Effectiveness of botanical preparations for the control of rice weevil (Sitophilus oryzae) during rice seed storage and their impact on the rice seed viability : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Seed Technology at Massey University, Palmerston North, New Zealand
Food security and the maintenance of seed quality from harvest to planting are key issues for peasant farmers. In Sierra Leone, up to 28% of rice seed can be damaged by rice weevil in the six months storage period. The use of chemical insecticides to control this insect is not practical for traditional farmers. Some tribes use pepper powder (Capsicum spp.) as a seed protectant. In this study, I have compared the effects of neem (Azadirachta indica) oil, neem powder, pepper (Capsicum frutescens cv. "Habanero") powder and lentil (Lens culinaris cv. "Raja") powder on the survival of adult rice weevil (Sitophilus oryzae) and weevil offspring during rice (Oryza spp.) seed storage, and on the germination of the rice. Treatment of stored rice with neem oil, neem powder and lentil powder gave some protection from rice weevil damage. Neem oil at the rate of 0.005ml/kg rice seed effectively controlled weevil damage without reducing the seed germination. Lentil and neem powders at the rate of 0.02g/kg rice seed gave effective protection against rice weevil damage with no reduction in viability of the seeds. Pepper powder did not kill adult rice weevil. Neem oil reduced the development of weevil offspring in rice seed, but the powders of neem, lentil and pepper did not. Low relative humidity of 42.5% in seed storage environment and a reduction in seed moisture content below 10% enhanced the mortality of adult rice weevils on rice seed.