Relative Susceptibility of Four Coleopteran Stored-product Insects to Diatomaceous Earth SilicoSec®

Abstract

Laboratory bioassays were conducted to evaluate the insecticidal effect of diatomaceous earth (DE), SilicoSec against Callosobruchus maculatus (F.), Rhyzopertha dominica (F.), Sitophilus zeamais (Motschulsky), and Tribolium castaneum (Herbst) in cowpea, maize and wheat, at 25-32 °C and 54-68% relative humidity (r.h.). SilicoSec was applied at rates: 0 (untreated control) 250, 500, 750 and 1,000 mg/kg of commodity. Adult mortality was measured after 3 to14 days of exposure. Progeny production was assessed after 40 or 56 days. The tested species varied in sensitivity to SilicoSec, with S. zeamais being most susceptible, but no significant differences in mortality levels observed between R. dominica, C. maculatus or T. castaneum after three days of exposure. After 5 days of exposure, all C. maculates adults died on cowpea treated at 1,000 mg/kg. Similarly, after 14 days of exposure all adults of the other species died on grains treated at 1,000 mg/kg, and were ranked in decreasing order of susceptibility S. zeamais > T. castaneum > R. dominica. SilicoSec treatments suppressed progeny production (30 to 100%) in all the tested species. The implications of these findings to DE-based control strategy are discussed.