First Finding of Melanic SylvaticTriatoma infestans(Hemiptera: Reduviidae) Colonies in the Argentine Chaco

Abstract

Triatoma infestans (Klug), the most important vector of Chagas disease in southern South America, is a highly domiciliated species with well-known sylvatic foci only in the Bolivian Andean valleys and in the Bolivian Chaco, where melanic insects designated as “dark morphs” were found. After the tentative identification of two melanic bugs collected from parrot nests in a forest reserve in the Argentine Chaco as T. infestans, we conducted an intensive search there using mouse-baited sticky traps in summer 2006 and 2007. Four live T. infestans bugs were collected in trees without parrot nests in 288 trap-nights, whereas no bug was collected from inside trees with active parrot nests in 51 trap-nights. To increase bug captures, hollow tree trunks that recently had had Amazona aestiva (Berlepsch) and Aratinga acuticaudata (Vieillot) parrot nests were treated with insecticide fumigant canisters exhibiting strong knockdown power. Four (22%) of 18 trees were positive for T. infestans with a dark phenotype. A fragment of the mitochondrial gene COI of 8 of the 14 triatomine bugs collected was successfully sequenced and confirmed as T. infestans. Most of the bugs were captured from Aspidosperma quebracho-blanco (Schlechter) hollow tree trunks harboring parrot nests. All of the T. infestans collected from the nearest house located at 10 km from the sylvatic foci displayed normal chromatic characters. The repeated finding of T. infestans in sylvatic habitats, albeit at very low density, shows that this species is capable of maintaining viable sylvatic foci in the absence of human hosts and immigration from domestic populations. These are the first confirmed findings of sylvatic T. infestans colonies in Argentina and of dark morphs in the Argentine Chaco.

Wild Triatoma infestans, a potential threat that needs to be monitored

“…They are found inside the trunks of emergent trees, in hollows occupied by blue-fronted parrots (Amazona aestiva). The very low T. cruzi infection rate detected in the dark morph (2.5%) supports its ornithophilic tendency , Ceballos et al 2009). The stage-structure pattern of the dark morph population is still unknown.…”

“…Wild T. infestans populations have also been found outside the Andes, in the lowlands of the Boreal Chaco (Noireau et al 1997). The existence of wild populations in the Chaco biogeographical region was later suspected in Paraguay (Yeo et al 2005) and confirmed in the Chaco province of Argentina (Ceballos et al 2009). Finally, sylvatic colonies of T. infestans were recently reported in the Metropolitan Region of Chile (Bacigalupo et al 2006).…”

Sylvatic foci of the Chagas disease vector Triatoma infestans in Chile: description of a new focus and challenges for control programs

“…These wild populations could also be derivatives of domestic insects recolonizing wild habitats (Noireau 2009). Another e�planation for the presence of T. infestans in central Chile is passive transport from Argentina, a country that has already proven the e�is-tence of wild foci of this species (Mazza & Schreiber 1938, Mazza 1943, Ceballos et al 2009), as previously suggested by wing morphometric analysis (Cristi 2001). The notion of sylvatic sites should be interpreted as geo- graphically restricted records, such as those registered in our study, which probably represent point occurrence data from more widespread populations (Noireau 2009).…”

“…This wide range of infection was suggested to be the result of different sources of their blood meal hosts, with the lower levels resulting from feeding mainly on birds -which are not susceptible to T. cruzi -and the higher levels resulting from feeding mostly on mammals' blood (Noireau et al 2000, Cortez et al 2006. In the first focus reported in the Argentine Chaco, all of the 14 T. infestans captured in trees were negative for T. cruzi using microscopic e�amina-tion, probably because they were mainly associated with birds (Ceballos et al 2009). …”

“…The first sylvatic population of T. infestans was reported in Cochabamba, Bolivia, inhabiting rock piles associated with wild guinea pigs (Torrico 1946). Other reports have shown T. infestans in Argentina (Mazza & Schreiber 1938, Mazza 1943, Ceballos et al 2009), Paraguay (Velasquez & González 1959) and Brazil (Barretto et al 1963) under rocks or trunks of fallen trees, in hollow trees, under bark, in shelters or burrows of marsupials and rodents and in bird nests occupied by owls, parrots or small rodents (Noireau et al 1997). Wild T. infestans has been found in an e�tended geographical region throughout Chaco and three Andean departments of Bolivia: Cochabamba, La Paz and Potosí (Noireau et al 1999, Cortez et al 2007.…”