The adaptive nature of the foam proteome produced by Mahanarva spectabilis (Hemiptera: Cercopidae) when infesting forage grasses with different levels of antibiosis-type resistance

The spittlebug Mahanarva spectabilis (Distant, 1909) (Hemiptera: Cercopidae) produces a stable extracellular foam during its nymphal stage, which plays a critical role in survival and host plant interactions. In this study, we present the first comprehensive proteomic characterization of foam secreted by M. spectabilis nymphs, using a shotgun LC-MS/MS approach. We analyzed the foam produced by nymphs feeding on four forage cultivars showing different levels of antibiosis-type resistance against M. spectabilis, as follows: Cenchrus purpureus cv. Pioneiro (moderately resistant) and cv. Roxo de Botucatu (susceptible); Urochloa brizantha cv. Marandu (resistant), and Urochloa decumbens cv. Basilisk (susceptible). A total of 196 proteins were identified, including a substantial fraction of unannotated proteins with high abundance, suggesting specialized foam-specific functions. Functional annotation revealed enrichment in hydrolases, oxidoreductases, and binding proteins, highlighting potential roles in microbial regulation, stress response, and structural maintenance. Comparative analysis revealed consistent up-regulation of cytoskeletal and metabolic proteins in resistant/moderately resistant hosts, alongside repression of proteins related to carbohydrate and lipid metabolism. Multivariate and GO-based analyses confirmed host genotype-dependent modulation of foam composition. The findings demonstrate that higher levels of resistance to M. spectabilis are associated with two key strategies: (1) the suppression of metabolic pathways, likely limiting nutrient availability to the insect, and (2) the activation of defence-related proteins, such as antioxidant enzymes, which enhance the plant's ability to cope with stress. These findings underscore the dynamic and adaptive nature of the foam proteome, reflecting both environmental and physiological constraints. Our results provide new insights into the molecular basis of foam function and its relevance for insect survival, offering promising avenues for the development of novel strategies targeting foam-mediated defence mechanisms.