N-Acylated N-methylcarbamates have been prepared and tested for contact/stomach poison and systemic insecticidal activities, mammalian toxicity and in vitro anticholinesterase activity. The N-acyl derivatives in general have lower mammalian toxicities and somewhat lower insecticidal activities than the corresponding unacylated N-methylcarbamates and are relatively poor inhibitors of bee cholinesterase. Tentative reasons are given for these effects. IntroductionStedman,' following earlier work on the nature of the alkaloid physostigmine, synthesised a number of aryl N-methylcarbamates with anticholinesterase activity from phenols containing quaternary ammonium substituents. These derivatives were not insecticidal and Kolbezen et aL2 concluded that, because of their highly polar nature, such compounds are unable to penetrate the lipoid sheath of insect nerves. They synthesised a number of non-ionised N-substituted carbamates which were shown to have insecticidal properties. The present communication deals with the N-acylation of certain N-methylcarbamates and its effect on biological activity.

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Carbaryl (1‐naphthyl N‐methylcarbamate) and its N‐acetyl derivative have been compared in respect of toxicity (LD50), rates of kill and anticholinesterase activity in vitro and in vivo, using the honeybee as test organism. Results obtained indicate that carbaryl does not act solely on brain cholinesterase. Alternative suggestions are discussed, together with observations supporting the idea that the N‐acetyl derivative iS metabolised to a more potent cholinesterase inhibitor.

The toxicity of a number of topically applied pyrethroids has been tested against adult male desert locusts, Schistocerca greguriu: the most potent proved to be 5-benzyl-3-furylmethyl (+)-truns-chrysanthemate (bioresmethrin) with a weighted mean LDSo of 4.0 pg/g. The remaining compounds may be ranked in order of toxicity as follows : 5-benzyl-3-furylmethyl (f)-cis-truns-chrysanthemate (resmethrin) > 4-allyl-2,6-dimethyl-benzyl(+)-truns-chrysanthemate > Callylbenzyl (+)-trans-chrysan t hemate =-2,4,6-trimet hylbenzy 1 (+)-cis-trans-chrysanthemate > 2,3,CtrimethylbenzyI (+)-cis-truns-chrysanthemate z 2,4-dimethylbenzyl (+)-cistrans-chrysanthemate; 2-methylbenzyl (&)-cis-trans-chrysanthemate. A small factor of synergism (4.2) was obtained with bioresmethrin following pretreatment with sesamex, but with resmethrin the synergistic ratio (1.6) was of little practical significance.