Ekkarat Kaewnang-O, Aran Ngampongsai, Sanan Subhadhirasakul, and Teerapol Srichana

pp. 43 - 49

Abstract

The larvicidal activity of various concentrations of fixed oil and crude extract from sa-dao-thiam, Azadirachta excelsa
(Jack) seed kernel was assayed on an Aedes aegypti (L.) test population under controlled laboratory conditions. Concentration levels of responses at 24, 48, 72, and 96 hrs were evaluated. The LC₅₀ values of the fixed oil and the crude extract were
403.6 and 518.7 ppm, respectively. One hundred percent mortality in 24 hrs-post treatment was achieved at 2,000 and 4,000
ppm for the oil and crude extract, respectively. It suggested that the oil is more toxic to Ae. aegypti larvae than the crude
extract. Further investigation suggested the occurrence of molting inhibition of Ae. aegypti larvae by the fixed oil and crude
extract as indicated by the small number of emerged adults. In addition, histological study suggested that damages on the
epithelial cells of the midgut could result from the effects of the oil and crude extract. Hypertrophy and degeneration of the
epithelial cells were observed, resulting in a presence of some cytoplasmic material in the alimentary canal. Further studies
should be taken into account to identify their stability and residual activity of these products under field conditions.