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

The molecular mechanisms underlying insect gall formation remain unclear. A major reason for the inability to identify the responsible genes is that most insect galls are produced on woody plants and therefore cannot 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 during 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 most gall-forming weevils, including S. madaranus, belong to a single lineage, suggesting that gall-forming traits evolved in a specific lineage within Smicronyx. The efficacy of RNA interference (RNAi) in S. madaranus was confirmed by targeting 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.