Migration and Gene Flow Among Domestic Populations of the Chagas Insect Vector Triatoma dimidiata (Hemiptera: Reduviidae) Detected by Microsatellite Loci

Abstract

Triatoma dimidiata (Latreille, 1811) is the most abundant and significant insect vector of the parasite Trypanosoma cruzi in Central America, and particularly in Guatemala. Tr. cruzi is the causative agent of Chagas disease, and successful disease control requires understanding the geographic distribution and degree of migration of vectors such as T. dimidiata that frequently re-infest houses within months following insecticide application. The population genetic structure of T. dimidiata collected from six villages in southern Guatemala was studied to gain insight into the migration patterns of the insects in this region where populations are largely domestic. This study provided insight into the likelihood of eliminating T. dimidiata by pesticide application as has been observed in some areas for other domestic triatomines such as Triatoma infestans. Genotypes of microsatellite loci for 178 insects from six villages were found to represent five genetic clusters using a Bayesian Markov Chain Monte Carlo method. Individual clusters were found in multiple villages, with multiple clusters in the same house. Although migration occurred, there was statistically significant genetic differentiation among villages (FR T = 0.05) and high genetic differentiation among houses within villages (FSR = 0.11). Relatedness of insects within houses varied from 0 to 0.25, i.e., from unrelated to half-sibs. The results suggest that T. dimidiata in southern Guatemala moves between houses and villages often enough that recolonization is likely, implying the use of insecticides alone is not sufficient for effective control of Chagas disease in this region and more sustainable solutions are required.

Keywords: Chagas disease; Triatoma dimidiata; dispersal; genetic diversity; vector control.

Fig. 1.

Map showing the location of the six villages in Jutiapa, Guatemala.

Fig. 2.

Similarity of the genetic variability of seven microsatellite loci in T. dimidiata from six villages in Jutiapa, Guatemala, based on allelic richness and Nei’s H_S.

Fig. 3.

Variability in average pairwise relatedness among houses with >2 insects (A–E,•) and for the 28–30 insects from each village (Village, ○). Values are ± SEM. Note values can be negative due to sampling error.

Fig. 4.

Linear regression (…….) showing that genetic differentiation between insects increases with geographical distance. Data are pairwise genetic distances among six villages (28–30 insects per village. Linear regression: ê = 0.0719 + 0.0165 * ln(distance); 95% confidence interval for slope [0.0061, 0.292]).

Fig. 5.

Distribution of five genetic clusters (indicated by colors) among villages, based on Bayesian MCMC simulation. Vertical black lines separate the six villages, indicated below the figure. White lines separate the houses. Each insect is represented by a thin vertical line partitioned into colored segments indicating one of K = 5 genetic clusters. For example, the first house in Calderas contained four insects from the green cluster, an orange–green–blue admixture, and an orange–purple admixture. Only houses with more than two insects are delineated; the remaining insects are pooled in the rightmost partition for each village.