Efficacy of selected insecticide sprays against Indian meal moth (Lepidoptera: Pyralidae) wandering larvae on various surfaces

The Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), is a worldwide pest found in food product warehouses. Presence of P. interpunctella wandering larvae causes customer complaints and product rejection from customers. Its prepupal stage is susceptible to insecticide treatment due to their wandering behavior. We evaluated the efficacy of three insecticide sprays, ExciteR (0.017% pyrethrins, 0.174% piperonyl butoxide), Suspend SC (0.053% deltamethrin), and Transport Mikron (0.047% acetamiprid, 0.056% bifenthrin) against P. interpunctella wandering larvae by forced exposure to porous (vinyl tile, unpainted pinewood, concrete, and paper) and non-porous (steel, glazed ceramic) surfaces, and exposure to treated harborages made of two pieces of vinyl tiles, unpainted pinewood, and concrete. Under continuous exposure conditions, both ExciteR and Suspend SC caused significantly higher mortality (90–96%) than Transport Mikron (73–75%) on non-porous surfaces after 4 days (P < 0.05). But on porous surfaces, the three insecticides caused ≤63% mortality with Suspend SC being the most effective. When using 2× amount of insecticides as that in the previous test (2.1 gallon/1000 ft², which is 4.33, 1.20, and 2.33 mg a.i./m² of ExciteR, Suspend SC, and Transport Mikron, respectively), Suspend SC was the only insecticide causing high mortality (≥99%) through both forced exposure to concrete surface and exposure to treated concrete harborage. Whereas other treatments caused <12% mortality. Among the porous surfaces, residual efficacy of Suspend SC on concrete was significantly higher than that on vinyl tiles. Application of an effective liquid insecticide (such as 0.053% deltamethrin) into harborages or directly to the possible pupation sites, such as corners, cracks, and crevices could be an effective strategy for managing P. interpunctella wandering larvae in warehouse environment.