Phosphine resistance does not confer cross resistance to sulfuryl fluoride in four major stored grain insect pests

Abstract

Susceptibility to phosphine (PH3) and sulfuryl fluoride (SF) and cross resistance to SF were evaluated in two life stages (eggs and adults) of key grain insect pests, Rhyzopertha dominca (F.), Sitophilus oryzae (L.), Cryptolestes ferrugineus (Stephens), and Tribolium castaneum (Herbst). This study was performed with an aim to integrate SF into phosphine resistance management program in Australia. RESULTS Characterisation of susceptibility and resistance to phosphine in eggs and adults showed that C. ferrugineus was the most tolerant as well as resistant species. Mortality responses of eggs and adults to SF at 25 °C revealed T. castaneum to be the most tolerant species followed by S. oryzae, C. ferrugineus and R. dominica. A high dose range of SF, 50.8–62.2 mg L−1 over 48 h, representing a c (concentration) x t (time) products of 2438–2985 gh m−3 was required for complete control of eggs of T. castaneum, whereas eggs of the least tolerant R. dominca required only 630 gh m−3 for 48 h (13.13 mg L−1). Mortality response of eggs and adults of phosphine-resistant strain to SF in all four species confirmed the lack of cross resistance to SF. CONCLUSION Our research concludes that phosphine resistance does not confer cross resistance to SF in grain insect pests irrespective of the variation in levels of tolerance to SF itself or resistance to phosphine in their egg and adult stages. While our study confirms that SF has potentials as a “phosphine resistance breaker”, the observed higher tolerance in eggs stresses the importance of developing SF fumigation protocols with longer exposure periods.