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Effects of load type (pollen or nectar) and load mass on hovering metabolic rate and mechanical power output in the honey bee Apis mellifera

Erica Feuerbacher^1,*, Jennifer H. Fewell¹, Stephen P. Roberts², Elizabeth F. Smith³ and Jon F. Harrison^1,

¹ Department of Biology, Arizona State University, Tempe, AZ 85287-1501, USA
² Department of Biology, University of Nevada, Las Vegas, NV 89154-4004, USA
³ Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS 66045, USA
^* Present address: Department of Integrative Biology, University of California, Berkeley, 3060 Valley Life Sciences Building #3140, Berkeley, CA 94720-3140, USA

View larger version (14K): [in a new window]   Fig. 1. Stack graph showing the cumulative content (%) of the foragers of each type being scored as FF (2 fast alleles), MF (1 medium, 1 fast allele) or MM (2 medium alleles) for malate dehydrogenase-1 phenotype. All pair-wise comparisons between load types were significant (G tests). F, fast; M, medium.

View larger version (18K): [in a new window]   Fig. 2. Average total (bee + load) mass, thorax mass, and load mass of pollen (N=37) and nectar (N=49) foragers in the Regression experiment (A) and in the ANOVA experiment (B; N=10 for each forager type-status classification). In this and all subsequent figures, values are means ± S.E.M.

View larger version (16K): [in a new window]   Fig. 3. Metabolic rates during hovering of pollen (open circles) and nectar (filled circles) foragers (Regression experiment) versus total mass (bee + load). Pollen foragers had significantly higher total metabolic rates than nectar foragers, but there was no significant effect of total mass on metabolic rate (see Table 2).

View larger version (12K): [in a new window]   Fig. 4. Metabolic rates during hovering of loaded and unloaded pollen and nectar foragers from the ANOVA experiment. Both behavior (pollen versus nectar) and load status (unloaded versus loaded) affected hovering metabolic rate (see Table 3).

View larger version (17K): [in a new window]   Fig. 5. (A) The relationship between wingbeat frequency (wingbeat frequency) and total mass (bee + load, in mg) in pollen (open circles) and nectar (filled circles) foragers hovering in the Regression experiment. There was no significant effect of behavior or total mass on wingbeat frequency (see Table 2). (B) wingbeat frequency versus thorax mass in Regression experiment. For pollen foragers (solid line): wingbeat frequency=269–0.96 (thorax mass), r2=0.124, N=37, P=0.035; for nectar foragers (broken line): wingbeat frequency=276–1.12 (thorax mass), r2=0.130, N=49, P=0.025. The slopes differed significantly (analysis of covariance, F3,7 1= 3.56, P=0.020).

View larger version (10K): [in a new window]   Fig. 6. The effect of time (which is correlated with load amount) at the resource station on average wingbeat frequency for bees during the mechanical power output measurements. The increase in time represents a change from near zero to near-maximal pollen load. Wingbeat frequency did not significantly change with time (linear regression, N=24, P>0.05).

View larger version (14K): [in a new window]   Fig. 7. Stroke amplitude, inclination of stroke plane and body angle of unloaded and loaded (mean load=18% of body mass) pollen foragers. There were no significant differences between unloaded and loaded animals (t-tests, N=17, P>0.05).