TOXICITY AND BIOEFFICACY OF WEED ESSENTIAL OILS AGAINST COWPEA BRUCHIDS AND THEIR EFFECT ON MUNGBEAN SEEDS

Abstract

These investigations aimed to determine toxicity and bioefficacy of weed essential oils Bitter
bush (Eupatorium odoratum L.), Finger grass (Limnophila aromatica (Lamk.) Merr.), and Vietnamese mint
(Polygonum odoratum) derived by hydrodistillation against cowpea bruchids, Callosobruchus maculatus

(Fabricius) on stored mungbean. Experiments were assessed under laboratory conditions (30±2°C, 70-80%RH
and 16L:8D photoperiods). Results showed that weed essential oils from Bitter bush, Finger grass and
Vietamese mint leaves have contact toxicity on cowpea bruchids as shown by the impregnated filter paper test.
LC50 values were 137.15, 225.17 and 99.12 ppm at 48 h after exposure, respectively. Fumigant toxicity by the
fumigation method on cowpea bruchids showed all weed essential oils had high efficiency against the cowpea
bruchids (100% of mortality). Repellency toxicity test showed that weed essential oils from Bitter bush, Finger
grass and Vietnamese mint leaves have repellent toxicity on cowpea bruchids as LC50 values were 607.23,
141.93 and 109.81 ppm at 6 h after exposure, respectively. The potential of weed essential oils on reproduction
of the cowpea bruchids female adults had strong repellent activity for egg laid on mungbean seeds, were 100%
at 48 h. Three weed essential oils did not affect the seed germinating. These results suggested that essential
oils from three weed plants could be used as potential control agents for cowpea bruchids, and the database
can be used for active ingredient studies to develop commercial products in the future.