Reproductive Behavior of Laboratory-Reared Screw-Worm Flies (Diptera: Calliphoridae)

Abstract

Few matings of 1-day-old male or female screwworm flies, Cochliomyia hominivorax (Coquerel), were recorded, but the number of successful matings increased rapidly until the flies were 3 days old. Thereafter, male courtship declined and female receptivity increased very slightly until both were 14 days old. During exposure to 1- and 2-hr periods of light, 5-day-old males mated an average of 4.8 and 6.4 times, respectively; during exposure to 1- and 2-hr periods of dark, males mated 0.1 and 0.4 times, respectively. Time in copula was 1.6–3.8 min., with a mean and standard error of 2.6±0.1 min. Almost 75% of copulating males had transferred sperm within 15 sec. of the commencement of mating, and a maximum of about 90% of the males had transferred sperm by the time the copulations approached completion. The enhanced hatchability of eggs oviposited by mature mated female screw-worm flies that had been partially deseminated by cold treatment and then offered an opportunity to remate, compared with the reduced hatchability of eggs from similar females that were not offered an opportunity to remate, suggested that some females mated a 2nd time. Oviposition by mated females began and was very slight at 3 days, increased greatly at the 4th day, reached a maximum at 5 days, and declined after the 7th day. The reproductive behavior of cage populations of 10–50 newly emerged flies of each sex was essentially normal, but cage populations of only 5 flies of each sex were less fecund and fertile. Females isolated for the 1st 5 days of adult life and then mated were less fecund and fertile than females maintained in groups before mating. Optimum fecundity and fertility occurred when the relationship of males and females was 10:1, 5:1, 1:1, or 1:5. Newly emerged females exposed to newly emerged males for different periods, 1–7 days, laid about equal numbers of eggs when they were 1 week old and allowed to oviposit. However, the eggs were not viable before 2 days, and maximum viability was not attained before 3 days of association of the sexes. Newly emerged females exposed to sexually mature males for 1–10 days began laying eggs of normal viability on the 3rd day, and oviposition increased until the 5th day. However, when newly emerged males were exposed to sexually mature females for 1–10 days, oviposition and hatchability were low after 1 day of exposure, oviposition was maximum the 2nd day, and hatchability was maximum after the 3rd day.