Large bees fly better in hot weather than small ones

Researchers at Arizona State University found that large species of stingless tropical bees flew better in hot weather than small bees. A larger size can help some species of bees to better tolerate high body temperatures. The results run counter to the "well-established rule" temperature-size, which suggests that ectotherms – insects that depend on the external environment to control their temperature – are larger in cold climates and smaller in climates hot. The research will be presented today at the Comparative Physiology Conference: Complexity and Integration of the American Physiological Society (APS) in New Orleans.

Insects are divided into three categories:

• ectotherms (which depend on environmental temperatures for their own body temperature),
• poikilotherms (depends on the ambient temperature but can control its own temperature – or its thermoregulation – looking for sun and shade or other behaviors), or
• endotherms (which can warm up physiologically).

"Bees are falling into this range," said lead author Meghan Duell, a graduate student from Arizona State University. "More [insects] use behavioral thermoregulation means. As body size increases, it is more likely that insects will be able to thermoregulate their behavior and physiology, particularly in flying insects. Larger bees, such as bumblebees or larger species in the work I present, are partially endothermic. They can warm up by shivering the muscles of their flight to produce heat, but do not constantly regulate body temperature physiologically. "

Excessive heat, such as that prevailing in Panama's tropical rainforests, from which the bees come from this study, may limit their ability to fly. "If the bees stop flying as often in hot weather, the time they have to forage (and thus pollinate the flowering plants) diminishes.This may mean that they are not able to collect enough food to maintain the colony, "said Duell. "On a fairly large scale, this has a negative impact on the entire population of bees and the plants that they pollinate while collecting pollen and nectar as food."

Therefore, better flight performance is an advantage for bees in warm climates. Bees that can not fly in warm weather end up walking from flower to flower, which is much less effective than flying and means that they are subjected to even warmer temperatures on the surface of flowers and leaves .

In this new study, Duell and his collaborator, Jon F. Harrison, studied the air and chest temperatures of 10 stingless bee species (whose body mbad ranged from 2 to 120 milligrams). , in order to evaluate the high temperatures and the observed variations according to the size of the body. The researchers also measured leaf and flower surface temperature as well as air temperature in the sun and in the shade of bees' tropical canopy.

With the temperature-size rule in mind, researchers expected smaller bees to perform better in hot weather. Surprisingly, the opposite was true. Their results showed that large bees seem to be adapting to high temperatures and using their ability to maintain their own heat. This flight performance benefit has also been observed in the cooler altitudes of the Panamanian rainforest.

"The taller bees are exposed to higher temperatures – sometimes 10 degrees Celsius higher than the air temperature – because they produce a lot of heat in the air, and this same heat production capability gives them an advantage. in colder regions be active earlier in the morning, later in the evening or in cooler weather compared to smaller bees, "said Duell.

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