Journal of Experimental Agriculture International

Adult morphological variability among geographically distinct eri silkmoth populations in Assam remains incompletely characterised. This study examined three populations of Samia ricini (ERI4, ERI5 and Kamrup1) and one population of Samia canningi (ERI 9395) originating from different agroclimatic zones of Assam. Seed cocoons were collected and adult moths examined at Assam Agricultural University, Jorhat, during 2023–2025. Eleven external morphometric characters, two male genital measurements and qualitative characters of the wings and abdomen were assessed. Differences among population means were evaluated using the critical difference at the 5% significance level. Among the S. ricini populations, hindwing length, abdominal length and clasper length differed beyond the corresponding critical differences for specified population pairs. The remaining external measurements, including body length, thorax length, forewing length, wingspan and antennal dimensions, did not exceed their respective critical differences among these populations. Samia canningi differed from the three S. ricini populations in abdominal length and aedeagus length, while additional contrasts were observed in hindwing and clasper lengths. Forewing and hindwing coloration, antemedian line patterns, hyaline spot shape, fringe characteristics and the distribution of white scales on the abdominal tergum also varied. These findings identify a limited set of quantitative traits and several descriptive characters relevant to the characterisation of the sampled populations. Because each sampled agroclimatic zone was represented by one population, the observed variation cannot be attributed independently to geographic or genetic factors.