Differential responses of three stink bugs species to soybean defenses: Insights into the impact on digestive enzymes

The stink bugs Diceraeus furcatus, Piezodorus guildinii, and Nezara viridula (Hemiptera: Pentatomidae) are major pests of soybean (Glycine max; Fabales: Fabaceae) that feed on developing seeds. In response to herbivory, soybean plants synthesize protease inhibitors (PI) as a key defense mechanism. These inhibitors interact with digestive cysteine proteases in stink bug guts —such as cathepsins— thereby reducing nutrient assimilation. Because herbivory induces cysteine PI in soybean seeds, studying this regulation is important to decrease stink bug damage. Although some information is available on the effects of cysteine PI on N. viridula, little is known about how different stink bug species induce these defenses in field-grown soybean. In this study, we measured cysteine PI activity in soybean seeds following herbivory by D. furcatus, P. guildinii, and N. viridula. We compared cysteine PI activity between damaged and undamaged seeds at 24 and 72 hours post-feeding. We also analyzed cathepsin B and L activities in stink bug guts after feeding on growing seeds, with boiled seeds as controls, and recorded pod piercings to determine feeding behavior. Our results showed that cysteine PI activity increased significantly after herbivory but remained low in undamaged controls. Despite this increased defense, all stink bugs exhibited similar pod-piercing frequencies, approximately 25 piercings per pod. We observed that cathepsin B activity was inhibited in P. guildinii and N. viridula but not in D. furcatus, whereas cathepsin L activity was inhibited in D. furcatus and P. guildinii but not in N. viridula. Our findings reveal species-specific interactions between soybean defenses and stink bug digestive enzymes. Field-grown soybean plants recognize herbivory and induce cysteine PI as a defense strategy, but the efficacy of these inhibitors depends on the pest species. This insight could guide the development of targeted pest management strategies adjusted to specific stink bug species.