Caddisfly dives for oviposition: Record-shattering depths and poor life choices in a dammed river system

Abstract

Oviposition is a critical step in the life cycles of aquatic insects. Adult caddisflies exhibit a variety of oviposition methods. In some species, females enter freshwaters to oviposit on submerged substrates. Here, we compile information on North American caddisflies that are known to dive and swim to oviposit and have sexually dimorphic leg characteristics that may be adaptations for swimming, diving, or both. We also report unexpected underwater captures of adult females of 3 caddisfly species in Willamette Basin reservoirs in Oregon, USA, including the deepest dive depths ever recorded for adult female caddisflies. From these captures, we note sexually dimorphic leg widening in the species Hydropsyche centra Ross, 1938 for the first time, confirm widened mesothoracic leg segments of Hydropsyche occidentalis Banks, 1900 adult females, and note fringes of long hairs on meso- and metathoracic tibiae and basal tarsal segments of Hydroptila argosa Ross, 1938 females. We also note fringes of long hairs on the meso- and metathoracic legs of Hydroptila ajax Ross, 1938 females from the banks of the Willamette River. The presumed oviposition attempts of caddisflies underwater in large, deep reservoirs suggest that these caddisflies may misinterpret oviposition cues in altered habitats and waste reproductive efforts. Greater understanding of caddisfly oviposition methods and abilities may be important for long-term conservation and restoration efforts supporting biodiversity in freshwater habitats.