On the thermal limits for the use of stingless bees as pollinators in commercial greenhouses

Abstract

Stingless bees (Apidae, Meliponini) are frequently used as crop pollinators in tropical countries. The present study calls attention to the thermal limit for the use of these bees as pollinators in commercial greenhouses, in which the temperature frequently exceeds that of the outside environment. We assessed the thermal biology of Melipona subnitida, a stingless bee species that naturally occurs in north-eastern Brazil, a region characterized by elevated ambient temperatures all year round. The critical (CTN) and lethal limits (LTN) for worker bees under long-term temperature exposure (24 h) were 40 and 44 °C respectively when individuals had access to water, or 39 and 42 °C respectively without water. Due to limited active colony thermoregulation of this species, the temperatures inside the nests were similar to the ambient temperature. In their natural environment, nest temperatures never exceeded CTN. In strong contrast, inside a greenhouse, the nest temperatures exceeded the critical value nearly every day due to the high ambient temperatures in this closed environment. As a result, the colonies weakened critically and had to be removed from the greenhouse after 14 days. Our study emphasizes the need for both thermo-physiological investigations and management strategies when planning the use of bees as pollinators for greenhouse crops, particularly so in tropical regions, where temperatures in these enclosed environments may easily exceed the thermal limits of a species.