Combination insecticide treatments with methoprene and pyrethrin for control of Khapra beetle larvae on different commodities: A 12-month study

Trogoderma granarium Everts, the khapra beetle, is a serious pest of stored products throughout the world. Larvae pose a significant threat to stored products because they feed on >100 different commodities, possess the ability to enter facultative diapause, and are difficult are difficult to detect. Control methods for T. granarium include fumigation, contact insecticides, trapping, and insecticide-incorporated packaging. The objective of this study was to determine residual efficacy of two insecticide formulations (methoprene + deltamethrin + piperonyl butoxide synergist Gravista® and methoprene + deltamethrin, DiaconIGR® Plus). These insecticides were evaluated on three stored product commodities, corn, wheat, and rice, by exposing T. granarium larvae during a 12-month testing period. Both formulations significantly reduced adult emergence on corn and wheat for 12-months and on rice for up to 6-months. Adult emergence was highest at month 12 for corn (8, 41%), and rice (85, 88%), and month 9 for wheat (39, 52%), treated with DiaconIGR® Plus or Gravista® respectively. A biological index which measured development of exposed larvae to the pupal and adult stages was significantly lower on the treated corn compared to the untreated corn for all 12-months, and there was no significant difference between treated or untreated rice. Results show that each of these grain protectants could be potentially used in management programs for khapra beetle when and if this pest is detected at US ports of entry.