Screening barrier plants to reduce crop attack by sweet potato weevil (Cylas formicarius).

Background: Sweet potato weevil, Cylas formicarius (Fabricius) attacks stems and storage roots of sweet potato, Ipomoea batatas, and is a major pest of this globally significant crop. To minimize the immigration of weevils into sweet potato fields from nearby donor habitat, we assessed scope for a barrier plant approach. Here, we report a novel, two-stage, multiple choice olfactometer method to screen candidate barrier plant species and a field study of the effects of shortlisted barrier plants of weevil movement and plant damage.

Results: Initial work established that a combination of sweet potato foliage and storage root was significantly more attractive to adult C. formicarius than either tissue alone in the distal chamber of choice arms. Among 15 candidate barrier plant species in intermediate chambers in arms, spring onion, oregano, chilli, basil, sweetcorn, fennel, lime mint and lemongrass significantly reduced passage of C. formicarius. Of these, sweetcorn and lime mint significantly reduced the numbers of oviposition holes in sweet potato storage roots. A field study showed that basil and chives were effective barrier plants for reducing weevil damage to sweet potato storage roots.

Conclusion: Our method has utility for screening additional candidate plants, and suggests that weevil dispersal and subsequent oviposition are affected by passage through some plants, suggesting scope for barrier plants to contribute to the management of this major pest. © 2019 Society of Chemical Industry.