Effect of grain moisture content and storage time on efficacy of inert and botanical dusts for the control of Sitophilus zeamais in stored maize

Abstract

The effect of grain moisture content and time of storage on the efficacy of inert and botanical dusts, conventional and bacterial metabolite insecticides were evaluated in the laboratory. Maize grains at 10, 12, 14 and 16% moisture content were admixed with inert powder (diatomaceous earth Kensil Superfine®), maize cob and bean trash ashes, and botanical (neem seed cake powder) at a dose rate of 0.9% w/w. Actellic Super® and Spintor® dusts applied at the recommended rate of 50 g/90 kg grain and diatomaceous earth Dryacide® at 0.9% w/w were included as positive controls. Untreated maize grain served as the negative control. Thirty (30) unsexed two –week-old Sitophilus zeamais Motsch. adults were introduced in the treated maize. The treatments were replicated four times and held undisturbed for 14 days at ambient conditions (26 ± 2°C and 67 ± 3% r.h.), after which mortality was assessed. Results showed that grain moisture content significantly (p<0.05) affected efficacy of grain protectants and superior control was achieved when it did not exceed 12% for inert dusts and 14% for pesticides. For the evaluation of the effect of time of storage, 4 kg maize grain were admixed with each treatment except for Spintor® dust, maize cob ash, neem seed cake powder as described earlier and put into the 5 kg capacity hessian baglets, replicated four times. Untreated grain acted as the control. Adult S. zeamais (population of 1500) were put in the plastic Petri dish and left to infest the baglets naturally. The potency of the protectants began to wane significantly (p<0.05) after 6 months. Dryacide® followed by Kensil Superfine® dusts performed better than Actellic Super® with the grain weight loss of 2 and 4%, respectively, over a period of 9 months. The study demonstrates that Superfine® dust has the potential but should be further evaluated on – farm, for the control of storage insect pests and serve as another stored products protectant option. Key words: Sitophilus zeamais, inert dusts, natural dusts, actellic super, stored maize.