Evaluation of dichlorvos pest strips in shipping containers holding soybeans: Effectiveness against immature stages of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

Abstract

The efficacy of dichlorvos pest strips against immature stages of the Indian meal moth, Plodia interpunctella (Hübner), was evaluated in 6.1 and 12.2 m long shipping containers holding soybeans. Three tests with eggs, four tests with larvae, and three tests with pupae of P. interpunctella were conducted on different dates during 2022 by placing these stages confined in bioassay boxes either on the surface or just below the surface of soybeans. The results showed that eggs in containers with pest strips had reduced hatchability or failed to hatch. Dichlorvos pest strips also killed fifth instars and mixed instars in bioassay boxes, consequently resulting in few moths emerging compared to bioassay boxes placed in containers without strips. Eggs laid by moths emerging from larvae also showed a decrease in F1 progeny in containers with strips. Fewer pupae emerged as adults in containers with dichlorvos strips and these adults either failed to lay eggs or laid fewer eggs. In tests with eggs, larvae, and pupae, samples placed below the surface of soybeans in containers with dichlorvos strips showed that the adverse effects of strips were less pronounced. Since dichlorvos concentrations were not measured, we could not find a significant relationship between temperature and the adverse effects of dichlorvos on eggs, larvae, and pupae. Data reported on dichlorvos residues on soybean samples was lower than the established United States Environmental Protection Agency tolerance level of 500 ppb in containers with strips (range, 0–188.5 ppb). Our results suggest that dichlorvos pest strips had adverse effects on eggs, larvae, and pupae of P. interpunctella, and therefore the use of strips has potential in managing Indian meal moth infestations in containers holding soybeans that are shipped overseas.