Larval Polytene Chromosomes of Five Species of Blackflies (Diptera : Simuliidae) from Doi Inthanon National Park, Northern Thailand

Abstract

The standard photographic maps of five blackfly species from northern Thailand : i.e., Simulium (Nevermannia) caudisclerum, S. (Simulium) fenestratum, S. (S.) nakhonense, S. (S.) rufibasis and S. (Montisimulium) sp. G were constructed from larval salivary gland polytene chromosomes and are described herein. All the five species have three pairs of chromosomes (2n=6) which are arranged from the longest to the shortest. Chromosome I of all species are metacentric while most of the chromosome II and III are submetacentric. The centromeric regions of all chromosomes of S. (S.) nakhonense and S. (S.) rufibasis were expanded whereas the heavy centromeric bands were presented in S. (N) caudisclerum, S. (S.) fenestratum and S. (M.) sp. G. The nucleolar organizer of S. (N.) caudisclerum, S. (S.) fenestratum, S. (S.) nakhonense and S. (M.) sp. G is situated near the centromeric band of chromosome I. On the other hand, S. (S.) rufibasis has the nucleolar organizer on chromosome II. The Balbiani ring and double bubble are located near the tip of short arm of chromosome III in all species except for S. (S.) fenestratum, in which they are detected on chromosome II. Moreover, two types of B chromosomes and pseudochromocenters were also found in some larvae of S. (S.) nakhonense. There are no inversion polymorphisms detected in wild populations of these species. The five Simulium species have specific and fixed standard banding sequences which are different among species, although some banding sequences in chromosome arm IIIS show homology.