Penetration and metabolism of [14C]carbaryl in larvae of the gypsy moth,Lymantria dispar (L.)

The absorption and metabolism of topical doses of carbaryl by larvae of the gypsy moth, Lymantria dispar (L.), were determined using ¹⁴C-ring-labeled material. Carbaryl penetration followed four distinct phases of linear absorption, i.e., 0–5 min, 5–60 min, 1–3 hr, and 3–12 hr; the absorption rates for the four phases were 2.8, 0.57, 0.07, and 0.02% per minute, respectively. Ninety percent of the total metabolism of carbaryl occurred within the first 3 hr; over the next 9 hr, metabolism was exceedingly slow with a linear rate of ca. 0.8% per hour. Carbaryl was always the major radiocarbon in the larvae and the feces, amounting to ca. 16 and 9%, respectively, at 12 hr. At 12 hr the metabolite composition was 5-hydroxy carbaryl >N-hydroxy carbaryl > 1-naphthol > 4-hydroxy carbaryl > 5,6-dihydro-5,6-dihydroxy carbaryl. Small amounts of an additional product were detected but not identified. Much of the excretion of carbaryl and metabolites occurred without conjugation. The amounts of carbaryl metabolized by second, third, fourth, and fifth instars were directly correlated with the insecticide tolerances and mixed-function oxidase activity of the various larval stages. The synergistic action of 2,6-dichlorobenzyl-2-propynyl ether and piperonyl butoxide was also correlated with inhibition of the oxidative pathway.