A novel method to measure hairiness in bees and other insect pollinators

Abstract

Hairiness is a salient trait of insect pollinators that has been linked to thermoregulation, pollen uptake and transportation, and pollination success. Despite its potential importance in pollination ecology, hairiness is rarely included in pollinator trait analyses. This is likely due to the lack of standardized and efficient methods to measure hairiness. We describe a novel methodology that uses a stereomicroscope equipped with a live measurement module software to quantitatively measure two components of hairiness: hair density and hair length. We took measures of the two hairiness components in 109 insect pollinator species (including 52 bee species). We analyzed the relationship between hair density and length and between these two components and body size. We combined hair density and length measures to calculate a hairiness index and tested whether hairiness differed between major pollinator groups and bee genera. Body size was strongly and positively correlated to hair length and weakly and negatively correlated to hair density. The correlation between the two hairiness components was weak and negative. According to our hairiness index, butterflies and moths were the hairiest pollinator group, followed by bees, hoverflies, beetles, and other flies. Among bees, bumblebees (Bombus) and mason bees (Osmia) were the hairiest taxa, followed by digger bees (Anthophorinae), sand bees (Andrena), and sweat bees (Halictini). Our methodology provides an effective and standardized measure of the two components of hairiness (hair density and length), thus allowing for a meaningful interpretation of hairiness. We provide a detailed protocol of our methodology, which we hope will contribute to improve our understanding of pollination effectiveness, thermal biology, and responses to climate change in insects.

Keywords: functional diversity; functional trait; pilosity; pollinating efficiency; protocol; thermoregulation.

Figure 1

Pinned Andrena haemorrhoa female (a), body parts in which hairiness was measured (b: dorsal surface of the mesothorax, c: ventral surface of the mesothorax, d: face), and close‐up images of the dorsal mesothorax showing measurements of hair density (e) and hair length (f)

Figure 2

Scatter plots showing the relationship between hair density and hair length (a and b), between hair density and body size (c and d) and between hair length and body size (e and f); of the dorsal surface of the mesothorax for all pollinators (a, c, and e; 109 species) and for bees only (b, d, and f; 52 species). Each point corresponds to one species. See Table S2 for results of the ventral surface of the mesothorax and the face. DT, dorsal surface of the mesothorax; ITS, intertegular span

Figure 3

Mean ± SE hair density (a and b), hair length (c and d), and hairiness index (e and f) of the dorsal surface of the mesothorax (DT) of various pollinator groups and bee taxa. Different letters indicate significant differences among groups (post hoc Tukey's tests, p < .05). Groups with fewer than three species (in gray) were not included in the analyses

Figure 4

Pollinator groups (a) and bee taxa (b) ordered by increasing hairiness from left to right. (Photograph credits Nicolas J. Vereecken [all bees], Adrià Miralles [hoverflies] and Laura Roquer‐Beni [other flies, beetles and lepidopterans]. All images used with permission.)

Figure A1

Hair micropores in the dorsal thorax region of Scaeva albomaculata (left) and of Andrena haemorrhoa (right)

Figure A2

Measurement of hair length on the dorsal thorax region of Xylocopa violacea