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- Bioactivity of three essential oils and crude extracts against maize...
Bioactivity of three essential oils and crude extracts against maize weevil complex, Sitophilus spp. (Coleoptera: Curculionidae) and bean beetle, Callosobruchus chinensis (L.) (Coleoptera: Bruchidae).
Thesis Abstract:
The essential oils and crude extracts from three plant species (citronella,Cymbopogon nardus; langkauas, Alpinia pyramidata; and patchouli, Pogostemon cablin) were extracted through steam distillation and using acetone, respectively. The repellent activity and contract toxicity of the essential oils and crude extracts were evaluated against adult maize weevil, Sitophilus spp. and bean beetle, Callosobruchus chinensis (L.). The most active essential oils and crude extracts were selected and formulated as emulsifiable concentrate and evaluated for admixture grain treatment against Sitophilus spp. and C. chinensis.
The essential oil from citronella provided the highest repellency against adult Sitophilus spp. and C. chinensis while essential oils of citronella and patchouli provided 100 percent reduction in F1 emergence. Langkauas crude extract provided 100 percent reduction in F1 emergence in both Sitophilus spp. and C. chinensis.
However, none of the essential oils and crude extracts from the three test plants showed contact toxicity against Sitophilus spp. Citronella essential oil showed the highest contact toxicity (LD50 = 0.8619) against C. chinensis while langkauas crude extracts was the most toxic (LD50= 0.0854) at 48 h exposure.
For admixture grain treatment, all the essential oils were ineffective against the maize weevil while 7.5 percent langkauas (w/w) crude extract provided 100 percent reduction in F1 emergence. Meanwhile, the admixture treatment of mungbean seeds with 5 percent emulsifiable concentrate formulation of citronella essential oil caused 100 percent mortality of adult C. chinensis at seven days after exposure and caused 92 percent reduction in F1 emergence. Langkauas crude extract seemed to be more effective than the essential oil since the admixture treatment at the rate of 2 percent caused 100 percent mortality in C. chinensis after five days and provided 95 percent reduction in F1 emergence.
The crude extracts seemed to be more effective than the essential oils based on repellency test, contact toxicity, and admixture treatment against both Sitophilus spp. and C. chinensis. Between the two coleopteran test insects, C. chinensis was more sensitive to both essential oils and crude extracts of the test plants than Sitophilus spp.
Based on repellency, contact toxicity, and admixture treatment, langkauas was generally the most effective against Sitophilus spp. and C. chinensis. This provided the highest reduction in F1 emergence in repellency test and admixture grain treatment and exerted the highest contact toxicity having the lowest LD50values.
The formulation of langkauas crude extract into emulsifiable concentrate increased the toxicity of the extract by as much as 10 times against C. chinensis and 2.67 times against Sitophilus spp.
