated in the laboratory on common wasps. About 1500 overwintering cocoons and several hundred adults were produced. Parasit-oids were also propagated for several generations on

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Donovan et al-release and recovery of wasp parasitoid 357

German wasps. and about 300 overwintering cocoons and several score adults were produced.

From 10 September to 8 October 1985. about 50 female and 55 male parasitoids which had emerged within the laboratory were liberated in Christchurch City. A further 16femalesand26 males were released within a black beech (Nothofagus solandri (Hook.f.) Oerst) forest at Mt Thomas. Canterbury. about 40 km NNW of Christchurch.

On 8 October 1985, in Christchurch. 181 yellow cocoons were buried on a 1.5 mm gauge wire mesh ttay. 100 mm in diameter, 20 mm beneath the floor of a cavity in soil which had housed a common wasp nest the previous summer. The placement method was designed to replicate the environment in which yellow cocoons would be found after the collapse of a nest. The wire mesh tray allowed the passage of moisture. and the later relocation of cocoons for examination.

All further releases of parasitoids were from release boxes (Fig. 1). They were designed to simulate the conditions under which overwintering cocoons were thought to exist. and to offer maximum protec-tion. The sides and lids of release boxes were of un-treated. rough-sawn 25 mm thick Pinus radiata D. Don. Internally, the boxes were 240 mm square and 300 mm deep. The bottoms were covered in 1.5 mm gauge aluminium wire mesh to allow moisture move-ment, and to exclude animals such as rodents and beetles which could damage cocoons. A 25 mm diameter hole was drilled centrally in each side 140 mm below the top, and this was covered with 3.5 mm gauge steel mesh. This mesh size was chosen to be sufficiently large to allow parasitoids to escape freely from the box, but as small as possible to exclude the maximum number oflarger animals that may have destroyed cocoons. A telescoping lid made of P. radiata was screwed down when the box containing parasitoid cocoons was placed in the field. The roof was left unclad, to approximate to natural sites, where rain may seep through to cocoons. Yellow cocoons within each box were placed on a shallow tray of 1.5 mm gauge aluminium wire mesh about 160 mm square. The box was filled with 50 mm of heat-sterilised soil, free of obvious organic material, and the tray with cocoons was buried 20 mm in the soil.

In October 1985,469 yellow cocoons in four release boxes, and 208 yellow cocoons in two release boxes. were set out in Christchurch and Mt Thomas. respectively.

By late January 1986, all 100 yellow cocoons from one release box in Christchurch, a total of 50

cocoons from the other three Christchurch release boxes and the wire mesh tray in a nest cavity, and 208 cocoons from the two boxes at Mt Thomas, were taken back to the laboratory to obtain adultparasitoids for mass-rearing in the Lincoln labomtories.Emerg-ence from cocoons at recovery was not evaluated. However. by August 1987 after a second spring/ summer emergence period. 220 of the 500 cocoons in the remaining three Christchurch release boxes and the wire mesh tray, had produced adults. It is conceivable that about half this number may have emerged by late January 1986. From the frrstrelease of parasitoids in Christchurch on 4 March 1985, until recovery of cocoons from release boxes in late January 1986, about 252 parasitoids were known to have flown, comprising those from cocoons in a nest, released adults, and laboratory-reared yellow cocoons. As at least 55 of these were male, no more than 197 were female.

A further 111 adult parasitoids would have emerged from the four Christchurch release sites in spring/summer of 1986/87. Examination of the remaining cocoons at three sites in winter 1988, (one release box was destroyed) showed that49 parasitoids emerged in spring/summer of 1987/88. Mass releases in winter 1987. During winter 1987, 30 030 yellow cocoons which had been reared at Lincoln in the previous summer, were distributed in the South Island in 286 release boxes (105 cocoons per box). Afurther 1050 yellow cocoons from Lincoln were released in 10 boxes near Hamilton in the North Island (Table 1). Twenty-three release boxes were sited within the greater Christchurch area and 177 in the north and west of the South Island.

Emergence from cocoons in release boxes Daily emergence of paras ito ids from yellow cocoons raised in 1985, under a variety of conditions and times of year, was monitored using trap release boxes. Emergence occurred from August to May. with peaks in August and October.

