Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology
Hydrocarbons of Rhodnius prolixus, a Chagas disease vector
Introduction
Rhodnius prolixus (Hemiptera, Reduviidae, Triatominae) is the main vector of Chagas disease in Venezuela, Colombia and parts of Central America (Schofield, 2000). The Central American populations of R. prolixus appear to be derived from accidental transport from Venezuela, and they show fewer random amplified polymorphic DNA (RAPD) bands and a reduced size compared to their putative ancestral forms (Dujardin et al., 1998). As part of a larger project under the Latin American Network for Research on the Biology and Control of Triatominae (ECLAT), the aim of this study was to determine the hydrocarbon structure, composition, developmental changes, and sexual dimorphism in R. prolixus. Capillary gas chromatography (CGC) and mass spectrometry (MS) have proven to be useful in chemical taxonomy for the differentiation of various species of Anopheles (Carlson and Service, 1979, Milligan et al., 1986), tsetse flies (Nelson and Carlson, 1986), and different species of Triatominae (Juárez and Brenner, 1985, Juárez et al., in press), and these techniques are employed here. A long-term goal of this study is to determine the potential of these techniques to develop a biochemical marker useful for phylogenetic studies.
A further objective is related to biological control studies, where the complex biochemical interactions between microbial pathogens and the cuticular hydrocarbons of their insect hosts are yet to be fully understood. The fungus Beauveria bassiana has been proposed as a biological control agent against R. prolixus (Romaña and Fargues, 1992, Romaña, 1996). Various fungal strains have shown ability to degrade insect cuticular hydrocarbons, and the preferred alkane source was a hydrocarbon extract of Triatoma infestans, the major Chagas disease vector in Argentina (Napolitano and Juárez, 1997, Crespo et al., 2000, Juárez et al., in press). The characterization of R. prolixus hydrocarbons is a first step towards developing comparative studies on the biochemical mechanisms involved in the initial stages of fungal infection for this vector.
Section snippets
Insects
We analyzed epicuticular and internal hydrocarbons from adult males, females, and nymphs of Rhodnius prolixus. Insects were provided by Dr Jose Jurberg from a colony reared at FIOCRUZ, Rio de Janeiro, Brazil.
Hydrocarbon analysis
Cuticular hydrocarbons were extracted as previously described (Juárez and Brenner, 1986, Juárez and Blomquist, 1993). Individual insects, or pooled insects when required for mass spectrometry analyses, were washed with redistilled water to remove any water-soluble contaminants, transferred
Results
All the major hydrocarbon components of the epicuticular waxes and internal lipids of Rhodnius prolixus were identified by CGC-MS analysis (Table 1). A total of 54 components were identified, consisting of homologous series of n-alkanes, 3- and 5- methylalkanes, single components, and isomeric mixtures of monomethylalkanes, dimethylalkanes, trimethylalkanes, and tetramethylalkanes. Fig. 1 shows the GC profiles of Rhodnius prolixus hydrocarbons from the epicuticle of adult males and females (
Discussion
Studies on the epicuticular hydrocarbons of two Triatominae, Triatoma infestans and Triatoma mazzotti (Juárez and Blomquist, 1993), showed several qualitative differences between these species, mainly due to different positional isomers of some components. Studies on the developmental changes in cuticular hydrocarbon of T. infestans showed a marked shift between nymphs and adults, quite similar to that reported herein for R. prolixus, together with higher amounts of hydrocarbons present in the
Acknowledgements
This work was supported in part by the AVINA Foundation, Switzerland, and benefited from international collaboration through the ECLAT network. We thank Dr Jose Jurberg for providing the insects, and Mr Gustavo Calderón for help with the figures.
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