The sperm pump of the hangingfly Bittacus planus Cheng (Mecoptera: Bittacidae)

The males of antliophoran insects usually use a sperm pump to transfer liquid sperm into the reproductive tract of the female. However, the fine structure of the sperm pump and its ejaculatory mechanism has not been thoroughly clarified in many groups of Mecoptera. In this paper, the structure of the sperm pump was investigated in the hangingfly Bittacus planus Cheng, 1949 using light and scanning electron microscopy. The sperm pump mainly consists of a piston fused with a piston-carrying sclerite, a pumping chamber enclosed by the genital folds, which comprises the posterior region of the ejaculatory sac, an ostial sclerite, a phallobase, and other associated structures and muscles. The piston crown plays a major role in the piston movement. The ostial sclerite serves as a discharge valve and is controlled by two antagonistic muscles. No depressor muscles were found attached to the piston. The sperm pumping activity is mainly controlled by the combination of the levator of the piston and the retractor and protractor of the ostial sclerite. The ejaculatory mechanism and phylogenetic significance are briefly discussed based on the structure of the sperm pump.