Metabolism of Cycloprothrin in Rice Plants

Abstract

Absorption, translocation and metabolism of an insecticide, cycloprothrin [(RS)-α-cyano-3-phenoxybenzyl (RS)-2, 2-dichloro-1-(4-ethoxyphenyl)cyclopropane carboxylate], were examined in rice plants under laboratory conditions. When ¹⁴C-cycloprothrin was applied to simulated paddy water, the radioactivity in the rice plants in the 3.5-leaf stage increased with time to reach a maximum concentration within 7 days, and this level was retained to the mature stage. At the mature stage, the rice shoots and the hulled grains contained 0.161 and 0.157ppm ¹⁴C-cycloprothrin equivalents, respectively. A small amount of unchanged cycloprothrin was found in the shoots but not in the grains. ¹⁴C-Cycloprothrin topically applied on the leaf surface was not readily translocated to other untreated parts, and 98% of the applied radioactivity was recovered from the treated parts even after 28 days. When an emulsion of ¹⁴C-cycloprothrin was applied to rice plants in the heading stage, it adhered to the foliage at 9.33ppm and the level hardly lowered during the progression to the mature stage. Unchanged cycloprothrin remained in the shoots and hulled grains at 9.452 and <0.001ppm, respectively. The relative amount of optical isomers of Cycloprothrin did not change in the mature shoots after foliar application. Cycloprothrin was metabolized via ester cleavage, hydroxylation at the 4-ethoxy position, decarboxylation, hydrolysis of the CN group to CONH₂ and COOH groups and conjugation.