Original Contribution BIO-ACTIVITY OF THREE ESSENTIAL OILS EXTRACTED FROM EDIBLE SEEDS ON THE RUST-RED FLOUR BEETLE, TRIBOLIUM CASTANEUM (HERBST.) INFESTING STORED PEARL MILLET.

The ovicidal, repellent and toxic activities of three essential oils extracted from clove, Syzgium aromaticum (L.) Merril and Percy; West African black pepper (WABP), Piper guineense Schum and Thonn. and Ethiopian pepper, Xylopia aethiopica (Dunn) A. Rich were evaluated against the rust-red flour beetle, Tribolium castaneum (Herbst.) under laboratory conditions (20 – 39 O C; 41 – 58% RH). Five pairs of 2- to 3day old adult T. castaneum were allowed to oviposit for 20 days on 20 g of 20% broken pearl millet grain contained in 50 ml glass jar with a lid. After 20 days, all dead and live insects were removed from the jars. Thereafter, four rates (0.75, 1.50, 2.25 and 3.00 mg) of each essential oil carried in 2 ml analytical grade acetone were used to treat the seeds and progeny emergence was recorded for three generations. The same rates of essential oil as described above were assayed against thirty larvae and adults T. castaneum as repellant on a 30 cm 3 Whatman No. 1 filter paper. The number of insects repelled on both treated and untreated half discs of filter paper was recorded after 30 min. Both the ovicidal and repellent treatment were set up in a randomized complete block design with a split plot arrangement and replicated three times. In the toxicity study 30 unsexed adults and larvae of T. castaneum were treated with the same rates of essential oils carried in 2 ml analytical grade acetone and admixed with 20 g of 20% broken grain in a 50 ml glass jar with a lid. Adult and larval mortality was taken 24 h after and results were subjected to probit analysis. The experiment was carried out in a complete randomized design replicated three times. All the control batches were treated with 2 ml of pure analytical grade acetone alone. The three essential oils were able to reduce progeny emergence of T. castaneum significantly than in the control treatments. Higher number of adults emerged in Ethiopian pepper than in clove and WABP. There was however no significant difference (p≥0.05) between clove and WABP. The efficacy of the dosage rate was dose dependent as less number of adults emerged in higher concentration than in lower concentrations. The three essential oils evoked classes II - V repellency rates. There was no significant difference (p≥0.05) between the three oils, but the dosage rates were statistically different (p≤0.05) from each other. Values for repellency test against adult T. castaneum ranged for clove oil between 83.20 – 99.62%, WABP 88.50 – 99.62% and Ethiopian pepper 91.70 – 97.70%; while in the case of repellency for larva, 61 -100% for clove; 25.60 – 100% for WABP and 40.50 – 86.30% for Ethiopian pepper. In the toxicity test, the entire essential oil caused 100% mortality of both adult and larva of T. castaneum albeit at higher dosage rates. The LC50 for clove was 0.40 (adults), 0.46 (larvae); WABP 0.21 (adults), 0.54 (larvae) and Ethiopian pepper 1.78 (adults), 0.67 (larvae)/ 20 g seed.