Medical and Veterinary Entomology (1988) 2,401-404

SHORT COMMUNICATION

Dispersal flight by Triatoma infestans in an arid area of Argentina

NICOLAS* SCHWEIGMANN, s. VALLVE,* 0. MUSCIO,* M. GHILLINI, A. ALBERT1 and C. WISNIVESKY-COLLI Laboratory of Parasite Ecology, Biology Department, University of Buenos Aires and *CEPAVE, La Plata, Argentina

Key words. Triatorna infestans, Reduviidae, dispersal, flight, Argentina.

Triatoma infestam (Klug) (Hemiptera: Re- duviidae) is the most important domestic vec- tor of Trypanosoma cruzi Chagas (causative agent of Chagas’ disease) in Argentina and neighbouring countries. In these areas, disper- Five flights by T.infestans have an important influence in the epidemiology and transmission of Chagas’ disease.

Field and laboratory studies show that adult T.infestuns are more likely to initiate flight when starved for 2 or more weeks (Lehane & Schofield, 1981, 1982). Mark-release- recapture experiments in Brazil and Argentina using laboratory-reared male bugs demon- strated an effective flight range of at least 200 m (Lehane & Schofield, 1981) and laboratory models also suggest that this would be the effective range of flying bugs in terms of dispersal from one house to another (Schofield & Matthews, 1985; J. Jedwab, 1987, unpub- lished report, University of Cambridge). In contrast, laboratory studies show that T.infes- tans can fly at speeds of around 1.5 m/s for up to 30 min (Lehane & Schofield, 1976; Ward & Baker, 1982), which implies a potential flight range of up to 2.7 km.

Although dispersive flight has been studied in natural environments for other triatomine species, especially the North American T.pro- tracta (Uhler) (Ekkens, 1981; Wood, 1950), there are no reports for wild T.infestans, except anecdotally by Bejarano (1967) and

Correspondence: Lic. N. Schweigmann, Labor- atorio de Ecologia de Parisitos, Departamento de Biologia, 4toPiso Pab.11, Facultad de Ciencias Exactas y Naturales, Ciudad Universitaria, Nutiez (C.P. 1428), Capital Federal, Buenos Aires, Argentina.

Viana & Carpintero (1977). We report here our first observations of flight by wild T.infes- tuns which suggest a flight range of to 2 km.

Our observations were made in the province of San Juan, Argentina. This is an arid region (SW type according to Koeppen climatic classi- fication, with mean annual rainfall 10&150 mm) and, although mean annual temperatures are around 18”C, the summer is very hot and temperatures can be elevated, even in winter and early spring (August, September), due to a hot wind (known as ‘Zonda’) from the north west. At the time of the Zonda, local inhabi- tants report that adult T.infestans bugs often fly into their houses, even in the provincial capital city. During the winter, when people unpack their warmer clothes, they often report adult and nymphal bugs found in wardrobes, suitcases, etc.

During January 1987 we collected one male and one female T.infestans, and one male T.eratyrusiformis Del Ponte, at the outer lights of a tourist hotel in the Quebrada de Huaco, about 188 km north from the capital city and 6 km from the village of Huaco. At the outer lights of another hotel near Vallecito, about 60 km east from the capital city, we found twenty- one dead T.infestans (15M, 6F) with twenty- three dead T.eratyrusiformis (11M, 12F) and one live male. Between 23.30 and 00.10 hours one further male T.infestans and three T.eraty- rusiformis ( lM, 2F) flew in towards these lights.

The Vallecito hotel is a two-storey building located on a hill; it had been sprayed with deltamethrin 2 months earlier, and we found no bugs in our search of the hotel rooms.

401

403 Nicola~ Schweigtnann et al.

However, in a storeroom on the outskirts of Vallecito village. about 1-5 km from the hotel. we collected 1532 T.infestam and one fifth- instar nymph of T. erar]L.rusiforini.s. This storeroom was the sleeping place of a dog and tu'o chickens. and bloodmeal analysis of thirty of the bugs (using the agar double-diffusion technique of Wisnivesky-Colli et a/ . , 1980) showed twenty-three ( 7 8 % ) feeds on chicken, six (19?) on dog and one on man.

Prompted by these observations. which sug- gested active flight of T.infesratis and T.erat!- rztr{formi.r attracted to light. we bet up a simple light trap near the Vallecito hotel. but hidden from i t b y a low hill (Fig. 1 ) . The trap

consisted of a vertical white cloth (1x2 m) illuminated by a portable 25 cm fluorescent light.

Between 21.25 and 01.45 hours we collected seven T.iiifestans at this trap (3M, 4F). All these bugs appeared to be unfed, i.e. without bloodmeals by external observation (Monte- negro, 1983) and by posterior dissection, and only one of them gave a positive result against antihuman antiserum. Four of the bugs were found to be infected with flagellates identified microscopically as T.cruzi. Two of the female bugs contained immature eggs.

T. eratyritsiformzis was not taken at the light- trap and we did not find bugs in nearby

Dispersal flight by T.infestans in Argentina 403

bird-nests or animal burrows. The region around Vallecito is dry and rocky, representing the type of ecotope normally associated with T.eratyrusiformis. Since we could not find colonies of this species in the area, we do not know how far the bugs taken at the hotel lights had flown. According to Lent & Wygodzinsky (1979), T. eratyrusiformis has previously been collected at lights and in peridomestic habitats.

In the case of T.infestans, unless there is an unknown sylvatic focus of this species in the area, the nearest source of bugs taken at the hotel lights and at our light trap would be houses in Vallecito itself, because there were no other habitations within 30 km of the area. This suggests that T. infestans disperse by flight over distances of at least 1.5-2 km (Fig. 1). All bugs were unfed, in agreement with laboratory studies showing that flight initiation in this species is associated with poor nutritional sta- tus (Lehane & Schofield, 1982). The flights occurred between sunset and midnight, on warm calm evenings, in accordance with observations of flight by Rhodnius prolixus Stal in Venezuela (Tonn et al., 1978) and by North American species such as T.protracta (e.g. Wood, 1950; Sjogren & Ryckman, 1966; Ekkens, 1981).

Many species of Triatominae have been reported flying to light (Lent & Wygodzinsky, 1979) although, as far as we are aware, this is the first confirmed report of such behaviour by wild T.infestans. However, taken with the many anecdotal reports of these bugs flying into houses, and the recent experimental and theoretical studies of bug flight, we interpret our observations to support the idea that active dispersal by T.infestuns can be an important factor in the primary colonization of houses and the recolonization of houses treated with insecticides (Schofield, 1985). The apparent flight range implied by our observations sug- gests that active dispersal may be even more important than previously suspected.

Acknowledgments

We are grateful to the Provincial government, the Secretaria de Salud Publica and Servicio Provincial de Chagas of San Juan Province for helping us in different ways including trans- portation to the field. Special thanks are given

to Isidro Atencio for his invaluable collabora- tion in field work and to Dr C. J. Schofield for revision of the manuscript. The figure was drawn by Mr Mario Capovia. This work was partly financed by the Secretaria de Ciencia y Tecnica, Argentina.

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Accepted 32 May 1988