Abstract
The ability of bees to generate metabolic heat plays an important role in their ability to forage and pollinate because they must achieve a minimum temperature to activate their flight muscles. In honey bees and stingless bees, the thoracic temperature of feeding foragers is correlated with the caloric value of sucrose solution provided at feeders outside the nest. We provide the first detailed data showing that this phenomenon also occurs in the closely related bumble bee and thus may be homologous in all social bees of the Apidae. Using infrared thermography, we measured T(th) for Bombus wilmattae foragers (mass 0.17+/-0.11 g, length 15.0+/-1.5 mm) from six wild colonies, foraging on a range of sucrose concentrations (0.5-2.5 mol l(-1), 16-65% by mass) in foraging arenas. For all colonies, we measured significant increases in DeltaT(th) (P<0.0001) with increasing sucrose concentration, with significant differences (P<0.0001) between colonies due to different linear regression slopes (0.28-2.4) and y-intercepts (2.7-5.5). We suggest that this modulation of pitching T(th) to sucrose concentration is a general phenomenon in all social bees and may be a widespread adaptation facilitating rapid food collection in flying Hymenoptera.
Highlights
The modulation of body temperature by active or passive means at or near a specific set point is found widely among insects (Heinrich, 1993), in the Hymenoptera (Himmer, 1932)
B. pascuorum and B. hortorum began foraging at lower temperatures than honey bees and were expected to forage earlier in the morning and later in the afternoon than honey bees (Corbet et al, 1993), a potential example of how thermoregulation allows niche specialization
Based upon recent findings that stingless bee foragers (Meliponini, Melipona panamica) can maintain elevated Tth temperatures tuned to food caloric concentration while feeding (Nieh and Sánchez, 2005), and given that honey bees (Apini) do the same (Stabentheiner, 2001; Stabentheiner and Hagmüller, 1991), we examined whether their close relatives, the bumble bees (Bombini), possess a similar ability
Summary
The modulation of body temperature by active or passive means at or near a specific set point is found widely among insects (Heinrich, 1993), in the Hymenoptera (Himmer, 1932). Flight thermoregulation is widely found among bees (Stone and Willmer, 1989), including solitary bees [Xylocopa virginica (Baird, 1986)]. Thermoregulation plays a role in the ability of bees to fly (Coelho, 1991; Esch, 1976) and to visit flowers under cold conditions (Corbet et al, 1993). B. pascuorum and B. hortorum began foraging at lower temperatures than honey bees and were expected to forage earlier in the morning and later in the afternoon than honey bees (Corbet et al, 1993), a potential example of how thermoregulation allows niche specialization. Bumble bees (B. terrestris) have been shown to be able to associate warmth with floral color, preferring to visit warmer flowers in a flight arena (Dyer et al, 2006)
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