External changes in pupae of the fall webworm (Hyphantria cunea, Drury) parasitized by tachinid flies (Diptera: Tachinidae)

This study was conducted to evaluate whether external morphological changes in Hyphantria cunea pupae can be utilized as biological indicators of parasitism by tachinid flies (Diptera: Tachinidae). Final-instar larvae wandering prior to overwintering pupation were collected and reared individually, and were classified into groups with visible tachinid eggs and without visible eggs. External morphological characteristics of host pupae were then compared according to parasitism success. Three types of morphological abnormalities—abdomen elongation, wing deformity, and premature pupation—were observed in pupae from which tachinid emergence was confirmed. Among these, abdomen elongation was the most frequently observed abnormality. This condition was characterized by a straightened abdominal profile and an increased intersegmental distance between abdominal segments, with a mean intersegmental distance exceeding 0.20 mm. Notably, abdomen elongation was not observed in normal pupae or in individuals where oviposition occurred but parasitism failed, indicating a strong association with successful parasitism. In addition, cases of superparasitism and multiparasitism were recorded. These findings demonstrate that abdomen elongation can serve as a useful, non-destructive indicator of parasitism by certain tachinid species. Although this study focused on H. cunea , similar morphological indicators may also be applicable to ecological studies of other host species parasitized by tachinid flies. In the long term, these findings are expected to provide baseline data for evaluating parasitism and establishing biological control strategies using tachinid flies.