Emergence from yellow cocoons raised during summer 1987 was similarly monitored. From four ttap release boxes each containing 105 cocoons, the frrst adults appeared on 1 November 1987, peak emergence occurred on 9 November 1987 with 98 (23.3%) individuals. and ceased for the season on 24 December 1987. By then, 248 adults had emerged. The male: female sex mtio was 1 : 48.4 (5 males, 242 females. + 1 escapee. sex unknown). Further details will be presented elsewhere. If the same emergence data held for the 23 release boxes in the Christchurch

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358 New Zealand Journal of Zoology, 1989, Vol. 16

FIg. 1 A release box for S. v. vesparum.

area, about 1425 parasitoids would have emerged, of which about 29 would have been males, and 1396 would have been females.

In the north and west of the South Island, examination of cocoons in 43 release boxes showed that by winter 1988, on average 60.6 parasitoids (range 10-97, SE = 3.97) had emerged per box. At Pelorus Bridge, 266 adults, of which about 260 would have been females, emerged from the three release boxes.

Nest location, collection, and dissection From mid 1979, wasp nests were collected from the Canterbury area for laboratory propagation of S. v. vesparum. Nests were located by advertising in newspapers and on radio and television, and through contacts with pest destruction personnel. Nests that

were thriving were not examined closely for the parasitoid, because this would have rendered the comb useless for parasitoid propagation. However, some cells were opened by us as part of the process for preparing the comb for optimum parasitoid propagation, which would bave revealed any parasitoids in the opened cells. Wasps uncap many cells which contain cocoons, and remove remnants of wasp immatures, which would have exposed S. v. vesparum cocoons.

During summer 1988,17 sites with release boxes in the north and west of the South Island were searched for wasp nests (Fig. 2, see Moller et ale 1988a for detailed descriptions of sites). Most sites were in beech forests infested with honeydew scale insects (Ultracoelostoma assimile (Maskell», but nests were also collected from Nelson City, Hokitika,

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Donovan et al-release and recovery of wasp parasitoid 359

N

r 100km ,

*

*

Key

* Parasitoid release sites systematically searched for wasp nests

Parasitoid release sites • not systematically searched

for wasp nests

FIg.2 Location of parasitoid release sites in the north and west of the South Island which were searched for wasp nests.

Owen River, and Wangapeka. Ten sites were searched systematically to fmdevery nest in transects 8-14 m wide (width depending upon the number of searchers available). Transects were about 2 kIn long and were directed away from release boxes. Searchers 2-3 mapanwalkedslowlyalongacompass bearing. If time permitted, much of the area within a 200 m radius of the release box was also searched. These final searches were not exhaustive, so almost certainly, not all nests within a 200 m radius of each box were found. Searches were conducted from 29 February 1988 to 11 April 1988. Nests were staked

and mapped, and between 4 May and 22 June 1988, were poisoned with carbaryl or fumigated with petrol. Nests were excavated and frozen and later examined in detail. Each layer of each nest was exposed and inspected closely forparasitoid cocoons. For the first few nests the walls of every capped cell were removed. This proved very time-consuming, so only between 60% and 90% of the cells of the remaining nests were inspected in this way. An average of 91 % of the capped cells of all nests were examined for parasitoids. Parasitoid stages were counted, their placement and condition recorded,

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and more than half of all intact cocoons were opened to determine their stage of development at the time of freezing.

RESULTS Recoveries of parasitoids Christchurch. From the f1I'St release of parasitoids on 4 March 1985 to early November 1986, 25 German wasp nests and 16 common wasp nests were collected within about a20 1cm radius of Christchurch City. On 4 November 1986, a German wasp nest which had survived the previous winter was excavated in suburban Christchurch. The nest measured about 600 mm long, 400 mm wide, and 400 mm deep. All stages of brood of all three castes of wasp were present, and abundant new worker comb indicated that the nest had been growing rapidly. A piece of this nest containing mainly sealed worker comb, and measuring about 170 x 170 mm, contained one newly formed yellow parasitoid cocoon in a sealed, worker cell.

After the recovery of this cocoon, and until the release of2415 yellow cocoons in 23 release boxes in Christchurch during winter 1987, another 26 German and 86 common wasp nests were collected for parasitoid propagation. No parasitoids were recovered. In the following 12 months, from winter 1987 to winter 1988, 95 German and 178 common wasp nests were collected, but no parasitoids were recovered.

Nests were not collected from Mt Thomas.

Table 1 Number of parsitoid release boxes distributed per regional area during winter 1987.

Area

South Island Buller Canterbury (North) Canterbury (Mid) Canterbury (South) Central Otago Dunedin Marlborough and Sounds Nelson Otago Lakes Southland Westland

North Island Waikato (Hamilton)

Number of Boxes

4 9

49 9

11 10 76 70 11 10 27

10 296

New Zealand Joumal of Zoology, 1989, Vol. 16

North and west of the South Island. Near the 17 sites with release boxes, 173 nests were dug up (Fig. 3). Ten were V. germanica and 163 were V. vulgaris.

