Biopesticidal Activity of Balanites, Nigella, and Neem Essential Oils against <i>Callosobruchus maculatus </i>L. on Stored Cowpea (<i>Vigna unguiculata </i>L Walp) in Sudan Savanna, Nigeria

Abstract

An experiment was conducted to assess the oviposition deterrence effect and identify bioactive compounds in some essential oils (EOs) on cowpea weevil (Callosobruchus maculatus L.) infesting stored cowpea (Vigna unguiculata L Walp). Three EOs, obtained from balanite, black seed, and neem; a synthetic insecticide; and a control were tested alongside three local cowpea cultivars (Dan Misra, Kwankwasiya, and Kananado). The treatments were applied at a rate of 2.5 mL per 50 g of cowpea (equivalent to 0.05 mL/g v/w). Treatments were arranged in a Completely Randomized Design (CRD) and were replicated three times. Data were collected on adult mortality, oviposition, and progeny emergence. Bioactive compounds with pesticidal properties were also analyzed. The data were subjected to analysis of variance (ANOVA), and significant means were separated using Duncan’s Multiple Range Test (DMRT) at 5% probability. Adult mortality was significantly (P<0.05) higher in insecticide-treated cowpeas 24 hours after infestation, followed by balanite oil. Black seed and neem oils performed similarly and were significantly more effective than the control. Complete oviposition deterrence was observed in insecticide-treated cowpeas, but the effects were not significantly different (P>0.05) from those of the EOs. Balanite oil recorded the lowest number of eggs among the EOs. Progeny emergence was significantly (P<0.05) lower in the EOs, but was comparable to the insecticide treatment and significantly different from the control. Bioactive compounds with insecticidal and repellent properties were identified using Gas Chromatography-Mass Spectrometry (GC-MS), which included tetradecane, oleic acid, octadecanoic acid, tetradecanoic acid, 2,4-di-tert-butylphenol, and tetradecanoic acid in black seed and balanite oils, respectively. Based on these findings, essential oils, particularly balanite and black seed oils, could serve as environmentally friendly alternatives to synthetic insecticides for controlling bruchids in sustainable cowpea storage in the study area.