Phosphine resistance in the lesser grain borer, Rhyzopertha dominica - the North American perspective

The Lesser Grain Borer (LGB), Rhyzopertha dominica (F). is one of the most destructive pests of stored grains. In the last sixty years, phosphine has been the most widely used fumigant for the management of stored grain insect pests.  Its constant use has resulted in the selection of insects resistant to phosphine. Research into phosphine resistance has not been given regional attention after earlier studies in very few locations in the US. This study was therefore aimed at ascertaining the levels of phosphine resistance in different parts of U.S and Canada. Using the FAO method number 16; a discriminatory dose of 20 ppm phosphine for 20 hours distinguishes a susceptible LGB from a resistant one. Twenty-two locations from 7 states in the US had LGB tested for phosphine resistance whiles four locations in two provinces were tested from Canada. All but two of the localities surveyed so far have recorded varied levels of resistance compared to the lab susceptible strains.  All but three of the LGB population tested were above 50% with three locations having a resistance level greater than 90%. The Canadian populations have resistance levels between 0 and 19% which is very low compared to populations from the US. These results are of great importance to the grain industry, and presents a big issue to grain storage in the North-America