CONICET | Buscador de Institutos y Recursos Humanos

One of the great purposes related to Triatoma infestans control, the main vector of Chagas disease in the Gran Chaco region, is to know the origin of reinfesting individuals found in domestic habitats after the chemical control actions carried out for its elimination. Among others, factors that hinder T. infestans control in this region are the recurrent houses reinfestation due to failures in coverage or in pyrethroids application, and the presence of reinfesting T. infestans with probable sylvatic origin. The peculiarity of individuals collected in sylvatic environments is that they are mostly melanic individuals with a darker appearance than the non-melanic forms commonly collected in (peri)domestic environments. In a previous study done in this area, there were no differences in wing size of domestic and sylvatic populations and 53% of post-intervention individuals were allocated to the sylvatic group. Here we analyze the potential origin of reinfestant T. infestans in 12 de Junio, an indigenous community from the Central Chaco in Paraguay, using a colorimetric quantification analysis. First, an entomological survey for searching domestic triatomines in (peri)domestic environments of all houses of the study area was conducted (prespraying period) before residual insecticide spraying campaign. Then an entomological follow-up was conducted between 3 and 12 months (postspraying period). The collection of sylvatic T. infestans was carried out around 12 de Junio locality. Color was quantified from image data of T. infestans females. We used the right side of connexivum using a homologous rectangle of 6 x 64 mm. We analyzed a total of 32 females from prespraying, 21 from postspraying and 10 from the sylvatic environment. The colorimetric analysis was performed using the software Image Color Summarizer 0.76. A K-means clustering analysis was used to define the number of colorimetric groups present in the prespraying and postspraying periods and in the sylvatic environment. The optimal number of clusters for all the data set was determined using the elbow and average silhouette methods. Results showed that elbow and average silhouette methods defined two colorimetric groups, melanic and non-melanic. All individuals from for the prespraying period (100%) were assigned to the non-melanic group, 58% of the individuals from the postraying period were assigned to the non-melanic group while only 40% of sylvatic individuals were assigned to this group. These results provide new evidence that sylvatic and domestic populations could be highly related to each other in the Paraguayan Chaco and that sylvatic T. infestans populations could be the source of new individuals in the processes of (peri)domestic reinfestations.