Insecticidal effect of the combined application of diatomaceous earth and zeolite against three major stored-product insects in wheat

Abstract: Diatomaceous earths and zeolites are both promising alternatives to chemical grain protectants for the control of post-harvest infestations in dry, durable commodities. However, there is no report on the combined application of diatomaceous earth and zeolite against stored-product insects. In the present study, the insecticidal effect of eight diatomaceous earths and two zeolites of different origins was evaluated against adults of Sitophilus oryzae (L.) (Coleoptera: Curculionidae), Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae) and Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) at two doses (250 and 1000 ppm) and three exposure intervals (2, 7 and 14 d). After 2 d of exposure, mortality was low for all tested species and doses, whereas after 7 d mortality ranged between 21.7 and 93.3 for S. oryzae, and 26.7 to 98.3 for O. surinamensis at 1000 ppm. Complete control (100%) was achieved only in the case of S. oryzae and O. surinamensis after 14 d of exposure in wheat treated with the high dose. Tribolium confusum was the most tolerant to diatomaceous earth and zeolite among the species tested. In a second series of bioassays, the three best performing diatomaceous earths and the most effective zeolite were evaluated against the same beetle pests alone or in combinations at 250 and 500 ppm (total concentration of either one compound alone or both compounds). In all cases, no significant synergistic effect was observed after the combined application of diatomaceous earth and zeolite.