In understanding biodiversity, taxonomy and systematics work together, although the two terms are often confused. The objective of systematics is to understand the natural mechanisms responsible for the biodiversity, while the task of taxonomy is to set up a useful classification of the organisms concerned. The Triatominae (Hemiptera, Reduviidae) are the vectors of Chagas disease. Their classification faces frequent divergence between the modern concepts of systematics and the traditional, morphologically-based, classification. This chapter revises the main concepts of species in general, and their application to the Triatominae. We summarize the current classification of the vectors of Chagas disease, and offer ways in which the main species concepts might be usefully reviewed.

Publisher Summary Control of Triatominae (Hemiptera, Reduviidae) is a primary component of strategies to halt the transmission of Chagas disease, with serological screening of blood donors to reduce the likelihood of transmission through infected blood transfusions. In the early 1990s, an estimated 80% of Chagas disease cases were attributed to transmission from triatomine vectors. Since 1991, a series of multinational initiatives have focused on elimination of the domestic vector populations throughout the endemic areas of Latin America. Largely as a result of these initiatives, transmission rates have been steadily reduced, with corresponding reductions in infection prevalence. Current estimates suggest that around 7 million people are infected, down from the 1984 estimate of 24 million; annual transmission rates are probably fewer than 50,000 new cases per year. The geographical distribution of domestic vector populations has been drastically reduced, especially Triatoma infestans in Southern Cone countries and Rhodnius prolixus in Central America. Uruguay, Chile, and Brazil, together with several provinces and departments of Argentina and Paraguay, have been formally declared free of transmission due to T. infestans, and Guatemala has recently been declared free of transmission due to R. prolixus. In addition, there has been steady progress in blood donor screening, with coverage now approaching 100% in most of the endemic countries.

Perhaps the greatest challenge for the classification of Triatominae is the lack of a unifying concept of species. To discuss some of the conflicts that arise from applying modern concepts to traditional classification, and to highlight some recurrent practices regarding the systematics of the subfamily, this chapter develops this discussion in parallel with the traditional and modern concepts of species. In understanding biodiversity, one must understand that taxonomy and systematics work together, although the two terms are often confused. Divergence between the modern concepts of systematics starts at the definition given to the taxa they wish to analyze: single individuals, reproductively isolated populations, populations, or agglomerations of populations. In the case of the Triatominae, these problems are also evident from the epidemiological requirement and the increasing wealth of data offering new insights to their evolution. These problems are compounded by evidence that the Triatominae represent a polyphyletic group—yet it would make no epidemiological sense to try to reclassify them in that light—and also by their evident capacity for phenetic drift that can give rise to morphological and morphometric variants that tempt yet more specific designations. Other problems arise from the lack of clear consensus on taxonomic concepts. Not only is the subfamily itself poorly defined, such that some predatory Reduviidae have been erroneously described as Triatominae, but there is no consistent concept of features meriting tribal or generic rank, and there is considerable divergence on concepts of species, subspecies, and species complexes. This chapter summarizes the current classification and offers ways in which these concepts might be usefully reviewed.

Classification of the Triatominae has become a complex balance between traditional approaches and a wide variety of evolutionary interpretations. On the one hand is the need for a stable classification of practical use for those involved in vector surveillance and control. On the other is the desire to adequately reflect evolutionary theory derived from a range of molecular, cytogenetic and morphometric comparisons, with additional complications raised by current interpretations of the subfamily as a recently derived polyphyletic assemblage. Here we review key aspects of triatomine systematics and evolution, to derive a pragmatic classification that seeks to build on traditional morphological concepts within the context of current evolutionary theories.

COMPARATIVE MORPHOMETRIC ANALYSIS of shape variation in the wings of different tsetse species reveals close accordance with the phylogenetics of these species indicated by DNA sequence analysis. In practice, the morphometric analysis is economical and simple to carry out, suggesting that this could become a useful surrogate or complementary tool for large-scale studies of tsetse population genetics, designed to identify discrete population targets amenable to local elimination.

