THERMAL ECOLOGY OF MALE EUGLOSSINE BEES IN A TROPICAL WET FOREST - FRAGRANCE FORAGING IN RELATION TO OPERATIVE TEMPERATURE

Male euglossine bees, including Euglossa and Eulaema, collect fragrances from flowers and other sources and probably biochemically modify the fragrances and release them to attract females for mating. The fragrance-collecting activity follows a diel cycle that may be influenced by variation in the thermal environment. To ascertain the degree of the influence of the thermal environment on the activity of these tropical bees, we used Euglossa carcasses as temperature sensors to measure operative environmental temperatures (T(E)) of bees in forest openings (full sunlight) and in the forest understory (shade). We related activity levels of bees on fragrance baits in both locations to measured T(E), other environmental variables, and time of day. Shade T(E) had the strongest (although not significant) direct effect on Euglossa and Eulaema activity levels in the early morning. Operative temperature in the sun apparently had no direct effects on activity of both genera at any time of day. From mid-morning to late afternoon, only time of day (or an unmeasured variable correlated with it) had a significant effect on Euglossa activity levels; the relationship was positive near midday and negative in the early afternoon. Eulaema activity during midday could not be predicted from any measured variable. Eulaema activity in the late afternoon was negatively affected by time of day and shade T(E). From these and previous results we tentatively conclude that in tropical wet forests fragrance-collecting male euglossines may be limited by low air temperatures in the early morning; that neither Euglossa nor Eulaema usually thermoregulate by basking; that Eulaema activity may be depressed by overheating in the late afternoon; and that Euglossa activity drops in the late afternoon probably for reasons other than overheating.