Assessment of Platostoma africanum and Hyptis spicigera as Botanicals for Controlling Cowpea and Maize Weevils During Storage
Louis Agyemang
Department of Applied Biology, School of Environment and Life Sciences, University of Technology and Applied Sciences, Navrongo, Ghana.
Millicent Captain-Esoah
Department of Applied Biology, School of Environment and Life Sciences, University of Technology and Applied Sciences, Navrongo, Ghana.
Elijah Dakorah Angyiereyiri
Department of Applied Biology, School of Environment and Life Sciences, University of Technology and Applied Sciences, Navrongo, Ghana.
Martin Ntiamoah Donkor *
Department of Biochemistry and Forensic Sciences, School of Chemical and Biochemical Sciences, University of Technology and Applied Sciences, Navrongo, Ghana.
Dorothy Obuobi
Department of Parasitology, Noguchi Memorial Institute for Medical Research, College of Health Sciences, University of Ghana, Legon, Accra, Ghana, Center for International Health (CIHLMU), University Hospital, LMU Munich, Munich, Germany and Department of Conservation Biology and Entomology, University of Cape Coast, Cape Coast, Ghana.
Godwin Deku
Department of Conservation Biology and Entomology, University of Cape Coast, Cape Coast, Ghana, Centre for Chemical Biology, University Sains Malaysia, Penang, Malaysia and School of Hygiene, Ministry of Health, Korle-Bu, Accra, Ghana.
Theophilus Atio Abalori
Department of Applied Biology, School of Environment and Life Sciences, University of Technology and Applied Sciences, Navrongo, Ghana.
Oliver Awo
Department of Applied Biology, School of Environment and Life Sciences, University of Technology and Applied Sciences, Navrongo, Ghana.
Mawuli Kwamla Azameti *
Department of Applied Biology, School of Environment and Life Sciences, University of Technology and Applied Sciences, Navrongo, Ghana.
*Author to whom correspondence should be addressed.
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.
Keywords: Platostoma africanum, Hyptis spicigera, Sitophilus zeamais, Callosobruchus maculatus, botanical insecticide, stored-grain protection, postharvest storage, seed damage, weight loss, seed germination