T SETSE-FLIES OCCUR THROUGHOUT MOST of sub-Saharan Africa, over an area approaching 10 million km. They suck blood and transmit a range of trypanosome species, including those that cause human sleeping sickness, and others that are responsible for a fatal syndrome of anaemia and wasting in cattle known as ‘nagana’ (from a Zulu word meaning to be low or depressed in spirit). Not only does this limit the availability of meat and dairy products, it also curtails the availability of oxen or horses for transport and ploughing. This severely restricts agricultural production. Without oxen, only small areas of land can be tilled by hand, leaving communities vulnerable to food shortages, hunger, and even famine. Since the 1960s, the incidence of sleeping sickness has risen steadily, with epidemic outbreaks in several areas. The World Health Organization (WHO) now estimates that over 300 000 people are infected with African trypanosomiasis, and the UN Food and Agriculture Organization estimates that economic losses due to the livestock infections may reach around US$4.5 billion each year. Because African trypanosomes are able to present successive waves of different surface proteins (a process known as ‘antigenic variation’), it is unlikely that an effective vaccine can be developed. Treatment is possible, but relies largely on antiquated drugs such as melarsoprol, which is — loosely speaking — a mixture of arsenic and anti-freeze that will kill up to 10% of those treated (although all would succumb to the disease without treatment). There are other drugs with less severe side effects, and the WHO has now arranged that these can be provided free of charge to national treatment programmes. But it is a difficult task to find, diagnose, and treat all the patients who require such care. Recognizing the problems of tsetseborne trypanosomiasis, the heads of state and government of the 36 affected countries, meeting at the 2000 OAU summit in Togo, declared as priority the aim of ‘rendering Africa free of tsetse in the shortest time possible’. In response, the OAU (now the African Union) has set up a Pan-African initiative (known as AU-PATTEC) to promote and coordinate national and regional programmes to eliminate the problem of tsetse and trypanosomiasis. Several countries have already reflected this goal in their official poverty reduction strategy papers, developing or revitalizing their national programmes, and the African Development Bank is now providing a series of grants and loans through PATTEC to assist the first six countries (Ethiopia, Uganda, Kenya, Mali, Burkina Faso and Ghana) in their tsetse elimination programmes. Further grants are under discussion. Techniques to eliminate tsetse have been known since the eradication of Glossina palpalis from the Island of Principe in 1914, using a form of sticky traps carried by plantation workers. Today, a series of highly effective techniques is available, including an array of odour-baited traps and targets, sequential aerial spraying with ultra-low doses of biodegradable insecticides, and, where necessary, SIT — the use of sterilized male flies to reduce the already low reproductive rate of wild tsetse. The ‘proof-ofprinciple’ of this technological package was successfully demonstrated by eradication of tsetse (Glossina austeni) from the Island of Zanzibar during the 1990s. Zanzibar is now a nett exporter of meat and dairy produce, where previously it was a nett importer when tsetse and trypanosomiasis limited cattle and agricultural production. But this demonstration of the feasibility of tsetse elimination has been criticized, on the grounds that Zanzibar is a relatively small island whereas Africa is a rather large continent. So, the African Union, together with other organizations supporting the PATTEC initiative, is harnessing modern techniques of population genetics and geographic information systems (GIS) in order to find the ‘biological islands’ of tsetse distribution within the continent of Africa, so that these populations can be progressively targeted for elimination. The work is supported by the Leverhulme Trust in England, through a network currently involving research institutions in 19 African countries, the United Kingdom, France, and the United States. The article on page 132 of this issue presents the first study resulting from this new initiative. It is a comparison between gene sequencing and the developing science of morphometry as a means to differentiate tsetse populations. The techniques of geometric morphometry are statistically complex, but offer a very rapid way to screen large numbers of individuals (similar techniques are now used by the US immigration services to identify travellers by means of morphometric analysis of photographs taken when you present your passport). Those familiar with Greek mythology will perhaps recognize the concept of Procrustean analysis, through which shapes are compared by measuring the deformations required to superimpose one shape on another. (Procrustes was reputed to fit his victims into a bed — stretching them if they were too short, cutting their extremities if they were too long.) And although morphometrics relies on phenetic rather than genetic characters, the preliminary study reported here reveals strong congruence between the two, offering hope that the large-scale analysis required in preparation for effective tsetse elimination can be carried out quickly and at low cost. ❑

We present data on the molecular characterisation of strains of Trypanosoma rangeli isolated from naturally infected Rhodnius ecuadoriensis in Peru, from Rhodnius colombiensis, Rhodnius pallescens and Rhodnius prolixus in Colombia, and from Rhodnius pallescens in Panama. Strain characterisation involved a duplex PCR with S35/S36/KP1L primers. Mini-exon gene analysis was also carried out using TrINT-1/TrINT-2 oligonucleotides. kDNA and mini-exon amplification indicated dimorphism within both DNA sequences: (i) KP1, KP2 and KP3 or (ii) KP2 and KP3 products for kDNA, and 380bp or 340bp products for the mini-exon. All T. rangeli strains isolated from R. prolixus presented KP1, KP2 and KP3 products with the 340bp mini-exon product. By contrast, all T. rangeli strains isolated from R. ecuadoriensis, R. pallescens and R. colombiensis, presented profiles with KP2 and KP3 kDNA products and the 380bp mini-exon product. Combined with other studies, these results provide evidence of co-evolution of T. rangeli strains associated with different Rhodnius species groups east and west of the Andean mountains.

