New Gall-Forming Insect Model, Smicronyx madaranus: Critical Stages for Gall Formation, Phylogeny, and Effectiveness of Gene Functional Analysis

Simple Summary A new gall-forming model, Smicronyx madaranus, showed that gall formation consists of two processes: initiation by adults and enlargement by larvae. Phylogenetic analysis showed that gall-forming weevils belong to two distinct lineages that utilize different host plants, suggesting that gall-forming traits evolved independently in these Smicronyx lineages. This study demonstrates that RNAi is effective for functional gene analysis in S. madaranus. The S. madaranus model contributes to elucidating the mechanisms of gall formation and understanding the commonalities and diversity of insect galls. Abstract The molecular mechanisms underlying insect gall formation remain unclear. A major reason for the inability to identify the responsible genes is that only a few systems can be experimentally validated in the laboratory. To overcome these problems, we established a new galling insect model, Smicronyx madaranus. Our manipulation experiments using nail polish sealing and insecticide treatment revealed an age-dependent change in gall formation by S. madaranus; adult females and larvae are responsible for gall induction and enlargement, respectively. Furthermore, it has been suggested that substances released during oviposition and larval feeding are involved in each process. Phylogenetic analysis showed that gall-forming weevils, including S. madaranus, belong to two distinct lineages that utilize different host plants. This may indicate that gall-forming traits evolved independently in these Smicronyx lineages. The efficacy of RNA interference (RNAi) in S. madaranus was confirmed by targeting the multicopper oxidase 2 gene. It is expected that the mechanisms of gall formation will be elucidated by a comprehensive functional analysis of candidate genes using RNAi and the S. madaranus galling system in the near future.