Evaluation of Phosphine Resistance in Three Sitophilus Species of Different Geographical Origins Using Two Diagnostic Protocols

Abstract

Phosphine resistance occurs in many areas worldwide. The present study evaluated Sitophilus species from different geographical origins using two different protocols: (i) the Food and Agriculture Organization (FAO) protocol (30 ppm for 20 h) and (ii) the dose–response protocol (50–1000 ppm for 3 d). According to our results, most of the populations tested were susceptible to phosphine. In the FAO protocol, 13 field populations out of the 35 tested were categorized as resistant to phosphine. From the populations tested, only Sitophilus oryzae (L.) G1 showed 100% active individuals after 20 h or even 7 d post-exposure. In contrast, low survival was noted for all populations of Sitophilus granarius (L.) and no survival for Sitophilus zeamais Motschulsky. Based on the dose–response protocol, no active individuals were recorded after exposure to 700 ppm for any of the populations tested. For instance, the population G1 showed 89% survival after 3 d at 50 ppm, while the respective figure at 700 ppm was 1.1.%. No survival was recorded for all concentrations and populations of S. granarius and S. zeamais. Our data show that there are considerable similarities between the two diagnostic protocols used for the evaluation of phosphine resistance of these three species.