At the Pelorus Bridge site, 2 of 42 nests of the common wasp contained parasitoids. One nest (Nest 1) was 33 m from the nearest release box, and the other nest (Nest 2) was 625 m away from another release box in a different direction (Fig. 4). When poisoned, both nests were producing all castes of wasps, and new comb was being constructed.

Decay of soft tissues in Nest 1 after poisoning and prior to freezing obscured the presence or otherwise of parasitoid larvae, but 22 were detected in Nest 2 (fable 2). All were in the 11 th worker cell comb from the top of the nest White and yellow parasitoidcocoons occurred in both nests, and totalled 1483. Cocoons were present in all combs except the upper three and one worker combs, and the bottom two and one queen combs in Nests 1 and 2, respectively. The majority of cocoons occurred in worker cells, and were most numerous in the 8th worker comb in Nest 1 (148) and the 7th worker comb in Nest 2 (236). In Nest 1,42 queen cells were attacked and in Nest 2, 2 queen cells were attacked.

A total of 484 white cocoons were recorded in the two nests, of which 87 were intact, 393 were emerged, and four were chewed by wasps. The four chewed cocoons were adjacent to areas of comb containing chewed yellow cocoons and so had probably been partly removed by wasps trying to

Table 2 Data from the two nests of Vespula VUlgaris attacked by Sphecophaga vesparum at Pelorus Bridge.

Distance from nearest release box Layers of comb - worker - queen

Nest 1 Nest2 33m 625m

11 11 4 4 8 10 2 3

Worker combs with parasitoids Queen combs with parasitoids Parasitoid larvae (decayed) 22 White cocoons - intact -emerged -chewed Yellow cocoons - intact -emerged -chewed Minimum number of parasitoid stages Parasitised cells re-used by wasps Cells with 2 parasitoids in which I

developing wasp was killed Cells with 2 parasitoids in which 2

developing wasps were killed Minimum number of developing

wasps killed

62 25 152 241

2 2 30 525 14 72

211 147 471 1034

36 95 1 13

o 4

470 1021

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Donovan et al-release and recovery of wasp parasitoid 361

Fig. 3 Distance from release 70 boxes of wasp nests examined for parasitoids. The hatched area re-presents wasp nests at Pelorus Bridge.

(/) ..-(/) (!) Z

60

30

destroy the yellow cocoons. Of the total 999 yel-low cocoons, 555 were intact, 86 were emerged, and 358 were chewed. Seven emerged cocoons had been slightly chewed.

In both nests, a total of 131 cells containing parasitoid cocoons also contained wasp immatures that had been positioned there after the destruction of an earlier, developing wasp. Some white cocoons which had emerged were beneath wasp larval meconia. Eighteen cells contained two parasitoid cocoons. All combinations except two white cocoons were exhibited, including one cell with two yellow cocoons, one above the other. In four cells in Nest 2, one cocoon was positioned partly inside the remains of another. Examination of 293 of the 525 intact yellow cocoons from Nest 2 showed thatallcontained prepupae.

Parasitoids were not recovered from other sites.

DISCUSSION The most obvious means by which a female parasitoid may locate wasp nests is olfactory (MacDonaldetal. 1975). During spring 1986, the only overwintering wasp nest known to us in Christchurch was that from which the one parasitoid cocoon was recovered. New season nests at this time would have been no

400 800 1200 Distance from box (m)

larger than about 0.0001 m3, and probably much smaller (Donovan, unpubl. data), and would have produced much less odour than the attacked German wasp nest, which was about 0.1 m3•

The formation of a newly formed yellow cocoon of S. v. vesparum in a German wasp nest in Christchurch in early November 1986, is consistent with an attack by a female parasitoid in late October 1986. The trap release box emergence data indicate that female parasitoids would have been emerging steadily in early October. The attacking parasitoid may have originated directly from the nearest release box 4.75 km distant, or perhaps from a nest colonised during the previous summer. The possibility of it originating from nests colonised in early spring of 1986 is remote.

The lack of recovery of parasitoids from nests collected in the Christchurch area since late 1986 may have several explanations. If parasitoids attack nests during spring, the nests may be completely destroyed before developing a stream of foraging workers at the nest entrance, and thus they may remain undiscovered. Many nests are destroyed by pest controllers and the public, and some of these nests may have been parasitised. This would reduce the multiplication and dispersal of parasitoids.

