Heat domes increase vulnerability of native stingless bees by simultaneously weakening key survival traits

Abstract

Heatwave events increase in frequency and duration, yet there is a strong gap in assessing their nonlethal effects on tropical insects, including beneficial social species. The stingless bees are a highly diverse group of pantropical pollinators that provide key ecosystem services. Here, we simultaneously analyzed for the first time the effect of sublethal heat stress (HS) during immature (pupal) development on adult morphology (size, shape, symmetry) and immune response of the three castes/sexes in stingless bee colonies: workers, unmated queens (gynes) and males, as well as its impact on the onset of foraging and lifespan in workers. Individuals experimentally heat stressed during development had smaller body size and reduced symmetry as adults compared with control, non-heat stressed (NHS) individuals, though the strength of the effects of HS also varied between castes and sexes. Notably, males were more prone to the effects of HS compared with workers, and less so gynes; HS reduced the immune response of males, though not that of workers or queens. Workers had significantly earlier onset of foraging and a shorter lifespan when exposed as immatures to HS. Under a worst-case scenario, knock-on negative impacts on individual survival caused by HS could compromise colony fitness. In the long-term, heatwaves may also have repercussions for the persistence of stingless bee species, the sustainability of key ancestral activities like meliponiculture and ecosystem services. Measures to ameliorate the effect of climatic warming are urgently needed to protect these pollinators, which represent an iconic world heritage.

Keywords: Body size; Heatwave; Longevity; Melipona; Stingless bee; Symmetry.