Potential of Co-Fumigation with Phosphine (PH3) and Sulfuryl Fluoride (SO2F2) for the Management of Strongly Phosphine-Resistant Insect Pests of Stored Grain

Abstract

Resistance to phosphine (PH3) 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 PH3, 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 PH3 with another fumigant, sulfuryl fluoride (SO2F2-SF), with the goal of decreasing the time required for a successful fumigation. In this study, adult of two PH3-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 PH3 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 LC50 and LC99.9 of PH3, SF, and PH3 + SF. Co-fumigation of PH3 with SF resulted in a 50% reduction of the PH3 concentration required to achieve 99.9% mortality in two pest species. For example, the PH3 + SF mixture, reduced the amount of PH3 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 PH3 + SF mixture followed an "additive model" suggesting that mutual enhancement in toxicity can be achieved with this mixture specifically to control PH3-resistant insects.

Comparison of fumigation efficacy of methyl bromide alone and phosphine applied either alone or simultaneously or sequentially against Bactrocera correcta in Selenicereus undatus (red pitaya) fruit

“…The overall mortality response of B. correcta followed an ‘additive model’, 25,30 whether simultaneous or sequential fumigation was applied. There was no obvious synergistic effect on eggs or 1 st instar larvae, so the synergistic mechanism may be related to respiration.…”

Mortality of Tribolium castaneum and quality changes in Oryza sativa by indirect exposure to Non-Thermal Plasma

“…The resistance developed by major stored pests to phosphine and hazards due to improper handling of the chemical is a major concern in phosphine fumigation for the postharvest disinfestation. The dosage requirement for maintaining effective phosphine fumigation has increased to 710 ppm for 14 d [26] or 1000 ppm for 7 d [27]. making fumigation practices cumbersome under commercial storage conditions.…”

Pesticidal Toxicity of Phosphine and Its Interaction with Other Pest Control Treatments

“…Even fumigants that do not interact with phosphine mechanistically may improve fumigation outcomes when applied in combination. This is the case with sulfuryl fluoride, which has a mechanism of toxicity that does not intersect (or overlap) with that of phosphine, but which nonetheless exhibits complementary properties to those of phosphine that improve pest control efficacy: sulfuryl fluoride is fast acting and controls phosphine-resistant insects, whereas phosphine is more effective against the egg life stage and is much less expensive [ 21 , 24 ].…”