Isoenzymes Detect Variation in Populations of Triatoma brasiliensis (Hemiptera: Reduviidae: Triatominae)

Abstract

Triatoma brasiliensis is one of the most important vectors of Chagas disease in the semiarid Lent, 1941 and T. brasiliensis macromelasoma Galvão, 1956. These subspecies differ mainly in their cuticle colour pattern and were regarded as synonyms by Lent and Wygodzinsky (1979) Galvão, 1956. Their descriptions are based on the different chromatic patterns of pronotum, hemelytron and legs. A taxonomic key for the different subspecies can be found in Galvão (1956). These subspecies were synonymized by Lent and Wygodzinsky (1979), who simply asserted that "inter-grading forms are frequent". Whether T. brasiliensis consists of different melanic populations or the chromatic patterns observed are due to interspecific variation is unknown.In order to study this question, isoenzymatic, morphological and behavioural studies have been undertaken: morphological characters of the geni- tal structures show considerable individual heterogeneity, thus making the differentiation of the chromatic patterns with these structures impossible. However, observations on the homogeneity and stability of colour patterns of colonies reared in laboratory and the allopatry registered during field captures, indicate that T. brasiliensis presents distinct geographic populations (Costa et al. 1996c). Studies on the biology, feeding sources and natural infection of the different chromatic variants have been carried out (Costa et al. 1995a, b). The results using multilocus enzyme electrophoresis for comparing these distinct populations of T. brasiliensis are reported here. MATERIALS AND METHODSThe insects -One hundred and twenty specimens belonging to four chromatic populations of T. brasiliensis were tested: 30 F1 adults (15 females and 15 males) of each different chromatic patterns were used from colonies initiated with individuals collected from the field. The specimens captured were found in isolated colonies in different ecotopes. The localities where T. brasiliensis specimens were collected, the populations they represent and number of founder individuals are given in Table I. Voucher specimens are deposited in the Entomological Collection of Instituto Oswaldo Cruz-FIOCRUZ, Rio de Janeiro.

Chromosome homogeneity in populations of Triatoma brasiliensis Neiva 1911 (Hemiptera - Reduviidae - Triatominae)

“…Nei's genetic distance reaches values corresponding to those found at the interspecific level for other species of Triatominae (Costa et al, 1997a). The greatest distance was obtained between the brasiliensis and melanica populations.…”

“…Lent & Wygodzinsky (1979) considered these subspecies as synonymous based on the fact that intermediate forms seem frequent. Recently, a fourth chromatic pattern was collected in Juazeiro (Bahia), named as "juazeiro population" (Costa et al, 1997a).…”

Morphological Studies on the Triatoma brasiliensis Neiva, 1911 (Hemiptera, Reduviidae, Triatominae) Genital Structures and Eggs of Different Chromatic Forms

“…We did not record intermediate forms, reported by Lent and Wygodzinsky (1979). Maybe these intergrading forms could be present in the border lines where crossings among different colour patterns could be occuring; isoenzymatical data (Costa et al 1997) suggested a clear genetic differentiation among these populations of T. brasiliensis, reaching Nei's genetic distance values correspondent to those found at interspecific level, for other phylogenetic related species (Pereira et al 1996).…”

Molecular research and the control of Chagas disease vectors

“…The characterization of phenotypically diverse populations of T. brasiliensis seemed to represent an exception in that fixed allozyme differences were found between conspecific populations (Costa et al 1997). The alternative view that several distinct taxa were involved was later supported by DNA sequence analysis .…”

“…In general, when clear differences (diagnostic loci in sympatry or large genetic distances in allopatry) were detected between populations, the usual outcome was that more than one taxon was involved, either because of misidentification (e.g., R. colombiensis wrongly identified as R. prolixus) or cryptic speciation (as with T. sordida) , Noireau et al 1998. The characterization of phenotypically diverse populations of T. brasiliensis seemed to represent an exception in that fixed allozyme differences were found between conspecific populations (Costa et al 1997). The alternative view that several distinct taxa were involved was later supported by DNA sequence analysis .…”