Comparative Study of Psidium guajava and Ocimum gratissimum Leaf Oils on Adult Maize Weevil (Sitophilus zeamais M.)

Abstract

A laboratory study was conducted to determine the efficacy of Psidium guajava and Ocimum gratissimum leaf oils for Sitophilus zeamais control. The experimental design was a completely randomized design with three replications. The leaf oil was extracted using a Soxhlet extractor. The leaf oils at four levels of concentration were mixed with 20 g of disinfested maize in 2 by 5 cm containers. All treatments with the leaf oils showed a significant level of toxicity to the weevil. The highest concentration (4%) of the leaf oil of the plant material tested induced the highest mortality in S. zeamais after six days. Grains treated with the leaf oil extracts significantly reduced the number of progeny emergence of both F1 and F2 generations of S. zeamais, and evoked low weight loss and seed damage on grains treated with the highest dosage of the leaf oil extract. P. guajava was found to be the most effective, recording 100% mortality of S. zeamais after five days, lower LC50 value (1.94 µml/L), lower F1 and F2 emergence (0.000 ± 0.000), lower percentage weight loss (1.00%), lower percentage seed damage (11%), and higher viability (50%), which compared favorably with that recorded in the positive control. Further studies should be conducted to identify the most bioactive ingredient in these plant leaf oils.