The Reduviidae (Assassin bugs) form one of the largest and morphologically most diverse families of Hemiptera, with well over 6500 recognised species of worldwide distribution (Maldonado Capriles, 1990; Schuh and Slater, 1995). They have been variously grouped into up to 32 subfamilies, of which 22 were recognised by Davis (1969), 21 by Putchkov and Putchkov (1985), 25 by Maldonado Capriles (1990), and 22 by Schuh and Slater (1995). Most are predators on other invertebrates, although the subfamily Triatominae is customarily deWned on the basis of a blood-sucking habit and associated morphological adaptations (Jeannel, 1919; Lent and Wygodzinsky, 1979; Usinger, 1943). Over 130 species of Triatominae are currently recognised, currently grouped into up to 19 genera and 6 tribes (Galvao et al., 2003) of which the Triatomini and Rhodniini are the most numerous and most epidemiologically signiWcant (Table 1). In general, the various subfamilies of the Reduviidae have been assumed to be monophyletic, although in the case of the Triatominae several arguments have been advanced to suggest that these blood-sucking forms may have diVerent origins within the predatory subfamilies, thus representing a polyphyletic or paraphyletic group (SchaVer, 2003). Evidence to support this idea has been drawn from several comparative sources including overt morphology and biogeography (SchoWeld, 1988; SchoWeld and Dolling, 1993), morphometric comparisons (e.g., Dujardin et al., 2000), comparative sensilla arrays (e.g., Catala, 1997), mitochondrial and ribosomal DNA sequence comparisons (e.g., Garcia, 1999; Garcia and Powell, 1998; Lyman et al., 1999; Monteiro et al., 2000; Marcilla et al., 2001; Stothard et al., 1998) and the presence of markedly diVerent antihaemostatic compounds in the saliva of Rhodniini and Triatomini (Ribeiro et al., 1998). In addition, since a degree of at least facultative haematophagy has arisen in a range of other Hemiptera it has been suggested that this may be a relatively simple evolutionary step from an otherwise predaceous habit, so that polyphyletic derivation of haematophagy may be expected within this group (SchoWeld, 2000). Nevertheless, the assumption of monophyly within the Triatominae has persisted—at least implicitly—in several revisions (e.g., Schuh and Slater, 1995), and also in some DNA sequence-based comparisons (e.g., Hypsa et al., 2002). Moreover, all arguments so far advanced to support a polyphyletic concept of the Triatominae have been based on comparisons within the subfamily itself rather than on comparisons with other Reduviidae. We therefore present here an analysis of currently available gene sequence data—16S ribosomal DNA (mitochondrial gene)—for species of Triatominae representing the tribes Rhodniini and Triatomini (as deWned by Lent and Wygodzinsky, 1979) together with representatives of other subfamilies of the Reduviidae.

Triatoma brasiliensis is the most important Chagas disease vector in the drier regions of the “Brazilian Caatinga”, colonizing both sylvatic and domestic environments, usually forming abundant colonies. Control trials using insecticides against domestic and peridomestic populations suggest that the T. brasiliensis has a high capacity to repopulate treated habitats from the neighboring sylvatic populations, making its elimination more complex. The aim of this work was to determine genetic variability among sylvatic, peridomestic and domestic populations of T. brasiliensis using head morphometry and random amplified polymorphic DNA (RAPD). Both morphometric analysis and RAPD patterns showed a separation between sylvatic and domestic populations, being the peridomestic ones between them. Based on this data, we suggest that there exists a flow between natural and artificial environments, being the peridomestic population mainly responsible for this interchange. It is possible that the peridomestic environment is maintaining the variability on the insects found on artificial habitats, which guarantee T. brasiliensis success on adaptation in both environments and also increase the risk of introduction of new Trypanosoma cruzi strains in the domestic cycle of Chagas disease in this region.

