PARENT SESSION
Poster Session #3: Herbivory.
Monday, August 6, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Dynamics of defoliator activity along an urban to rural gradient in the Middle Rio Grande riparian corridor.

Eichhorst, Kim¹, ¹

ABSTRACT- Increasing pollution from urban areas can directly influence plant-insect interactions. Previous researchers found ozone-treated cottonwoods were preferred as forage by chrysomelid beetles in the laboratory. I monitored herbivory levels on cottonwoods (Populus deltoides spp. wislizenii) at five sites along a 177-km stretch of the Rio Grande in central New Mexico to determine if a similar trend was evident in the field. Two northern sites represented areas of urban influence, each approximately 10 km from Albuquerque's urban center. Two southern sites represented areas of rural influence, and there was one intermediate site. Ozone concentrations in the urban sites, ca. 100 ppb, were above levels at which cellular damage occurs in cottonwoods, and were twice the concentration measured near the rural sites. The major defoliator in the northern and intermediate sites was Chrysomela scripta, the cottonwood leaf beetle. Defoliation levels due to C. scripta were significantly higher in urban sites (1996: 30-41%; 1997: 34-49%, p < 0.05) and the intermediate site. Both herbivory and greenfall levels were low at the rural sites (herbivory: 10-20%; greenfall: < 15%). Percent beetle-chewed leaves correlated positively with distance from Albuquerque (R² = 0.90 and 0.95 for 1996 and 1997, respectively). C. scripta may respond to higher levels of ozone near urban sites as other factors did not correlate with herbivory.

KEY WORDS: Chrysomela scripta, Populus deltoides, ozone, greenfall