Particle Size Effect of Piper guineense in the Control of the ‘Sitophilus zeamais Motchulski’ on Maize

Sitophilus zeamais is perhaps the most important storage insect pest of maize. The negative health implication of synthetic pesticides necessitates research into botanicals. We investigated the efficacy of ground Piper guineense (particles sizes 150, 300, 600, 1180, and 2360 µm) in controlling S. zeamais. The botanicals were compared with pirimorphos methyl and control (untreated seeds). Completely Randomized Design was used with three replications. Each treatment was infested with 20 adult weevils. Weevils were withdrawn after 14 days and the experiment was observed for another 38 days to count emerged adult weevils, numbers of damaged grains and exit holes on seeds, and determine loss in seed weight. Progressive efficacy and significant differences were observed among the botanicals and Pirimorphos methyl from four days after treatment application (DAT) to 14 DAT (90%, 100%, 100%, and 46.67%for Pirimorphos methyl, 150, 300, and 2360 µm of Piper respectively) as the particle size decreases. Piper of 150 and 300 µm particle sizes produced no new adult weevil and no seed weight loss at 52 DAW compared to others. The efficacy of piper at different particle sizes from 4 DAT showed that graduating piper particle size has significant effects on its insecticidal activity. It was concluded that ground piper of particle size 150µm is the most effective and is therefore recommended for effective control of maize weevils in storage.