EFFICACY OF ESSENTIAL OILS FROM FIVE BOTANICALS AGAINST CALLOSOBRUCHUS MACULATUS (F.) AND SITOPHILUS ZEAMAIS (MOTS.)

Abstract

The insecticidal effects of essential oils of five botanicals: Tetrapleura tetraptera seed, Annona muricata seed, Aframomum melegueta seed, Eucalytus globulus leaf and Ficus exasperata leaf on storage pests of cowpea seeds Callosobruchus maculatus (Fabricius) and maize grain Sitophilus zeamais (Moltschulsky) were investigated. The study was carried out in the Pest Management laboratory in the Department of Crop, Soil and Pest Management, The Federal University of Technology Akure, Ondo State, Nigeria. The experiments were conducted under ambient laboratory conditions of, 28+30C temperature and 65+10% relative humidity. The essential oils were applied at the concentration of 1 ml/kg, 3 ml/kg and 5 ml/kg of cowpea seeds and maize grains, mixed evenly. Thereafter, 20 g of seeds were randomly selected from each of the container into containers with tightly fitted lids. A control was also setup without treatment application. All treatments and control were replicated 3 times. The seeds and grains were infested with 5 couples of day old C. maculatus and S. zeamais. Percentage beetle and weevil mortality were observed at 12, 24, 48 hours and at 24, 48 and 72 hours respectively. Data were also collected on number of eggs laid by C. maculatus, adult emergence and weight loss in cowpea seeds. From the maize grains, number of adult S. zeamais that emerged, inhibition in adult emergence and weight loss were recorded. Germination test was carried out on treated seeds and grains after 120 days of storage. The results from the study showed that the essential oils were effective in controlling both insects, their effectiveness were dependent on application concentration and time of exposure. A. melegueta essential oil significantly caused higher (P<0.05) mortality of both C. maculatus and S. zeamais. In treated cowpea seeds, A. melegueta essential oil was the most effective with LC50 value of 2.42 ml/kg and LC95 value of 4.86 ml/kg when compared to the other treatments as indicated by the application concentration which caused 50% and 95% mortality of cowpea beetles. A. melegueta essential oil caused above 50% insect mortality at the concentration of 3 ml/kg (76.67%) and at the concentration of 5 ml/kg it achieved 100% mortality of C. maculatus at 48 hours after application. In treated maize grains, A. melegueta essential oil was the most effective with LC50 value of 3.00 ml/kg and LC95 value of 5.98 ml/kg. A. melegueta essential oil at 5 ml/kg caused 80% mortality of S. zeamais 72 hours after application. Cowpea seeds treated with 5 ml/kg of E. globulus essential oil significantly reduced (P<0.05) oviposition compared to the other treatments. Cowpea seeds treated with 5 ml/kg of A. muricata essential oil reduced adult emergence (3.67) and weight loss (0.59). The least number of emerged adults was recorded on maize grains treated with 5 ml/kg of T. tetraptera essential oil. The maize grains treated with 5 ml/kg of A. muricata essential oil had the highest percentage inhibition concentration (81%) and also achieved the least weight loss (0.63). Cowpea seeds and maize grains treated with essential oils at different concentrations had no significant (P>0.05) adverse effect on seed germination after 120 days of storage. Therefore, based on the findings of this study, the essential oils could be explored as an alternative biopesticide to synthetic insecticide in the protection of stored cowpea and maize against C. maculatus and S. zeamais, respectively. It can also be used at lower concentration of application in preserving cowpea and maize seeds intended for planting