Courtship and mating in Empis (Xanthempis) trigramma Meig., E-tessellata F. and E. (Polyblepharis) opaca F. (Diptera : Empididae) and the possible implications of 'cheating' behaviour

The courtship and mating behaviour of three empidid flies Empis trigramma, E. tessellata and E. opaca are described. In E. trigramma the male appears to use his complex genitalia to introduce a liquid 'gift' into the female's abdomen during copulation. This 'gift' is subsequently discharged and imbi bed by the female. Such male 'gifts' may constitute a direct investment in their offspring, as females do not seem to acquire significant nutritional input from other sources. Males of E. opaca and E. tessellata present a 'gi ft' to the female, in the form of a dead insect, before mating takes place. Females will not mate with males which do not present a gift. Gifts presen ted during the period of sexual activity also appear to make a substantial contribution to female ovarian development. Some males seek to 'cheat' by p resenting substitute gifts in the form of the fluff-bearing seeds of willow s. In E. opaca such 'cheats' enjoyed a low rate of reproductive success, co mpared with males presenting food gifts. 'Cheating' appears to be an altern ative mating tactic for males of this species.