Abstract
Bioassay experiments were carried out in Calabar to compare the repellency activity of single compounds and the synthetic blends of Semiochemicals extracted from Afromomum melegueta and Dennittia tripetala. The aim of the experiment was to determine the efficacy of single compounds and the synthetic blends in suppressing the reproductive potential and adult emergence of Rhizopertha dominica, (Fabricius), a primary pest of stored cassava pellets and cereal grains in Sub-Saharan Africa. Insect culture of the adult R. dominica was set up in the laboratory at Federal College of Education Obudu to obtain fresh insects for the bioassay experiments. Dried seeds of A. melegueta (R. Schum) and D. tripetala (Baker f.) Schatz were procured from the main market in Obudu for the purpose of the research work. 100g each of the dried fruits of the spice plants were pounded separately with the laboratory pestle and mortar for the extraction of the essential oils (EOs). The oils extracted were tested for toxicity and reproductive potential deterrence against R. dominica. The chemical constituents of the essential oils were isolated, identified and tested against R. dominica. Synthetic blends of individual compounds were prepared based on their natural ratios and were also tested for toxicity and reproductive potential deterrence against the insect pests in the laboratory. The result showed that both the single compounds and the synthetic blends were toxic and repellent to the insect pest, and could significantly suppress the reproductive potential thereby inhibiting the emergence of adult insect. However, synthetic blends exhibited a stronger efficacy in their toxicity against the pest thereby providing a broad spectrum of insecticidal bioactivity against R. dominica than the single compounds. This action of the synthetic blends of extracts from the spice plants demonstrated their potential for development in stored products protection especially at the small scale resource poor farmer’s level in Nigeria.
Highlights
In Nigeria and in most African countries, farmers harvest their crops, dry them and store in traditional manner, which are open storage facilities that are only capable of holding just about 1000 to 1,500 kgs of the total grains harvested for the year (Duke et al, 2003)
Schum) and D. tripetala (Baker f.) Schatz were procured from the main market in Obudu for the purpose of the research work. 100g each of the dried fruits of the spice plants were pounded separately with the laboratory pestle and mortar for the extraction of the essential oils (EOs)
Toxicity effect The was no significant (P>0.05) difference in the mortality count of adult R. dominica at 24, 48 and 72 hours at 5μl compared to the control treatment in all the essential oils of the two spice plants
Summary
In Nigeria and in most African countries, farmers harvest their crops, dry them and store in traditional manner, which are open storage facilities that are only capable of holding just about 1000 to 1,500 kgs of the total grains harvested for the year (Duke et al, 2003). Greater part of this stored grains are often times damaged by insect pests that infest them. The insect is known to be a pest of whole cereals, even of rough rice which is resistant to the attack of most
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