Effects of Root Extract from Derris (Derris elliptica Benth) on Mortality and Detoxification Enzyme Levels in the Diamondback Moth Larvae (Plutella xylostella Linn.)

Abstract

Two types of ethanol extraction methods, Soxhlet and stirring soaking, were carried out. The rotenone content determined by the HPLC was 8.6 % w/w for the former method compared to 5.2% w/w for the latter one. Third instar larvae of the diamond back moth gave LD₅₀ of 24.25 PPM and 89.07 PPM for the Soxhlet and stirring methods, respectively. Triphenyl phosphate (TPP) and Piperonylebutoxide (PB) reduced the LD₅₀ upto ca. 4 folds and also significantly lowered the number of larvae in the field. The optimal medium for the detoxification enzymes, esterase, GSH-S- transferses and monooxygenases, was found to contain 0.1 M phosphate buffer pH 7.5 with 10 mM glutathione (reduced forms), 1 mM EDTA and 50% w/w PVPP. Protein concentrations (BSA as a standard protein) between 50-100 mg protein/g larvae/ml extracted from 2 – 4 instar larvae were used for all enzyme assays. Derris extracts induced ca. 10-20% of all enzyme activities. By adding TPP to the extracts, esterase activity was reduced by 20%. The coefficient of correlation, r² (mortality against esterase activity), was ca. 0.9. The addition of DEM showed a lower in r² value (0.62 – 0.77) (mortality against GSH-S-transferases activity). The highest fluctuation of r² (0.48 – 0.97) (mortality against monooxygenases activity) was observed by the addition of PB to both extracts.