Attached
The noticeable propensity towards a 'trek back to nature' has become evident over the past
decade in the field of synthetic insecticides resulting out of sheer necessity in replacing these
highly toxic chemicals w ith new er and greener strategies as stored grain protectants in the postharvest insect pest m anagem ent programs. In this context, th e potential of leaf pow der of Ruta
graveolens (Aruda) was investigated under laboratory conditions fo r its ability to protect stored
maize from the attack of Sitophilus zeamais. Efficacy of R. graveolens was determ ined by
exposing tw enty one w eek old S. zeamais adults to leaf powders, incorporated into 30 g each of
un-infested maize grains at th e doses of 1.0, 3.0, 5.0, 7.0 and 10.0 g. Adult m ortality in both
contact and vapor forms was assessed using cup-bioassays and m ortality rates at 3 hour intervals
up to 24 hours of post treatm en t w ere recorded. 100% weevil m ortality was observed at doses
of 7.0 and 10.0 g within 24 hours of exposure in contact toxicity test, whereas only 68.00 ± 3.54
% and 76.00 ± 4.18 % w ere recorded respectively in fum igation toxicity test after 24 hours.
M oreover, th e LD50 values obtained after 24 hours w ere 1.79g and 5.52g for contact and
fum igation toxicity tests respectively, indicating th at the contact effect of the leaf powder on
weevils is much higher than the fum igation effect. In conclusion, the leaf powders of R.
graveolens could be considered as a highly probable candidate in the developm ent of bioinsecticides as safer and economic alternatives to synthetic insecticides to suppress S. zeamais
populations.
