Combination insecticide treatments with methoprene and pyrethrin for control of khapra beetle larvae on different commodities

Authors: Scheff, Deanna; ARTHUR, FRANK - Retired ARS Employee; DOMINGUE, MICHAEL - Animal And Plant Health Inspection Service (APHIS); MYERS, SCOTT - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2024
Publication Date: 1/22/2024
Citation: Scheff, D.S., Arthur, F., Domingue, M., Myers, S. 2024. Combination insecticide treatments with methoprene and pyrethrin for control of khapra beetle larvae on different commodities. Insects. 15(1). Article 77. https://doi.org/10.3390/insects15010077.
DOI: https://doi.org/10.3390/insects15010077

Interpretive Summary: The khapra beetle is considered by many to be one of the most destructive stored product pests in the world. 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 human or animal consumption. If environmental conditions are not perfect, this insect can stay in an immature stage for years and will resume development to adulthood when conditions improve. Because the immature stage is so problematic, it is critical to identify effective management strategies, which could include fumigation, trapping, insecticide-incorporated packaging, and insecticides. In this study we investigated whether two different grain protectants applied to bulk corn, wheat, and rice could be efficacious for preventing feeding damage and development from larvae to adult. Both grain protectants reduced adult emergence on rice for 6 months of storage and wheat and corn for up to 12 months of storage, which will inhibit reproduction and population growth during 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 into the reduced efficacy of the grain protectants on rice compared to corn and wheat. Thus, grain protectants can be useful preventative tactics for beneficial to stored commodity managers against khapra beetle.

Technical Abstract: 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 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 used to measure 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 untreated 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 US ports of entry.