Integumental esteratic activity in Triatoma infestans and its contribution to the degradation of organophosphorus insecticides.

Esteratic activity was found in the integument of adult Triatoma infestans, principally located in the epidermis. Specific activity was on average 29.3 nM phenylthioacetate/hr per anatomical unit. Esteratic activity depends on the insect's age and its starvation state. A dramatic increase was observed 1 week after moulting followed by a slight decay as a function of the age. A significant decrease of the activity was observed with a longer fasting time. Integumental esterases were characterized as carboxylesterases, butyrylcholinesterases and aryl plus acetylesterases by using eserine and paraoxon as inhibitors and acetylthiocholine, butyrylthiocholine and phenylthioacetate as substrates. Epidermis homogenates were able to hydrolyse OP insecticides when incubated in vitro. Hydrolysis of the carboxyester linkage by malathion was established and cleavage of the P-S-C bond by parathion.