Direct lethality and time-delayed sublethal effects of multiple types of insecticide netting against stored product insects

Long-lasting insecticide-incorporated netting (LLIN) is being evaluated in agriculture as part of holistic integrated pest management programs. The aims of the current study were to (i) evaluate the efficacy of the commonly used LLINs (deltamethrin, alpha-cypermethrin, and etofenprox) for direct lethality, (ii) assess the baseline mobility after exposure, and (iii) to evaluate the sublethal effects among LLINs against Rhyzopertha dominica and Tribolium castaneum. To accomplish this, we exposed cohorts of both species to 0.4% (w/w) deltamethrin, 0.34% alpha-cypermethrin, or 8% etofenprox for periods of 5, 60, or 120 min in the laboratory, and checked individuals for the condition after a duration of 0, 24, 72, or 168 h. The movement of alive and affected adults was assessed using Ethovision software over 60-min trials after a 5- or 60-min exposure to LLIN immediately or 72 h after exposure. After exposure for 60-min to deltamethrin and alpha-cypermethrin LLIN, mortality for both species was 86% to 98% higher when compared to the controls without insecticide. Etofenprox performed worse than the other active ingredients (AIs). In the baseline mobility assay, R. dominica netting exhibited a thigmotactic effect on movement, but not for T. castaneum. For both species, the movement was reduced by 77% to 99% deltamethrin netting above and beyond the thigmotactic effects. There was a sublethal reduction in movement after a 60-min exposure to both LLINs by 95% to 98% compared to control netting without insecticide. Overall, this study helps delineate the relationship in efficacy between these AIs for 2 cosmopolitan, destructive stored product insects.