Soybean resistance to stink bugs ( N ezara viridula and P iezodorus guildinii) increases with exposure to solar UV- B radiation and correlates with isoflavonoid content in pods under field conditions.

Solar UV- B radiation (280-315 nm) has a significant influence on trophic relationships in natural and managed ecosystems, affecting plant-insect interactions. We explored the effects of ambient UV- B radiation on the levels of herbivory by stink bugs ( N ezara viridula and P iezodorus guildinii) in field-grown soybean crops. The experiments included two levels of UV- B radiation (ambient and attenuated UV- B) and four soybean cultivars known to differ in their content of soluble leaf phenolics. Ambient UV- B radiation increased the accumulation of the isoflavonoids daidzin and genistin in the pods of all cultivars. Soybean crops grown under attenuated UV- B had higher numbers of unfilled pods and damaged seeds than crops grown under ambient UV- B radiation. Binary choice experiments with soybean branches demonstrated that stink bugs preferred branches of the attenuated UV- B treatment. We found a positive correlation between percentage of undamaged seeds and the contents of daidzin and genistin in pods. Our results suggest that constitutive and UV- B-induced isoflavonoids increase plant resistance to stink bugs under field conditions. [ABSTRACT FROM AUTHOR]