Abstract Mechanisms producing inhibition of remating in mated female Mediterranean fruit flies Ceratitis capitata, were investigated by matings with surgically altered males. Comparison of remating by females mated with either intact control males or males with a shortened penis, showed that ejaculate or a physical stimulus of penis insertion caused remating inhibition for at least 10 days after first mating. Remating frequency at two days after mating was significantly higher in females mated to castrated (spermless) males than in females mated to sham-operated control males. This difference disappeared by day four after mating, indicating that sperm cause a shorter-term inhibition of remating than does a normal first mating. Other factors in addition to sperm must therefore play a role in inhibition of remating.