Potential of pyrethroid-synergised pyrethrum on stored product insects and implications for use as prophylactic sprays.

Abstract

The study was conducted to evaluate the synergistic effects of 2% pyrethrum extract with synthetic pyrethroids on the mortality of stored product insects. Contact toxicity was performed at variable concentrations observing mortality at 12, 24 and 48h durations. The results of the present study indicated that, pyrethrum + deltamethrin combination (25:1 ratio) was effective on the adults of Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst). On the other hand, pyrethrum + cypermethrin combination proved effective against Sitophilus oryzae (L.). The efficacy of the tested combination showed reasonable increase in mortality response in treated insects over increasing exposures. At 48h, 450ppm pyrethrum + deltamethrin combination induced 25, 90 and 97% mortalities in S. oryzae, T. castaneum and R. dominica adults; while, pyrethrum-cypermethrin combination recorded 75, 45 and 75% mortalities respectively. On the other hand, it was observed that, among the pyrethrum alone treatments i.e. at 300, 450 and 600ppm concentrations, maximum mortality (62.5%) was observed in S. oryzae exposed to 600ppm pyrethrum for 48h. The effective LC50 concentrations for pyrethrum (600ppm) + deltamethrin combination was estimated to be as 0.1987 and 0.7039µl/cm2 for R. dominica and T. castaneum adults respectively. Contrastingly, for treatments with S. oryzae, a LC50 value of 0.8673µl/cm2 was recorded for pyrethrum (600ppm) + cypermethrin mixture. This investigation strengthens the fact that pyrethrum along with pyrethroids is effective against storage insect pests which can be promisingly a safer insecticidal combination.