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Background information

Environmental risks of biological control

Reducing the risk

It must be accepted that the risk of adverse impacts from biological control releases can probably never be eliminated. However, carefully conceived containment or quarantine studies can almost certainly reduce risk. Protocols for host specificity testing of weed biological control agents have been developed which depend upon a system of 'centrifugal phylogenetic testing' (Wapshere 1974). This means that non-target species from those most closely related to the target weed to those more distantly related are exposed in sequence to the proposed biological control agent. This enables a profile of the host range of the organism to be developed and facilitates the decision on whether or not to proceed with field release. With insects, assembling a suitable list of potential non-target species to be tested is more difficult because of the much larger number of species involved, and the lack of precise taxonomic information. However, the principles of the system used for weed biological control agents can to some extent be extended to insects.

There has been considerable debate about the desirability of host specificity in proposed biological control agents. While some contend that the presence of alternative hosts can assist the biological control agent through periods when the target host is scarce (Nechols et al. 1992), others maintain that it is irresponsible to release any biological control agent unless it can be demonstrated to be completely host specific. Then again, it is argued that laboratory tests can be unreliable because in confinement in an artificial environment, some proposed biological control agents attack species that would not be attacked in the field (Sands 1993) and vice versa. There is still a great deal of research that needs to be carried out to underpin the design of reliable and feasible protocols. A possible approach is to verify the pre-release predictions of host range made from laboratory tests with post-release field studies to determine realised host range in the field (Barratt et al. 1997). This can help to build up a database which can assist decision makers in the future. Clearly, the environmental risks associated with the introduction of a biological control agent have to be weighed against the economic benefits of controlling a pest, or in some cases, the environmental cost of doing nothing.


Barratt B.I.P., Evans A.A., Ferguson C.M., Barker G.M., McNeill M.R. and Phillips C.B. (1997). Laboratory nontarget host range of the introduced parasitoids Microctonus aethiopoides and Microctonus hyperodae (Hymenoptera: Braconidae) compared with field parasitism in New Zealand. Environmental Entomology 26: 694-702.

Nechols J.R., Kauffman W.C. and Schaefer P.W. (1992). Significance of host specificity in classical biological control. Pp. 41-52 In: Selection Criteria and Ecological Consequences of Importing Natural Enemies, W.C. Kaufmann and J.E. Nechols (Ed.) Entomological Society of America, Lanham, Maryland, USA.

Sands D.P.A. (1993). Effects of confinement on parasitoid-host interactions: interpretation and assessment for biological control of arthropod pests. Pp. 196-199 In: Pest Control in Sustainable Agriculture, S.A. Corey, D.J. Dall and W.M. Milne (Ed.) CSIRO, Canberra, Australia.

Wapshere A.J. (1974). A strategy for evaluating the safety of organisms for biological weed control. Annals of Applied Biology 77: 201-211.