CURRENT KNOWLEDGE BACTROCERA DORSALIS COMPLEX (August 2013)
Background
The Bactrocera dorsalis species complex was first recognised by Hardy (1969), and greatly expanded
by Drew and Hancock (1994). Several other taxa have been placed in the complex outside of these
two revisions, of which the only one of current relevance is B. invadens (Drew et al. 2005). While the
majority of species within the B. dorsalis complex are easily diagnosed on morphological characters,
this is not the case for a small group of cryptic taxa which have been the focus of the current project:
B. dorsalis s.s. (Hendel), B. papayae Drew & Hancock, B. philippinensis Drew & Hancock, B.
carambolae Drew & Hancock and B. invadens Drew, Tsuruta & White.
Quite quickly after their original discriptions, concerns were raised as to the biological validity of B.
papayae, B. carambolae and B. philippinensis, most notably by Prof Keng Hong Tan and colleagues
(Nishida et al. 1988, Tan & Nishida 1996), but these views were subsequently reviewed and
dismissed (Clarke et al. 2005, Drew et al. 2008). Nevertheless, repeated failure to find robust and
consistent biological markers for these taxa (with the possible exception of B. carambolae), has
meant that the question of whether the taxonomic species correctly align with the biological species
has never been fully resolved. This component of the CRP was established to (i) accurately delimit
the biological species of this clade; and (ii) having done so develop appropriate diagnostic markers.
Current status
Very signficant research has been undertaken, within an integrative taxonomic framework, to
biologically delimit the target taxa. The tools used have included: i) morphological examination,
including traditional morphology, morphometrics of genitalic characters, and fine-scale wing shape
analysis using geometric morphometrics; ii) molecular-based approaches using both phylogenetic
and population genetic analyses of nuclear DNA sequence and microsatellite data coupled with
mitochondrial DNA sequence analysis and comparative transcriptome analysis; iii) studies of mating
and post-zygotic sexual compatibility; iv) analysis of rectal gland (= pheromone) constituents; and v)
comparative polytene chromosone analysis. Not all work has yet been published, but much has (Tan
et al. 2011, Khamis et al. 2012, Schutze et al. 2012a, Schutze et al. 2012b, Boykin et al. 2013, Krosch
et al. 2013, Schutze et al. 2013, Tan et al. 2013).
With one exception, all data so far presented by CRP participants have failed to find evidence of any
species level biological differentiation between B. dorsalis, B. papayae, B. philippinensis and B.
invadens. Any genetic and morphological differences which have been found are best explained as
intra-specific variation (i.e. population level variation), not inter-specific variation.
Data
(pheromonal, genetic, behavioural) suggests that B. carambolae is a biologically unique, albeit very
closely related species to the other four taxa. It is important to recognise that some critical data sets
for B. invadens (e.g. sexual compatability trials) have still to be publically presented, but this
‘missing’ data will be presented in Argentina and is consistent with the other data sets so far
presented. The one exception to the general patterns seen in the data sets was a verbal paper
presented by Prof Drew at the 2nd RCM (Brisbane, Jan 2012), who analysed thoracic color patterns
of B. invadens from Africa and B. dorsalis from China and concluded that the frequency of colors
(predominantly red-brown in the African flies and black in the Chinese flies) confirmed these two
species as described. Because such color variation might also be interpreted as intra-specific
variation in one wide-ranging biological species, more work in this area has been done in the last 18
months and will be presented in Argentina.
It is believed that Prof Drew has formally synonymised B. philipinnensis with B. papayae in a soon to
be published monograph, but no other taxonomic changes have been made.
Conclusions
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All evidence so far suggests that B. dorsalis, B. papayae and B. philippinensis are one
biological species, while B. carambolae is a closely related but biologically unique species,
albeit natural hybrids between B. carambolae and B. papayae have been detected in the
Penisular Malaysia (Tan, 2005, Wee and Tan 2005).
B. invadens should also be likely considered a junior synonym of B. dorsalis, but some
additional data sets need to be publically presented and peer considered before this can be
assumed.
The strength of the case for considering the synonymisation of B. papayae, B. philippinensis
and B. invadens with B. dorsalis rests not on the strength of any one approach (i.e. mating,
pheromone, genetics), but the highly consistent results of all of these independent
approaches.
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