A new perspective on the selection of test plants for evaluating the host-specificity of weed biological control agents: the case of Deuterocampta quadrijuga, a potential insect control agent of Heliotropium amplexicaule

This paper describes the host-specificity testing of the leaf-beetle, Deuterocampta quadrijuga, a candidate agent for the biological control of blue heliotrope, Heliotropium amplexicaule, in Australia. Selection of plants for testing was based on three elements of potential risk; phylogenetic relatedness, biogeographic overlap, and ecological similarity. A phylogenetic analysis of the test data showed a strong relationship between the host-choice behavior of D. quadrijuga and the phylogenetic relatedness of the test plant. It also showed that that the inclusion of plants solely because of their economic or conservation status did not add to the information obtained from the tests. D. quadrijuga was shown to pose a very small risk of causing short-term damage by temporary feeding on nontarget species, and an even smaller risk of causing long-term harm by colonising them. On the basis of these results, it was approved for field release in Australia in July 2001. The paper makes a number of general recommendations for host-specificity testing of arthropods used in weed biological control, namely that: (1) testing protocols specifically address two components of risk, colonization of nontarget plants and collateral feeding damage, (2) the selection of test plants should be based strictly on phylogeny where data is available, i.e., based on representative clades rather than named hierarchical taxa, (3) geographic overlap and ecological similarity should be used to select representative species within clades to ensure assessment of the highest level of risk, and (4) the testing of safeguard economic species that have no phylogenetic justification is unnecessary and should be abandoned.