Comparative responses to essential oils by the obliquebanded leafroller (Choristoneura rosaceana) and the rosy apple aphid (Dysaphis plantaginea)

The obliquebanded leafroller (Choristoneura rosaceana) and the rosy apple aphid (Dysaphis plantaginea) are two serious pests of apple crops in British Columbia and elsewhere. In an effort to find new products to control these pests, a selection of 17 essential oils and 4 carrier oils were screened against both pest species and two oils (patchouli oil and thyme oil) demonstrated the greatest potential for further development (results presented at the 2007 ESA meeting). However, during the course of screening these oils, it was noted that not all essential oils have the same effect on the insects, and that application method (e.g. topical application vs. spraying an aqueous solution) can play a significant role in the strength of response (e.g. LC₅₀). Initial responses typically occur quickly; however, it is evident that detoxification mechanisms play a role in the final response to these oils. The research presented will provide a synopsis of the relative toxicity of these oils to both pests and will attempt to address the potential role for detoxification enzymes in the recovery response (or lack thereof) observed in both insect species.