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

Authors: MING, QINGLEI - Kansas State University; Morrison Iii, William; ZHU, KUN YAN - Kansas State University; Campbell, James; Scully, Erin

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Contact insecticides are critical components of integrated pest management programs for stored product insects as they can quickly knock down insects and prevent them from infesting grain and food products. Long-lasting insecticide-incorporated netting (LLIN) has been used to deliver contact insecticides for management of stored product insects in food facilities; however, resistance and the ability to recover after exposure to these contact insecticides in the presence of food are growing concerns. A potential approach for increasing the effectiveness of LLIN is through the use of insecticide synergists to inhibit insect detoxification enzymes, which are often linked to resistance and recovery. In this study, we determined whether three different synergists– piperonyl butoxide (PBO), diethyl maleate (DEM) and triphenyl phosphate (TPP) – could increase the efficacy of LLIN against the red flour beetle and the lesser grain borer. We found that the lesser grain borer was more susceptible to LLIN than red flour beetle as the time it took to achieve 50% mortality was 11.7 hours compared to over 110 hours for red flour beetle. We found no effect of DEM and TPP on mortality or ability to inhibit recovery in the presence of food in either insect species. However, exposure to PBO increased mortality after intermediate exposure times in red flour beetle (3 and 5 days) and after short exposure times in lesser grain borer (2 and 12 hours). Although food increased recovery in red flour beetle, PBO did not inhibit this recovery, indicating that detoxification enzymes are not solely responsible for recovery in the presence of food. This study shows that PBO in conjunction with LLIN can increase mortality in both species, but that more research is needed to develop tactics to inhibit recovery in the presence of food.

Technical Abstract: Long-lasting insecticide-incorporated netting (LLIN) has been used to deliver pyrethroids for management of 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 increasing 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 three 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 (Fauvel). Pre-exposure to PBO resulted in higher mortality after exposure to LLIN for T. castaneum and for 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 combined exposures. This study provides baseline data towards improving the efficacy of LLIN against stored product pests.