(Z)-11-Octadecenyl acetate (Z11-18∶Ac) was identified as the aggregation pheromone ofDrosophila mauritiana, D. yakuba, andD. rajasekari. The amount of pheromone in the ejaculatory bulb of male flies increased with age, reaching plateau levels of ca. 240, 800, and 1100 ng/fly forD. mauritiana, D. yakuba, andD. rajasekari, respectively. Thirty to 50% of the pheromone in the ejaculatory bulb was transferred to the female during mating, with the majority transferred to the female's reproductive tract. In the subsequent 6-hr period, over half the pheromone in the female's reproductive tract was transferred to the surroundings. In a wind-tunnel olfactometer,Z11-18∶Ac was attractive toD. yakuba andD. mauritiana; however,D. rajasekari required food or food odors in combination withZ11-18∶Ac to demonstrate aggregation activity.Z11-16∶Ac andZ11-20∶Ac were not attractive forD. mauritiana, D. yakuba, andD. rajasekari. For all three species, food was synergistic withZ11-18∶Ac and both sexes were attracted.