Sugars in Nectar Sources and their Use by Butterflies (Hesperioidea and Papilionoidea) in the Sierra Nevada, California

Previous laboratory and controlled experiments demonstrated that some species of butterflies may prefer sucrose to other sugars. However, sugar use has not been quantified for an assemblage of butterflies in the field. The abundance of nectar-producing plants, and the volume and concentration of the nectar in those plants, peaks in the initial years following a fire, facilitating investigation of nectar use by butterflies. In 2014 and 2015, we surveyed butterflies and vegetation within the boundary of the Rim Fire event (Stanislaus National Forest, Tuolumne County, California), a major wildfire that occurred in 2013. We quantified the masses of glucose, fructose, and sucrose for all plant species on which we observed butterflies feeding. We tested whether intensity of use of each 20 nectar sources (the number of butterflies observed taking nectar from each source across both years) was associated with the total sugar mass, mass of sucrose, or relative proportion of sucrose. We found no evidence that intensity of butterfly use was associated with sugar mass, mass of sucrose, or the relative proportion of sucrose. Instead, butterflies appeared to use indiscriminately any nectar sources that were available to them. The difference between apparent sugar preferences in the laboratory and in the field may be explained in part by resource availability, and may change as vegetation succession progresses.