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, CypnPh3-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.