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Key • Nest * Parasito id release

box

C""'J Bush margin

~ Buildings

... Parasitised nest

Systematic • search area

New Zealand Journal of Zoology, 1989, Vol. 16

o 100m , .

Fig. 4 Positions of parasitoid release boxes, and wasp nests examined at Pelorus Bridge.

Nevertheless, the lack of recovery of parasitoids from the 385 nests collected since November 1986, suggests that establishment of the parasitoid in Christchurch is unlikely.

At Pelorus Bridge, the attack on two nests may have originated initially from only one female

successfully colon ising one nest. The subsequent production of all forms of progeny, when only 5~ males emerged from the release boxes, suggests that in the field, very few males are needed (if any) for females to reproduce. Winged females, newly emerged from the rust attacked nest, may have

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Donovan et al-release and recovery of wasp parasitoid 363

colonised the second nest. The presence of emerged yellow cocoons in both nests indicates that winged females did fly from nests to seek out and colonise other nests. However, because the nests were each closer to a different release box than they were to each other, two independent attacks by females from separate release boxes seems more likely.

The distances between the release boxes and attacked nests suggests that parasitoids will attack nests that are close to the cocoons from which they emerge (33 m), and that parasitoids can radiate at least 625 m from cocoons and successfully attack. However, since limited areas were searched, it is not known whether parasitoids may have colonised and dispersed from other undiscovered nests before reaching the furthest attacked nest

The presence of parasitoid larvae in one nest and their almost certain presence in the other (Table 2), plus the occurrence of white cocoons which were yet to produce brachypterous females, indicates that parasitoids were propagating rapidly when the nests were poisoned. Because both nests contained all stages of wasp brood, and new comb was being constructed by large workerforces, parasitoids would have completed at least one and possibly several further generations before nest collapse in winter. If so, the numbers of cocoons at nest termination would have been much higher than at the time of nest poisoning. Donovan & Read (1987) counted 5432 yellow cocoons in a nest of the common wasp imported from Europe.

The total number of intact, yellow cocoons in the two nests (555) was more than double the number of adult parasitoids (266) that emerged from all three release boxes in the area. If each nest was colonised by only one female parasitoid, then the females had left 471 and 1034 descendants, respectively (Table 2).

The occurrence of diapausing prepupae in 293 of the 525 yellow cocoons examined from Nest 2 suggests that emergence of winged adults had ceased for the season, and that all 525 yellow cocoons would have been available to produce winged adults in subsequent seasons.

The presence of 86 emerged yellow cocoons suggests that at least this number of winged parasitoids, most of which would have been female, left the nests. Signs of chewing by wasps on seven yellow cocoons from which parasitoids had emerged, suggests that the 358 chewed yellow cocoons had produced parasitoids before being chewed. Observa-tions indicate that the emergence hole in yellow cocoons may provide a purchase point from which

wasps can begin to tear down the cocoons. If para-sitoids emerge before cocoons can be chewed, then 444 winged parasitoids may have left the two nests. This is 1.7 times the number of adults that emerged from the three release boxes. Since some chewed yellow cocoons were reduced to bases only, others may have been removed entirely so that more than 444 winged parasitoids may have left the two nests.

The presence of four chewed, white cocoons shows that these may also be entirely removed. Indeed, their flimsy construction compared to the more resistant yellow cocoons must make this possibility very likely. However, since brachypterous adults emerge 10-12 days after oviposition, their cocoons would be vacated before wasps removed the decaying remnants of wasp immatures, which would then expose white cocoons to attack. The occurrence of emerged, intact white cocoons beneath wasp larval meconia suggests, however, that these cocoons were overlooked by wasps when the remains of the dead host were removed. Then followed wasp oviposition, larval growth, and defaecation by the larva over the emerged white cocoon.

The presence of two discrete parasitoid cocoons in the same cell indicates that their development was simultaneous and that only one developing wasp was destroyed. The siting of, for example, a cocoon within the base of a chewed yellow cocoon indicates that the development of one cocoon followed that of the other, and that two hosts were destroyed. The positions of the cocoons indicates that the sequence of events was probably: the development of one yellow cocoon on a host, the chewing down to the base of the cocoon (after adult parasitoid emer-gence?), the rebuilding of the cell, the occupation of the cell by a second wasp immature, and its subsequent destruction by a second parasitoid, which formed a cocoon. In the four cells in Nest 2, which showed evidence of double wasp occupancy and parasitism, eight wasp immatures would have been destroyed.

