The effect of photobleaching on bee (Hymenoptera: Apoidea) setae color and its implications for studying aging and behavior

Authors: KOCH, JONATHAN - Utah State University; Love, Byron; Klinger, Ellen; Strange, James

Submitted to: Journal of Melittology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2014
Publication Date: 8/26/2014
Citation: Koch, J.B., Love, B.G., Klinger, E.G., Strange, J.P. 2014. The effect of photobleaching on bee (Hymenoptera: Apoidea) setae color and its implications for studying aging and behavior. Journal of Melittology. 38:1-9.

Interpretive Summary: For bees, certain characteristics of their exoskeleton change relative to the increasing age. For example, the wings of the bee will get an increasing number of tears along the edges as it flies more, and, at the same time, a bee that is exposed to extended periods of sunlight will become lighter in color. In many studies of bee behavior, knowing the relative age of a bee is important to predicting its behavior, and, in taxonomic studies, changes in color can lead to misidentifying the species. Therefore, understanding the dynamics of color change (photobleaching) is important. We experimentally subjected freshly-killed, lab-reared bumble bees to sunlight to study how the color of the bee hair changes with solar exposure. Bees that received solar exposure were significantly lighter than unexposed bees after the experiment. Additionally, we compared bee hair color to the wear on bee wings in museum specimens and found that wing wear is correlated to photobleaching. We discuss the implications of our findings for pollination biologists and taxonomists.

Technical Abstract: Studies of foraging ecology and plant-pollinator interactions benefit from a number of bee (Hymenoptera: Apoidea) characteristics including morphometric measurements, natural history and age. Historically, bee age has been estimated using measurements of wing wear and integument color change. Wing wear is speculated to be affected by the behaviors associated with foraging, nesting, and mating activities. Setal color change may be an additional parameter used to measure bee age if it is affected by sun exposure during these same activities. The objectives of this study were to experimentally assess the effect of direct sun exposure on setae (unicellular hair-like processes of the integument), and determine whether wing wear and integument photobleaching are correlated. To quantify photobleaching of setae, we measured changes in hue of lab-reared Bombus huntii (Apidae) exposed to natural sunlight. We found that sun exposure was a significant variable in determining setal bleaching. To assess the relationship between wing wear and setal photobleaching, we scored wing wear and measured setal hue of B. huntii, Melecta pacifica (Apidae), and Osmia integra (Megachilidae) from museum specimens. Wing wear and setal hue values were positively correlated for all three species; however, the strength of the relationship varies across bee species as indicated by correlation coefficient estimates. Our results suggest that setal color change is affected by sun exposure, and is likely an accurate estimate of bee age. We suggest that future investigations of bee aging consider a suite of morphometric characteristics due to differences in natural history and sociobiology that may be confounded by the use of a single characteristic.