Efficacy of filter cake and Triplex against stored- product insects on concrete surfaces and grain: safer alternatives to protect stored grain of Ethiopian smallholder farmers

Abstract

Filter cake and Triplex are powdered by-products of aluminum sulfate and soap factories, respectively. Studies were designed to determine elemental composition of these two powders and evaluate the efficacy against stored product insect species on concrete surfaces and commodities. Elemental composition of the powders was determined using conjugated scanning electron microscopy and Energy-dispersive X-ray spectroscopy. No heavy metals were found in both powders, and the dominant elements found were silicon and oxygen in the form of silicon dioxide. The efficacy of filter cake and Triplex against the maize weevil, Sitophilus zeamais Motschulsky; rice weevil, Sitophilus oryzae (Linnaeus); lesser grain borer, Rhyzopertha dominica Fabricius; red flour beetle, Tribolium castaneum (Herbst); saw-toothed grain beetle, Oryzaephilus surinamensis (Linnaeus); and Indian meal moth, Plodia interpunctella (Hübner), was determined using a range of concentrations and exposure times. On concrete surfaces ≥ 7.5 g/m² of filter cake produced more than 99% mortality of S. zeamais and S. oryzae adults within 12–24 h, whereas more than three times the concentration of filter cake was required to achieve similar mortality of both species in Triplex treatments. At 3 g/m² of filter cake, 99% mortality S. zeamais and S. oryzae adults was achieved within 22–27 h of exposure. The corresponding exposure time at 9 g/m² of Triplex was 39 h to achieve 99% mortality of both species. For both powders, lower concentrations and exposure times were required to achieve complete suppression of progeny production, percentage of insect damaged kernels, and percentage of grain weight loss compared to the concentrations and exposure times required for 00% mortality. Filter cake treated wheat at concentrations above 0.7 g/kg produced more than 99% mortality of S. zeamais and S. oryzae adults. Similarly, filter cake concentrations above 2 g/kg on wheat produced more than 99% mortality of R. dominica, T. castaneum, and O. surinamensis adults. However, on maize ≥ 3 g/kg of filter cake concentration was required to achieve similar mortality of R. dominica, T. castaneum, and O. surinamensis. Higher concentrations of Triplex were required to achieve similar mortalities of tested species on maize and wheat. Reduction in progeny production was greater when adults were exposed to higher concentrations than lower concentrations. Complete suppression of live larvae and adult emergence of P. interpunctella was achieved after exposure of eggs for 21 and 42 d to ≥ 2 g/kg of filter cake treated maize and to ≥ 0.5 g/kg of filter cake treated wheat. Similarly, complete suppression of live larvae and adult emergence was achieved when eggs were exposed to ≥ 6 g/kg of Triplex treated maize and to 3g/kg of Triplex treated wheat. In general, our study consistently showed that filter cake was more efficacious compared to Triplex against all tested species on both surfaces and commodities. Filter cake and Triplex should be recommended for protecting grain stored by smallholder farmers in Ethiopia to discourage farmers from using dangerous chemical insecticides. However, field studies should be done using both powders against stored product insects in smallholder farmers’ traditional storages structures in Ethiopia to determine concentrations that are practical under field conditions. The effective duration of protection offered by these powders should also be investigated.