Molecular and Structural Characterization of Foam Proteins from <i>Mahanarva spectabilis</i> (Distant, 1909) (Hemiptera: Cercopidae) Nymphs Reveals Adaptive Features and Potential Targets for Pest Control

During its nymphal development, the spittlebug Mahanarva spectabilis (Distant, 1909) (Hemiptera: Cercopidae) secretes a persistent extracellular foam that functions as a multifunctional barrier against environmental stressors. In this study, we present a molecular and structural characterization of the foam proteins using LC-MS/MS and AlphaFold-based structural modeling. Although no significant differences were observed in total protein concentration across different host plant genotypes, proteomic analyses revealed the down-regulation of specific high-abundance proteins in nymphs feeding on resistant/moderately resistant grasses. This suggests a potential impairment of foam functionality and reduced nymphal fitness under field conditions. Peptides from individual SDS-PAGE bands mapped to multiple distinct unigenes, indicating that proteins encoded by different transcripts share highly conserved sequence motifs, domain architectures, and structural folds. This was particularly evident for the most abundant protein, likely reflecting post-translational modifications such as signal peptide cleavage, proteolytic processing, or alternative splicing. AlphaFold structural predictions revealed the presence of adhesive and matrix-related domains, such as WSC, S-layer, ankyrin repeats, and apolipophorin folds, across several foam proteins. The dominance of extended α-helices and the predicted dimerization interfaces reinforce the hypothesis that these proteins participate in the formation of supramolecular scaffolds essential for the mechanical stability and adhesion of the foam. Collectively, these findings suggest that M. spectabilis foam proteins have undergone evolutionary specialization to assemble a multifunctional extracellular matrix that ensures nymphal protection. These insights highlight potential molecular targets for novel pest control strategies and contribute to the broader understanding of insect-derived extracellular secretions with biomimetic relevance.