SI Medical and Veterinary Entomology (1992) 6, 51-56 r’ Dispersive flight by Triatoma infesfans under natural climatic conditions in Argentina C. J. SCHOFIELD, M. J. LEHANE, P. McEWEN, S. S. CATALA” and D. E. GORLA” School of Biological Sciences, University of Wales, Bangor, Wales, U.K., and *Centro de Investigaciones Entomologicas, Universidad de Cordoba, Argentina Introduction Abstract. Male and female T. infestans were released on two consecutive nights in the salinasof Cordoba Province, Argentina, when air temperatures during the flying period averaged 28S”C. 136 males (43% of the total released) and 170 females (57%) flew on the first night, and 6 males (18%) and 7 females (27%) on the second. Of these, we recovered 23 males and 14 females within lOOm, and a further female within 200m, all from the first night’s release. The remainder appear to have flown more than 100m and possibly more than 200 m. In support of this conclusion 4 male and 5 female bugs were recovered in an abandoned brick house 550 m from the release point. Since the proportion of bugs apparently flying more than 200 m is considerably greater than that deduced from previous experiments at lower temperatures (Lehane & Schofield, 1981) it is possible that temperature influences not only the proportion of bugs flying but also the distance flown. Flight appears to be affected by wind speed. On the first night, when there was negligible wind, 43% of male and 57% of female bugs flew. On the second night, with winds gusting at 4-5 m/s, only 18% of the male and 27% of the female bugs flew. Key words. Triatoma infestans, flight, dispersal, wind-speed, Argentina. e Triatoma infestans Klug (Hemiptera: Reduviidae), the main vector of Chagas disease throughout the southern part of Latin America, can be controlled effectively i by house spraying with residual insecticides (Dias, 1987, 1988). Following such campaigns the capacity of this species for dispersive flight from untreated foci will have a , major influence on rates of house reinfestation (Schofield, 1985). Our understanding of dispersive flight is increasing and it is clear that flight initiation is associated with poor nutritional status of the bug and high ambient temperatures (Lehane & Schofield, 1981, 1982; Lehane et al., 1992; Williams & Schofield, 1985).Simulationmodels based on data from mark-release experiments under natural con- ditions in Argentina and Brazil, indicate an average effec- tive flight range for T.infestans of around 200m (Jedwab, 1987; Schofield & Matthews, 1985). However, wind tunnel experiments indicate that T.infestans can make sustained Correspondence: Dr M. J. Lehane, School of Biological Sciences, University of Wales, Bangor LL57 2UW, U.K. flights for lo-15 min at speeds of 1- 1.5 m/s, suggesting a flight range of at least 600-1350m (Lehane & Schofield, 1978), and recent light trap collections in Argentina lend support to this (Schweigmann et al., 1988). In an attempt to verify the typical flight range of T.infestans under natural conditions, and to gain further information about factors involved in flight initiation and dispersal, we report here data from mark-release experiments carried out on the salt flats (salinas) of central Argentina. During the course of this work we were also able to make some observations on the dispersive flight of T.sordida, the results of which are reported elsewhere (Schofield et al., 1991). Materials and Methods Two groups of adult T.infestans were used in this study, both originating from wild-caught females from the Province of Cordoba, Argentina. Group A (301 males and 366 females) were reared under semi-natural conditions in artificial chicken houses and insectaries in the Province of Cordoba; group B (120 males and 86 females) were reared 51