Helping our partners: Herbivore-induced plant volatiles increase natural enemy attraction and function in an agro-ecosystem

Agricultural intensification, i.e., use of pesticides and selective breeding, can disrupt biological control. A novel way to mitigate this risk is through the use of herbivore-induced plant volatiles (HIPVs) to attract natural enemies in agro-ecosystems; however, whether this attraction leads to increased predation has rarely been investigated. Here, I hypothesized that HIPVs increase predator attraction and function in cranberries. In greenhouse cage studies, I determined if convergent lady beetle, Hippodamia convergens, adults are attracted to methyl salicylate (MeSA), a commonly-emitted HIPV; and if this attraction increases predation of “sentinel” European corn borer eggs. In the field, I identified which predators are attracted to MeSA and assessed their role on egg predation. I also conducted a 2-year mark-release-recapture study to determine the range of attraction of lady beetles to MeSA-baited traps. In greenhouse cages, I found that H. convergens adults are attracted to artificial plants baited with MeSA, which resulted in a 90% increase in predation. Video camera recordings showed that MeSA also attracts lady beetles in the field, and that this attraction leads to a 10% increase in egg predation. Field experiments with marked H. convergens showed that the maximum range of attraction to MeSA-baited traps is approx. 60 m, indicating that placing traps at least this distance apart should avoid direct interference. In conclusion, lady beetle adults are attracted to MeSA, which led to increased predation in both greenhouse and the field. These results indicate that HIPVs, such as MeSA, could increase predator abundance and their function in agro-ecosystems.