While gall-inducing insects exert a high level of control over their host development and physiology, the molecular mechanisms underlying these manipulation processes are still poorly understood. One way to address this question is to focus on effectors produced by insects and susceptible to undermine the plant immune system and modulate the cellular processes. To find candidate effectors involved in gall induction, we compared the gene expression in the larvae of the micromoth Caloptilia cecidophora (Lepidoptera, Gracillariidae) that induces galls on Glochidion obovatum (Phyllanthaceae) to the larval transcriptome C. ryukyuensis, a closely related non-gallinducing species both sympatric and growing of host plant of the same genus. Three independent methods were used to analyze the transcriptomic data. First, we isolated genes showing a peak of expression at the initiation of the gall induction (third instar), and 505 genes were significantly upregulated in third instar compared to the second and the fourth instars. Among them 22 were specific in C. cecidophora transcripts and successfully annotated. Secondly, we selected genes with expression patterns matching gall-induction using a principal component analysis and a self-organizing map. Ortholog comparisons revealed 36 genes showing an opposite expression pattern between the two species. Finally, we looked for candidate genes based on literature and compared their expression patterns between the two species and among instars. All together, we obtained a list of 58 genes coding for possible effectors. Preliminary results point toward the production of anti-oxidant enzymes and chitinases and suggest the implication of secreted auxin in gall formation.