Changes in gall density and morphology of Dryocosmus kuriphilus (Hymenoptera: Cynipidae) along an elevation gradient in the Northeastern Türkiye

Abstract

The Asian chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu, 1951 (Hymenoptera: Cynipidae), induces gall formation on chestnut trees, causing severe damage and economic losses. Ecological conditions significantly influence D. kuriphilus biology and behavior, making it essential to understand these factors in order to apply effective management strategies. This study aims to investigate the elevation-dependent variation in gall density and morphology of D. kuriphilus. This field study was conducted in mid-May 2024, and covered the entire elevational distribution range of Castanea sativa, Anatolian chestnut forests in Trabzon Province, Northeastern Türkiye, with ten sampling plots (min 488 m-max 1100 m). In each plot, galls were counted on ten randomly selected trees, and branch samples were collected from five of these trees to assess D. kuriphilus damage and characterize gall morphology. Gall density and chamber count increased with elevation, with low-elevation groups differed markedly from medium and high-elevation groups. No significant differences in gall volume, width, or length were observed among the elevation groups. A significant correlation was found between the total gall count on the tree and gall counts in each cardinal directions. Inter-directional correlations were generally high, though north–south gall counts showed relatively weaker correlations. The mean gall density in the region was calculated as 12.05 per branch. Galls were similarly distributed on buds-shoots and leaves, but their forms varied significantly. Gall volume exhibited a weak-to-moderate positive correlation with the number of chambers. This study demonstrates that elevation significantly influences gall abundance and morphology in D. kuriphilus-induced galls, with distinct variation across elevation groups.