Biocontrol introduction
Target pest: Vespula germanica (Hymenoptera: Vespidae), German wasp
Agent introduced: Sphecophaga vesparum vesparum (Hymenoptera: Ichneumonidae)
Imported:
1980, 1981, 2016, 2017
Import source:
1980 Switzerland, Germany and Austria; 1981 Switzerland and Austria; 2016, 2017 south-western UK
Import notes:
Cameron et al. (1989) - three shipments of S. v. vesparum totalling 7,524 cocoons in combs of Vespula vulgaris collected in Switzerland, Germany and Austria were received at Lincoln, Canterbury during September and October 1980. Three further shipments totalling 7,524 cocoons (781 from nests of Dolichovespula saxonica, the rest from nests of V. vulgaris) were received during October and November 1981 from Switzerland and Austria. From 33 female parasitoids that emerged shortly after the 1980 importation, three generations were reared on German wasps (V. germanica). In December 1984 the last of the imported parasitoid cocoons produced 14 females, from which a continuous breeding population was established on common wasps (V. vulgaris).
Landcare Research (2016m) - common wasp (Vespula vulgaris) nests were collected in the UK (from the same geographic range New Zealand's common wasps come from [south-western UK - see Brown and Groenteman (2017), Bob Brown (Landcare Research) (2018 - pers. comm.) entry in 'General comments' section]) in September and October 2016 and imported into containment at Lincoln, Canterbury. A good proportion of cells appear to be parasitised with S. v. vesparum.
Landcare Research (2017h) - for some yet unknown reason the first lot of S. v. vesparum cocoons from the material collected in the UK in September and October 2016 all turned out to be overwintering pupae. There is no way to know what proportion of them will emerge this coming spring, which will affect planned releases.
Landcare Research (2017i) - thirteen Vespula nests collected in southern UK in late-summer 2017 were imported into quarantine at Lincoln, Canterbury. Parasitoids present included well over 1,000 S. v. vesparum pupae, which, added to the material imported in 2016, will boost the genetic variance of the quarantine population.
Released:
1985
Release details:
Cameron et al. (1989), Donovan et al. (1989) - parasitoids raised in quarantine were released into seven Vespula vulgaris (common wasp) and six Vespula germanicus (German wasp) nests in Canterbury at Southbridge, Lincoln, Christchurch and Mt Thomas (North Canterbury) from early-March to mid-May 1985. By October 1985, a further 858 cocoons were released into nests at Christchurch and Mt Thomas. In 1987 more than 30,000 overwintering cocoons were distributed over the South Island as follows: Buller (420), North Canterbury (945), Mid-Canterbury (5,145), South Canterbury (945), Central Otago (1,155), Dunedin (1,050), Marlborough and Marlborough Sounds (7,980), Nelson (7,350), Otago lakes (1,155), Southland (1,050), Waikato (1,050) and Westland (2,835). A further 1,050 overwintering cocoons were released near Hamilton in the North Island.
Read et al. (1990) - public and private organisations contributed financially to the project to rear and release S. v. vesparum and were provided with parasitoids to release at sites of their choice. As a result of this funding, 108,400 parasitoids were released (as overwintering pupae in protective release boxes) throughout New Zealand (including Stewart Island) between 1987 and 1989.
Landcare Research (2016m) - pending disease freedom, releases of the S. v. vesparum collected in the UK in September and October 2016 [see Brown & Groenteman (2017), Bob Brown (Landcare Research) (2018 - pers. comm.) entry in 'General comments' section for rationale for new releases] will begin in January 2017, as adult parasitoids emerge from the imported wasp comb.
Brown and Groenteman (2017) - the new genetic stock of S. v. vesparum imported from UK in 2016 has passed through one generation in containment and is expected to be released into the wild in early-2018.
Landcare Research (2017h) - as all S. v. vesparum cocoons from the material collected in the UK in September and October 2016 all turned out to be overwintering pupae an autumn 2017 release was not possible. There is no way to know what proportion of them will emerge this coming spring (2018), but field releases at that time will probably not be as numerous as had been hoped.
