EFFICACY OF SELECTED ESSENTIAL OILS AGAINST MAIZE WEEVIL (SITOPHILUS ZEAMAIS (MOTSCHULSKY) UNDER LABORATORY CONDITION

Maize (Zea mays Linnaeus), a prominent cereal crop of Nepal, which suffers significantly from storage pest, particularly maize weevil (Sitophilus zeamais (Motschulsky)), during storage by creating holes and consuming the internal part. Effective management of the pest and reduction grain loss is crucial. To address this problem, a study was conducted at the Nepal Agricultural Research Council in Khumaltar, Lalitpur, from April to August, 2023, evaluating the efficacy of essential oils of Acorus calamus Linnaeus, Cuminum cyminum Linnaeus, and Piper nigrum Linnaeus against S. zeamais. Essential oils were extracted using the Clevenger type steam hydrodistillation method. Concentrations of essential oils (5%, 2.5%, 1.25%, 0.63%, 0.31%, 0.15%) were tested in a two factor completely randomized design (CRD) using oils and doses as the two factor, with four replications and control group. The study assessed lethal concentration, weight loss, and repellence tests in petridishes. Progeny of maize weevils (1-7 days old) were introduced into petridishes having 7mm diameter of Whatman filter paper to evaluate the mortality and repellency effect. The number of insects on both side of the petridish (treated and untreated paper) was counted as part of the repellence test. Mortality in treated grains was observed over a 20 days, and with weight loss measured after 60 days. Results showed significant insecticidal activity, with the median lethal concentration (LC50) of A. calamus oil at 24 and 72 hours calculated as 1.24% and 0.43%, respectively in laboratory bioassay. The LC50 for A. calamus treated maize was 4.70% and 0.70% for 1 and 20 days, respectively, followed by C. cyminum and P. nigrum. Acorus calamus Linnaeus oil demonstrated the highest repellent activity (90.00%) at 5% concentration after 4 hours of treatment. Moreover, maize treated with A. calamus oil showed significantly lower weight loss (0.62%) compared to the control. This study indicated the potential of A. calamus oil for pest control, concerns remain regarding its suitability for feed and food purposes due to associated health risks. These findings underscore the need for further research to explore safer alternatives for pest management in maize storage.