Laboratory and field bioassays were conducted to determine whether adults of the cactus weevil, Metamasius spinolae (Gyllenhal), produce attractant compounds. The attraction of males in a dual choice olfactometer to male volatiles combined with volatiles of prickly pear, Opuntia ficus indica (L.), was greater than attraction of males to females or to host volatiles alone. Response of weevils to female volatiles alone or in combination with prickly pear was not different from response to controls. In field tests using pitfall traps baited with live male or female weevils in covered cages, significantly more females responded to traps baited with males than to traps baited with females or controls. Attractancy responses in laboratory and field studies suggest that a male-produced aggregation pheromone is the prevalent mechanism of chemical communication among cactus weevils. This study is the first report of such a pheromone system for this tropical species.