INSECTS ASSOCIATED WITH SALTCEDAR, BACCHARIS AND WILLOW IN WEST TEXAS AND THEIR VALUE AS FOOD FOR INSECTIVOROUS BIRDS: PRELIMINARY RESULTS

Authors: KNUTSON, ALLEN - TEXAS A&M UNIVERSITY; MUEGGE, MARK - TEXAS A&M UNIVERSITY; Robbins, Thomas; Deloach Jr, Culver

Submitted to: Saltcedar and Water Resources in the West Symposium
Publication Type: Proceedings
Publication Acceptance Date: 1/1/2003
Publication Date: 7/16/2003
Citation: Knutson, A., Muegge, M., Robbins, T.O., Deloach, C.J. 2003. Insects associated with saltcedar, baccharis and willow in west texas and their value as food for insectivorous birds: preliminary results. Proceedings of the Symposium, Saltcedar and Water Resources in the West. p. 41-50.

Interpretive Summary: Native saltcedars from Asia and the Mediterranean area that have invaded western riverbottoms and lakeshores have replaced the native plant communities that grew there, reduced the numbers and kinds of insects that develop on the plants, and of the birds that feed on the insects. We compared insect types and numbers that we collected in saltcedar with those collected in native willows and seepwillow baccharis along the western Rio Grande, the upper Colorado, and the Canadian rivers of Texas in both spring and fall of 2002 and 2003. Total numbers of insects were greatest on saltcedar but 86 to 94% of these were of one species of small leafhopper that entered the U.S. together with saltcedar. However, the number of native insect species and types was 7 to 9 times greater on the native willows and baccharis than on saltcedars along these rivers. While some birds feed readily on leafhoppers, many insect-feeding birds do not, and prefer the native insect species. This research helps to explain the harmful effects of the saltcedar invasion on native plants, insects, birds and other animals.

Technical Abstract: The recent invasion of southwestern riparian ecosystems by exotic saltcedars (Tamarix spp. from Asia and the Mediterranean area) has greatly altered the composition of native plant communities, the species diversity and abundance of the insects that develop in the plant communities, and may affect the species diversity and abundance of the birds that depend on insects as a food resource. We compared species and populations of both adult and immature insects that we collected from saltcedars compared with native willows (Salix spp.) and baccharis (Baccharis salicifolia). We sampled the insects along the Rio Grande, the Colorado, and the Canadian rivers of Texas; in both spring and fall of 2002 and 2003. We identified all insects collected from 600 stems each 45 cm long, from each plant species, at each date, along each river. Total numbers of insects was greatest on saltcedar along all rivers but 86 to 94% were of one species of the small, exotic leafhopper, Opsius stactogalus. Species diversity was much greater in willows and baccharis, although numbers and species composition varied between these plants and between the rivers. While some birds feed readily on leafhoppers, many insectivorous birds do not, and prefer the native insect types present on the willows and baccharis. This research helps to explain the harmful effects of the saltcedar invasion on native plants, insects, birds and other animals.