SCREENING OF SOME BOTANICAL INSECTICIDES AGAINST MAIZE WEEVIL, SITOPHILUS ZEAMAIS MOTSCH. (COLEOPTERA: CURCULIONIDAE), ON MAIZE

Abstract

Maize is one of the major cereal crops grown for food in Ethiopia and the maize weevil, Sitophilus zeamais is a major insect pest of stored maize. Controlling of the pest by use of synthetic insecticides is raising serious concern on the environmental safety, consumer health hazards and high costs for subsistence farmers and thus there is a need to develop alternative safe and cheap methods of insect control strategies such as the use of insecticidal botanicals against the storage pest. The aim of this study was to evaluate the efficacy of powders of seeds of Azadrichta indica, Millettia ferruginea and Jatropha curcas, leaves of Croton macrostachyus and Euphorbia schimperiana and to screen the minimum effective dose of each botanical for the management of maize weevil. The plant materials were collected air-dried under shade, ground separately into a fine powder using micro plant grinding machine. Three, four, and five grams of powder of each botanical were added to each 100 g of clean maize in each 250 cm³ glass jar and mixed uniformly by shaking. A standard insecticide, Pirimiphos-methyl 2 % dust (2 g) and untreated check were included for comparison. Twenty-six newly unsexed emerged adult weevils were placed in each jar and covered with muslin cloth. The treatments were arranged in completely randomized design (RCD) with three replications. Weevil mortality was recorded at 3, 7, 14, 21, and 28 days after initial infestation. During the last counting, both dead and alive weevils were counted and removed and the grains were kept under the same conditions for the emergence of F₁ generation. The numbers of F1 progeny weevils emerging were recorded every other day for 33 days. Seed germination was tested using 15 randomly picked seed from undamaged grains from each jar. A significant difference (P < 0.05) was observed between all the botanicals at all rates and the untreated control three to 28 days after treatment. The cumulative mortality 28 days after infestation was very high (97.43 –100%) and there was no significant difference between all the botanicals at all rates and the standard chemical. No significant difference was observed (P > 0.05) in the number of emerged F₁ among the botanical treatments and the chemical insecticide, but significant difference was recorded between these treatments and the control at 1 and 2 days and cumulative emerged progeny after 28 days. Seed germination test generally revealed over 77 seed viability and no significant difference was found among all the treatments. The study revealed that the botanicals can be used as components of maize weevil management options as they caused high weevil mortality and very low fecundity and showed insignificant effect on seed viability. However, the impacts of consumption of the botanically treated maize on humans need further study.