Influence of Target Pest Feeding Niche on Success Rates in Classical Biological Control

Data were extracted from published information to evaluate the influence of pest feeding niche on the past performance of classical biological control against holometabolous insect pests. Data were tallied and analyzed to account for confounding variables and to minimize potential sources of sampling bias. For the two orders with adequate sample sizes, biological control was much more successful against pest species that feed in relatively exposed locations (i.e., folivores) than against species that feed while deeply concealed within plant tissue or below ground. In the Lepidoptera, partial or better success was achieved against 61% of folivorous species (e.g., free-feeders, leaf rollers, leafminers, etc.) but against only 15% of deeply concealed pests (e.g., borers); in the Coleoptera, success rates were 57 and 22%, respectively. Rates of establishment of introduced parasitoids and the effectiveness of established parasitoids were also greater against exposed than against deeply concealed pests. In addition, importation of ectoparasitoids, a group usually restricted to concealed hosts, was strongly associated with biological control failure. Contrary to expectations, the performance of biological control was not poorer against pests using feeding niches that permit greater mobility. In the Coleoptera, biological control was more successful against pests in types of feeding niches that typically support larger numbers of parasitoid species.