Relation of AChE and AliE Inhibition of Anti-AChE Insecticides, TIA-230, Fenitrothion and Carbaryl, to Their Insecticidal Activity in Spodoptera litura Larvae(Lepidoptera : Noctuidae)

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Abstract
Insecticidal activities of three AChE inhibiting insecticides, TIA-230, fenitrothion and carbaryl, were compared in Spodoptera litura larvae. Inhibitory activities of the insecticides to AChE of isolated nerve cords and to AliE of fat body and haemolymph were also investigated. By injection, TIA-230 was the most insecticidal with an LD50 1/7.5 that of carbaryl. Fenitrothion was the least active, but its activated form, fenitroxon, showed the same level of activity as TIA-230. There was no correlation between insecticidal activity and AChE inhibition. Fenitroxon showed very high affinity to AliE, so sequestering of this compound by AliE seemed to be one of the degradation factors. In TIA-230, the sequestering was not a degradation factor because of its low affinity to AliE. These results explained well why TIA-230 showed potent activity and fenitrothion did not. As to carbaryl, atlhough oxidation and sequestering were ruled out as main degradation factors, the main factor could not be identified in these studies.