Honeydew sugars in wild-caught female deer flies (Diptera: Tabanidae)

Female deer flies (Chrysops spp.) were collected from 2 habitats in Algonquin Provincial Park, ON. Using thin-layer chromatography, 11 sugars were detected in the digestive tracts of these flies; these occurred in 41 different combinations. We argue that combinations including melezitose, stachyose, or both can be used to indicate when flies recently have fed on homopteran honeydew. Accordingly, 85.7% of Chrysops excitans (n = 49) and 61.1% of Chrysops mitis (n = 18) collected from an abandoned airfield and 69.8% of C. excitans (n = 53) and 60.0% of C. mitis (n = 15) from a bog habitat tested positive for these honeydew indicator sugars. The difference between species was significant at the airfield only. Possible reasons for this habitat-dependent difference are discussed.