This section provides guidance on testing methods that can be used for weed and arthropod biological control agents in containment. The results of these tests are a vital component of the information that needs to be given in the application form for general or conditional release of new organisms, in this case, biological control agents.
Weed biocontrol agents
The objective of host specificity assessment in weed biocontrol is to quantify the ability of prospective biological control agents to attack non-target plant species after introduction (Marohasy 1998). Plant species are chosen for host range testing on the basis of their taxonomic relationship to the target species (Wapshere 1989, Harley and Forno 1992). By exposing prospective agents to progressively less related plant species (i.e. to different varieties of the target host, then to different species in the same genus, then to different genera in the same tribe, and so on) it is thought that all plant species that might support populations of the agent will be identified (Tallamy 1999). A more novel approach is to expose the agent to plants with similar signatures of secondary metabolic compounds, regardless of their taxonomic affiliation with the target species (Tallamy 1999).
If the majority of host specificity testing occurs in containment then the risk that laboratory studies will generate conservative results increases. In weed biocontrol, host specificity testing has to balance two potentially conflicting needs; avoiding the introduction of an agent that may cause unacceptable damage to a non-target plant but arguably, just as important is avoiding the rejection of a potentially effective agent unnecessarily.
Pre-release host specificity testing is carried out to assist in the prediction of the likely post-release field host range and impact of introduced biological control agents. Strictly monophagous parasitoids are rare, and in some taxonomic groups, non-existent. While it is often stated that a high degree of host specificity is desirable in the interests of minimising non-target effects, there is also a view (now less widely advocated) that the availability of alternate hosts can be important for the success of the biological control in the long-term (e.g. Nechols et al. 1992). The decision to be made by the EPA to allow any biological control release is a compromise based on incomplete knowledge, and must be the result of a risk/benefit analysis. The benefit is usually easy to determine in economic terms, but it is far more difficult to place a value on indigenous species, environmental integrity and biodiversity (Barratt et al. 1999).
Barratt B.I.P., Ferguson C.M., McNeill M.R. and Goldson S.L. (1999). Parasitoid host specificity testing to predict host range. Pp. 70-83 In: Host specificity testing in Australasia: towards improved assays for biological control, T.M. Withers, L. Barton-Browne and J.N. Stanley (Ed.) CRC for Tropical Pest Management, Brisbane, Australia.
Harley K.L.S. and Forno I.W. (1992). Biological control of weeds. A handbook for practitioners and students. Inkata Press, Melbourne. 74 pp.
Marohasy J. (1998). The design and interpretation of host-specificity tests for weed biological control with particular reference to insect behaviour. Biocontrol News and Information 19: 13-20.
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.
Tallamy D.W. (1999). Physiological issues in host range expansion. Pp. 11-26 In: Proceedings: Host specificity testing of exotic arthropod biological control agents: The biological basis for improvement in safety, N.R. Spencer (Ed.) Bozeman, Montana.
Wapshere A.J. (1989). A testing sequence for reducing rejection of potential biological control agents for weeds. Annals of Applied Biology 114: 515-526.
Test species selection