Relationships between Microhabitat Characteristics and the Abundance of a Chagas Disease Vector, Rhodnius pallescens, in Central Panama

Abstract

Background: The sylvatic triatomine, Rhodnius pallescens, is the main vector of Chagas disease in Panama and resides in the locally abundant Attalea butyracea palm. However, triatomine abundance varies highly across palms, within and across land-use types. This may result from a difference in the quality of microhabitats offered by different palms. A firmer understanding of microenvironmental risk factors could inform sustainable environmental modification approaches to reducing Chagas disease prevalence in Latin America. While prior research has focused more on domiciliated species, such as R. prolixus, less is known about the influence of microenvironmental variation in the R. pallescens- A. butyracea system. This research aims to explore how individual palm “microhabitat” characteristics may influence triatomine infestation and microclimate fluctuations within and across palms in human-modified environments. Methods: 35 A. butyracea palms were sampled at three sites in central Panama. 24-hour fluctuations in temperature and RH within the palms were recorded using loggers placed at two different points in each tree. R. pallescens was sampled using live-bait traps. Microhabitat factors, such as tree height, new and dead leaves, connections with other trees and palms were counted and measured. Palms were ranked by their level of dead organic matter (DOM) on a semi-quantitative scale. Regression analyses were used to identify potential predictors of vector abundance and microclimate stability. Results: The most parsimonious model of R. pallescens relative abundance included total levels of dead organic matter on the palm (p < 0.001) and surrounding canopy cover at the point of the palm (p < 0.001) as significant predictors of the response variable. The number of connections between the palm and other trees was also significantly and positively related to per palm vector abundance. Relative to the external environment, palm niches experienced reduced ranges of temperature (mean reduction = 5.48±4.22 °C) and RH (mean reduction: 21.39±14.66 %) and significantly neutralized extremes, particularly in daytime maximum temperature (mean reduction: 4.99°C ±3.98 °C) and minimum RH (mean increase: 18.54±13.20%). Controlling for all other variables, total levels of DOM were also significantly associated with greater reductions in palm temperature fluctuations relative to external fluctuations. Conclusion: This study suggests potential predictors of R. pallescens abundance for future risk mapping and modelling. “High-risk” palms were well-shaded, with large amounts of dead organic matter and several connections with other trees and palms. A strategy of selective clearance of high-risk Attalea palms may be an effective and sustainable approach to disease risk reduction, given detailed knowledge of local risk factors.