Evaluation of resistance development by Tribolium confusum Du Val (Coleoptera: Tenebrionidae) to diatomaceous earth under laboratory selection

Laboratory selection experiments were undertaken in order for the resistance development of Tribolium confusum adults to diatomaceous earth (DE) to be assessed. Adults from an initial laboratory reared population (P) were selected by exposure on hard wheat treated with 800 ppm of DE for 4 days at 25 °C and 65% r.h. The surviving adults and their progeny were maintained on flour and 5% brewer's yeast until the emergence of the next generation of adults. The emerged (F1) adults were again exposed on treated hard wheat, as described above, and the whole procedure was repeated for 10 consecutive generations. Mortality of the emerged adults was assessed through bioassays that were undertaken in each generation at 25 °C and 65% r.h. In each bioassay, five dose levels of DE (250, 500, 800, 1000 and 1500 ppm) and four exposure intervals (24, 48 h, 7 and 14 days) were tested. Mortality of confused flour beetles generally declined at each dose rate and exposure interval with each generation, and significant differences were observed between the initial population (P) and after five or more (F5+) generations of selection.