FEMALES INFLUENCE SPERM STORAGE AND USE IN THE YELLOW DUNG FLY SCATHOPHAGA-STERCORARIA (L)

The influence of the female on the process of sperm storage and use wa s examined. Copula duration, the condition of the female and whether o r not a copula terminated naturally influenced the number of spermathe cae (of three) in which once-mated females stored sperm. Females store d more sperm the larger their mate and the sperm from larger males wer e stored more unevenly amongst the spermathecae than were those from s maller males. Double-mated females had sperm in fewer spermathecae the larger the second of their mates and these spermathecae tended to be the ones which lay together within the female. The P2 values over thre e successive clutches were constant and sperm precedence was complete when the larger male was second to mate but began low and increased ov er subsequent clutches when the smaller male mated second. These resul ts suggest females prefer, and are able, to use the sperm of larger ma les to fertilise their eggs. It is proposed that multiple spermathecae in Diptera have evolved to VC females better control over offspring p aternity.