Effects of Irritant Chemicals on Aedes aegypti Resting Behavior: Is There a Simple Shift to Untreated “Safe Sites”?

Aedes aegypti, the primary vector mosquito of dengue virus, typically lives near or inside human dwellings, and feeds preferentially on humans. The control of this mosquito vector remains the most important dengue prevention method. The use of chemicals at levels toxic to mosquitoes is currently the only confirmed effective adult vector control strategy with interventions usually applied following epidemic onset. However, research indicates that sub-lethal chemical approaches to prevent human-vector contact at the house level exist: contact irritancy and spatial repellency. The optimum efficacy of an intervention based on contact irritant actions of chemicals will, however, require full knowledge of variables that will influence vector resting behavior and thereby chemical uptake from treated sources. Here we characterize the resting patterns of female Ae. aegypti on two material types at various dark:light surface area coverage ratios and contrast configurations under chemical-free and treated conditions using a laboratory behavioral assay. Change in resting behavior between baseline and treatment conditions was quantified to determine potential negative effects of untreated surfaces (“safe sites”) when irritant responses are elicited. We show that treatment of preferred resting sites with known irritant compounds do not stimulate mosquitoes to move to safe sites after making contact with treated surfaces

Evolutionary ecology of Chagas disease; what do we know and what do we need?

International audienceThe aetiological agent of Chagas disease, Trypanosoma cruzi, is a key human pathogen afflicting most populations of Latin America. This vectorborne parasite is transmitted by haematophageous triatomines, whose control by large-scale insecticide spraying has been the main strategy to limit the impact of the disease for over 25 years. While those international initiatives have been successful in highly endemic areas, this systematic approach is now challenged by the emergence of insecticide resistance and by its low efficacy in controlling species that are only partially adapted to human habitat. In this contribution, we review evidences that Chagas disease control shall now be entering a second stage that will rely on a better understanding of triatomines adaptive potential, which requires promoting microevolutionary studies and –omic approaches. Concomitantly, we show that our knowledge of the determinants of the evolution of T. cruzi high diversity and low virulence remains too limiting to design evolution-proof strategies, while such attributes may be part of the future of Chagas disease control after the 2020 WHO's target of regional elimination of intradomiciliary transmission has been reached. We should then aim at developing a theory of T. cruzi virulence evolution that we anticipate to provide an interesting enrichment of the general theory according to the specificities of transmission of this very generalist stercorarian trypanosome. We stress that many ecological data required to better understand selective pressures acting on vector and parasite populations are already available as they have been meticulously accumulated in the last century of field research. Although more specific information will surely be needed, an effective research strategy would be to integrate data into the conceptual and theoretical framework of evolutionary ecology and life-history evolution that provide the quantitative backgrounds necessary to understand and possibly anticipate adaptive responses to public health interventions