Exposure to elevated temperature during development affects bumblebee foraging behavior

Abstract

Bee foraging behavior provides a pollination service that has both ecological and economic benefits. However, bee population decline could directly affect the efficiency of this interaction. Among the drivers of this decline, global warming has been implicated as an emerging threat but exactly how increasing temperatures affect bee foraging behavior remains unexplored. Here, we assessed how exposure to elevated temperatures during development affects the foraging behavior and morphology of workers from commercial and wild Bombus terrestris colonies. Workers reared at 33 °C had a higher visiting rate and shorter visiting time than those reared at 27°C. In addition, far fewer workers reared at 33 °C engaged in foraging activities and this is potentially related to the drastic reduction in the number of individuals produced in colonies exposed to 33 °C. The impact of elevated developmental temperature on wild colonies was even stronger as none of the workers from these colonies performed any foraging trips. We also found that rearing temperature affected wing size and shape. Our results provide the first evidence that colony temperature can have striking effects on bumblebee foraging behavior. Of particular importance is the drastic reduction in the number of workers performing foraging trips, and the total number of foraging trips made by workers reared in high temperatures. Further studies should explore if, ultimately, these observed effects of exposure to elevated temperature during development lead to a reduction in pollination efficiency.

Keywords: Bombus terrestris; body size; colony development; foraging behavior; geometric morphometrics; global warming.

Figure 1

Impact of developmental temperature on bumblebee foraging behavior. (A) Visiting time (s) for Borago (n = 169). (B) Visiting time (s) for Campanula (n = 88). (C) Visiting rate (visited flowers per minute) for Borago (n = 82). (D) Visiting rate (visited flowers per minute) for Campanula (n = 66). Letters at the top of the boxplots indicate significant differences when the letters are different.

Figure 2

(A) Total number of foraging trips per temperature and colony origin. (B) Total number of workers performing the foraging trips per temperature and colony origin. No colors corresponding to the wild colonies reared at 33 °C can be found on the pie chart because no workers from this treatment performed foraging trips.

Figure 3

Impact of developmental temperature on bumblebee morphological traits. (A) ITD (mm), (B) centroid size (mm), (C) antennal length (mm), and (D) tongue length (mm). Letters at the top of the boxplots indicate significant differences when the letters are different. Green dots indicate specimens from commercial colonies, purple dots indicate specimens from wild colonies.

Figure 4

Ordination of the workers reared at the two developmental temperatures along the two first axes of a principal component analysis based on wing shape. Red points represent data from workers that developed in 33 °C, blue points represent data from workers that developed in 27 °C. Squares represent workers from commercial colonies, circles represent workers from wild colonies.