Collections of volatiles were obtained from calling males of the Caribbean fruit fly,Anastrepha suspensa(Loew), under natural light cycles in tests conducted in a greenhouse and compared with collections from males tested under standard laboratory conditions. There was no effect on total amount of pheromone or in amounts of individual components released between 0400 and 2100 hours (EST); i.e., from 2 h before until 2 h after a 12-h photophase. Pheromone periodicity under either regime was fit best by a bimodal distribution, but there were shifts in times of peak production. Under laboratory conditions, there was a small early morning peak at the start of photophase (0600 hours) and a broad afternoon peak ≍4 h before the end of photophase. Under greenhouse conditions, there was a small, broad early morning peak at 0700 hours and a sharp afternoon peak at ≍1700 hours. Flies in the laboratory released significantly higher amounts of volatiles from 1230 to 1630 hours, whereas those in the greenhouse produced Significantly higher levels from 1700 to 2100 hours. Under greenhouse conditions, pheromone production was positively correlated with relative humidity and negatively correlated with light intensity, as indicated by overall light levels measured in lux. It is speculated that high light intensities and low relative humidity, to which males under natural light cycles are exposed, inhibit pheromone production during the middle part of the day, and that environmental variables work in concert with circadian rhythm to control periodicity of pheromone release.