Delayed recovery and sublethal effects on the semiochemical-mediated taxis by khapra beetle after exposure to long-lasting insecticide-incorporated netting

Abstract

Trogoderma granarium, or khapra beetle, is a quarantined pest with a history of interceptions in countries where it is excluded. Long-lasting insecticide-incorporated netting (LLIN) may be able to provide additional quarantine security against this pest as a strategy for high-risk commodities. The aims of this study were to evaluate 1) direct lethality, and 2) sublethal effects of exposure to two LLINs on semiochemical-mediated foraging and movement by T. granarium. Direct lethality was examined on larvae after a 5- or 60-min exposure to control netting (without insecticide), a 0.34% alpha-cypermethrin (Carifend, BASF), or 0.4% deltamethrin LLIN (D-Terrence, Vestergaard, Inc.) over 168 h. Sublethal changes in movement were evaluated immediately after a 5-min exposure. Finally, semiochemical-mediated foraging was evaluated 24-h after LLIN exposure by larvae in a release-recapture assay using pitfall traps baited with either no stimulus, food cues, or the sex pheromone for T. granarium. The recovery of larval T. granarium dramatically rose and peaked 72–168 h after exposure to LLINs, while the percentage of alive individuals in the control remained consistently high. Larvae spent 6–10% more time in low acceleration and not moving after exposure to alpha-cypermethrin and deltamethrin LLIN compared to the control netting. There was a 6.6-fold higher capture of larvae in traps after exposure to control compared to deltamethrin netting. Elevated response to food cues was suppressed after exposure to LLIN. Overall, there is evidence of significant impacts of LLIN on T. granarium, but high recovery after short exposures and subsequent unresponsiveness to pheromone-baited traps, which are critical for species detection, suggest limitations for using LLIN in management for T. granarium.