Efficacy of Botanical Extracts Against Storage Insect Pest Tribolium confusum (confused flour beetle) and Sitophilus oryzae (Rice Weevil)

Abstract

Storage insect pests are inflicting severe economic loss leading to food insecurity and hunger. Research evidence suggests that synthetic chemicals are toxic to humans and are creating deleterious impacts on biodiversity. Therefore, this study evaluated natural plant extracts as alternatives to synthetic insecticides in controlling storage insect pests in an eco-friendly manner. Fresh and dry leaves, and seed kernel extracts of Azadirachta indica, Gliricidia sepium, Ocimum tenuiflorum, Cascabela thevetia were tested against storage insect pests Tribolium confusum and Sitophilus oryzae. Cascabela thevetia fresh leaves, flowers, seed kernels, and fresh leaves of A. indica, G. sepium, and O. tenuiflorum were collected and aqueous extracts were derived. Two laboratory trials were conducted. The first one was to understand the toxicity of aqueous extracts on pests. Therefore, 100 adult insects of red flour beetles and rice weevils were topically applied with treatments at the rate of 10g/100 mL. The second trial was to test the repellent properties of the aqueous solutions. Therefore, extracts were applied over the sealed bait bags in a large closed container at the same rate. Immediately after treatment application, 100 adult insects of each group were released into the container containing baits, and the container closed. Both trials were arranged in a completed randomized design (CRD), replicated three times including the untreated control. From the first trial, the number of live insect per treatments was counted after 30 seconds, 1 minute, 5-minute, 10-minute, 1 h, 2 h, and 24 h, and mortality percentage were calculated. From the second trial, the number of insects inside the sealed bags was counted 24 h, 48 h, 5 d after treatment. The data were subjected to ANOVA using SAS 9.1. Tukey’s HSD multiple comparison test was used to identify the best treatment combination. The result showed that C. thevetia dried seed kernels exhibited highly significant mortality of 50% against rice weevils and 100% against flour beetles, after an hour and one minute, respectively, at P <0.01. Ocimum tenuiflorum and A. indica showed 100 % mortality against flour beetles after 24 h, but not in rice weevil. Repellency percentage was highly significant in C. thevetia dried leaf extract (91.30% and 75.00%) and fresh leaf extract (86.36% and 78.05 %) after 24 hours and five days, respectively at P <0.01. In the repellency treatment, C. thevetia dried leaf and seed kernel extract showed highly significant repellency of 96.91% and 98.99%, respectively, against red flour beetles. The repellency percentage of C. thevetia dried leaf, seed kernel extract and O. tenuiflorum were 81.79%, 66.67%, and 59.15% after 24 hours, respectively, and significant at P <0.05. The results suggest that leaf and seeds of C. thevetia have high insecticidal properties and can be used to repel storage insects in warehouses once potential toxicity to humans is determined.