Geographic variation of phosphine resistance in the red flour beetle, Tribolium castaneum

As insect pests have a huge impact on stored grain, controlling them is a very important part of cost-effective production of good quality grain. Fumigation is a control method that is used frequently to kill insect pest populations already present in stored grain. Registered fumigants are limited in the US, and phosphine is the most commonly used, with most farmers and grain elevators exclusively using it and no other insecticides or management strategies. Phosphine resistance was first documented in the U.S. in 1990 in Oklahoma. Resistance levels in Oklahoma were revisited 12 years later, with a much higher percent resistant being found. The rest of the United States has little to no phosphine resistance data available, but resistance is strongly suspects in many regions.

Phosphine resistance in the red flour beetle, Tribolium castaneum, a common grain pests, was determined for multiple sites across the U.S., with an emphasis on Kansas locations. Resistance was determined using the FAO discriminating dose bioassay at 30 ppm for weak resistance and 180 ppm for strong resistance. Two sites in Alabama showed survival greater than 90% for the weak resistance discriminating dose bioassay, and 76 and 84% survival at the strong resistance phenotype discriminating dose. For sites in Kansas, many populations were found to have 40% or higher survival in the weak bioassay, and one population had greater than 70% survival at the strong discriminating dose. Kansas populations are being revisited and many more populations will be assayed, with a focus on coastal port storage.