ABSTRACT
Cowpea, Vigna unguiculata is a popular agricultural produce known as poor man's meat among Africans because it is very cheap and affordable. In spite of its importance, its infestation by cowpea seed bruchid, Callosobruchus maculatus has been a major constrain hindering its storage. Considering the high level of infestation of cowpea by C. maculatus and the high level of pollution caused by agricultural products, this research investigated the entomotoxicant effectiveness of rice husk, wheat husk and groundnut pod ash and powder in the control of cowpea beetle in storage. This study was carried out under laboratory condition of ambient temperature 28 ± 2 °C and 70 ± 5% relative humidity. The wastes (rice husk, groundnut pod and wheat husk) were pulverized separately and another portion was burnt to ashes at 525 °C. The powders and the ashes were analyzed for their proximate composition, phytochemical content (powders) and silica content (ashes). The powders and the ashes were tested at 0.1, 0.2, 0.3, 0.4 and 0.5 g/20 g of cowpea. Rice husk ash resulted in the highest mortality of 100% of adult beetles at dosage of 0.5g/20g cowpea after 96 h post-application. Wheat husk ash at 0.4 and 0.5 g per 20 g cowpea seed had the highest protectant ability on cowpea as it reduced fecundity to 4.67% and prevented adult emergence, seed damage and weight loss. The ash of the wastes caused more mortality of the adult beetles than their powders. The results obtained showed that the wastes caused high mortality of C. maculatus. It was also found that the wastes had some phytochemicals which might be responsible for the recorded high mortality. The findings showed that the tested agro-wastes have a promising insecticidal potential against C. maculatus, and can be used as possible alternatives to synthetic chemical insecticides for the control of stored product insects.
ABSTRACT
Essential oils have emerged as an alternative to synthetic insecticides in the control of stored grain pests. The toxicity and repellency of the essential oils of four basil cultivars and three basil hybrids and the monoterpenes linalool, citral, and (E)-methyl cinnamate were evaluated in the stored grain pests Callosobruchus maculatus and Sitophillus zeamais. The essential oils of the cultivar Genovese and the hybrid 'Genovese' x 'Maria Bonita' were more toxic to C. maculatus. Conversely, the essential oils of the cultivar Sweet Dani and the hybrid 'Cinnamom' x 'Maria Bonita' were more toxic to S. zeamais. Among the monoterpenes, (E)-methyl cinnamate was the most toxic to both pests, taking 0.14 and 0.34 µ L.mL-1 to kill 50% of the C. maculatus and S. zeamais populations, respectively. All essential oils from cultivars, hybrids, and monoterpenes were repellent to S. zeamais, except for (E)-methyl cinnamate. For C. maculatus, this effect was lower, being citral the most repellent compound. Results demonstrate the insecticidal potential of the essential oil of O. basilicum and its monoterpenes in the control of stored grain pests.
Os óleos essenciais surgem como alternativa aos inseticidas sintéticos no controle das pragas de grãos armazenados. A toxicidade e a repelência dos óleos essenciais de quatro cultivares e três híbridos de manjericão e dos monoterpenos linalol, citral e (E)-cinamato de metila foram avaliadas nas pragas de grãos armazenados Callosobruchus maculatus e Sitophillus zeamais. Os óleos essenciais da cultivar Genovese e do híbrido 'Genovese' x 'Maria Bonita' foram mais tóxicos para C. maculatus. Já para S. zeamais, os óleos essenciais das cultivar Sweet Dani e do híbrido 'Cinnamom' x 'Maria Bonita' apresentaram maior toxicidade. Dentre os monoterpenos, o (E)-cinamato de metila foi o mais tóxico para ambas as pragas. Foram necessários 0,14 e 0,34 µ L.mL-1 para matar 50% da população de C. maculatus e S. zeamais. Todos os óleos essenciais das cultivares, dos híbridos e dos monoterpenos foram repelentes a S. zeamais, com exceção do (E)-cinamato de metila. Já para C. maculatus, este efeito foi reduzido, sendo o citral o composto mais repelente. Nos resultados demonstram o potencial inseticida dos óleos essenciais de O. basilicum e seus monoterpenos para o controle de pragas de grãos armazenados.
