title: Resisting infection by Plasmodium berghei increases the sensitivity of the malaria vector Anopheles gambiae to DDT.
abstract: BACKGROUND
  The evolution of insecticide resistance threatens current malaria control methods, which rely heavily on chemical insecticides. The magnitude of the threat will be determined by the phenotypic expression of resistance in those mosquitoes that can transmit malaria. These differ from the majority of the mosquito population in two main ways; they carry sporozoites (the infectious stage of the Plasmodium parasite) and they are relatively old, as they need to survive the development period of the malaria parasite. This study examines the effects of infection by Plasmodium berghei and of mosquito age on the sensitivity to DDT in a DDT-resistant strain of Anopheles gambiae.
  
  
  METHODS
  DDT-resistant Anopheles gambiae (ZANU) mosquitoes received a blood meal from either a mouse infected with Plasmodium berghei or an uninfected mouse. 10 and 19 days post blood meal the mosquitoes were exposed to 2%, 1% or 0% DDT using WHO test kits. 24 hrs after exposure, mortality and Plasmodium infection status of the mosquitoes were recorded.
  
  
  RESULTS
  Sensitivity to DDT increased with the mosquitoes' age and was higher in mosquitoes that had fed on Plasmodium-infected mice than in those that had not been exposed to the parasite. The latter effect was mainly due to the high sensitivity of mosquitoes that had fed on an infected mouse but were not themselves infected, while the sensitivity to DDT was only slightly higher in mosquitoes infected by Plasmodium than in those that had fed on an uninfected mouse.
  
  
  CONCLUSIONS
  The observed pattern indicates a cost of parasite-resistance. It suggests that, in addition to the detrimental effect of insecticide-resistance on control, the continued use of insecticides in a population of insecticide-resistant mosquitoes could select mosquitoes to be more susceptible to Plasmodium infection, thus further decreasing the efficacy of the control.
authors.affiliation: Division of Biology, Faculty of Life Sciences, Imperial College London, Silwood Park Campus, Ascot, Berkshire, SL5 2PZ, UK. adamsaddler.as@gmail.com.|Faculté des Sciences, Institut de Biologie, Université de Neuchâtel, Rue Emile-Argand 11, CH-2000, Neuchâtel, Switzerland. adamsaddler.as@gmail.com.|Department of Health Interventions, Swiss Tropical and Public Health Institute, Socinstrasse, 57, CH-4002, Basel, Switzerland. adamsaddler.as@gmail.com.|Ifakara Health Institute, Box 74, Bagamoyo, Tanzania. adamsaddler.as@gmail.com.|University of Basel, Petersplatz 1, Basel, 4003, Switzerland. adamsaddler.as@gmail.com.
authors.forename: Adam
authors.initials: A
authors.lastname: Saddler
authors.affiliation: Institute of Cell Biology, University of Bern, Bern, Switzerland. paul-christian.burda@izb.unibe.ch.
authors.forename: Paul-Christian
authors.initials: PC
authors.lastname: Burda
authors.affiliation: Faculté des Sciences, Institut de Biologie, Université de Neuchâtel, Rue Emile-Argand 11, CH-2000, Neuchâtel, Switzerland. jkoella@gmail.com.
authors.forename: Jacob C
authors.initials: JC
authors.lastname: Koella
mesh_terms: D000367:Age Factors; D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000469:parasitology*; D003634:DDT / Q000494:pharmacology*; D060467:Disease Resistance; D005260:Female; D007306:Insecticides / Q000494:pharmacology*; D008807:Mice, Inbred BALB C; D010962:Plasmodium berghei / Q000302:isolation & purification*; D016019:Survival Analysis
chemical_list: D007306:Insecticides; D003634:DDT