Cotesia rubecula; REPRODUCTIVE-BEHAVIOUR; MIMICRY-; Female mimicry; Significance as postcopulatory mate guarding mechanism; INTRASPECIFIC-COMPETITION; Males, alternative mating tactics & female mimicry; Postcopulatory mate guarding significance; SOUTH-AUSTRALIA; Adelaide; Alternative mating tactics & female mimicry significance. none In species in which several males compete for a single female, males may evolve elaborate morphological and behavioural traits that function in competitive situations. The present study shows that, in the polygynous parasitic wasp Cotesia rubecula, competition between males for mates is intense and males use one of three alternative mating tactics: they (1) perform an acoustic and vibratory courtship display (full-courtship); (2) exploit the courtship display of another male (short-circuit behaviour); or (3) attempt to distract their rival using female mimicry and then approach the female that the rival had been courting. Courting rival males frequently approached mating pairs and, although most females mated only once, results suggest that there was a brief window of time after the first mating when they would accept a second mate. In 64 of 84 laboratory observations of mating behaviour, the first-mating male responded to courting rivals by employing a post-copulatory female-mimicking behaviour, which attracted the courtship effort of 55 of the 64 rivals. The hypothesis is investigated that female mimicry in this instance is a post-copulatory mate-guarding mechanism.