Potential of Co-Fumigation with Phosphine (PH 3 ) and Sulfuryl Fluoride (SO 2 F 2 ) for the Management of Strongly Phosphine-Resistant Insect Pests of Stored Grain

Abstract

Resistance to phosphine (PH 3 ) in key insect pests of stored grain is increasing, with a requirement for maintaining a dose as high as 1 mg l -1 for 14 d for effective fumigation, which is difficult to achieve under most commercial storage conditions. There is no suitable replacement for PH 3 , as most of the available alternatives suffer from specific weaknesses, creating an urgent need to increase the efficacy of this fumigant. One such possibility is co-fumigation of PH 3 with another fumigant, sulfuryl fluoride (SO 2 F 2 - SF), with the goal of decreasing the time required for a successful fumigation. In this study, adult of two PH 3 -resistant strains in each of four key grain insect pests, Rhyzopertha Dominica, (F.) (Coleoptera: Bostrichidae) Tribolium castaneum Herbst (Coleoptera: Tenebrionidae), Sitophilus oryzae (L.) (Coleoptera: Curculionidae), and Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) were fumigated with PH 3 and SF individually as well as in combinations at 25°C over 48 h. Mortality responses in each species were subjected to probit analysis to determine the LC 50 and LC 99.9 of PH 3 , SF, and PH 3 + SF. Co-fumigation of PH 3 with SF resulted in a 50% reduction of the PH 3 concentration required to achieve 99.9% mortality in two pest species. For example, the PH 3 + SF mixture, reduced the amount of PH 3 required from 14.2-14.5 to 5.6-6.36 mg l -1 and from 2.71-5.03 to 0.93-1.2 mg l -1 , respectively, for C. ferrugineus and S. oryzae. The overall mortality response to the PH 3 + SF mixture followed an "additive model" suggesting that mutual enhancement in toxicity can be achieved with this mixture specifically to control PH 3 -resistant insects.