Establishment:
Cameron et al. (1989) - evidence of establishment was seen in Canterbury following 1985 releases: post-release examination of the nests into which S. v. vesparum was released in March-May 1985 showed six V. vulgaris and three V. germanica nests had been attacked with at least one generation of parasitoid adults having emerged in four V. vulgaris nests and one V. germanica nest, and in November 1986 one parasitoid overwintering cocoon was recovered from an overwintered V germanica nest in Christchurch. In 1988, the parasitoid was recovered from two V. vulgaris nests at Pelorus Bridge, Marlborough.
Donovan et al. (1989) - one S. v. vesparum cocoon was recovered from a German wasp nest in Christchurch in November 1986 [see Cameron et al. (1989) entry above]; however, the lack of recovery of parasitoids from 385 nests collected in this area since November 1986 suggests that establishment of the parasitoid in Christchurch is unlikely. The parasitoid was recovered from two V. vulgaris nests at Pelorus Bridge, Marlborough in 1988 [see Cameron et al. (1989) entry above]; because parasitoids had multiplied in the nests (all propagation stages of the life cycle had been completed) and dispersed from them, it is likely S. v. vesparum has established at Pelorus Bridge.
Read et al. (1990) - Vespula nests were examined at 22 sites in the South Island and one at Ruakura, Waikato, North Island in the summer and autumn of 1988/89, and one at Pelorus Bridge, Marlborough, South Island in January 1990. Sphecophaga vesparum vesparum was only found at the Pelorus Bridge site; as these must have been field-developed individuals, this parasitoid is now considered established in New Zealand.
Moller et al. (1991) - establishment of S. v. vesparum was monitored in summer/autumn 1987, 1988 and 1989 at 39 sites where releases were made in spring 1987, 1988 or 1989. One site was near Taupo in the North Island, the rest in the Nelson, Marlborough, and West Coast regions of the South Island. The parasitoid overwintered and has probably become established at Pelorus Bridge near Nelson. In 1990, an infested nest was recovered 7.1 km from this release site, indicating that the parasitoid can disperse at least 2.37 km per year. However, the proportion of nests parasitised at Pelorus Bridge has increased only slightly in the first 3 years after release. No S. v. vesparum were recovered at the other 38 sites where they were released and monitored. This may reflect the small number of parasitoids that emerged from release boxes at some sites, the small number of nests inspected at others, or a low parasitoid population density. However, combined data from this and other studies (e.g. no evidence of parasitism in 80 Vespula nests near Christchurch in the South Island, despite a large number of parasitoids released in the vicinity) suggests that the parasitoid is having difficulty establishing in many areas.
Beggs et al. (1996) - thirty-three release sites (in Otago, Canterbury, West Coast, Nelson and Marlborough in the South Island, and Waikato and Auckland in the North Island) were checked for establishment of S. v. vesparum 2-3 years after release at each site. The parasitoid appears to be firmly established at Pelorus Bridge (Marlborough) and is dispersing from the initial release site. The level of parasitism has varied substantially from year to year but is tending to increase. The parasitoid has also established at Ashley Forest, a beech forest in the Canterbury foothills. Two parasitised nests were detected there in years that nests were being inoculated and/or cocoons released, one in 1990 and one in 1991. In addition, one parasitised nest was found in 1993, a year after the last releases, indicating the parasitoid had successfully over-wintered in the wild and attacked nests in the season after release. The parasitoid has apparently not established at any of the other sites checked. Many more parasitoids were released at the two sites where establishment is confirmed than at most sites where establishment failed, potentially a crucial factor with respect to likelihood of establishment. Additionally, S. v. vesparum released in New Zealand can be traced to one female from Switzerland, Germany or Austria; although fertile males are produced, the parasitioid can reproduce parthenogenetically and the importance of mating is poorly understood. The stock currently established in New Zealand may have a low genetic variability and may be a strain not well adapted to New Zealand conditions.
