PROTECTIVE EFFECTS OF MINTWEED, KITCHEN MINT AND KAFFIR LIME LEAF EXTRACTS AGAINST RICE WEEVILS, STITOPHILUS ORYZAE L., IN STORED, MILLED RICE

Abstract

The protective effects of the extracts of three edible aromatic plants, mintweed Hyptis suaveolens, kitchen mint Mentha cordifolia and kaffir lime Citrus hystrix, against rice weevil Sitophilus oryzae infestation in stored, milled rice were investigated. The efficacy of the ethanolic and the water leaf crude extracts on the repellency, insecticidal activity, grain weight loss protection, and growth inhibition of rice weevil progeny was assessed. The ethanolic extracts affected rice weevils higher than the water extracts. The extract toxicity on rice weevil adults and larvae compared as kitchen mint > kaffir lime > mintweed. The highest repellent efficacy, 24 h, of the ethanolic extract was from kaffir lime with EC50 of 13.23 mg/ml or 3.4 fold of the control and of the water extract was from kitchen mint with EC50 of 19.04 mg/ml or 3.6 fold of the control. Rice weevils were totally ridded within 20 days by kitchen mint ethanolic extracts. All extracts highly protected over the grain texture and the loss of grain weight, and inhibited the growth of rice weevil progeny. The treated grain weight loss was approximately 2% in 35 days and 16% in 49 days. The progeny emergence was inhibited ranging from 55% (water extract) to 89% (ethanolic extract). Obviously, the leaves of these three aromatic plants are highly toxic to rice weevil adults and larvae. This finding is very promising to further develop bio-insecticidal agents from mintweed, kitchen mint and kaffir lime for protecting stored, milled, rice in larger scales, household and industrial storages.