Abstract
The ability to accurately estimate bee mass through measurements of intertegular distance (ITD) is an important tool for field biologists. ITD is the distance between the bases of the 2 wing tegulae on the bee’s thorax. However, the relationship between ITD and bee mass can vary based on species and sampling region. A collection of 92 bees—representing 3 species—was examined to assess the accuracy of ITD in estimating dry mass for bees in northwest Ohio. The focus was on 3 species: silky striped sweat bees (Agapostemon sericeus), honey bees (Apis mellifera), and common eastern bumble bees (Bombus impatiens). Overall, there was a positive correlation between ITD and dry mass across all individuals sampled (R2 = 0.77), but within species the degree of correlation varied significantly. The results suggest that ITD accurately estimates dry mass in silky striped sweat bees (R2 = 0.93), but the correlation weakens in common eastern bumble bees (R2 = 0.54) and is non-existent in honey bees (R2 = 0.39). Field biologists interested in using ITD to estimate bee mass should take preliminary measurements when investigating bumble bees, and should avoid ITD estimates in honey bees.
Highlights
Increasing evidence suggests that bees are in decline globally (Potts et al 2010), but it is unclear whether these declines impact ecosystem services
This study examined the accuracy of intertegular distance (ITD) in estimating dry mass for 3 bee species: silky striped sweat bees (Agapostemon sericeus), honey bees (Apis mellifera), and common eastern bumble bees (Bombus impatiens)
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Summary
Increasing evidence suggests that bees (order: Hymenoptera) are in decline globally (Potts et al 2010), but it is unclear whether these declines impact ecosystem services. Recent studies have established libraries of bee functional traits, but certain traits are hard to measure in field studies. Bee body size (dry mass) is an important trait that is often used as a proxy for foraging distance (Greenleaf et al 2007), and body size has a strong influence on which flowers bees pollinate (Peat et al 2005). Bee mass can be estimated using the length between the 2 wing tegulae (i.e., intertegular distance (or span; ITD)). Cane (1987) found intertegular distance to be highly correlated with dry mass across 20 solitary bee species. There are drawbacks to the accuracy of ITD in estimating bee mass. It is unclear whether ITD is a good estimator of dry mass in eusocial species. Relationships between ITD and dry mass are strong when making interspecies comparisons, but weaken for intraspecies comparisons. Cane (1987) recommends taking preliminary measurements
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