Assessment of Platostoma africanum and Hyptis spicigera as Botanicals for Controlling Cowpea and Maize Weevils During Storage

Abstract

In sub-Saharan Africa, maize (Zea mays L.) and cowpea (Vigna unguiculata (L.) Walp) are essential for food security, but infestation by storage weevils — Sitophilus zeamais Motschulsky and Callosobruchus maculatus Fabricius — can cause postharvest losses greater than 30%. This study investigated two Lamiaceae species, Platostoma africanum P. Beauv. and Hyptis spicigera Lam., as environmentally friendly alternatives to synthetic insecticides. The exploration of these plant-based alternatives offers a promising approach to sustainable pest management in stored products, particularly for smallholder farmers who require affordable and accessible solutions.Different doses (0, 2.5, 5.0, and 10.0 g per 100 g of grain) were applied to uninfested maize and cowpea and monitored for 28 days at 27±2°C and 65±5% RH. Five parameters were evaluated: cumulative adult mortality, F1 progeny suppression, grain damage, weight loss, and seed germination. The 1:1 (w/w) combination at 10.0 g gave the best performance, with cumulative mortality reaching 95.31±1.11% for S. zeamais and 94.77±1.67% for C. maculatus on day 28. It lowered seed damage to 19.67±0.67% in maize and 25.33±0.88% in cowpea (compared to 60.67±1.45% and 60.33±0.88% in untreated controls) and reduced weight loss to 9.94±0.34% and 12.80±0.45% (versus 30.64±0.74% and 30.47±0.44% in controls) (ANOVA, Tukey's HSD, p<0.05). Importantly, seed viability was maintained, with germination of 73.5±1.1% for maize and 71.2±0.9% for cowpea at the 10.0 g combined dose, against 26.67% in controls, confirming no phytotoxic effect. The combined botanical treatment at 5.0–10.0 g/100 g may provide a sustainable and low-cost protectant for smallholder farmers.