Post-fumigation sub-lethal activities of phosphine and ethyl formate on survivorship, fertility and female sex pheromone production of Callosobruchus chinensis (L.)

Abstract

Phosphine (PH₃) and ethyl formate (EF), the two popular fumigant disinfectants of stored product insect pests, are primarily evaluated for their knock down effects without considering their post-fumigation sub-lethal activities. The sub-lethal activities (adult survivorship, fecundity, sterility and female sex pheromone production) of the fumigants were evaluated on a field-to-storage insect pest adzuki bean beetle, Callosobruchus chinensis (L.). The adults' survivorship and female fecundity, both were dose-dependently affected by sub-lethal PH₃ and EF fumigation exposures. Hatchability of the eggs laid by fumigated female adults were also significantly affected. Gas-chromatography mass-spectrometry analysis of solid-phase micro-extraction from virgin fumigated C. cinensis females revealed that the PH₃ LC₂₅ (the lethal concentration required to kill the 25% of the population) fumigated female C. chinensis released significantly less amount of the pheromone components. In contrast, EF LC₂₅ exposure did not affect the pheromone release. This study unveils the facts that the EF and PH₃ fumigation have detrimental bioactivities against C. chinensis. Notably, this suggests to consider the sub-lethal EF and PH₃ fumigation rather than the dose required to instantly kill all the C. chinensis individuals for disinfestation of stored adzuki bean.