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

Abstract

Analysis of mitotic karyotypes of wild specimens of larvae of the Bactmcera tau-like fruit flies (Diptera: Tephritidae) in Thailand has revealed seven distinct chromosome forms, based on the amount and distribution of heterochromatin in sex chromosomes and autosomes. Such cytological differences are perfectly correlated with morphological observations and molecular genetics data. These findings clearly suggest that B. tau is a cluster of at least seven closely related species temporarily designated as species A (= B. tau), B, C, D, E, F and G. On the basis of the gross quantity of heterochromatin accumulation in the genome, three groups of mitotic karyotypes can be recognized. Group 1 comprises species A and E. Species E specifically occurs only in fruits of Shychnos 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 celastrineur fruit, whereas species F and G attack the same host species, the medically important plant, Hydnocarpus anthelminthicus, albeit in different localities. Group 3 includes species C and D, each of which comprises larger amounts ofpericentric heterochromatin in all chromosomes than the other two groups. Hence, these two species are cytologically remote from those of groups 1 and 2. Species C and D occur allopatrically but they attack the same host plant species, Momordica c0chinchinenSi.s. Thus, genetic differentiation at the chromosomal level to specific host plant species and geographic isolation seem to play an important role in speciation of members of the B. tau complex. 0 2000 The Linnean Society of London ADDITIONAL KEY WORDS:-Bachocera tau complex -metaphase chromosome heterochromatin -karyotypic evolution.

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“…tau C is common and has become the dominant species on the host plant M. cochinchinensis (Table 1), in agreement with previous work 2,7 . In this study, B. tau C specimens were pooled into 3-month groups for the discriminant analysis (Fig.…”

“…One difficult problem in fruit fly control is to accurately identify the pest species. B. tau in Thailand now consists of eight forms: A, B, C, D, E, F, G, and I, which are common in different host plant species and habitats 2,3 . Species identification in the B. tau complex is difficult, and therefore they have been classified within the single taxon B. tau.…”

“…However, the wings of B. tau A and C were successfully distinguished by geometric morphometric analysis 7 . B. tau C is associated with a specific host plant species, Momordica cochinchinensis (gac fruit) while B. tau A is a generalist infesting several cucurbit species and occasionally M. cochinchinensis 2,7 . Intraspecific variation within B. tau A was found to be associated with host plant species in the Cucurbitaceae 7 .…”

“…As B. tau C has been historically associated with M. cochinchinensis 2,7 , this host may provide the natural habitat for morphometric variation of B. tau C, since it produces fruit over several months of the year. If so, variation in wing shape could be associated with environmental conditions as a consequence of differential developmental responses.…”

First detection of the pest fruit fly, Bactrocera tau (Diptera: Tephritidae), in the field in Japan: Evidence of multiple invasions of Ishigaki Island and failure of colonization

“…Although the taxon B. tau in Thailand has recently been proven to contain at least seven cryptic species (the B. tau complex) that can be separated 542 S. OHNO et al by mitotic karyotypes (Baimai et al, 2000) and allozyme electrophoresis profiles (Saelee et al, 2005), separation of these cryptic species based on morphology has not yet been established (White and Hancock, 1997;Clarke et al, 2001); therefore, we treated the trapped specimens simply as a single taxon B. tau. All the trapped B. tau were deposited at OPPPC as voucher specimens.…”