Phosphine resistance in populations of Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) in Oklahoma

Phosphine gas (hydrogen phosphide or PH₃) is the method of choice worldwide for fumigating stored grain and grain value-added products for the control of stored-product insect pests. PH₃ resistance in stored-product insect pests has been reported in many countries as a major problem presenting challenges to the continued effective use of this fumigant. In 2013, several populations of Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) collected from various wheat storage facilities in Oklahoma were reported to have detectable PH₃ resistance. Two of the populations, namely, DK Farm 20 and JE had extremely high resistance frequencies of up to 100%. Based on the resistance frequencies reported in 2013, we conducted dose-response studies on all C. ferrugineus populations with detectable resistance to determine their levels of PH₃ resistance. Probit analyses of dose-response data determined that the LC₉₉ values for the susceptible strain, JE, and DK Farm 20 populations were 12, 792, and 835 ppm, respectively. The most resistant DK Farm 20 population was 72-fold more resistant than the susceptible strain and the JE population was 68-fold more resistant. Levels of resistance of other populations will be presented. This study demonstrates the need to determine presence and extent of PH₃ resistance in stored-product insect pests in all wheat growing regions of the United States and to develop PH₃ resistance management strategies for these pests.

Key Words: fumigation, stored-product pest, rusty grain beetle, phosphine resistance management