The prior arrival of red sunflower seed weevil (Smicronyx fulvusLeConte) males on early season sunflowers and on greenhouse-grown sunflowers appeared to have been the stimulus for female weevils to settle on plants. There were no observations in which females discovered an anthesis stage sunflower before males had been established. Anthesis stage sunflower alone was more attractive to males than was anthesis stage sunflower infested with females. Sunflowers artificially infested with males attracted four times more females than males and attracted nearly five times more weevils than sunflowers alone. When hexane extractions were made of either sex, male extract attracted 40 times more females than males, and female extracts attracted no insects at all. An aggregation pheromone produced by males was established to have a role in the discovery of host sunflowers by female weevils.