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Susceptibility of the selected Nigerian cultivars of twelve crops to Sitophilus zeamais Motschulsky was evaluated in the laboratory (28 ± 2°C temperature and 69 ± 5% relative humidity). The crops were: maize (Zea mays L.), millet [Pennisetum glaucum (L.) X R. Br.], sorghum [Sorghum bicolor (L.) Moench], rice (Oryza sativa L.), and yam (Dioscorea rotundata Poir). Others were cassava (Manihot esculenta Crantz), pepper (Capsicum annuum L.), cowpea [Vigna unguiculata (L.) Walp], groundnut (Arachis hypogaea L.), melon [Citrullus lanatus (Thunb.)], soybean [Glycine max (L.) Merr.] and bambara groundnut [Vigna subterranea (L.) Verdc]. The result of antixenosis prescreen shows that S. zeamais preferred cereals and tubers to legumes and oil crops. S. zeamais preference for maize was highest at 1, 24 and 48 hours after infestation (HAI) and was not significantly different from its preference for pepper, millet, sorghum and yam. At 48 HAI, S. zeamais preference for cereals, tubers and pepper was not significantly different. Soybean and bambara groundnut were the least preferred species. The highest level of damage was observed in cereals and tubers. Millet suffered significantly greater damage than maize at 2-8 weeks after infestation (WAI). Damage done to maize was not significantly different from damage done to tubers at 6 and 8 WAI. Pepper, legumes and oil crops suffered significantly lower levels of damage than maize throughout the experimental period. Cumulative number of adult was significantly higher in small-seeded cereals than maize and was of the order: sorghummilletrice. Cowpea, soybean and pepper did not support reproduction and longevity of S. zeamais. Longevity was best supported by cassava. The results show that in storage, cereals and tubers were more susceptible to S. zeamais infestation than legumes, spices and oil crops.
Studies were carried out in the laboratory to determine the efficacy of powders from plant parts of Ricinodendron heudelotii against the storage pests Sitophilus zeamais and Callosobruchus maculatus on stored maize and cowpea, respectively. Leaf, bark and root powders were added as admixtures to 100 g of grains to assess contact toxicity, damage assessment, progeny production and grain germination. Results indicated that the plant materials were toxic to the two insect species with over 30% and 75% mortality for S. zeamais and C. maculatus, respectively. Observable damage level was significantly (p ≤ 0.05) lower in treated grains while progeny production by both insect species was significantly (p ≤ 0.05) reduced. Grain germination of both crops was not affected by the powders. The potential use of P. heudelotii in storage pest management is discussed.
Freshly prepared garlic (Allium sativum L.) juice, containing the antimicrobial allicin, was evaluated as a possible grain pro-tectant against the maize weevil, Sitophilus zeamais (Motsch.). Each experiment was set out in Completely Randomized Design (CRD) with four replications, and there was a control treatment. Adult mortality and weight loss percentage were investigated. There was an observed increase in adult mortality following days of exposure in all treatments. Statistically significant (p < 0.05) reduced grain loss was also observed in all the treatments when compared with the control. The juice samples were freshly prepared from an indigenous Nigerian garlic cultivar (GUN) and a cultivar purchased from a supermarket in Germany (GAG). These garlic juice samples exhibited lethal effects causing at least 90% adult mortality in contact toxicity tests. The amount of allicin in GUN was 1.88 mg/ml according to High Pressure Liquids Chromatography (HPLC) analysis, while the amount of allicin in GAG was 3.50 mg/ml. This study highlights the potential of A. sativum containing allicin for biorational control of maize grains against S. zeamais infestation and damage.
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