Biological Control
Landcare Research is developing a range of tools for controlling wasps. Some are for widespread long-term control, and others for localised short-term control. It is likely that several control tools will be needed to solve the wasp problem.
Classical Biological Control
Classical biological control offers a long-term, self-sustaining and environmentally friendly way of reducing wasp numbers. However, wasps would never be eliminated because the control agents depend on wasps for their own survival. We need an organism that will attack wasps and do well in New Zealand conditions but not harm other insects such as honeybees. Finding suitable biological control agents is a long, slow process. Identifying an appropriate agent and screening it to make sure it attacks only wasps can take many years. Once an agent is set free in the environment, it may take many more years to have any noticeable effect.
Sphecophaga vesparum vesparum
Wasp parasitoid searching wasp comb for place to lay eggs |
Since 1987, a parasitoid (called Sphecophaga vesparum vesparum) has been released at hundreds of sites throughout New Zealand. This parasitoid was brought from Europe where it attacks the same wasp species we have here. It lives in wasp nests, feeding on and thus destroying developing wasps. |
The wasp parasitoid can reproduce without mating. There are two female forms of the parasitoid: one winged, the other brachypterous,with very short wings and incapable of flying. Both forms lay eggs that give rise to three kinds of cocoons. Within 14 days, adults are produced from two of these, but the third strongly built cocoon over-winters in the remains of the host nest for up to four seasons.
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| Parasitoid lifecycle |
The parasitoid is established in at least two sites: Ashley Forest, north of Christchurch, and Pelorus Bridge in Marlborough. We have monitored the Pelorus Bridge site since the parasitoid established there in 1988. Each year, the parasitod infests an average of about 8% of nests within 2 km of the release site. However, there has been no detectable reduction in wasp numbers that could be attributed to the parasitoid. Mathematical modelling suggests that the parasitoid may suppress wasp density by a maximum of 25% after 20–30 years, but only if 50% of spring nests are killed. There is no evidence that any spring nests are killed. If only 10% of spring nests are killed, then the predicted reduction in wasp numbers falls to near zero.
Sphecophaga vesparum burra
Another subspecies (close relative) of parasitoid, called S. v. burra, has been brought to New Zealand from North America. More than 35 000 cocoons were released at seven sites in New Zealand between 1996 and 1998. Most cocoons were released at two South Island sites: Binser Track in Arthur’s Pass National Park (13 200 cocoons) and Tennyson Inlet in the Marlborough Sounds (13 660 cocoons). More than 5000 adult parasitoids emerged at both of these sites over 4 years. By 2001, more than 300 wasp nests had been dug to check for establishment of the parasitoid, but there was none. The other 5 sites have not yet been checked. |
Sites where S. v. burra were released. |
The following scientific papers have more information:
Barlow, N.D; Beggs, J.R.; Barron, M.C. in press: Dynamics of common wasps in New Zealand beech forests: a model with density-dependence and weather. Journal of Animal Ecology.
Barlow, N.D.; Moller, H.; Beggs, J.R. 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: 31–34.
Beggs, J.R., Harris, R.J., Read, P.E.C. 1996: Invasion success of the wasp parasitoid Sphecophaga vesparum vesparum (Curtis) in New Zealand. New Zealand Journal of Zoology 23: 1–9.
Harris, R.J.; Rose, E.A.F. 1999: White and yellow cocoon production in the vespid parasitoid Sphecophaga vesparum (Hymenoptera: Ichneumonidae). New Zealand Journal of Zoology 26:89–96.
Moller, H.; Plunkett, G.M.; Tilley, J.A.V.; Toft, R.J.; Beggs, J.R. 1991: Establishment of the wasp parasitoid, Sphecophaga vesparum (Hymenoptera: Ichneumonidae), in New Zealand. New Zealand Journal of Zoology 18: 199–208.
Toft, R.J.; Malham, J.P.; Beggs, J.R. 1999: Mortality and emergence pattern of over-wintering cocoons of the wasp parasitoid Sphecophaga vesparum vesparum (Hymenoptera: Ichneumonidae) in New Zealand. Environmental Entomology 28 (1): 9–13.
Inundative Biological Control
Pathogens (agents causing diseases) are a factor regulating many insect populations. For example, research into controlling honeybee diseases is of ongoing importance to the beekeeping industry. Pathogens are also beginning to be used to control social insects such as termites and fire ants.
We are exploring the usefulness of those pathogens already in New Zealand, as additives to bait for the control of wasps. The advantage of using a pathogen is that it should multiply within the nest, killing it as effectively as an insecticide would, but without the wasps needing to collect so much bait. Laboratory tests have established that wasps are highly susceptible to a wide range of generalist insect pathogenic fungi. Fungi spores were also transferred readily between individuals, and larvae and worker wasps were killed. However, field trials with pathogens were less successful. Fungi did not spread through an active wasp colony, despite trying several different application methods. |
Wasp forager covered in fungus |
| Wasps have a natural defence against some pathogens. They have antibiotics in their saliva and venom, and can quickly detect and remove infected individuals from the nest before disease spreads. It may be possible to overcome this cleaning behaviour by combining chemicals with pathogens, and trials are continuing to look at this. |  |
The following scientific papers have more information:
Glare, T.R.; Harris, R.J.; Donovan, B.J. 1996: Aspergillus flavus as a pathogen of wasps, Vespula spp., in New Zealand. New Zealand Journal of Zoology 23: 339–344.
Harcourt, S.J.; Harris, R.J.; Rose, E.A.F.; Glare, T.R.; Nelson, T.L. 1997: The potential of Beauveria bassiana for the control of common and German wasps (Vespula vulgaris L. and V. germanica F.) in New Zealand. Proceedings of 4th International Workshop on Microbial Control of Soil Dwelling Pests.
Harris, R.J.; Harcourt, S.J.; Glare, T R.; Rose, E.A.F.; Nelson, T.L. 2000: Susceptibility of Vespula vulgaris (Hymenoptera: Vespidae) to generalist entomopathogenic fungi and their potential for wasp control. Journal of Invertebrate Pathology 75: 251–258.
Gut microflora of wasps
| One approach to developing novel wasp control options is via a Trojan horse – using organisms that wasps don’t recognise as a threat to defeat these persistence invaders. We are working on the idea that through genetic modification we can alter organisms that would otherwise be harmless associates of wasps to kill them. |  |
| Rickettsia in the fat body of an insect. The small particle are 6 um long. |
What we need to make this process work is a microbe exclusively associated with wasps, so that no other insects would be affected. We are collaborating with researchers in Australia to screen wasps in both countries. All insects carry microbes, so we are looking to see what microbes wasps carry in their guts. So far, the results have been disappointing. Wasps do not have many bacteria in their guts and what they do have is picked up from the environment, probably with food. So, although we have been able to identify a number of bacteria from wasp guts, no single species of bacteria that we are able to culture has been found in all wasps, and there are no obvious candidates for bacteria associated only with wasps.
All is not lost, however, as Australian researchers have found an organism smaller than a bacterium which is present in their wasps. This organism is not able to be grown outside a wasp body and is very likely to be specific to wasps. We are currently trying to determine if this sub-bacterial organism is present in New Zealand wasps, and working with the Australians to find out what it does (is it harmful, helpful or neither?). This organism may be our best chance to develop a self-sustaining control for wasps in New Zealand.