Sex pheromone communication in the screwworm,Cochliomyia hominivorax: Ontogenetic and strain effects.

A laboratory behavioral assay was used to examine ontogenetic and strain effects on sex pheromone production and reception in the screwworm, which employs a female-produced contact pheromone to stimulate male copulatory attempts. Pheromone levels peaked between three and six days after adult emergence in females of two strains that had been colonized fewer than 50 generations. Pheromone was detectable at low levels in newly emerged flies of both sexes but disappeared from males by two days of age, when males first became responsive to females. A similar decline in pheromone with ontogenetic age was previously described for females of a strain colonized over 100 generations. Interstrain tests between the two newer strains, which differed by 35 generations in duration of colonization, demonstrated lower female pheromone activity but higher male responsiveness to pheromone in the older strain, despite the similar shape within these strains of curves relating female age and pheromone activity. The data suggest that conditions of screwworm colonization result in gradual loss of the pheromone peak that develops three to six days after emergence in newly colonized females. Higher male responsiveness associated with longer colonization involved change in both thresholds and dose dependency and may be relevant to control of the screwworm via the sterile insect technique.