This must impose other effects, such as dis-turbances to the sequential cycles of brood rearing, and extra energy expenditure needed for the removal of cocoons and comb rebuilding. These effects would increase as parasitoids multiplied.

There may bea question as to why more attacked nests have not been located in the north and west of the South Island. A major reason may be that the size of the parasitoid population that flew from release boxes was almost certainly miniscule compared to that which would exist where parasitoids have long been established. The chances of locating attacked

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wasp nests after the release of so few parasitoids, where probably many hundreds of wasp nests occurred within the flight range of the parasitoid, must be very small indeed. Therefore, the location of two attacked nests at Pelorus Bridge, suggests that many more nests may have been attacked.

Moller et al. (1988a) found a nest density at Pelorus Bridge during summer 1988 of 10.5/ha (n = 20, SE = 3.0). On this basis then, within a radius of 625 m from all 3 release boxes, and allowing for nest-free areas such as roads and the riverbed, there were probably about 1700 nests within the known flight range of the parasitoid. If more nests were attacked, the number of parasitoids that emerged the following spring from these nests would have been much greater than the number that emerged the previous spring from release boxes. The potential for a large increase in parasitoid numbers in future, with the likelihood of a much higher recovery rate of attacked nests, would appear to be very great Whether wasp numbers will be reduced remains to be seen.

CONCLUSIONS

Theattackbythewaspparasitoid,S. v. vesparumon both V. germanica and V. vulgaris from the release of at most a few hundred adults in each of two areas, indicates that: 1 the procedures for laboratory rearing of the

parasitoid and method of field release have been successful;

2 both species of wasp are hosts in New Zealand; 3 the climate of Marlborough is suitable for

establishing the parasitoid; 4 parasitoids can disperse at least 4.75 kIn in a

season following emergence in spring, and at least 625 m within a season;

5 parasitoids can enter, multiply in, and disperse from common wasp nests within a few months of emergence from release boxes;

6 parasitoids can multiply many times beyond the number released within a single season.

New Zealand Journal of Zoology, 1989, Vol. 16

ACKNOWLEDGMENTS The rearing and distribution of parasitoid cocoons was financed by contributions from local body Councils,private organisations, and individuals. Research in the west and north of the South Island was fmanced mainly by the Department of Conservation, but also by Entomology and Ecology Divisions of the Department of Scientific and Industrial Research. Ross Caley, David Leathwick, John Marris, Richard Harris, and Anne Howie assisted with parasitoid propagation and release box construction. Members of the Department of Conservation and the public helped fmd study areas and nest sites, and allowed access to their land. Chris Pugsley provided liaison and administrative support from the West Coast region of the Department of Conservation. Noel and Doreen Wilson, Peter Ward, Jolm Davey, Wendy Gibbs, Jason Malharn, Elspeth Waghorn, Losalina Whitana, Joanna Rees, Kim Reiersen, and Richard Toft helped in the field and laboratory. Warren Thomas and Dan Pearson commented on an earlier draft of this manuscript To all the above, we express our sincere thanks.

REFERENCES

Clapperton, B. K.; Alspach, P.; Matheson, A.; Moller, H. 1989: The impact of common and German wasps (Hymenoptera: Vespidae) on the New Zealand beekeeping industry. New Zealand journal of zoology 16: 325-331.

Donovan, B. 1.; Read, P. E. C.1987: Attempted biological control of social wasps, Vespula spp., (Hymenoptera: Vespidae) with Sphecophaga vesparum(Curtis) (Hymenoptera: Ichneumonidae) in New Zealand. New Zealand journal of zoology 14: 329-335.

MacDonald, J. F.; Akre, R. D.; Hill, W. B. 1975: Nest associates of Vespula atropilosa and V. pensylvanica in southeastern Washington State. Journal of the Kansas Entomological Society 48, 1: 53-63.

Moller, H.; Plunkett, G. M.; Tilley, J. A. V.; Ward, P. J.; Wilson, N. 1. 1988a: The wasp problem on the West Coast: First year research report Ecology Division report 12: 22 p.

Moller, H.; Tilley, 1. A. V. 1989: Beech honeydew: seasonal variation and use by wasps, honey bees and other insects. New Zealand journal of zoology 16: 289-302.

Moller, H.; Tilley, 1. A. V.; Alspach, P.; Millar, I. R.; Plunkett, G. M.1988b: Impact ofVespula wasps on native insects and birds: first year research report. Ecology Division report No. 13, 45 p.

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