Chromosomal variation in Agromyzidae (Diptera)

The polytene chromosomes from the gastric coeca of Cerodonta (Butomomyza) eucaricis Nowakowski are described. There are five long and one dot-like chromosome, the latter with indistinct bands. The X chromosome is number 5 and shows an allocyclical behaviour: In male larvae the bands are less distinct and the whole chromosome is much shorter than in female larvae. A material of 1444 larvae has been cytologically investigated. From their chromosomal morphology they could be classified as belonging to two different semispecies or perhaps sibling species. 1061 larvae belonged to the first semispecies and 349 to the other. The two semispecies occur as a rule sympatrically and may hybridize in nature. The hybrids are fertile, at least to some extent. The semispecies differ in one fixed inversion in the X chromosome and in five floating autosomal inversions. The two semispecies do not share any polymorphisms, but by occasional hybridization inversions could be transferred from one of the two semispecies to the other. Possible mechanisms for reproductive isolation and taxonomic state are discussed.