Morphometric Variation across Developmental Stages of Corcyra cephalonica (Stainton) Reared on Walnut Kernels

Abstract

The rice moth, Corcyra cephalonica (Stainton), is an important stored-product insect whose growth and developmental characteristics may vary with rearing substrate and environmental conditions. Although morphometric information is available for the species under different rearing conditions, stage-specific morphometric data for C. cephalonica developing on walnut kernels remain limited, warranting systematic documentation under laboratory conditions. The study documented morphometric variation across developmental stages of the rice moth, Corcyra cephalonica (Stainton), reared on walnut kernels under laboratory conditions. Morphometric observations were recorded for the egg, successive larval instars, pupa, and adult using a stereomicroscope. Five specimens from each developmental stage were measured, and mean values were calculated for the recorded characters. Egg length and breadth were 0.48 and 0.34 mm, respectively. Larval body dimensions increased progressively across successive instars, with mean length rising from 1.62 mm in the first instar to 11.50 mm in the sixth instar, while mean breadth increased from 0.37 to 2.08 mm. The pupa measured 10.22 mm in length and 1.82 mm in breadth, showing a slight reduction in length relative to the sixth larval instar. Adult females were marginally larger than males, with mean body lengths of 11.25 and 10.88 mm, respectively, and wing spans of 15.68 and 15.61 mm. Overall, the observations showed a clear stage-wise progression in body size during larval development, followed by the expected transition to pupal and adult forms. The findings provide condition-specific baseline morphometric information for C. cephalonica reared on walnut kernels and may support identification and description of its developmental stages under comparable laboratory conditions.