Genetic Loads in Two House Fly1 Populations Treated with Substerilizing Doses of X-Rays for Thirty-Two Generations

Abstract

Three colonies of the house fly, Mitsca domestica L. (Diptera: Muscidae), were established from an Orlando, Florida, wild-type stock to study the cumulative effects of substerilizing doses of X-rays on house fly populations. Two of the colonies were subjected to irradiation pressure in each generation for 32 generations while the 3rd colony received no irradiation and served as a control. In 1 irradiated colony untreated females from each generation were mated with X-rayed males (1.2 kR) from the parental Orlando stock. In the 2nd irradiated colony, males and females were crossed inter se in every generation following the treatment of males with 1.2 kR of X-rays. Egg hatchability in the irradiated colonies decreased from an average of 60 to 20% during the study, but quickly returned to the level of the control colony when treatments were discontinued. The treated colonies also had a reduced but relatively constant level of larvato-adult survival (about 75–90%) compared with the control colony, but the lifespan of adults of the F28 generation was not adversely affected. Males with irradiation histories were not as sexually competitive as males from the Orlando stock, based on egg hatch percents recorded when irradiated males and untreated males and females were combined. Tests with flies of the F28 generation indicated that X-irradiation altered the frequency of deleterious recessive mutations on autosome III in the irradiated colonies when compared to the control colony.