Interactive Effects of Pesticides in the Hybrid Red-Legged Partridge

Abstract

Laboratory studies were carried out with hybrid red-legged partridges to investigate inter- active effects of combinations of pesticides which may arise as the consequence of induction of an activating enzyme or inhibition of a detoxifying enzyme. The ergosterol biosynthesis inhibitor (EBI) fungicide, prochloraz, was found to be a potent inducer of liver enzymes in this species. Pretreatment with prochloraz strongly increased the toxicity of the organophosphorus insecticide malathion, and this was attributed to the induction by prochloraz of one or more forms of cytochrome P450 responsible for malathion activation. Pro- chloraz pretreatment resulted in greater inhibition of serum cholinesterase activity at 24 h after dosing with the organophosphorous insecticides dime- thoate (P<0.05) and chlorpyriphos (P<0.1). Partial inhibition of blood B-esterase activity by pretreatment with malathion was associated with a strong amplification of carbaryl toxicity to par- tridges. Brain cholinesterase inhibition was depressed by 88% and some birds died where the compounds were used in combination. The inter- action between malathion and carbaryl was greater than additive with respect to both the lethal effect, and to the inhibition of brain cholinesterase