The effect of light on the mating behaviour of the Queensland Fruit fly Strumeta tryoni (Frogg.)

Abstract

The effects of light during both the dusk and day periods on the mating behaviour of Strumeta tryoni (Frogg.) have been studied. In nature the flies mate only at dusk. The effects of several components of dusk illumination were examined. The area of the source of artificial dusk and the distance between it and the flies are not important so long as the angle subtended by the source exceeds 25º, below which sexual activity is reduced. The illuminance in the cages and not the luminance per unit area (brightness) of the source determines the amount of sexual activity. The higher the illuminance during the day period the higher is the optimal illuminance at dusk. The rate of change from day to dusk appears to be unimportant. Light during the day periods influenced the age at which both females and males became sexually active. For females only the effect of daily period was studied. At 240 lm/sq. ft those receiving light for 2 hr/day became sexually active later in life than those receiving light for 7.5 hr/day. The age at which females become active is probably controlled by the state of the ovaries, whose rate of development is influenced by light. Males become active later in life when kept under 120 lm/sq. ft for 7.5 hr/day than when kept under either 60 or 240 lm/sq. ft for the same daily period. Those receiving 240 lm/sq. ft for 2 hr/day become active later in life than those receiving this illuminance for either 4 or 7.5 hr/day. Since light does not influence the development of the testes, it is probable that light directly affects the mating behaviour of the males. Light also influences the time at which the males begin and end sexual activity each day and the period for which they remain active. Those under 120 lm/sq. ft begin and end activity later than those under either 60 or 240 lm/sq. ft and remain active for a shorter period. The greater the daily period of illumination the earlier do they begin and end activity. At 240 lm/sq. ft those illuminated for 7.5 hr/day remain active longer than those illuminated for 4 or 2 hr/day.