Sex chromatin and chromosome numbers in Lepidoptera

Three classes of sex chromatin (SC) distribution have been encountered in a sample of Canadian Lepidoptera. In 78 of the 103 species examined, females were SC positive and males were SC negative. In another 24 species, females and males were SC negative. Females and males of a single species, Eucordylea resinosae, had two equal-sized SC bodies in interphase nuclei. In no species were females found to be SC negative and males SC positive. Usually presence of SC indicates an XX male and XY female sex determining mechanism, and its absence, XX male; XO female, but the exceptional occurrence of SC in females and males of a species suggests the need for caution in too universal an application of this interpretation. Chromosome numbers have also been determined for 53 of the 103 species. Male haploid numbers ranged from 11 to 61, but 30 was most frequently encountered.