Seasonality and Relative Abundance of Tabanidae (Diptera) Captured on Horses in the Pantanal, Brazil

Vol. 96(7): 917-923, October 2001

AntonioThadeu M Barros

Embrapa Pantanal, Rua 21 de Setembro 1880, 79320-900 Corumbá, MS, Brasil

Once a month, from June 1992 to May 1993, collections of tabanids on horse were conducted in the Nhecolândia, Pantanal State of Mato Grosso do Sul, Brazil. Tabanid catches using hand nets were conducted from sunrise to sunset at grassland and cerradão (dense savanna) habitats. A total of 3,442 tabanids from 21 species,12 genera, and 3 subfamilies were collected. Although species abundance varied seasonally depending on habitat, no habitat specificity was observed for the most abundant species. In the grassland, 1,625 (47.2%) tabanids belonging to 19 species were collected, while 1,817 (52.8%) tabanids from 17 species were caught in the cerradão. The number of tabanid species varied from 7 during winter (July/August) to 15 in the spring (October). Tabanus importunus (56%) was the most abundant species, followed by T. occidentalis (8.2%), and T. claripennis (8.1%). The tabanid peak, in October, coincided with the beginning of the rainy season. The population peak of most species, including those with higher vector potential, suggests that the rainy season can be considered as the period of potentially higher risk of mechanical transmission of pathogens by tabanids to horses in the region.

Key words: tabanid - horse fly - deer fly - ecology - Pantanal - Brazil

Tabanids are known worldwide as important mechanical vectors of virus, bacteria, protozoans, and helminths, which cause diseases in wild and domestic animals (Krinsky 1976, Foil 1989). Equine diseases prevalent in the Pantanal, such as trypanosomiasis (Franke et al. 1994, Silva et al. 1995) and equine infectious anemia (Silva 1997), have their agents mechanically transmitted by tabanids (Hawkins et al. 1976, Krinsky 1976, Foil et al. 1983). Despite the fact that studies on vector ecology are essential to understand, predict, and control insect-borne diseases, relatively few studies have been conducted on tabanids in Brazil. In fact, only in the Amazon region have such ecological studies been extensively conducted (Rafael & Charlwood 1980, Gorayeb 1993, 1999). In the Pantanal, there is a single more comprehensive study on tabanid ecology, based on trap collections (Barros & Foil 1999).

The purpose of this study was to identify the tabanid species which attack horses in the Pantanal, as well as to determine their seasonality and relative abundance in different habitats. The present study, based on tabanid captures on horses, complements some of the information previously reported for the region (Barros & Foil 1999).

MATERIALS AND METHODS

RESULTS

DISCUSSION

ACKNOWLEDGEMENTS

To Drs Lane Foil (Louisiana State University) and Larry Hribar (University of Florida) for help in establishing the initial reference collection, and to Drs GB Fairchild (in memoriam) and Inocêncio S Gorayeb (Museu Emílio Goeldi) for the taxonomic classification of the material. To Wibert Avellar, Waldomiro Lima e Silva, and Geraldo N do Nascimento for their assistance in field activities and to Valdete Sanchez and Cecília Baracat for technical assistance. To the staff of the Nhumirim ranch for logistic support.

REFERENCES

Fig. 1 | Fig. 2 | Fig. 3 | Table I | Table II

Fax: +55-67-231.1011. E-mail: thadeu@cpap.embrapa.br

Received 28 March 2001

Accepted 6 June 2001