Abstract
Studies were conducted to determine the component fruit part of ackee (Blighia sapida Koenig) that had the most repellent properties against stored-product insect pests, namely, Callosobruchus maculatus, Cryptolestes ferrugineus, and Sitophilus zeamais. In Experiment 1, B. sapida fruits were harvested at stages 2, 3, 5, and 7 of development and soaked for 48 h in 400 mL of either acetone, ethanol, or water (100°C) before being tested against the three insect pests. Based on the results of Experiment 1, Experiment 2 was conducted. Blighia sapida fruit parts (epidermis, pulp, aril, and seed) at Stage 3 of fruit development were soaked for 48 h in each of two solvents, acetone and ethanol, after which they were tested against the three stored-product insect pests. The third experiment was conducted to determine the dosage that would repel 50% of the insect population (RD50) for each insect pest species and to determine the longevity of each extract before re-application on stored products. In the fourth experiment, the RD50 dosage obtained for each insect pest species was used to treat either holding bags or chickpea (Cicer arietinum) to determine the longevity of protection. The results of Experiment 1 indicated that Stage 3 of development of B. sapida was the most effective in repelling the three insect pests, and acetone and ethanol were better at extracting the repellent properties than water. There was also high mortality (>60%) when C. maculatus was left exposed to the extracts for >24 h. In the second experiment, the results indicated that all fruit parts had a significant effect on the three insect pests, and although the pulp and aril statistically had the greatest repellency, only the epidermis significantly repelled all three pests. The results of the third experiment indicated that the RD50 for C. maculatus was 1.14 mL L-1 at 10-50% extract concentration (epidermis-acetone extract), for S. zeamais it was 58.85 mL L-1 at 75% extract concentration (aril-acetone extract), and for C. ferrugineus it was 136.20 mL L-1 at 100% extract concentration (pulp-ethanol extract). The results of Experiment 4 showed that treating chickpea (Cicer arietinum) seeds and holding bags with the respective RD50 concentrations, that C. maculatus was repelled for at least 12 days, S. zeamais for 7 days, and C. ferrugineus for approximately 5 days.