Sixty-six T. rangeli strains isolated between 1983 and 2004 from R. ecuadoriensis, R. colombiensis, R. pallescens and R. prolixus were ordered into two primary lineages, based on kDNA and mini-exon gene amplification, and each lineage was associated with different Rhodnius species-groups. All strains isolated from R. ecuadoriensis, R. colombiensis and R. pallescens presented the characteristic T. rangeli KP1(-) molecular profile whilst strains isolated from R. prolixus or R. neglectus presented the T. rangeli KP1(+) molecular profile. There thus appears to be a consistent association of T. rangeli KP1(+) with Rhodnius species from the prolixus group (represented by prolixus and neglectus) and a similarly consistent association of T rangeli KP1(-) with Rhodnius species from the pallescens group (pallescens, colombiensis and ecuadoriensis), suggesting a degree of co-evolution between vector and parasite.

This chapter discusses the taxonomy, distribution, morphology, biological development, population dynamics, dispersal, evolution and population genetics of Triatominae.

Eye colour of Triatoma infestans is controlled at a single autosomal locus, with black-eye as the dominant gene and red-eye as the recessive. Inheritance of these characters follows a classical Mendelian system, enabling eye colour to be used as a marker for studies of mating frequency. We found no significant differences in oviposition rates and egg hatching rates irrespective of parental phenotypes. Different mating schedules between red-eye and black-eye parents showed that eye colour did not affect mating competence. Females mated with a single male or with different males together or in succession produced similar numbers of fertile eggs, with the eye colour of the offspring reflecting exposure to the different males. We conclude that although a single mating can provide sufficient sperm for the whole reproductive life of the female, multiple matings can result in balanced assortative sperm usage from the spermatheca.

Discovered in 1909, Chagas disease was progressively shown to be widespread throughout Latin America, affecting millions of rural people with a high impact on morbidity and mortality. With no vaccine or specific treatment available for large-scale public health interventions, the main control strategy relies on prevention of transmission, principally by eliminating the domestic insect vectors and control of transmission by blood transfusion. Vector control activities began in the 1940s, initially by means of housing improvement and then through insecticide spraying following successful field trials in Brazil (Bambui Research Centre), with similar results soon reproduced in São Paulo, Argentina, Venezuela and Chile. But national control programmes only began to be implemented after the 1970s, when technical questions were overcome and the scientific demonstration of the high social impact of Chagas disease was used to encourage political determination in favour of national campaigns (mainly in Brazil). Similarly, large-scale screening of infected blood donors in Latin America only began in the 1980s following the emergence of AIDS. By the end of the last century it became clear that continuous control in contiguous endemic areas could lead to the elimination of the most highly domestic vector populations - especially Triatoma infestans and Rhodnius prolixus - as well as substantial reductions of other widespread species such as T. brasiliensis, T. sordida, and T. dimidiata, leading in turn to interruption of disease transmission to rural people. The social impact of Chagas disease control can now be readily demonstrated by the disappearance of acute cases and of new infections in younger age groups, as well as progressive reductions of mortality and morbidity rates in controlled areas. In economic terms, the cost-benefit relationship between intervention (insecticide spraying, serology in blood banks) and the reduction of Chagas disease (in terms of medical and social care and improved productivity) is highly positive. Effective control of Chagas disease is now seen as an attainable goal that depends primarily on maintaining political will, so that the major constraints involve problems associated with the decentralisation of public health services and the progressive political disinterest in Chagas disease. Counterbalancing this are the political and technical cooperation strategies such as the "Southern Cone Initiative" launched in 1991. This international approach, coordinated by PAHO, has been highly successful, already reaching elimination of Chagas disease transmission in Uruguay, Chile, and large parts of Brazil and Argentina. The Southern Cone Initiative also helped to stimulate control campaigns in other countries of the region (Paraguay, Bolivia, Peru) which have also reached tangible regional successes. This model of international activity has been shown to be feasible and effective, with similar initiatives developed since 1997 in the Andean Region and in Central America. At present, Mexico and the Amazon Region remain as the next major challenges. With consolidation of operational programmes in all endemic countries, the future focus will be on epidemiological surveillance and care of those people already infected. In political terms, the control of Chagas disease in Latin America can be considered, so far, as a victory for international scientific cooperation, but will require continuing political commitment for sustained success.

