Effects of Abiotic Factors on Insect Populations in Riparian Restoration Sites

The objectives of this research program are to (1) determine the relationships between plant water and nitrogen contents and abundances, diversities, and nutrient-contents of arthropods (insects and spiders), and (2) develop methods for manipulating plant water and nitrogen contents.

Eight species of birds (southwestern willow flycatcher, yellow-billed cuckoo, gilded flicker, Gila woodpecker, vermilion flycatcher, Arizona Bell’s vireo, Sonoran yellow warbler, summer tanager) and four species of bats (western red bat, western yellow bat, California leaf-nosed bat, Townsend’s big-eared bat) included in the Lower Colorado River Multi-Species Conservation Program eat arthropods.  Creating and maintaining habitat for these vertebrate species will require providing an adequate supply of arthropods for food.  This is especially difficult at the habitat creation sites being developed, because riparian vegetation is being planted in non-riparian farmland (ie. where water tables are lowered, soil salinities are elevated, and spring flood flows are absent).  Growing plants will not by itself guarantee arthropod abundances large enough to feed and support bird and bat populations.  Two abiotic factors, plant water content and plant nitrogen content, greatly influence abundances of plant-feeding insects.  Both of these factors can be manipulated, depending on soil conditions, by controlling plant irrigation and fertilization.

Work completed in 2008 examined the increase in arthropod biomass produced by fertilizing coyote willows and cottonwoods with nitrogen.  Applying nitrogen fertilizer once during spring elevated leaf nitrogen concentrations throughout the growing season.  Biomasses of one insect group, the hemipteran suborder Homoptera (mostly aphids and leafhoppers) increased with nitrogen application to cottonwoods and coyote willows.

For additional information on this project, please refer to Work Task C5: Effects of Abiotic Factors on Insect Populations in Riparian Restoration Sites (PDF). Find Technical Reports for this Work Task here.

Updated October 14, 2011