In this study, the mitochondrial genomes (mitogenomes) of two walnut leaf insect pests,Gastrolina depressa depressaandG.depressa thoracica, were sequenced by Sanger sequencing technology. The mitogenome ofG.depressa thoracicawas complete at 16,109 bp in length, while the mitogenome ofG.depressa depressa(14,277 bp) was partial. The genomic analyses indicated that both mitogenomes have the typical gene content and arrangement. The formerly identified elements, ‘TAGTA’ betweentrnSer(UCN) andnad2, and ‘ATGATAA’ betweenatp8andatp6, were more conserved than that betweennad4Landnad4, which was ‘ATGTTAA’ in Coleoptera excluding Polyphaga. Phylogenetic analyses of the 13 protein-coding genes from 36 coleopteran species well supported a close affinity between the subfamily Chrysomelinae includingG.depressa thoracicaandG.depressa depressaand Galerucinae, as well as a sister relationship of ((Eumolpinae + Cryptocephalinae) + Cassidinae) within Chrysomelidae.

Long-horned beetles are among the major insect pests that can cause significant economic and ecological damage globally. The control of long-horned beetles is crucial to sustain the forest ecosystem. Dastarcus helophoroides, an economically important ectoparasitoid of long-horned beetles, is widely utilized in biological control strategies. However, the number of larval instars in D. helophoroides remains underexplored. Larval instar determination is crucial for constructing growth prediction models and ecological life tables for insect populations. In this study, we analyzed the frequency distribution of head capsule widths utilizing a visual approach, followed by a non-linear least squares (NLLS) estimation, and found that D. helophoroides undergo four larval instars before entering the pupal stage. The theoretical and observed data for each larval instar yielded identical mean Brooks–Dyar’s ratios (1.80). Re-correlation of the number of instars with their respective mean head capsule widths using linear regression (R²) verified that no larval instar was missed. The Crosby’s growth ratio (1% and 2%) indicates a very low likelihood of misclassifying an instar into an adjacent one. Given that the accurate determination of larval instars is crucial for developing effective control programs and predicting future population levels, our findings provide valuable insights for implementing biological control strategies against long-horned beetles.