Abstract
Features of pesticide synergism and acetylcholinesterase (AChE) inhibition (in vitro) were studied using a selected range of organotin compounds against the early 4th instar larvae of a highly resistant strain of the diamondback moth (DBM), Plutella xylostella, a major universal pest of cruciferous vegetables. Fourteen triorganotin compounds were evaluated for their ability to enhance the toxicity of the microbial insecticide, Bacillus thuringiensis (BT) and of the commercial insecticide, Malathion to Plutella xylostella larvae. Supplemental synergism was observed with triphenyl- and tricyclopentyltin hydroxides in combinations with Bacillus thuringiensis. Increased synergism was observed with an increase in the number of cyclopentyl groups on tin in the mixed series, Cypn Ph3-n SnX, where X = OH, and 1-(1,2,4-triazolyl). The combination of (p-chlorophenyl)diphenyltin N,N-dimethyldithiocarbamate at LD10 and LD25 concentrations with sublethal concentrations of Malathion as well as of tricyclohexyltin methanesulphonate at the 0.01% (w/v) concentration with Malathion exerted strong synergistic effects (supplemental synergism) with toxicity index (T.I) values of 7.2, 19.8 and 10.1, respectively. Studies on the in vitro inhibition of acetylcholinesterase prepared from the DBM larvae showed that while most of the triorganotin Compounds tested were without effect on the enzyme, compounds containing the thiocarbamylacetate or the dithiocarbamylacetate moieties demonstrated appreciable levels of inhibition, being comparable in efficacy to commercial grades of Malathion and Methomyl.
Highlights
Insecticide synergists have considerable practical importance in the control of arthropod pests by "making more efficient the economical use of insecticides, thereby increasing the spectrum of activity of an insecticide and restoring its activity in a resistant strain"
For the in vitro inhibition studies on ACHE, early fourth instar diamondback moth (DBM) larvae of the susceptible strain obtained from National Chung-Hsiang
It was of considerable interest to examine a selected range of triorganotin compounds for their potency as synergists when combined with the microbial biocide Bacillus thuringiensis and the commercial insecticide Malathion towards the DBM larvae
Summary
Insecticide synergists have considerable practical importance in the control of arthropod pests by "making more efficient the economical use of insecticides, thereby increasing the spectrum of activity of an insecticide and restoring its activity in a resistant strain". It was of considerable interest to examine a selected range of triorganotin compounds for their potency as synergists when combined with the microbial biocide Bacillus thuringiensis and the commercial insecticide Malathion towards the DBM larvae. 2a’2 Whereas organophosphates and carbamates have been extensively studied as potent AChE inhibitors, there are no reports todate of a systematic screening of triorganotin compounds substituted with organophosphate or carbamate moieties in them as potential inhibitors against this enzyme This has prompted the additional investigation reported of the in vitro inhibition of the above enzyme, isolated from resistant strains of Plutella xylostella larvae, by a limited range of triorganotin compounds, selected in most cases, on the basis of their high acute larval toxicity. Included among the compounds are several which have previously been shown to be effective inhibitors of glutathione -S- transferase, 2s a major detoxifying enzyme present in relatively high levels in resistant strains of DBM larvae. 18
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