Sexual Aggressiveness of Male Screw-Worm Flies Measured by Effect on Female Mortality

Abstract

The effect of accelerated female mortality owing to harassment by male screw-worms, Cochliomyia hominivorax (Coquerel), was utilized in a test for sexual aggressiveness (SAG test) of males based on female mortality resulting from males present at a 3:1 ratio. Strains mating well in the SAG test also mated well in competitive tests, but inferior males mated effectively in the absence of competition. Data from earlier tests in which flies were held in a 1:1 male-female ratio after irradiation were re-examined. Apparently because of relief from harassment by males, female mortality was reduced and treated females lived as long as untreated. Fallacy of longevity data as an index of sexual vigor was demonstrated in SAG tests in which some inactive males lived as long as sexually aggressive males. The SAG test showed greatly reduced male activity as the radiation dose increased from 3 to 12 kr for 5-day-old pupae; however, for 6- and 7-day pupae only minor reductions occurred. Both Florida (Fla) and yellow eye (y) mutant males effectively reduced y female longevity, but y males were ineffective against Fla females. Males from both strains mated twice as many y as Fla females when an abundance of females of both strains was present.