In the absence of a fossil record, theories relating to the evolution of protozoa have, for most of the twentieth century, been based on morphological and life cycle data despite their known limitations. However, recent advances in molecular methodology, notably the wide availability of accurate, automated DNA sequencing, have made it possible to deduce the evolutionary relationships of extant species from their genes. This paper focuses on new findings concerning the evolution of the Trypanosomatidae, based on the ever-expanding body of molecular data now available. Classically, the evolution of digenetic parasitism in kinetoplastids has centred around two opposing theories--invertebrate first or vertebrate first--depending on which was the original host of the monogenetic parasite. However, data supporting a close phylogenetic relationship between genera of monogenetic insect parasites and digenetic vertebrate parasites challenge the simplicity of these hypotheses and suggest that the transition may not have been a major evolutionary barrier. The implications of these observations for the evolution of parasitism within the group are discussed. Phylogenetic analysis of a diverse selection of trypanosomatid species suggests that the genus Trypanosoma is monophyletic and that the human parasites, T. brucei, T. cruzi and Leishmania spp., have fundamentally different patterns of evolution. T. brucei clusters with mammalian trypanosomes of African origin, suggesting an evolutionary history confined to Africa. T. cruzi shows association with trypanosomes from bats, T. rangeli, and trypanosomes from a range of South American mammals and an Australian kangaroo. The origins of most parasites within this clade lie in South America and Australia, suggesting an ancient southern super-continent origin for T. cruzi, possibly in marsupials. The divergence between the Leishmania and Trypanosoma lineages is also ancient. The topology of Leishmania phylogenies suggests an independent transition to digenetic parasitism, a neotropical origin and an early tertiary radiation of the parasite.

The surface hydrocarbons of the blood-sucking insect, Rhodnius prolixus, a major Chagas disease vector in Venezuela, Colombia and Central America, were characterized by capillary gas chromatography coupled to mass spectrometry (CGC-MS). A total of 54 single or multicomponent peaks of saturated, straight-chain and methyl-branched hydrocarbons were identified. Major n-alkanes were n-C27, n-C29, n-C31 and n-C33 hydrocarbons. In the branched fraction, methyl groups were at positions 3, 5, 7, 11, 13, 15 and 17- for monomethyl isomers, and separated by three or five methylene groups for the trimethyl or tetramethyl derivatives. For the higher molecular weight components of 37, 39 and 41 atoms in the carbon skeleton, the di-, tri- and tetramethyl branches were usually separated by three or five, and sometimes 7, 11 or 13, methylene groups. The internal hydrocarbon pool contained larger amounts of the higher molecular weight methyl-branched components. Qualitative differences among epicuticular and internal hydrocarbon compositions were detected, both in adult and nymphal stages. No significant sexual dimorphism was detected, but a significant shift in the major n-alkane components was evident from the nymphal to the adult stage, differing also in the relative amounts of the higher molecular weight methyl-branched chains. Comparison of the hydrocarbon components to that of other Chagas disease vectors is discussed.

Quantitative analysis of morphological characters of the head was used to reconstruct the evolutionary history of the tropicopolitan bug Triatoma rubrofasciata (De Geer) (Hemiptera: Reduviidae) and seven species of Old World Triatoma . Multivariate analysis demonstrates that T. rubrofasciata and the Old World species have a high degree of similarity with Nearctic Triatoma species, particularly T. rubida (Uhler). We interpret this to imply a common ancestry for these groups. Dissemination of T. rubrofasciata and subsequent derivation of the Old World species of Triatoma is deduced to have occurred over a period of not more than 350 years.

The nucleotide sequences of the rDNA second internal transcribed spacer (ITS-2) of 31 populations of 12 and 3 species of the two main Triatominae tribes Triatomini and Rhodniini, including the most important Chagas disease vectors, were obtained. Sequence comparisons and parsimony, distance, and maximum-likelihood analyses indicate that ITS-2 is a useful marker for resolving supraspecific, specific, subspecific, and even sometimes population-level relationships in Triatominae. Results were markedly different between species of Triatomini and Rhodniini, suggesting polyphyly. Phylogenetic trees support an old divergence between South American and North-Central American Triatomini and query the validity of some genera (Dipetalogaster, Psammolestes). The very low sequence variation between species of the phyllosoma complex suggests that subspecific ranking would be more appropriate. Triatoma dimidiata proves to be a clearly differentiated species, with several populations evidencing a clinal variation along a north-south axis and a population from Yucatan showing differences consistent with specific status.