Evaluation of a candidate classical biological control agent and critical assessment of suggested host specificity testing guidelines

The leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae), is a Palaearctic pest of Allium crops. It is considered a threat to crop production and wild Allium biodiversity in Canada, where it was unintentionally introduced and continues to spread. This research explores the potential for a classical biological control programme against leek moth in Canada.;A life table study of leek moth in its native range revealed that total pre-imaginal mortality varied between 96.4 and 99.6% over the three years of the study. Natural enemies contributed significantly and consistently to mortality in the pupal stage only. The pupal parasitoid, Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae) was selected for evaluation as a candidate biological control agent.;Several cold exposure experiments were run to test the cold hardiness of D. pulchellus. Parasitoids still developing inside their hosts were less tolerant of extended periods of cool (above-freezing) or freezing temperatures than adults, suggesting that D. pulchellus overwinters in the adult stage. Females survived cold treatments better than males and were able to survive for several weeks at temperatures that would be experienced under a layer of snow during the winter months in Canada. Thus, this agent is expected to be suitable for the Canadian climate.;During oviposition trials in the laboratory, motivation to oviposit was influenced by the physiological and informational state of the parasitoids. In particular, parasitoid age and nutritional status both had a significant effect on the number of host pupae killed. In contrast, previous host experience and parasitoid density had weaker and inconsistent effects while mating status, arena size and the presence/absence of the host plant had no observable effect. When young and old D. pulchellus females were used in no-choice host specificity tests, there was no difference in the acceptance rate of non-target species. However, changing the ratio of target to non-target hosts in choice tests affected the oviposition response of old, but not young, parasitoids, indicating that there is an age effect. Manipulation of biological control agents to increase their motivation to oviposit in host range tests will require knowledge of the specific effects of endogenous and exogenous factors on their foraging behaviour.