Does what falls in affect what flies out? The effect of leaf quality on insect emergence

Streams and their surrounding terrestrial environments are inter-related. Leaf litter provides food for aquatic invertebrates while emerging aquatic insects provide food for terrestrial animals. Although leaf types differ in decomposition rates and associated aquatic invertebrates, this is the first study testing how leaf quality affects insect emergence. We compared insect emergence between narrowleaf and Fremont cottonwoods. Large leaf packs (0.5 m³) were submerged in Wet Beaver Creek, Arizona in the spring and fall. These novel packs were large enough to measure emergence at a realistic spatial scale. Collections were taken by attaching emergence traps lined with microfiber mesh nets connected to containers filled with 70% ethanol. Results show high variability among sites and subtle differences in the number and types of insects between leaf type. Fall insect emergence was slightly higher on leaf packs with Fremont relative to narrowleaf leaves. In the spring, differences among litter type were minimal. Total emergence was higher in the spring than the fall although more shredders emerged in the fall. This was the first study testing how differences in leaf quality affect aquatic insect emergence and demonstrates that riparian restoration projects should consider how tree species affect food availability for riparian predators.