Efficacy of Storcide™ II and liquid formulation of spinosad (Sensat™) against phosphine-resistant Rhyzopertha dominica and Tribolium castaneum on wheat

Highly phosphine-resistant populations of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) have recently been found in Oklahoma grain storage facilities. The phosphine-resistant R. dominica and T. castaneum populations found are up to 1,519 and 119 times, respectively, more resistant than their susceptible counterparts. These findings call for development of a phosphine resistance management strategy to ensure continued effective use of phosphine. Our objectives were to investigate the efficacy of Storcide™ II and a liquid formulation of spinosad (Sensat™) against phosphine-resistant insects on wheat and to assess effects of pesticide degradation over time on their mortality. Storcide™ II was effective against phosphine-resistant R. dominica and resulted in 100 and 83% mortality in grain held for 2 d and 48 wk, respectively, after pesticide treatments were applied. Storcide™ II caused 99 and 37% mortality in phosphine-resistant T. castaneum in grain held for 2 d and 48 wk, respectively. Storcide™ II resulted in total progeny suppression in both species for both time periods. Sensat™ was effective against phosphine-resistant R. dominica but not T. castaneum. Sensat™ caused 98 and 96% mortality in R. dominica for the 2 d and 48 wk time periods, respectively; in T. castaneum, mortality was 2 and 1%, respectively. Sensat™ totally suppressed progeny production in phosphine-resistant R. dominica but not T. castaneum for the time periods tested. Implications of these data for the use of Storcide™ II and Sensat™ for resistance management are discussed.

Keywords: Stored products, red flour beetle, lesser grain borer, insecticide resistance, phosphine resistance management