Male age and strain affect ejaculate quality in the Mexican fruit fly.

Aging in all organisms is inevitable. Male age can have profound effects on mating success and female reproduction, yet relatively little is known on the effects of male age on different components of the ejaculate. Furthermore, in mass-reared insects used for the Sterile Insect Technique, there are often behavioral differences between mass-reared and wild males, while differences in the ejaculate have been less studied. The ejaculate in insects is composed mainly of sperm and accessory gland proteins. Here, we studied how male age and strain affected (i) protein quantity of testes and accessory glands, (ii) the biological activity of accessory gland products injected into females, (iii) sperm viability, and (iv) sperm quantity stored by females in wild and mass-reared Anastrepha ludens (Diptera: Tephritidae). We found lower protein content in testes of old wild males and lower sperm viability in females mated with old wild males. Females stored more sperm when mated to young wild males than with young mass-reared males. Accessory gland injections of old or young males did not inhibit female remating. Knowledge of how male age affects different ejaculate components will aid our understanding on investment of the ejaculate and possible postcopulatory consequences on female behavior.

The male ejaculate as inhibitor of female remating in two tephritid flies.

The inhibition of female receptivity after copulation is usually related to the quality of the first mating. Males are able to modulate female receptivity through various mechanisms. Among these is the transfer of the ejaculate composed mainly by sperm and accessory gland proteins (AGPs). Here we used the South American fruit fly Anastrepha fraterculus (where AGP injections inhibit female receptivity) and the Mexican fruit fly Anastrepha ludens (where injection of AGPs failed to inhibit receptivity) as study organisms to test which mechanisms are used by males to prevent remating. In both species, neither the act of copulation without ejaculate transfer nor sperm stored inhibited female receptivity. Moreover, using multiply mated sterile and wild males in Mex flies we showed that the number of sperm stored by females varied according to male fertility status and number of previous matings, while female remating did not. We suggest female receptivity in both flies is inhibited by the mechanical and/or physiological effect of the full ejaculate. This finding brings us closer to understanding the mechanisms through which female receptivity can be modulated.

Female receptivity in Anastrepha ludens (Diptera: Tephritidae) is not modulated by male accessory gland products.

In numerous insects, accessory gland products (AGPs) transferred from males to females during mating are responsible for female sexual inhibition, but these products can be affected by male condition. Here, we investigated the effect of AGPs on female receptivity of the Mexican fruit fly Anastrepha ludens (Loew), and the effect of male and female strain, male irradiation, AGP dose and sexual activity period on the effectiveness of these AGPs in inhibiting female remating. Injections of aqueous extracts of male accessory glands into the abdomen of females did not reduce their receptivity either at 0.2 or 0.8 male equivalent. Females injected with AGPs behaved like virgin females and not as mated females. Neither male origin, female origin (wild versus mass-reared), nor male irradiation (sterile versus fertile males) had an effect in inhibiting female remating. Also, injections of glands obtained during the sexual calling period of males, or obtained during the morning when males are not sexually active had no effect on female remating behavior. Mated mass-reared females were more likely to remate than wild females. We conclude that inhibition of female sexual receptivity of A. ludens is mediated by factors other than AGPs, such as the number of sperm stored by females, the stimulus of copulation per se or more probably, mediated by a combination of factors. More research is needed to elucidate the role of AGPs in this species.