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Research: Larval environment influences vector competence of the malaria mosquito Anopheles gambiae

June 29, 2016 - 09:34 -- MalariaWorld Journal
Antoine M.G. Barreaux, Priscille Barreaux, Kevin Thievent, Jacob C. Koella
MWJ2016, 7, 8
Article type: 
While environmental factors such as temperature can influence the vector competence of mosquitoes directly, for example by affecting the longevity of the mosquito and the development of the malaria parasite they may also have an indirect impact on the parasite’s transmission. By influencing larval development, they may affect the adult traits that are important for the parasite’s development and transmission. We studied the influence of two larval environmental factors, food availability and temperature, on the probability that mosquitoes infected with the malaria parasite survived to harbour sporozoites in their salivary glands. Anopheles gambiae larvae were reared at 21oC, 25oC or 29oC, and fed either a standard larval diet or half of it. Adults could blood feed on mice harbouring the infectious gametocytic stage of Plasmodium berghei ANKA transformed with green fluorescent protein (GFP). Survival was assessed every 24 hrs up to 21 days post infection, when surviving mosquitoes were dissected to check the salivary glands for sporozoites with a fluorescent microscope sensitive to GFP. Using a binomial GLM we analysed ‘vector competence’, i.e. if mosquitoes survived until dissection and harboured sporozoites in their salivary glands. Vector competence dropped by about a third if we fed larvae half the standard food regime. The effect of temperature during the larval period depended strongly on the food regime. At low food, increasing temperature from 21oC to 29oC increased vector competence from about 0.18 to 0.48, whereas at standard food, vector competence dropped from about 0.67 at 21oC to 0.56 at 29oC. Thus, perceptions and models about the role of environmental change on the transmission of malaria should include how the environment changes adult life-history by influencing larval development.

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Submitted by Clive Shiff (not verified) on
I find this of interest, but I do worry if the results are used in modelling vector competence because in the field conditions will almost never be similar for a sustained period covering larval development. The aquatic system is dynamic, and particularly with temperature will stratify, even in small ponds so larvae do have opportunity to select their temperature preference which I expect will vary through the stages of development. Too often our mathematical colleagues use lab data and prorate it into models which then become highly publicised. A good example of this lies in the projected temperature limitations both maxima and minima that regulate the global distribution of many vector species and which are reflected in some of the maps used to delineate distribution. But in the field the mosquitoes will select where they rest and take advantage of microclimate conditions that exist in shrubbery and other resting sites and are influenced by nuances of the habitat we cannot replicate. I think the conclusions of the paper should have noted this.