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

Abstract

Replicated field experiments with large plastic filters were carried out in Buenos Aires (Argentina, 34° S) to study the impacts of current levels of solar UV-B radiation (λ ≤ 315 nm) on soybean (Glycine max L.) crops and their interactions with chewing insects, in particular the soybean worm Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae). Solar (near-ambient) UV-B induced changes in the leaves that reduced their attractiveness to A. gemmatalis larvae in laboratory "choice" bioassays. When the A. gemmatalis larvae were forced to consume leaves from field plots that received solar UV-B, they grew slightly less rapidly and suffered more mortality than their counterparts fed with leaves from plots covered with polyester films that excluded the UV-B component of sunlight. Exposure of the larvae themselves to ambient UV-B under a soybean canopy during the feeding trials did not lower their life expectancy. At the whole canopy level, we found that solar UV-B exclusion resulted in a two-fold increase in the number of leaf lesions inflicted by various species of chewing insects that naturally invaded the field plots. Leaves from canopies exposed to solar UV-B showed significantly higher levels of soluble phenolics and lower levels of lignin than leaves that developed in canopies covered by polyester films. No differences in specific leaf mass, leaf nitrogen or hemicellulose content were detected between the control and the solar-UV-B exclusion treatments. 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.