Bioassay of Aqueous Extracts from Six Tropical Plants against Tribolium castaneum (Coleoptera: Tenebrionidae)
Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is a very important insect pest of stored products causing economic damage to several stored grains. Laboratory bio-assay of aqueous extracts of six plants namely; Azadirachta indica (Neem), Xylopia aethiopica (Grain of selim), Cymbopogon citratus (Lemon grass), Piper guineense (African black pepper) Zingiber officinale (Ginger) and Ocimum gratissimum (African basil) were conducted for their contact and residual toxicity to adult T. castaneum under ambient temperatures of 27±2ºC and 80 ±5% relative humidity. Aqueous extracts of the test plant were applied in crude form at1 ml and 2 mls /5adult insects for contact and residual assays respectively. The mortality of adult T. castaneum were recorded at 20 minutes intervals for 24hours, data collected were subjected to Analysis of Variance and significant means were separated using Duncan Multiple Range Test (DMRT). The results showed that aqueous extracts of all the plants evaluated had toxic effects on adult T. castaneum ranging from 60.0% - 86.6% and 33.4% - 86.6% mortality for contact and residual toxicities, respectively at 24 hours post application. Highest mortality of 86.6% was observed in A. indica and Z. offiinale extracts for contact and residual toxicities, respectively. The aqueous extracts of plant materials evaluated showed great potentials against T. castaneum under laboratory conditions. Hence, their usage should be encouraged as a viable alternate to synthetic insecticide for stored products pest management to mitigate health and environmental hazards associated with synthetic pesticides application.
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