The effect of light on the fecundity of the Queensland fruit-fly, Strumeta tryoni (Frogg.)

Abstract

The number of eggs laid by Strumeta tryoni (Frogg.) was affected both by illuminance and by the daily period of illumination. Flies kept in constant darkness laid no eggs. When the daily period of illumination was 74 hr, flies under 120 lm/sq. ft. laid fewer eggs than those under either 60 or 240 lm/sq. ft. At 60 and 240 lm/sq. ft. the flies laid approximately equal numbers of eggs. At an illuminance of 240 lm/sq. ft., the longer the daily period of . illumination (up to 72 hr) the greater was the number of eggs laid. Light had these effects on fecundity by influencing the amount of feeding, the rate of maturation of eggs, the readiness with which eggs were laid, and the age at which the flies mated. In constant darkness the flies fed very little, matured no eggs, laid few eggs even when gravid, and did not mate. When the daily period of illumination was 75 hr, flies under an illuminance of 120 lm/sq, ft. fed less, matured eggs more slowly, and mated later in life than those under either 60 or 240 lm/sq. ft. The act of egg laying was not influenced by illuminance within the range 60-240 lm/sq. ft. When the illuminance was 240 lm/sq. ft., the longer the daily period of illumination (up to 78 hr/day) the greater was the amount of feeding, the rate of maturation of eggs, and the number of eggs laid by mature females, and the earlier in life did the flies mate. It is probable that the effects of light on feeding and egg laying were due to the influence that light had on the activity of the flies. They were inactive in darkness and were less active at 120 lm/sq. ft. than at either 60 or 240 lm/sq. ft. The effect of light on the rate of maturation of eggs can be explained by the effect of light on the amount of feeding.