Studies on the insecticidal action of DDT (1,1, BIS (4,4’ Dichlorophenyl) 2,2,2- Trichloroethane) and regulated compounds, with a view to correlating this action with chemical structure.

The toxicity of synthetic organic compounds was evaluated by techniques involving impregnated substrata (filter paper or glass), direct spraying of the test animals (Drosophila melanogaster), and exposure to vapours only. The techniques are described and compared. Eighteen compounds were tested. 666 and the difluoro analogue of DDT were the only compounds more toxic than DDT. Of these, 666 exhibited a strong fumigant effect, while the difluoro analogue rapidly lost its toxicity. In compounds having two phenyl groups para substitution in both phenyl radicles is essential for high toxicity. No other halogen can replace the chlorine atoms on the phenyl groups and still leave the compound with a high residual toxic effect. There is a suggestion of an inverse relationship between toxicity and the length of the para-substituted radicles, with alkoxy and alkyl substitutions. Apparently toxicity is lowered by any alteration in the trihalogen grouping