Assessing the locomotor behavior of phosphine-susceptible and -resistant Rhyzopertha dominica (Coleoptera: Bostrichidae) and Tribolium castaneum (Coleoptera: Tenebrionidae) after exposure to controlled release materials with different active ingredients

Long-lasting insecticide-incorporated netting (LLIN) with deltamethrin has been effectively used against stored-product pests for intercepting immigrating insects. To improve the existing IPM programs, there is interest in developing controlled release materials (CRMs) with novel modes of action that might improve resistance management and reduce the risk posed by phosphine-resistant populations. In this research, we evaluated the efficacy of different CRMs (LLIN or woven bags) with different active ingredients in each (deltamethrin, permethrin, indoxacarb, or dinotefuran) and compared them to control netting or bags without insecticide in reducing movement of phosphine-susceptible and -resistant Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and Tribolium castaneum (Coleoptera: Tenebrionidae). Adults were exposed for 30 s, 2-, or 60 min, and their movement was assessed for 1 h immediately after exposure, or 24 and 168 h afterward using video-tracking and Ethovision software. We recorded how the total distance traveled and velocity of adults varied. Finally, we tested higher rates of each compound on standardized sized cheesecloth and varied exposure time to develop LT₅₀ values for each compound and strain. We found that exposure to LLIN with deltamethrin significantly reduced the movement of both species compared to the other CRMs regardless of their susceptibility to phosphine. Deltamethrin was the most effective AI for both species, while dinotefuran and indoxacarb were the least effective for R. dominica and T. castaneum, respectively. Hence, our results demonstrate that deltamethrin LLIN can be an additional approach to combat phosphine-resistant populations to reduce dispersal of conspecifics into or around food facilities.