Effects of synergists on the efficacy of long-lasting insecticide-incorporated netting against Tribolium castaneum (Coleoptera: Tenebrionidae) and Rhyzopertha dominica (Coleoptera: Bostrichidae).

Long-lasting insecticide-incorporated netting (LLIN) has been used to deliver pyrethroids for management of stored product insect pests in food facilities. However, the development of resistance to pyrethroids in stored product pests is a widespread and urgent problem, which threatens the efficacy of commercially available LLINs. A potential approach for enhancing LLIN efficacy is the use of insecticide synergists to inhibit detoxification enzymes and exacerbate the effects of pyrethroids. Here, we evaluated the synergistic properties of 3 detoxification enzyme inhibitors-piperonyl butoxide (PBO), diethyl maleate (DEM), and triphenyl phosphate (TPP)-with LLIN against the red flour beetle Tribolium castaneum (Herbst), and the lesser grain borer Rhyzopertha dominica (Fabricius). Pre-exposure to PBO resulted in higher mortality after exposure to LLIN for T. castaneum and R. dominica. With pre-exposure to PBO followed by LLIN exposure, there was a trend for lower LT50 values for both species, while the extent of synergistic effects was greater on R. dominica than T. castaneum. In contrast, with pre-exposure to DEM and TPP followed by LLIN exposure, there were no significant reductions in LT50 values for both species. In addition, the presence of food had a significant effect on the recovery and delayed mortality in T. castaneum and R. dominica, reducing the efficacy of synergist and LLIN in combined exposures. This study provides baseline data towards improving the efficacy of LLIN against stored product pests.