The structure of the genitalia and the volumes of sperm stored in male and female Nesciothemis farinosa (Foerster) and Orthetrum chrysostigma (Burmeister) (Anisoptera: Libellulidae)

Female O. chrysostigma possess a very small bursa able to hold only about 26% of the sperm stored in this species, the remainder being contained in the long, narrow spermathecae. The male has a penis with a long barbed flagellum which may be able to enter and reach the distal ends of the spermathecae. It may hook out the sperm of other males from the storage organs of the female during the long copulations sometimes seen in this species. In contrast, in N. farinosa, a sympatric species of similar size and colour, the female storage organs can contain over a hundred times more sperm than in O. chrysusligma: about 83% of it being kept in the bursa. This species makes relatively short copulations, and the male has a penis whose structure suggests that it compresses pre-existing sperm in the bursa but cannot enter the spermathecae. One male O. chrysusligma carries enough sperm in the secondary genitalia to furnish about 6 females, whereas one female N. farinusa has stores large enough to contain the contributions of about 6 males. In both species, towards the end of copulation new sperm is probably injected through a bursal valve, whereas during fertilisation sperm leaves the bursa through a small posterior pore under muscular control.