Effect of oilseed type on the efficacy of five diatomaceous earth formulations against Tribolium castaneum Herbst (Coleoptera: Tenebrionidae)

The insecticidal efficacy of five diatomaceous earth (DE) formulations, Protect-It^®, SilicoSec^®, Insecto^®, Perma-Guard^? D-10 and Dryacide^® was evaluated against adult Tribolium castaneum Herbst, the red flour beetle, on three oilseeds: safflower, sunflower and sesame. The DE formulations were applied at three rates: 0.5, 1 and 1.5 g/kg. The experiment was carried out at 26°C and 55 (±5)% RH in the dark. The mortality of T. castaneum adults was measured after 3, 7, 14 and 21 days exposure. After the 21-day mortality count, all surviving insects were removed and the samples retained under the same conditions for a further 45 days to assess progeny production (F1). Significant differences were recorded among the three oilseed types as well as between the DE formulations tested. After 21 days exposure, even at the lowest treatment rate, adult mortality was high (>90%) in safflower for all DE formulations. In contrast adult mortality was significantly lower in the case of sesame. Increased application rates improved the efficacy of DEs in sunflower and sesame. Even at the lowest rate the complete suppression in progeny production was achieved on treated safflower. The greatest number of progeny was recorded for treated sunflower seeds. Protect-It^® and Dryacide^® were the most efficient DE formulations against T. castaneum.