Barlow et al. (1998) - measurement of S. v. vesparum parasitism rates at Pelorus Bridge, Marlborough from the time of release (1987 and 1988) until 1993 indicates a rate of spread of 1 - 1.5 km per year. However, there is a very low rate of local increase (in the area it is already present), suggesting an approximate 3-fold increase in the total parasitoid population each year.
Donovan et al. (2002) - recovered from one German wasp (V. germanicus) nest in Christchurch (Mid-Canterbury) in 1986, and considered to have established at Pelorus Bridge (Marlborough) by 1988. By 1995 it was being recovered from 10% of common wasp (V. vulgaris) nests in foothills west of Christchurch and in 1998 was found in one common wasp nest in Christchurch.
Landcare Research (2016l) - the distribution of S. v. vesparum is limited to one site in Marlborough and one in Canterbury (both in the South Island). The poor establishment was probably the result of a genetic bottleneck due to rearing difficulties (one, or at best two, founder females) and a geographic mismatch between the target (originating from the UK) and agent (sourced from Switzerland, Germany and Austria) populations.
Landcare Research (2018l) - surveys for S. v. vesparum were carried out in 2018 in the View Hill area near Oxford, Canterbury and the Pelorus River area upstream of the Pelorus River Bridge in Marlborough; areas still known to have S. v. vesparum populations as recently as 2016. No S. v. vesparum were found in Vespula nests from View Hill, despite a highly-infested nest being found there in 2016. Of 42 nests surveyed in the Pelorus area, two nests had low level infestations of the parasitoid. This site has had intensive poison baiting over the past several years; it was reassuring there were any Sphecophaga recovered there at all.
Impacts on target:
Barlow et al. (1996) - S. v. vesparum has established at low levels at two sites; the Pelorus Bridge site near Nelson has been studied in detail. Here parasitism levels (% autumn nests parasitised) of Vespula [in this case V. vulgaris, the other target pest for S. v. vesparum] have remained around 5% for the five years since the initial releases, with a slight suggestion of an upward trend. A 50% reduction in queen output from parasitised autumn nests was observed but contributes little to host suppression because it occurs before density dependence operates in the host's life cycle. A model based on the Pelorus Bridge data suggests that ultimate parasitism levels depend almost entirely on the parasitoid's effective ratio of increase (the number of spring adults produced per [previous] spring adult), which is estimated at 1.3 - 1.6 at Pelorus Bridge, close to the lower limit of 1 for persistence. Such values suggest an ultimate suppression of wasp nest density and level of parasitism of about 10% and 25%, respectively. The low ratio of increase and the parasitoid's limited likely impact appear to be due to a combination of delayed emergence of overwintering cocoons, low cocoon survival, and low production of cocoons per parasitised autumn nest. Additionally, a reduced or variable attack rate may contribute to the parasitoid's lack of establishment at other sites, possibly due to poor synchrony between spring emergence of wasp queens and adult parasitoids.
Beggs et al. (1996) - Sphecophaga vesparum vesparum has been established at Pelorus Bridge (Marlborough) since 1988 and annually infests an average of 8.5% of nests within 2 km of the release site. Although the parasitism rate has tended to increase since 1988, there has been no corresponding decrease in the density of wasp nests compared with non-parasitised sites. A preliminary mathematical model [see Barlow et al. (1996) entry above in this section] of wasp population dynamics based on New Zealand data suggests that an equilibrium level of approximately 20% of nests parasitised will be reached eventually, but that the parasitoid is unlikely to reduce wasp density by more than 10%, meaning many sites would still have wasp densities well above the threshold levels that impact on native fauna.
Barlow et al. (1998) - while S. v. vesparum appears to be spreading relatively quickly at Pelorus Bridge, Marlborough, with an overall high rate of population growth [see Barlow et al. (1998) entry in the ‘Establishment’ section], the carrying capacity, or local equilibrium level for the parasitoid appears to be low, in the sense that only about 10% of available Vespula nests are actually parasitised. It is the apparent low local equilibrium level and/or slow rate of local increase, rather than poor dispersive ability, which is likely to limit its future impact as a biological control agent of wasps.
