Project lead: Chelsea Gowton
Volatile organic compounds (VOCs) produced by plants and plant products can attract, repel or harm insects 6,7. Peppermint oil VOCs can reduce attraction of SWD compared to ripe fruit odours8, suggesting that there is potential for peppermint plants to be used as volatile producing intercrops in berry plantings, as well as peppermint oil based deterrents, as part of a SWD management program.
To evaluate peppermint VOC use in the field, we conducted an intercropping experiment at the UBC Farm, a 24-hectare certified organic production and research farm with the Centre for Sustainable Food Systems (CSFS). Overall, we found that peppermint plants slightly delayed SWD arrival in the field compared to our control, but we experienced relatively low counts of SWD throughout all treatments during the 2018 growing season, which made evaluation of this agronomic practice difficult.
In the lab, we evaluated the effects of VOCs from peppermint essential oil on adult emergence of SWD through a series of environmentally-controlled bioassays at UBC. Exposure to peppermint oil volatiles decreased the successful emergence of SWD and this effect was stronger in dry conditions. SWD emergence increased with decreasing concentration of peppermint oil volatiles, indicating a dose dependent response.
An optimal pest management strategy works in conjunction with or enhances efficacy of the multiple management practices growers may use to combat pest loads. Pachycrepoideus vindemmiae is a parasitic wasp indigenous to British Columbia9 and can oviposit in SWD pupae. We evaluated whether peppermint VOCs decreased the efficacy of P. vindemmiae biological control of SWD through lab bioassays. P. vindemmiae reduced successful emergence of SWD, however, we observed higher P. vindemmiae mortality when exposed to peppermint oil volatiles compared to the control, and decreased parasitism success. Read more about our laboratory trials in our recent publication.
Overall, our initial trials suggest that peppermint oil volatiles can negatively impact SWD emergence, especially in dry conditions. However, the use of peppermint oil volatiles for SWD management will likely decrease the efficacy of SWD natural enemies, particularly the parasitoid P. vindemmiae. P. vindemmiae has the potential to reduce emergence of SWD, but exposure to peppermine oil volatiles decreased its survival and ability to parasitize SWD pupae. Ongoing trials at the UBC Farm will continue to evaluate peppermint and other aromatic intercrops for pest load reductions and beneficial insect attraction.
Funding for the project was provided by the BC Blueberry Council, the Organic Science Cluster, the Natural Sciences and Engineering Research Council of Canada (NSERC), the Centre for Sustainable Food Systems, UBC Farm, and Faculty of Land and Food Systems.