American cockroaches toxicity tests

As mentioned above, to apply to insects a conclusion drawn directly from tests on mammals may sometimes be misleading.3 For instance, American cockroaches have a remarkably high tolerance for acetylcholine,4 but, on the other hand, a substance showing some of the pharmacological properties of acetylcholine does accumulate in flies and cockroaches poisoned with D.D.T. Similarly, Hopf, working with locusts, was unable to demonstrate any increase in toxicity of eserine or T.E.P.P. resulting from the subsequent injection of acetylcholine. From this, Lord and Potter infer that acetylcholine may not be directly involved in the insecticidal action of organo-phosphorus compounds, either because the enzymes which hydrolyse acetylcholine are not inhibited to any considerable extent in vivo or because the functions performed by acetylcholine in mammals are performed by another substance in insects. 

Neither I nor II was toxic to American cockroaches or tobacco homworms when up to 300 ppm of compound was injected. However, at 10 ppm, both I and n caused an immediate, but temporary paralysis of lesion nematodes which lasted for 24 hours. Unfortunately, within 48 hours the nematodes recovered and movement was normal for the remaining three days of observation. In additional tests of compound II, it was shown that II was inactive in a standard mite screen (50 ppm) and that II was lethal to crayfish at 100 ppm. The crayfish showed neurotoxic symptoms to II at concentrations as low as 30 ppm. It is clear that aldiough the target structures possess a hint of the in vitro and in vivo activity seen in avermectin, the potency is dramatically reduced. 

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