Cytological evidence for a complex of species within the taxon Bactrocera tau (Diptera : Tephritidae) in Thailand

Analysis of mitotic karyotypes of wild specimens of larvae of the Bactrocer a tau-like fruit flies (Diptera: Tephritidae) in Thailand has revealed seve n distinct chromosome forms, based on the amount and distribution of hetero chromatin in sex chromosomes and autosomes. Such cytological differences ar e perfectly correlated with morphological observations and molecular geneti cs data. These findings clearly suggest that B. tau is a cluster of at leas t seven closely related species temporarily designated as species A (=B. ta u), B, C, D, E, F and G. On the basis of the gross quantity of heterochroma tin accumulation in the genome, three groups of mitotic karyotypes can be r ecognized. Group 1 comprises species A and E. Species E specifically occurs only in fruits of Strychnos thorelii while species A attacks many kinds of host plants. Group 2 contains species B, F and G. Species B has been found only in Siphonodon celastrineus fruit, whereas species F and G attack the same host species, the medically important plant, Hydnocarpus anthelminthic us, albeit in different localities. Group 3 includes species C and D, each of which comprises larger amounts of pericentric heterochromatin in all chr omosomes than the other two groups. Hence, these two species are cytologica lly remote from those of groups 1 and 2. Species C and D occur allopatrical ly but they attack the same host plant species, Momordica cochinchinensis. Thus, genetic differentiation at the chromosomal level to specific host pla nt species and geographic isolation seem to play an important role in speci ation of members of the B, tau complex. (C) 2000 The Linnean Society of Lon don.