Sunthorn Pipithsangchan, Sanan Subhadhirasakul, Parichart Palintorn, Supreeya Yuenyongsawad, and Kan Chantrapromma

pp. 511 - 521

Abstract

Crude n-hexane and methanolic extracts from the seeds of Azadirachta excelsa Jack. (Tiam) and
A. indica var. siamensis Valeton (Neem), Bacillus thuringiensis var. kurstaki HD-1 and permethrin were tested
for mortality effect on the 2^nd, 3^rd and the 4^th instar larvae of cotton leafworm (Spodoptera litura F.) by topical
application and spraying methods. Among the seed extracts, crude methanolic extract from A. excelsa was
the most effective. Its LC₅₀, by topical application, at 72 hours after tested on the 2^nd, 3^rd and the 4^th instar
larvae was 5.26, 8.83 and 19.69 g/l, respectively, and by feeding was 1.59, 3.67 and 4.72 g/l, respectively.
Crude methanolic extract was more effective than the crude n-hexane extract in each particular plant. Among tested samples, permethrin, a semi-synthetic chemical insecticide, showed the highest insecticidal
effect. Its LC₅₀, by topical application, at 72 hours after tested on the 2^nd, 3^rd and the 4^th instar larvae was 0.12,
0.18 and 1.44 g/l, respectively, and by feeding was 0.08, 0.11 and 0.34 g/l, respectively. Use of the crude
methanolic extract of A. excelsa to reduce the population of the 2^nd instar larvae of cotton leafworm on
Chinese kale (Brassica alboglabra Bailey) was more effective than that of crude methanolic extract of A.
indica var. siamensis.