Age-associated male mating success in three swarming caddis fly species (Trichoptera: Leptoceridae)

Abstract. 1. In the three caddis fly species, Athripsodes albifrons (L.), A. cinereus (Curtis) and Mystacides azurea (L.) (Leptoceridae; Trichoptera), males swarm above the water surface of lakes or rivers. Receptive females fly to swarms and are chased and/or courted by males. After one of the swarming males has grasped an approaching female, the pair flies in tandem to the shore where they copulate.
2. In males, wing wear indices were negatively correlated with the ratio of fat/dry weight. In the only species in which comparisons were possible between newly emerged and swarming males (M. azurea), the former had significantly lower indices. Unmated females on average had lower wing wear indices than spent females. These facts suggest that wing wear reflects relative age.
3. The tandem males had significantly less wing wear than those in swarms, and are probably therefore younger. Age is therefore likely to be significant in relation to mating success.
4. Among males of the same relative age, tandem males had higher fat ratio than swarming ones, indicating that male mating success was also influenced by traits other than age. It is suggested that the shortest possible duration of the period of adult prematurity is adaptive, especially in insects with marginal adult food intake.