Mem Inst Oswaldo Cruz, Rio de Janeiro, 91(2) Mar/Apr 1996
Seasonality of Phaeotabanus fervens (Diptera: Tabanidae) in the Pantanal Region, Brazil
Centro de Pesquisa Agropecuária do Pantanal/EMBRAPA, Rua 21 de Setembro 1880, 79320-900 Corumbá, MS, Brasil
Phaeotabanus fervens (Linnaeus), 1758is a neotropical tabanid species distributed from Venezuela to Argentina (GB Fairchild 1971 Ed Mus Zool Univ São Paulo 28: 28-56). This horsefly is one of the few species reported biting exclusively on caimans (Caiman sclerops, Melanosuchus niger, Paleosuchus palpebrosus and Paleosuchus trigonatus) only on their head (F Medem 1981 Cespedesia 10: 123-191). Probably due to its host specificity very few data about this species are available. Caiman feeders such as Lepiselaga crassipes (F.), Phaeotabanus cajennensis (F.) andPhaeotabanus fervens (Medem loc. cit.) occur in the Pantanal region and unidentified general photographic records are available (H Palo Jr 1992 Pantanal Ed Cor/Ação 123 pp.).
The Center of Agricultural Research for Pantanal (CPAP/EMBRAPA), located in the Corumbá town near the Bolivian frontier at the western border of the Brazilian Pantanal, mantained some caimans (Caiman crocodilus yacare) for biological studies. On some occasions P. fervens could be frequently observed flying against window glasses around the caiman pools. These tabanids were basically seen only at these sites and despite the lack of feeding observations it seemed obvious that their presence was due to the caimans (the only host present except humans).
A few sporadic tries to capture tabanids using caimans as bait were carried out on a ranch 150 km from town but no individuals were caught. Also monthly surveys, carried out from 1992 to 1994 with canopy traps and horses, were unsuccessful for catching P. fervens in the same area. It is possible that the collections were conducted outside of the spatial or temporal distribution of the flies and/or the techniques used were not the most effective methods for this species.
In more than 300 observations, from 1988 to 1993, 77 P. fervens voucher specimens were caught manually or with sweep nets from the windows near the caiman pools at CPAP. It was verified that this species showed a very defined seasonal pattern, occurring from September to November, after the beginning of the rainy season. In Colombia, Medem (loc. cit.) found P. fervens from November to March during collections over five years, however, he gathered some specimens in September and October during an expedition to the Brazilian Amazon. In the Pantanal the population peak of P. fervens was generally observed in October (also in November) and none was seen in December. This distribution coincides with the peak of most tabanid species in the region.
Since other haematophagous flies are recorded as trypanosome vectors for crocodiles (CA Hoare 1929 Trans R Soc Trop Med Hyg 23: 39-56) and there is a high prevalence (46%) of Trypanosoma spp. infection in C. c. yacare from Pantanal (VLB Nunes, ET Oshiro, personal communication), it would be important to investigate a possible role played by tabanid species in trypanosome transmission to caimans.