Graded-Concentration Bioassays for Controlling All Stages, Including Diapausing Larvae, of Trogoderma granarium Using Liquid Ethyl Formate

The khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), is a significant stored-product pest and is listed among the 100 worst invasive species globally. With continuing rises in volumes of international trade, the importance of khapra beetle control continues to increase. The mortality effectiveness of liquid ethyl formate (EF) was tested on all life stages of T. granarium in empty 2.65 L glass desiccators at various dosages ranging from 3.3 to 111.0 mg L−1. The life stages—eggs, larvae (first to late instars) sampled directly from the colony, diapause-induced larvae, pupae, and adults—were exposed to liquid EF at 26 ± 1.2 °C and 55 ± 5% relative humidity for 6 h. Mortality responses were analyzed using Probit analysis (p < 0.05) to estimate the concentrations causing 50% and 99% mortality (LC50 and LC99) for each developmental stage, and lethal concentrations were compared using lethal concentration ratio tests. Mortality was assessed the following day for mobile stages (adults and larvae) and after 3–30 d for immobile stages (eggs and pupae). Pupae had the highest LC50 (58.6 mg L−1) and the highest estimated LC99 (109.1 mg L−1), although at the LC99 level they differed significantly only from first- and third-instar larvae. Late diapausing larvae had an estimated LC99 of 101.3 mg L−1. Adult and egg stages were comparatively more susceptible. Diapausing larvae had significantly higher LC50 values than colony larvae of the corresponding instars (1.17–1.82-fold), whereas no significant difference was found at the LC99 level. These findings demonstrate differential susceptibility across developmental stages and suggest that EF has potential as an alternative to methyl bromide (MB) for controlling T. granarium, although further research under commercial conditions is required to confirm its suitability for quarantine applications.