Memórias do Instituto Oswaldo Cruz Fundação Oswaldo Cruz, Fiocruz ISSN: 1678-8060 EISSN: 1678-8060 Vol. 90, Num. 3, 1995, pp. 325-328

Ecology of Triatoma rubrovaria (Hemiptera, Triatominae) in Wild and Peridomestic Environments of Uruguay

Roberto Salvatella, Raquel Rosa, Yester Basmadjian, Andres Puime, Luis Calegari, Jorge Guerrero, Maria Martinez, Gabriela Mendaro, Daniel Briano*, Carlos Montero**, Cristina Wisnivesky- Colli***

Departamento de Pamsitologia/Unidad de Biologia Parasitaria, Instituto de Higiene, Universidad de la Republica, Av. A. Navarro 3051, CP 11600, Montevideo, Uruguay *Departamento de Higiene, Municipalidad de Rivera **Departamento de Higiene, Municipalidad de Artigas, Uruguay ***Unidad de Ecologia de Reservorios y Vectores de Parasitos, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina

Code Number: OC95064
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Key words: Triatoma rubrovaria - triatomines - Uruguay - ecology

Triatoma rubrovaria (Blanchard) (Hemiptera, Reduviidae) was first described as Conorhinus rubrovarius in 1843, from specimens collected at Maldonado, Uruguay (Lent 1942). Its distribution covers parts of northeastern Argentine, Southern Brazil and Uruguay (Lent & Wygodzinsk 1979) where it is often found amongst outcorps of rocks (pedregales). In Uruguay, T. rubrovaria sustains the enzootic cycle of Trypanosoma cruzi (Salvatella 1986) and is commonly found in the peridomestic habitats, wherever pedregales are close to human habitations and/or people use rocks 10 construct fences. Moreover recent observations from Rio Grande do Sul (Silveira et al. 1984) and the Northern Departaments of Rivera and Paligas in Uruguay, (Salvatella et al. 1991) detected indoor colonies in houses of different construction types. T. rubrovaria may therefore assume greater importance in domestic transmission of T. cruzi, especially where the main domestic vector, T. infestans has been controlled by insecticide spraying.

This paper describes the habitat, espacial distribution and population structure of wild and peridomestic populations of T. rubrovaria from Northern Uruguay.

MATERIALS AND METHODS

Two rural sites, Las Piedras and La Bolsa located in the Departament of Artigas, near the Brazilian border were chosen for this study (Fig. 1). Criteria selection were: (a) frequent presence of T. rubrovaria populations and (b) contrasting features of the two areas: Las Piedras represented a typical wild habitat and La Bolsa met the conditions promoting peridomestic invasion of bugs from nearby rocky outcrops.

The semicircular sampling area was divided in seven or eight triangular sectors of 200x100m each, that were further subdivided every 50m. In Las Piedras, the landscape of basaltic outcrops scattered in the prairie was fairly homogeneous and the sampling area was centered on an elevated point (Fig. 2). In La Bolsa, the centre was a house surrounded by a complex peridomestic area with several outdoor premises: storeroom, stone fenced corrals, chicken coop. Neighbouring dwellings were also included in the sampling.

At La Bolsa, the triangular sectoors were sequentialy examined in October and November 1990, January, March, May, June, October and November 1991. In Las Piedras, observations were made on the same dates, except for October 1991 when the area was inaccessible due to climatic conditions.

All ecotopes suitable for T. rubrovaria were first recorded on a diagram, and then thoroughly examined. Pedregales were dismantled and peridomestic structures and dwellings sampled by timed manual collection (Wisnivesky-Colli et al. 1987).

Fig. 1: A - Map of Umguay, Department of Artigas in dotted lines. B - Area of the Depaxeffanent of Artigas with location of study areas: Las Piedms and La Bolsa.

Fig.2: scheme of sampling seetom at Las Piedms, wild natural environment. Natural stone grounds are drawn: white infested; black non infested.

Fig. 3: scheme of sampling sectors at La Bolsa, rural area with peridomestic environment. D: domiciles. C: stone yards. M: stone walls. G: henhouses. The rest are stonegrounds (untouched or modified) and piled stones.

Piedras - A total of 58 pedregales suitable to shelter T. rubrovaria were identified in the seven sections examined and 84% were colonized (Table I). Suitable ecotopes were those made up by overlapping flat stones on dry soil. Those sectors examined in May and June had few pedregales, but all harboured triatomines.

At total 1063 T. rubrovaria was collected of which 978 (92%) were nymphs (Table I). Abundance varied by season, eaking in October-November (spring). Throughout the year, more than 60% of the population was made up by third, fourlh and fifth instar nymphs. The latter predominated in winter samples. Adults were found from October to March, males appeared before but females disappeared later.

Animals found with the T. rubrovaria colonies were as follows: vertebrates: Homonora uruguayensis (Vaz-Ferreira & Sierra) gekonid lizard (in 32 ecotopes, 65% of total colonized pedregales), Tupinambis teguixin (L.) iguana (in four ecotopes, 8% of the total), Leptotyphlops munosi Orejas-Miranda apodous saurian ( in two ecotopes, 4% of the total), Leptodactylus mistac- (Cope) frog (in one ecotope, 2% of the total), Didelphis albiventris (Temminck) opossum (in one ecotope, 2% of total), Tropidurus sp. iguana (in one ecotope, 2% of the total); invertebrates: Blaptica dubia (Serville) cockroach (in 29 ecotopes, 59% of the total), Grillus sp. cricket (in nine ecotopes, 18% of total), Zelurus sp. predatory bug (in three ecotopes, 6% of total), Triatoma circummaculata (Stal, 1859) tfia- tomine, (in three ecotopes, 6% of the total), termite (in two ecotopes, 4% of the total). There were also Bothriurus bonaeretnsis (Koch) scorpion, Gramostola sp. spider, butterfly larva and miriapod, each one of those in one ecotope.

