Test species selection
Arthropod biological agents
The number of insect species which could be considered for host range testing will always far out-number those for plants, and our knowledge of insect phylogeny is often far less comprehensive than that for plants. Indeed, in New Zealand many insect species remain undescribed, and undiscovered. This makes the adoption of the test species selection method for host specificity testing far much more difficult than it is for weed biological control agents. Furthermore, rearing insects in sufficient numbers for robust tests is often more challenging than for plants. Nevertheless, attempts to develop test insect selection methods have been made.
Selecting the test insect list
Some factors to be considered in selecting test species for host specificity testing have been discussed elsewhere in detail (Goldson and Phillips 1990, Goldson et al. 1992, Barratt et al. 2000). Depending upon the nature of the insect pest that is the proposed target of biological control, sometimes significant amounts of preliminary information can be gleaned on a proposed biological control agent from various sources in the public arena (Hoddle 2004, Sands and Van Driesche 2004). Many potential pitfalls such as taxonomic synonymy and misidentifications can be avoided if awareness of the possibilities is high (Sands and Van Driesche 2004). One process that could be followed in obtaining a suitable host testing list is (Barratt et al. 1999):
- Examine phylogenetic affinities between the target host and non-target species, and rank them as far as possible into species and genera from those closely related to those distantly related.
- The New Zealand Arthropod Collection (NZAC) [http://www.landcareresearch.co.nz/resources/collections/nzac] has information available for some insect taxa.
- Examine ecological affinities between native fauna and target hosts by listing species that occupy a similar niche or feed on related plant species, e.g. leaf miners, seed feeders, grassland dwellers, canopy feeders etc, irrespective of phylogenetic affinities.
- Investigate the extent to which potential non-target species and target hosts occur in mixed populations and use this as a guide to taxa most immediately at risk. This may require additional targeted field surveys.
- Use the data above to prioritise the list of test species and expose those considered most 'at risk' to parasitoids in laboratory tests. Include exotic beneficial species such as other valued biocontrol agents, as well as insects of commercial, cultural or aesthetic significance (Sands and Van Driesche 2000), in a priority test list.
- Finally evaluate the results of initial tests to determine the need for further testing (Barratt et al. 1999).
Another approach similar to that described above has been published recently where the list compiled using phylogenetic and ecological criteria is filtered by eliminating species which have different spatial, temporal and morphological characteristics which do not coincide with the target species (Kuhlmann et al. 2006).
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.
Barratt B.I.P., Goldson S.L., Ferguson C.M., Phillips C.B. and Hannah D.J. (2000). Predicting the risk from biological control agent introductions: A New Zealand approach. Pp. 59-75 In: Nontarget effects of biological control introductions, P.A. Follett and J.J. Duan (Ed.) Kluwer Academic Publishers, Norwell, Massachusetts, USA.
Goldson S.L. and Phillips C.B. (1990). Biological control in pasture and lucerne and the requirements for futher responsible introduction of entomophagous insects. Bulletin of the Entomological Society of New Zealand 10: 63-74.
Goldson S.L., McNeill M.R., Phillips C.B. and Proffitt J.R. (1992). Host specificity testing and suitability of the parasitoid Microctonus hyperodae (Hym.: Braconidae, Euphorinae) as a biological control agent of Listronotus bonariensis (Col.: Curculionidae) in New Zealand. Entomophaga 37: 483-498.
Hoddle M.S. (2004). Analysis of fauna in the receiving area for the purpose of identifying native species that exotic natural enemies may potentially attack. Pp. 24-39 In: Assessing host ranges for parasitoids and predators used for classical biological control: a guide to best practice, R.G. Van Driesche and R. Reardon (Ed.) USDA Forest Service, Morgantown, West Virginia.
Kuhlmann U., Schaffner U. and Mason P.G. (2006). Selection of non-target species for host specificity testing. Pp. 15-37 In: Environmental impact of invertebrates for biological control of arthropods: methods and risk assessment F. Bigler, D. Babendreier and U. Kuhlmann (Ed.) CABI Publishing, Wallinford, Oxford.
Sands D.P.A. and Van Driesche R.G. (2000). Evaluating the host range of agents for biological control of arthropods: rationale, methodology and interpretation. Pp. 69-83 In: Host-specificity testing of exotic arthropod biological control agents: the biological basis for improvement in safety, R.G. Van Driesche, T. Heard, A.S. McClay and R. Reardon (Ed.) USDA Forest Service Bulletin, Morgantown, West Virginia, USA.
Sands D.P.A. and Van Driesche R.G. (2004). Using the scientific literature to estimate the host range of a biological control agent. Pp. 15-23 In: Assessing host ranges for parasitoids and predators used for classical biological control: a guide to best practice, R.G. Van Driesche and R. Reardon (Ed.) USDA Forest Service, Morgantown, West Virginia.
Weed biological control agents
Host range testing methods