The karyotype of Axarus festivus (Say) and a comparison with species of Lipiniella (Chironomidae: Diptera)

Larvae of Axarus and Lipiniella share several apparantly apomorphic features of the mouth-part structure, however adults of Lipiniella show possible relationships to Demeijerea and Chironomus. In order to assist in refining the relationships of Axarus to Lipiniella the karyotype of Axarus festivus was determined and compared to the karyotypes of Lipiniella arenicola and L. moderata. Larvae of A. festivus from a population in Kansas were monomorphous, with 2n=8, the Ist, IInd and IIIrd chromosomes metacentric, and IVth acrocentric. Axarus festivus therefore differs from L. arenicola in chromosome number (2n=6), however homologous sections of all chromosomes were identified. Inversions were detected in the Ist, IInd and IIIrd chromosomes of A. festivus relative to L. arenicola. It was determined that both species have high functional activity, as indicated by the presence of three Balbiani rings, and more than one nucleolus per genome. Differing degrees of polyteny, a feature previously described for L. arenicola, were observed in the salivary glands, with highest degrees of polyteny in cells near the salivary duct. These similarities of chromosome structure indicate close genetic relationships between A. festivus and L. arenicola. However, we did not find evidence for similarity of A. festivus to L. moderata, which supports the previous conclusions by Kiknadzeet al. (1989) regarding L. arenicola and L. moderata.