The Resistance of Strains of D. melanogaster to DDT and Dieldrin

Abstract

1. The level of DDT-resistance of eighteen strains of D. melanogaster collected from ten localities in Europe, Africa, Asia and North and South America was tested by exposure to 4 per cent DDT test paper prepared by the WHO in Geneva. The level of dieldrin resistance of eleven strains of five localities was tested by exposure to 0.8 and 0.4 per cent dieldrin test paper. 2. The total average mortalities of these strains after exposure for varying times were almost linear when plotted on normal logarithmic section paper. The expression of resistance to DDT and DL is, therefore, normally distributed in populations. 3. From the results of analyses of variance using numbers of dead flies 25 hours after exposure to DDT, DL and control test papers, significant differences in resistances to both insecticides were observed between localities and between strains. Significant differences between strains but not between localities were found in resistance to desiccation. 4. Cross-resistance between DDT and DL was observed; it was concluded that these resistances are the result of different genetic systems of which some factors are common to both.