Cytogenetics of the Hessian fly: I. mitotic karyotype analysis and polytene chromosome correlations

The somatic haploid chromosome set of the Hessian fly, Mayetiola destructor (Say),consists of two autosomes and two sex chromosomes. Female somatic cells have pairs of each of these chromosomes (2n = 8). Male somatic cells have two pairs of autosomes and two monosomic sex chromosomes. C-banding revealed pericentromeric heterochromatin on one arm of each chromosome. Mitotic chromosomes were karyotyped using relative lengths, centromeric positions, presence of secondary constrictions, and position and length of C-positive regions. Silver nitrate stained pericentromeric, heterochromatic regions on all four chromosomes but did not stain the entire C-positive regions. In female larvae, four distinct polytene chromosomes were found in the basal region cells of the salivary glands. In male larvae, two distinct and two diffuse polytene chromosomes were found in basal region cells. Differential polytene chromosome morphology in male and female larvae, polytene chromosome indexes, and the position of the nucleolus were used to establish correlations between mitotic and polytene chromosomes. The diffuse morphology of the polytene sex chromosomes in male larvae was probably related to dosage compensation. The number of sex chromosomes in male and female larvae is discussed in relation to sex determination and the production of monogenous progenies.