PHARMACOKINETICS AND INVIVO METABOLISM OF GAMMA-HEXACHLOROCYCLOHEXANE IN A SUSCEPTIBLE STRAIN OF THE EGYPTIAN COTTON LEAFWORM, SPODOPTERA-LITTORALIS (BOISD)

The fate of gamma-HCH (hexachlorocyclohexane) was studied in a susceptible strain of the Egyptian cotton leafworm, Spodoptera littoralis (Boisd.). A non-lethal dose (0.2 mug larva-1) was topically applied to fourth-instar larvae, and the pharmacokinetics of the insecticide were studied for a period of 48 h following treatment. Penetration showed biphasic kinetics, with a rapid increase of the internal gamma-HCH concentration during the first 6 h after the application, followed by a plateau up to 48 h. The rate of metabolic degradation was highest between 6 and 24 h. During this period, the rapid decrease in the amount of gamma-HCH in the larvae was associated with an accelerated excretion of metabolites. A compartmental model with curve-fitting was used to quantify the rates of uptake through the cuticle (penetration) and of loss from the tissues (degradation and elimination). Chromatographic analysis of the aqueous and organic fractions extracted from the larvae and their faeces provided direct evidence that our susceptible strain of S. littoralis was able to metabolise a nonlethal dose of gamma-HCH.