Donovan et al. (2002) - during 1999 and much more so 2000-2002 the numbers of wasp nests were unusually low over wide areas. The cause of the collapse of wasp populations is unknown; however, the establishment of S. v. vesparum is the only new factor known to be killing wasps. If this parasitoid has established widely and is attacking small early-season nests, then it could be contributing to the reduced numbers of wasps observed later in summer.
Beggs et al. (2008) - every year from 1988 to 2004, Vespula nests at Pelorus Bridge [near Nelson in the South Island] were dug up to assess the impact of S. v. vesparum. A maximum of 17% of nests parasitised was reached in 1999, but the parasitism rate was highly variable of often considerably lower than this and there was no significant increase with time. Not only were few wasp nests parasitised but there was an exponential reduction in the number of parasitoids produced per parasitised nest from a peak of 570 per nest in 1990 to only 15 in 2004. Even when S. v. vesparum density was high, the parasitoid had no detectable impact on the number of small cells or the total host nest size, but it halved the number of large (reproductive) cells produced. This may have resulted in fewer queens produced per parasitised nest, but this does not mean Vespula populations would necessarily decrease, because there is a strong density-dependence regulating wasp populations which operates after queen production and there is usually an oversupply of queens each year. There was no evidence that Vespula population density at Pelorus Bridge had declined relative to five other study sites where the parasitoid had not established. The parasitoid is unlikely to have had any significant effect on wasp populations to this point in time, nor is it likely to impact host populations in the future.
Brenton-Rule et al. (2018) - mitochondrial DNA sequencing detected two V. germanica haplotypes in New Zealand, one common and one rare (found only in Auckland). The common haplotype was an exact match to the most common haplotype in the United Kingdom; the rare haplotype is genetically similar to populations from Central Europe. Natural enemies such as parasitoids coevolve with their host prey, which can lead to distinct host-strain relationships that vary geographically. The S. vesparum vesparum released in New Zealand were sourced from Austria, Germany and Switzerland; part of the reason for its failure to significantly impact V. germanica in New Zealand may be a mismatch between the geographically distinct social wasp and parasitoid strain.
Lester & Beggs (2019) - although the number of S. v. vesparum per parasitised nest was initially high, this was not sustained. These poor results could be due to the low genetic variability of the released parasitoids [see Beggs et al. (1996) entry in ‘Establishment’ section above, noting that S. v. vesparum released in New Zealand can be traced to one female from Switzerland, Germany or Austria] and/or a mismatch between the origin of the parasitoid and the wasp host [see Brenton-Rule et al. (2018) entry above in this section, which reports the common New Zealand haplotype of V. germanica matches a haplotype from the UK]. However, they may just reflect actual parasitism rates; one study in the native range found S. v. vesparum was rare, with a maximum of only 0.4% of brood was parasitised.
General comments:
Brown & Groenteman (2017), Bob Brown (Landcare Research) (2018 - pers. comm.) - in 2016 permission was granted to re-introduce new genetic stock of Sphecophaga vesparum vesparum. This involved an Environmental Protection Authority (EPA) ruling that S. v. vesparum was present in New Zealand prior to 29 July 1998 and therefore not a "new organism", so that EPA approval to import this species was not required, and Ministry for Primary Industries (MPI) import permits were issued in 2016 and 2017. The rationale in revisiting S. v. vesparum as a control agent was that insects collected for the original introductions came from a geographic range that poorly matched the geographic origin of Vespula in New Zealand, and that better-matched parasitoids may have a better capacity to evade nest hygiene and have an impact on Vespula populations. Recent DNA analysis has determined that the origin of New Zealand's common wasp is probably south-western UK.
References
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Barlow ND, Moller H, Beggs JR (1996). A model for the effect of Sphecophaga vesparum vesparum as a biological control agent of the common wasp in New Zealand. Journal of Applied Ecology 33(1): 31-44 https://doi.org/10.2307/2405013
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