Stage-specific sex determination in potato tuber moth, Phthorimaea operculella (Zeller) using morphological traits

The potato tuber moth, Phthorimaea operculella (Lepidoptera: Gelechiidae), is a major pest of potato crop worldwide, causing significant economic losses by infesting tubers both in the field and in storage. Early detection of the pest across its developmental stages is crucial for implementing timely management strategies. In this study, stage-specific sex differentiation was analysed through external morphological examinations at the larval, pupal, and adult stages. In the fourth instar larvae, males were identified by the presence of developing gonads, visible as two dark elliptical structures on either side of the midline on the fifth abdominal segment, which were absent in females. At the pupal stage, males and females were differentiated based on the distance between the genital and anal openings, which was greater in female pupae than in male pupae. In adults, females were identified by a distinct X-shaped marking on the forewings, whereas males exhibited series of black dots during resting posture. Detailed morphological identification including wing venation and genitalia dissection was conducted using eosin staining and ethanol clearing techniques. The study identified reliable morphological characters for distinguishing male and female at the larval, pupal and adult stages, providing practical criteria for stage-specific sex identification for laboratory and taxonomic studies.