DDT Resistance in an Italian Strain of Musca domestica L.

Abstract

1. Flies of 9–10 and 16–19 days old were more susceptible to DDT than 4–5-day-old flies. Female flies were less susceptible than males, and large flies less susceptible than small flies to residual deposits of DDT. It is clearly important that flies used in comparative toxicity tests should be standardised for age, sex and size.2. The strain Torre in Pietra was 3·6 times more resistant to dry deposits of DDT on Essex board than the Roma strain, but this resistance declined after culturing the strain in the laboratory for 22 generations.3. The DDT-resistant strain (Torre in Pietra) was as susceptible as the non-resistant (Roma) strain to deposits of γ BHC on Essex board but was slightly resistant to pyrethrins.4. The DDT resistance of the Torre in Pietra strain was increased readily by selection, yet a similar selection with DDT on the Roma strain was unsuccessful. This failure in the Roma strain may be due to the purity of the stock.