Stable isotope analysis identifies morphologically indistinguishable caddisflies

Abstract

Stable nitrogen isotope values (δ15N) were used to identify the morphologically indistinguishable adult females of Olinga feredayi and O.jeanae (Trichoptera: Conoesucidae), captured in Malaise traps at Cass, inland Canterbury, New Zealand. In the study area, larvae and pupae of the two species were abundant in two different streams and had distinct δ15N values, presumably reflecting differences in the stable nitrogen ratios of organic materials assimilated by larvae. In contrast to δ15N, stable carbon isotope values (δ13C) were more variable and overlapped in the two species. Trapped adult females formed two discrete groups with δ15N signatures that corresponded to those of larvae and pupae in the two streams and with those of adult males that can be identified using wing and genitalic characters. The successful identification of otherwise indistinguishable females depended on their larvae having habitat-specific isotopic signatures that were carried through into the adult stage. Successful identification will not always be possible, but where it is, otherwise unavailable information on the distribution, abundance and dispersal of the adults of aquatic insects can be obtained. © 2007, Copyright Taylor & Francis Group, LLC.