Insecticidal Activity of Crude Plant Extracts Against Sitophilus spp. (Coleoptera: Curculionidae) and Callosobruchus chinensis (L.) (Coleoptera: Bruchidae)
The crude extracts from three plant species (citronella, Cymbopogon nardus (L.) Rendle; langkauas, Alpinia pyramidata (Blume) Merr.; and patchouli, Pogostemon cablin (Blanco) Benth. were extracted using acetone. The repellent activity and contact toxicity of the crude extracts were evaluated against the adult maize weevil Sitophilus spp. and the bean beetle Callosobruchus chinensis (L.). Citronella crude extract provided the highest repellency against Sitophilus spp. but langkauas provided 100% reduction in F1 emergence. In contrast langkauas, citronella and patchouli provided similar level of repellency against C. chinensis but langkauas provided 100% oviposition deterrence and reduction in F1 emergence. None of the three crude extracts showed contact toxicity against Sitophilus spp., but langkauas crude extract was the most toxic (LD50 = 0.0854) against C. chinensis at 48 h exposure. The crude extract with the highest biological activity was selected and formulated as emulsifiable concentrate (EC) and evaluated for admixture grain treatment application. The grain admixed with formulated langkauas crude extracts at 7.5% (w/w) provided 100% reduction in F1 emergence in Sitophilus spp. Similarly, the admixture treatment of 2% langkauas crude extract in mungbean caused 100% mortality in C. chinensis in 5 d and provided 95% reduction in F1 emergence. C. chinensis was more sensitive to the three crude extracts than Sitophilus spp. Langkauas crude extract proved to be the most effective against Sitophilus spp. and C. chinensis, providing the highest reduction in F1 emergence both as repellent and admixture grain treatment. Additionally, it had the highest contact toxicity as shown by the lowest LD50 values.
Key Words: admixture treatment, Alpinia pyramidata, Callosobruchus chinensis, contact toxicity, plant-based insecticide, repellent, Sitophilus spp.
Abbreviations: DAT – days after treatment, EC – emulsifiable concentrate, FLCE – formulated langkauas crude extract, LCE – original langkauas crude extract, PR – percent repellency