Bioefficacy of some plants ethanolic extracts against maize weevil (<I>Sitophilus zeamais</I>) infestation of stored maize grains

Abstract

The experiment was conducted to determine the efficacy of three plants ethanolic extracts against maize weevil (Sitophilus zeamais) on stored  maize grains (Zea mays). Five different ethanolic concentrations (0.5 mg/L, 1.0 mg/L, 2.0 mg/L, 4.0 mg/L and 8.0 mg/L) were made from the leaves of Hyptis suaveolens, Alstonia boonei and Tephrosia vogelii with 0.0 mg/L as the control (ethanol) and applied onto the maize grains by dipping. The
experiment consists of six treatments (including control) and was laid in completely randomized design (CRD) with three replications. Data were collected for adult mortality, number of eggs, larval development and percentage grain damage. The data were subjected to analysis of variance (ANOVA) at 5% probability level with Duncan's Multiple Range Test (DMRT) used to separate the means that were significant. The result obtained
revealed significant difference (P≤ 0.05) between the concentrations over the control in terms of toxicity, oviposition, induced adult mortality and progeny suppression. However, the extracts from Tephrosia vogelii are the most toxic and produced the best effect with LC of 4.85 mg/L at 24 hours of exposure and 1.94 mg/L at 48 50 hours of exposure. Similar result was found in terms of adult mortality and oviposition suppression. The effect
of the extracts is concentration-dependent increase with increase in concentration. The percentage decrease in weight due to the weevil's  infestation was found to be reduced with increase in concentrations. Thus, 8.0 mg/L of the ethanolic extracts of Tephrosia vogelii is recommended for biological control of Sitophilus zeamais against stored maize grains.

Key Words: Concentrations, Ethanolic Extracts, Maize, Weevil.