Bioactivity of Powder and Extracts from Garlic, Allium sativum L. (Alliaceae) and Spring Onion, Allium fistulosum L. (Alliaceae) against Callosobruchus maculatus F. (Coleoptera: Bruchidae) on Cowpea, Vigna unguiculata (L.) Walp (Leguminosae) Seeds
Laboratory bioassays were conducted to investigate the bioactivity of powders, extracts, and essential oils from Allium sativum L. (Alliaceae) and A. fistulosum L. (Liliaceae) against adults, eggs, and larvae of Callosobruchus maculatus F. (Coleoptera: Bruchidae). On the basis of 48？hr median lethal toxicity ( L C 5 0 ), test plant powders and extracts from A. sativum were more toxic to C. maculatus adults than those from A. fistulosum. The 48？hr L C 5 0 values for the powder against the test insect species were 9.66？g/kg and 26.29？g/kg for A. sativum and A. fistulosum, respectively. Also the 48 hr L C 5 0 values obtained show that aqueous extracts of the test plant species, 0.11？g/L (A. sativum) and 0.411？g/L (A. fistulosum) were more toxic to C. maculatus than the corresponding ethanol extracts. There was no significant difference in the toxicity of vapours from the two test plant species against C. maculatus, although A. sativum gave lower values. The study shows that A. sativum and A. fistulosum have potentials for protecting stored cowpea from damage by C. maculatus. 1. Introduction Grain storage has often resulted in quantitative and qualitative losses due to physical, chemical, and most importantly biological factors such as pests which may be birds, rodents, fungi, or insects [1–3]. The most important among storage pests are insects because apart from their direct damage they create conditions that allow secondary infestation by rot organisms mainly fungi [1, 4]. Once infestation is established pest insects cause gradual and progressive damage leading to losses in weight, nutritional, organoleptic, and aesthetic quality of stored grains. Osuji [1] listed 40 insects affecting stored grains, the most important among which is the cowpea weevil, Callosobruchus maculatus F. (Coleoptera; Bruchidae) responsible for up to 100% infestation of cowpea, Vigna unguiculata (L.) Walp (Leguminosae) during storage [1, 3, 5]. These observations justify the control of insect pests like C. maculatus in order to reduce losses in stored cowpea. Several methods are used in controlling insects in stored grains, including physical (smoking, sun-drying, heating), cultural, biological (male insect sterilization, natural enemies, resistant grain varieties), and chemical (synthetic and natural products) methods. The most common and widely used is the chemical method involving mainly the use of synthetic insecticides. Several workers have reported the successful wide scale use of synthetic organic insecticides, commencing with the organochlorines in the middle 1940s,
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