Age-dependent insemination success of sterile Mediterranean fruit flies

The Sterile Insect Technique (SIT) is used in many regions worldwide to man age wild populations of the Mediterranean fruit fly ('medfly'). an importan t pest species. This technique relies on released sterile malts outcompetin g their wild counterparts in fertilizing ova of wild females. Numerous stud ies have investigated the ability of sterile males to secure copulations, a n essential step toward overall success. Here we progress further along the mating sequence by studying reproductive barriers that may remain ahead of sterile males that manage to secure copulations in field cage experiments and whether ability to pass these barriers is influenced by a males age, di et and size, or the size of his mate. Amongst those virgin males that succe eded in copulating, both the number of sperm stored by mates and the chance s of having any sperm stored at all decreased with age. Sperm tended to be stored asymmetrically between the females two spermathecae, and this tenden cy was mon apparent when few sperm were stored. In accord with effects of m ale age on number of sperm stored, sperm of older males were stored more as ymmetrically than that of young males. We found no evidence that male size, male diet or female size influenced copula duration, number of sperm store d or allocation of sperm between the female's two spermathecae. The decline in number of sperm stored as males aged was not accompanied by age-depende nt changes in copula duration, indicating that copula duration and insemina tion success are not deterministically linked. We discuss these results in light of their relevance to SIT and the medfly mating system.