Author : Win Myint Thein

Summary : The essential oils and crude extracts from three species (citronella, Cymbopogon nardus; langkauas, Alpinia pyramidata; and patchouli, Pogostemon cablin) were extracted through steam distillation and using acetone, respectively. The repellent activity and contact 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 fro 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% reduction in F1 emergence. Langkauas crude extract provided 100% reduction in F1 emergence in both Sitophilus spp. and C. chinensis. However, none of the essential oil 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 extract is the most toxic (LD50 = 0.854) at 48 hrs exposure. For admixture grain treatment, all the essential oils were ineffective against the maize weevil while 7.5% langkauas (w/w) crude extract provided 100% reduction in F1 emergence. Meanwhile, the admixture treatment of mungbean seeds with 5% EC formulation of citronella oil caused 100% mortality of adult C. chinensis at 7 days after exposure and caused 92 % 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% caused 100% mortality in C. chinensis after 5 days and provided 95 % 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 s . 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 the 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 LD50 values. The formulation of langkauas crude extract into emusifiable concentrate (EC) increased the toxicity of the extract by as much as ten times against C. chinensis and 2.67 times against Sitophilus spp. Key words: Alpinia pyramidata, Pogostemon cablin, Cymbopogon nardus, Callosobruchus chinensis, Sitophilus spp., repellent, contact toxicity, admixture treatment, botanical insecticides.