Abstract
Some flies having a killing agent were found in sampled flies of Drosophila melanogastey from a natural population in 1964. The number of their offspring was reduced distinctly, and the distorted segregation of second chromosomes in the offspring was observed by using dominant marker genes.
The killing agent was transmitted from both females and males to their progenies. The agent had been maintained by a carrier strain, though its all original chromosomes were substituted with marked chromosomes. However, most strains, having the killing agent originally, had lost it within a year. The killing agent seemed to have been transmitted by copulation from males to females and by contact of larvae. The rate of development or multiplication of the agent at 30°C was faster than that at 20°C. Flies under two days old could not transmit the agent to their progenies. Such experimental results indicated that the killing agent might be an infective microorganism for flies.
The survival rates of flies carrying Cy, L, Pm or bwD chromosomes respectively to the killing agent were observed to be different. The similar experiment was performed by using 184 second chromosomes isolated from a natural population. The survival rate of flies carrying chromosomes derived from the carrier strain was higher than that of flies having no infection. Flies carrying a lethal chromosome reduced the survival rates more than flies carrying a quasinormal chromosome.
