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

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 48 h 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 48 h, 450 ppm 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 600 ppm concentrations,
maximum mortality (62.5%) was observed in S. oryzae
exposed to 600 ppm pyrethrum for 48 h. The effective
LC50 concentrations for pyrethrum (600 ppm) ?
deltamethrin combination was estimated to be as 0.1987
and 0.7039 ll/cm2 for R. dominica and T. castaneum adults
respectively. Contrastingly, for treatments with S. oryzae, a
LC50 value of 0.8673 ll/cm2 was recorded for pyrethrum
(600 ppm) ? 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.