Modeling the development ofTriatoma infestansthrough temperature: Estimating generation time in Bolivia
Authors: Lardeux Frédéric , Depickère Stéphanie , Tejerina Rosenka 
Published: September 2023

Background

In Bolivia, controllingTriatoma infestans, the primary vector of Chagas disease, remains challenging in the hot regions of the country. The study aims to establish a temperature-based model of development forT. infestansand explore phenological factors that could partially explain the failures in vector control within these regions of high ambient temperature.

Methods

We employed the Briere-1 model to describe the development time from egg-hatch to adults ofT. infestanswith temperature. Given that the entire developmental cycle can exceed two years under cooler temperature conditions, direct study of this duration was not undertaken. Instead, simulation was employed. For this purpose, insect cohorts encompassing all six stages (egg, N1, N2, N3, N4, N5) were concurrently raised within temperature-controlled climate chambers. The number of days required for molting between consecutive stages was recorded. Using this recorded dataset, the development time from eggs to adults was statistically simulated for various constant temperatures. The Briere-1 model was then calibrated using the dataset from each molting phase and applied to the simulated complete development cycle. The model was then used in conjunction with field temperatures from four representative localities within Bolivia to compute development times and generation intervals. A GIS approach was also used to map development times and generation intervals in the geographical distribution range ofT. infestans.

Findings

The model suggests that the minimum temperature required for the development ofT. infestansis approximately 15°C. The temperature at which its development attains maximum efficiency is around 33°C, while the threshold for lethal temperature stands at approximately 39°C. In the warmer regions of Bolivia,T. infestansexhibits an almost bivoltine cycle, with the number of yearly generations (G) ranging from approximately 1.5 to 2.5. In contrast, within the cooler Dry Inter-Andean Valleys, its cycle becomes univoltine or even less frequent (G≤1). The model could potentially offer insights into the correlations between insecticide resistance and the number of yearly generations, thereby clarifying why the control ofT. infestansin hotter regions proves more challenging to achieve.

Interpretation

The notion of generation time arises as a pivotal consideration in the management ofT. infestans, especially within Bolivia’s warmer regions. In areas marked by higher temperatures, the generation time of the vector diminishes, leading to a notable increase in the population growth rate. This, in turn, accelerates the emergence of insecticide resistance, as evidenced by the findings of this current study.

Author summary

In Bolivia, the bugTriatoma infestansis the main carrier ofTrypanosoma cruzi, the parasite responsible for Chagas disease. This study aims to understand how these bugs develop in different temperatures and how temperature affects efforts to control Chagas disease.

Experiments in controlled environments with different temperatures were carried out and results revealed that the Briere-1 model can accurately imitated how the bugs’ growth rate changes with temperature: following a sigmoid pattern, higher temperatures make the bugs grow faster up to a maximum before slowing rapidly down. Using this model, the study looked at how long it takes for a new generation of bugs to develop and therefore estimated the generation time as a function of temperature. It appeared that in warmer places, the bugs can have more than one generation in a year, which makes their population grow quickly and increases the risk of Chagas disease spreading.

The study also looked at whether the bugs’ resistance to insecticides is correlated to the generation time and it appeared that areas where bugs reproduce quickly tend to have more resistance to insecticides.

This research emphasizes how important it is to consider temperature when trying to controlT. infestans. Indeed, in areas with higher temperatures, the bugs reproduce more quickly and show a greater tendency to develop higher levels of resistance to insecticides. This dynamic complicates efforts to control them effectively. This information holds the potential to inform the development of improved strategies to curtail the spread of Chagas disease.