La Bolsa - Habitat heterogeneity was the principal feature of the peridomestic sampling area at La Bolsa (Fig.3). Examined ecotopes included: natural stonegrounds (pedregales), either untouched or modified by stone extraction, stone walls, stone fences of yards, henhouses, piled bricks, storerooms and houses.

A total of 67 ecotopes suitable to shelter T. rubrovaria was identified in the eight sections examined, and 32 were colonized (Table II) Searching of 11 man made structures, excluding yards, rendered three T. rubrovaria nymphs found in two henhouses located close to stone walls.

A total of 291 bugs was captured of which, 91% were nymphs. Adults were found only in October and November; eight males in 1990 and nine males and five females in 1991. Instar distribution of bugs in pedregales differed from those at Las Piedras, frequent some instars were about and there was not a progressive sequence of stages. Table II shows the proportion of different ecotopes that were infested, as well as the median number and range of T. rubrovaria bugs found in each one. Stone walls and yards were the most heavily infested.

Animals cohabiting with T. rubrovaria in pedregales at La Bolsa were as follows: vertebrates: H. uruguayensis (in eight ecotopes, 25% of the total), chicken (in five ecotopes, 16% of the total), Didelphis albiventris opossum (in two ecotopes, 6% of total), cricetid rodents (in two ecotopes, 6% of the total); invertebrates: B. dubia cockroach (in 18 ecotopes, 56% of the total), Strophocheilus sp. terrestrial snail (in six ecotopes, 19% of total), Lycosa raptoria (Walkenaer) spider (in five ecotopes, 16% of total), Gramostola mollicoma (Ausserer) spider (in two ecotopes, 6% of total), Segestria ruficeps Guerin spider, together with butterfly larva, termite and mirapod, each one of those in one ecotope. As in Las Piedras, the lizard H. uruguayensis and the cockroach B. dubia predominated, but overall were fewer wild associated vertebrates.

TABLE I

Colonized ecotopes and Triatoma rubrovaria bugs collected in natural stonegrounds at Las Piedms, Department of Afligas, Uruguay (October 1990-November 1991)

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Date   Section  A^a  Nymphs     Adults      Adults
                              M        F    Total       Total
---------------------------------------------------------------
Oct. 90    A    8/8    469    42       9      51         520
Nov. 90    B    10/13   81    4        4      8          89
Jan. 91    C    10/11   88    1        2      3          91
Mar. 91    D    6/6     34    -        2      2          36
May 91     E    2/2     24    -        -      -          24
Jun. 91    F    4/4    133    -                          133
Nov. 91    H    9/14   149    9        12     21         170
---------------------------------------------------------------
Total      -    49/58  978    56       29     85        1063
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TABLE 11

Infested ecotopes and median density of Triatoma rubrovaria in La Bolsa, Depaflment of Artigas, Uruguay (October 1990- November 1991)

----------------------------------------------------------------

                           No.       No.          Median bug
                         examined  positive (%)    density
                                                   (range)
-----------------------------------------------------------------
Stone walls and stone yards     8      7 (88)       19 (8-33)
Natural altered stonegrounds    8      3 (38)       3(1-9)
Stone heaps                     38     18 (47)      6 (1-29)
Houses and peridomestic 
premises                        11     2 (18)       2 (2)
Natural stonegrounds (untouched) 2     2 (100)      15 (15)
-----------------------------------------------------------------
Total                           67     32 (48)      6 (1-33)
-----------------------------------------------------------------

Las Piedras represents the natural habitat for T. rubrovaria where big colonies develop in the extense pedregales of the prairie, especially in those located at the most elevated points. Suitability of this environment is shown by the high proportion of colonized ecotopes. Highest relative abundance was found in those pedregales formed by overlapping flat stones on dry soil that made up a laberinthic structure suitable to shelter vertebrates, including small mammals.

T. rubrovaria colonies showed the typical instar distribution already reported for other wild triatomine species, being predominantly immature stages (Forattini et al. 1977, Wisnivesky- Colli 1993). Abundance was strongly correlated with climatic conditions, as reported for other silvatic triatomines (Rabinovich 1985). First instar nymphs were present all year around, although numbers increased in spring and summer. However adults were not collected from April to October and those few nymphs found in winter could be insects that hatched during late summer and experienced slower growth during the following winter. In the cold season fifth instar nymphs predominated, probably due to the higher resistance of older nymphs to adverse environmental conditions (Salvatella et al. unpublished data). Males appeared earlier than females, although females seemed to live longer.

In the peridomestic environment of La Bolsa, T. rubrovaria colonized stone walls and stone fences. Colonized ecotopes were always those close to houses. Comparison of colony pattems between La Bolsa and Las Piedras suggest that human activity affects the development of T. rubrovaria, for example by extracting stones from natural pedregales by burning and clearing the fields, by planting trees, by piling up rubbish, and by raising domestic animals that may displace wild vertebrates. Peridomestic colonies showed an irregular instar distribution but the overall insect collection was smaller than in Las Piedras, in spite of the presence of abundant local food sources. In January 1991, only four bugs were caught in natural stonegrounds (sector C); these showed the characteristic pattern of suitable ecotopes but were shaded by cultivated Eucaliptussoces.

Association of T. rubrovaria with the geckonid H. uruguayensis and the cockroach B. dubia was common in both wild and peridomestic environments. This strongly suggested that those animals could have a trophic relationship with T. rubrovaria, a fact lately confirmed in our laboratory (Salvatella et al. unpublished data).

REFERENCES

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Copyright 1995 Fundacao Oswaldo Cruz

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