Developing a “quick test” for phosphine resistance in the lesser grain borer, Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae)

Several species of stored grain insect pests have developed resistance to the fumigant gas hydrogen phosphide, known as phosphine. A rapid assay to detect phosphine resistance in the lesser grain borer, the most serious pest of stored wheat and rice in the US, is a primary step for proactive early management. Established methods recommended by the UN-FAO for discriminating between susceptible and resistant insects rely on a 14-day mortality assessment following a 20-hr exposure to a discriminating dose of phosphine. This method is technical and time-consuming in providing results for many samples in adequate time for a management decision. An easy, same-day test to determine phosphine resistance is therefore important in helping grain handlers manage resistance. Following a review of literature on quick tests with other species, a method to detect resistant phenotypes in R. dominica was developed.  Results from this new method were compared to results with the same beetle populations subjected to the FAO method. Initial studies to survey the geographic variation in phosphine resistance in the United States will be discussed.