Effects of ambient UV-B radiation on soybean crops: Impact on leaf herbivory by Anticarsia gemmatalis

Replicated field experiments with large plastic filters were carried out in Buenos Aires (Argentina, 34 degrees S) to study the impacts of current lev els of solar UV-B radiation (lambda less than or equal to 315) on soybean ( Glycine max L.) crops and their interactions with chewing insects, in parti cular the soybean worm Anticarsia gemmatalis Hubner (Lepidoptera: Noctuidae ). Solar (near-ambient) UV-B induced changes in the leaves that reduced the ir attractiveness to A. gemmatalis larvae in laboratory "choice" bioassays. When the A. gemmatalis larvae were forced to consume leaves from field plo ts that received solar UV-B, they grew slightly less rapidly and suffered m ore mortality than their counterparts fed with leaves from plots covered wi th polyester films that excluded the UV-B component of sunlight. Exposure o f the larvae themselves to ambient UV-B under a soybean canopy during the f eeding trials did not lower their life expectancy. At the whole canopy leve l, we found that solar UV-B exclusion resulted in a two-fold increase in th e number of leaf lesions inflicted by various species of chewing insects th at naturally invaded the field plots. Leaves from canopies exposed to solar UV-B showed significantly higher levels of soluble phenolics and lower lev els of lignin than leaves that developed in canopies covered by polyester f ilms. No differences in specific leaf mass, leaf nitrogen or hemicellulose content were detected between the control and the solar-UV-B exclusion trea tments. Our results are consistent with the idea that present-day solar UV- B has an important regulatory influence on the interactions between plants and phytophagous insects.