Insecticidal activity of Euphorbia antiquorum L. latex and its preliminary chemical analysis

Abstract

Insecticidal properties of Euphorbia antiquorum (Euphorbiaceae) (in Sinhala: Daluke) latex was studied using the samples collected from Eppawala (Anuradhapura District), Ibbagala (Kurunegala District) and Halloluwa (Kandy District). Seven solvents i.e. dichloromethane, petroleum ether, acetone, methanol, n-hexane, distilled water and xylene were used and it was found that the insecticidal components were best extracted by xylene. Potters' sprayer method was found to be better for insect bioassays than the leaf-dip, hand sprayer and microapplicator methods. Xylene-latex extract was tested against six insect pest species, two predatory Coccinellid species and a predatory spider. The latex extract was highly toxic to soft bodied insects/spiders. Latex collected from dry, intermediate and wet zones showed significant differences in insecticidal activities. Insecticidal activity was independent of seasonal variations. Crude extracts and cheap detergents were used to make formulations which were effective in field usage. A preliminary analysis of toxic compounds of the latex extract was done using chromatographic techniques. Only xylene and methanol extracts gave clear spots in Thin Layer Chromatography (TLC). Comparative TLC of xylene and methanol extracts showed two additional spots in the xylene extracts. Xylene-latex extract was subjected to Florisil Column Chromatography (FCC) and eluted with n-hexane followed by petroleum ether and dichloromethane. Fourth n-hexane fraction had the highest insecticidal activity (53.25% mortality). It gave a clear spot in TLC and a peak at 1.006 min in High Performance Liquid Chromatography (HPLC). Crude xylene-latex extracts also had the same TLC spot and the HPLC peak indicating that FCC can be used to partially purifiy the active compounds. On storage (4°C), both the xylene-latex extract and the 4th n-hexane fraction were highly stable showing only a 3% decline of activity after one year.