| Abstract: | The outcome of our earlier work suggested that the transport of contact insecticides into insects does not involve the haemolymph, but that the chemical probably reaches the internal organs by migrating in and/or over integumental tissue. This applies to various insects having quite different integumental organisation, and to various groups of insecticides differing widely in physical and chemical characteristics. The present work has shown that carbamates (1-alkylthioacetaldoxime carbamates) with high water solubility are no exception. The permeability of the body wall of the housefly for the methyl homologue (methomyl) which is the most water-soluble of the series, although relatively high, is not high enough to account for the toxicity of the compound if it followed the haemolymph route. Methomyl when injected with water instead of an organic solvent was also found to be less toxic than the equivalent amount topically applied. Lateral migration in the integument could be demonstrated with all the carbamates tested and dissimilarities in rates were apparent. Methomyl migrated the most rapidly and the cyanomethylene homologue the most slowly. Differences in mobility may be partly responsible for inequality in toxic effect, but it is thought that metabolic detoxication is of over-riding importance. |
