Some take it cool, some like it hot—A comaprative study of male mate searching tactics in two species of hymenoptera (colletidae and sphecidae)

Abstract

Comparative studies of the mating behaviour of coexisting but seasonally separated species may reveal microclimatic effects on insect mating systems. I studied two species of gregarious Hymenoptera, an early spring bee ( Colletes cunicularius, Colletidae) and a digger wasp ( Bembix rostrata, Sphecidae) emerging later in summer, during their mating periods in Sweden. Both species occupy sandy and sunny habitats, males are protandrous and polygynous, whereas females are monandrous. During mate searching males normally spent more than 50% of their active time in flight, patrolling the ground for emerging virgin females. In the bee, male mate searching was constrained by low ambient temperatures, in the wasp mainly by high temperatures. Measurements of thoracic flight temperatures indicated interspecific differences in thermoregulation between these two ectothermic species. While the bee raised its thoracic flight muscle temperature faster than through passive heating, the wasp was found to depress temperatures excess during flight at very high ambient temperatures, although it still had higher (2 ×) temperature excess values as compared to the bee. Large males were at an advantage during low ambient temperature, although for different reasons in the two species. Large bees were successful because they could generate enough heat to fly, whilst large wasps depressed their body temperature and avoided overheating only when it was not too hot. Some male wasps switched from patrolling to territoriality as a mate acquisition tactic during low male density and high ambient temperatures, probably to avoid overheating during flight.