INTRASPECIFIC VARIATION IN KEY MORPHOLOGICAL CHARACTERS OF CULISETA-MELANURA (DIPTERA, CULICIDAE)

Culiseta melanura (Cog.), the enzootic vector of eastern equine enceph alitis in North America, is polymorphic for a trait used as a key diag nostic character. The absence of white abdominal bands distinguishes t his species in several prominent keys to North American mosquitoes. Ho wever, this is an environmentally induced, nongenetic trait that canno t be used as a key character for diagnosing Cs. melanura. In light tra p collections, banded specimens occur in early spring and summer, and nonbanded adults appear in late summer-autumn. Larvae reared in labora tory conditions produce nonbanded adults. Progeny reared from banded m others are uniformly nonbanded. Biochemical genetic results indicate t hat banding is not correlated with a distinctive genotype or presence of cryptic species. In 18 enzyme loci screened, neither diagnostic all eles nor large differences in allele frequencies were detected between held-collected representatives of the two forms. Genetic variability was relatively low in the 28-year-old laboratory colony (average heter ozygosity = 7%: average number of alleles per locus = 1.4), whereas in field samples, the variability was typical of field populations (aver age heterozygosity = 12-19%; average number of alleles per locus = 1.6 -1.8), with the presence of both polymorphic and private alleles. The population genetic profile and comparisons among geographically distin ct populations represent the first such presentation for any species i n the genus Culiseta.