Effect of host plant chemistry on genetic differentiation and reduction of gene flow among Anastrepha fraterculus (Diptera: Tephritidae) populations exploiting sympatric, synchronic hosts.

Herbivore host specialization includes changes in behavior, driven by locally induced adaptations to specific plants. These adaptations often result in sexual isolation that can be gauged through detection of reduced gene flow between host associated populations. Hypothetically, reduced gene flow can be mediated both by differential response to specific plant kairomones and by the influence of larval diet on some adult traits such as pheromone composition. These hypotheses could serve as a model to explain rapid radiation of phytophagous tephritid fruit flies, a group that includes several complexes of cryptic species. The South American Fruit Fly Anastrepha fraterculus (Wiedemann) is a complex of at least seven cryptic species among which pheromone mediated sexual isolation resulted in rapid differentiation. Cryptic species also exhibit differences in host affiliation. In search of a model explaining rapid radiation in this group, we studied host plant chemical composition and genetic structure of three host associated sympatric populations of A. fraterculus. Chemical composition among host plant fruit varied widely both for nutrient and potentially toxic secondary metabolite content. Adaptation to plant chemistry appears to have produced population differentiation. We found host mediated differentiation to be stronger between populations exploiting sympatric synchronic hosts differing in chemical composition, than between populations that exploit hosts that fruit in succession. Gene flow among such host associated populations was extremely low. We propose as a working hypothesis for future research, that for those differences to persist over time, isolating mechanisms such as male produced sex pheromones and female preferences resulting from adaptation to different larval diets should evolve.

Phylogeographic studies on natural populations of the South American fruit fly, Anastrepha fraterculus (Diptera: Tephritidae).

Anastrepha fraterculus is an important pest of commercial fruits in South America. The variability observed for morphological and behavioural traits as well as genetic markers suggests that A. fraterculus represents a complex of synmorphic species rather than a single biological species. We studied the correlation between geographical distribution and genetic variation in natural populations from Argentina and south Brazil. Fragments of the mitochondrial gene COII were sequenced in 28 individuals. The matrix of aligned sequences was phylogenetically analysed by parsimony, yielding a cladogram of haplotypes. Based on Templeton's nested method, no clade showed any geographic pattern for the gene COII, indicating lack of significant association between haplotypic variability and geographic distribution. The analysis of nucleotide substitution distances by Neighbour-Joining algorithm showed that geographically distant populations exhibit low genetic distances. The corresponding trees clustered the populations without showing any geographic pattern. This result suggests that the populations studied are not reproductively isolated.

Dispersive flight and house invasion by Triatoma guasayana and Triatoma sordida in Argentina

Flight activity and invasion of houses by Triatoma sordida and T. guasayana were studied in the Province of Santiago del Estero, Argentina. Spontaneous findings of both species in houses were recorded from 1982 to 1989. Light trap collections were performed in 1982, 1983 and 1984, at the woods surrounding the settlements of Amamá (43 houses) and Trinidad (19 houses). Most of the 101 triatomines collected, were unfed and negative for Trypanosoma cruzi. T. guasayana predominated over T. sordida, and both appeared on the lighted screens between 19-31 min (mean 24) after dusk and the catch time was 30-45 min. Although entomological evaluation of 41 houses at Amamá performed in September 1985, just before insecticidal spraying, showed that Triatoma infestans predominated, adults of T. guasayana were collected in sleeping places, in 7 houses (17%). Most triatomines invading houses from then up to 1990 were flying T. guasayana (20/27) and females outnumbered males. Three non infected T. guasayana females were fed on man and two T. guasayana males positive for "T. cruzi like" trypanosomes were unfed. Therefore, visiting hungry adults could transmit T. cruzi to people and introduce wild parasites to the domestic cycle. T. guasayana stands as the main potential substitute of T. infestans in the studied area, and it might play there the same role as T. sordida in Brazil

A new host of Trypanosoma cruzi from Jujuy, Argentina: octodontomys gliroides (Gervais & D'Orbigny, 1844) (Rodentia, Octodontidae)

To identify wild hosts of Trypanosoma cruzi, surveys were conducted in the subandean valleys of Jujuy Province, Argentina, between June 1986 and March 1987. Seventy two mammals from 13 different species were examined by xenodiagnosis. Fifty two of them were mostly roedents trapped at the localities of Maimará, León and Tilcara, and the remainder had been kept in captivity at the Estación Biológica Experimental, in Jujuy. Trypanosoma cruzi infection was detected only in 2 Octodontomys gliroides (2 pos./8 exam. 25%) from all 72 examined mammals. Isolates were called Octodontomys Argentina 1 and 2 (OA1 and OA2). Both infected animals were caught at the archaelogical ruin of Pucará, at Tilcara. Repeated searches for triatomines in the ruin itself and in neighbour houses rendered negative results. Groups of mice inoculated with either OA1 or OA2 isolates became infected between 7 (OA1) to 12 days (OA2) postinoculation PI. Parasitemia peaks were observed between day 12th - 14th PI. Scarce amastigote nests were found in myocardium and skeletal muscle. Mortality was observed only for mice inoculated with OA1. Isoenzyme patterns of OA1 and OA2 were identical to one found in dogs and slightly different from that of human parasites in Argentina. Bones from Octodontomys sp., were recently found in a cave, dated 10200-8600 BC, in Pumamarca, near Tilcara, Jujuy. There are evidences that O. gliroides cohabited with man in ancient times and was associated to the domestic cycle of T. cruzi transmission, playing a role like that of domestic cavies. in Bolivia

Dynamics of transmission of Trypanosoma cruzi in a rural area of Argentina: III. Persistence of T.cruzi parasitemia among canine reservoirs in a two-year follow-up

Foi realizada em 1984 uma nova pesquisa epidemiológica dos cäes domésticos e seguimento dos indivíduos que apresentaram parasitemia dois anos antes a fim de compreender a relaçäo entre a parasitemia e a idade dos cäes, empregando para isso técnicas sorológicas e xenodiagnóstico. A persistência da parasitemia foi independente ou pouco relacionada à idade, confirmando assim o padräo observado em 1982. Da mesma maneira, nos cäes soropositivos näo se registrou nenhuma diminuiçäo significativa com respeito a idade em: a) a probabilidade de descobrir parasitas por meio de um seguimento durante 2 anos; b) sua capacidade de infecçäo para a ninfas de 3ª e 4ª fase de T. infestans, medido pela porcentagem de barbeiros infectados que se observou em cada um dos xenodiagnósticos dos cäes. A capacidade infectante dos cäes soropositivos foi aproximadamente constante ao longo da vida, e significativamente maior que a registrada para as crianças no presente estudo, e para os agrupamentos humanos pesquisados por outros investigadores. Assim sendo e considerando as altas freqüências de alimentaçäo no cäo que säo observados nas populaçöes pelo T. infestans, espera-se que o cäo contribua para o total de barbeiros infectados existentes nas áreas rurais da Argentina. Esta característica deveria ser suficiente para incriminar definitivamente os reservatórios caninos como um fator de risco para as pessoas residentes na mesma casa. A alta intensidade da parasitemia registrada entre os cäes na presente pesquisa poderia estar relacionada com a acentuada desnutriçäo característica dos cäes nas áreas rurais pobres da Argentina, o que poderia afetar a capacidade do hospedeiro para controlar a infecçäo