Combination Insecticide Treatments with Methoprene and Pyrethrin for Control of Khapra Beetle Larvae on Different Commodities.

Simple Summary: The khapra beetle is considered by many to be one of the most destructive stored product pests in the world and it is a quarantine species of significant concern in the United States. This beetle is known to feed on >100 commodities, leaving behind frass, broken and damaged grain kernels, and cast skins, which can make products unsuitable for consumption. Because its immature stage is so problematic, it is critical to identify effective management strategies, which could include fumigation, trapping, and insecticides. In this study, we investigated whether two different grain protectants applied to bulk corn, wheat, and brown rice could be efficacious for inhibiting the development from larvae to adult. Both grain protectants reduced adult emergence on brown rice for 6 months of storage and wheat and corn for up to 12 months of storage. Additional studies are needed to directly measure the amount of frass, feeding damage, and/or insect-damaged kernels (IDK), and larval weight, which would provide further insight on the relationship between commodity type and the efficacy of the insecticide application. Reducing adult emergence inhibits reproduction and population growth during storage. Thus, grain protectants can be a useful preventative tactic for stored commodity managers against the khapra beetle. 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 to detect. Control methods for T. granarium include fumigation, contact insecticides, trapping, and insecticide-incorporated packaging. The objective of this study was to determine the 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 brown 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 brown rice for up to 6 months. Adult emergence was highest at month 12 for corn (8.41%), and brown rice (85.88%), and month 9 for wheat (39.52%), treated with DiaconIGR^®Plus or Gravista^®, respectively. A biological index used to measure the development of exposed larvae on the treated grain from the larval stage (low values) to adult emergence (high values) was lower (fewer adults) on corn and wheat compared to controls. Despite differences in formulations, each of these grain protectants could be utilized by stored commodity managers to protect commodities during storage and transportation for T. granarium when and if this pest is detected at USA ports of entry. [ABSTRACT FROM AUTHOR]