Efficacy of fumigant allyl isothiocyanate against phosphine-resistant strains of Sitophilus oryzae (L.) and Cryptolestes ferrugineus (Stephens)

Abstract

Resistance to phosphine (PH3) in a range of insect pests of stored products poses a significant challenge to the grain industry. Recent research and development are focused on identifying alternative fumigants to sustain the industry's ability to manage this resistance problem effectively and maintain profitability and market access. In the current study, we evaluated the efficacy of synthetic allyl isothiocyanate (AITC) in the laboratory against mixed-life-stage populations of phosphine-resistant (PH3-R) and susceptible (PH3-S) strains of two major grain insect species, the rice weevil, Sitophilus oryzae (L.), and the rusty grain beetle, Cryptolestes ferrugineus (Stephens). The study also examined the sorption of AITC by two commodities, wheat and sorghum. Our results obtained from adult mortality and progeny emergence revealed that AITC at a dose rate of 10 μL L−1 over a 3-d exposure period can achieve complete control (100%) of all life stages of S. oryzae and C. ferrugineus. No differences in mortality responses were observed between PH3-R and PH3-S strains, suggesting a lack of cross-resistance to AITC in PH3-R pest strains. However, our investigation on sorption indicates that AITC is highly sorptive and no active ingredient remained in the headspace of the fumigation chamber at 72 h after fumigation, irrespective of the doses (5 and 10 μL L−1) and commodities (wheat and sorghum) tested. While AITC was highly effective against PH3-R insect pests, its sorptiveness in grain commodities may pose a challenge for developing suitable application rates for large commercial storages.