title: Aging partially restores the efficacy of malaria vector control in insecticide-resistant populations of Anopheles gambiae s.l. from Burkina Faso.
abstract: BACKGROUND
  The operational impact of insecticide resistance on the effectiveness of long-lasting insecticide nets (LLINs) and indoor residual spraying (IRS) is poorly understood. One factor which may prolong the effectiveness of these tools in the field is the increase in insecticide susceptibility with mosquito age. In this study, LLINs and IRS were tested against young (three to five days) and old (17-19 days) pyrethroid resistant Anopheles gambiae s.l. from Burkina Faso.
  
  
  METHODS
  Blood-fed adult Anopheles gambiae s.l. were collected from south-west Burkina Faso and identified to species/form level. Cohorts of the F1 progeny of An. gambiae s.s. S-forms were exposed to deltamethrin (0.05%) at three to five or 17-19 days post-emergence and tested for the frequency of the resistance allele 1014F. Isofemale lines of the M, S- form of An. gambiae s.s. and Anopheles arabiensis were exposed in WHO cone tests to either a) LLINs deployed in households for two years or (b) bendiocarb sprayed walls.
  
  
  RESULTS
  Mortality rates in response to deltamethrin (0.05%) increased from levels indicative of strong resistance in three to five day old F1 mosquitoes, to near full susceptibility in the 17-19 day old cohort. On exposure to LLINs sampled from the field, the mortality rate in isofemale lines was higher in older mosquitoes than young (OR = 5.28, CI 95% = 2.81-9.92), although the mortality estimates were affected by the LLIN tested. In general, the LLINs sampled from the field performed poorly in WHO cone bioassays using either laboratory susceptible or field caught mosquito populations. Finally, there was a clear relationship between mortality and age on exposure to bendiocarb-sprayed walls, with older mosquitoes again proving more susceptible (OR = 3.39, CI 95% = 2.35-4.90).
  
  
  CONCLUSIONS
  Age is a key factor determining the susceptibility of mosquitoes to insecticides, not only in laboratory studies, but in response to field-based vector control interventions. This has important implications for understanding the epidemiological impact of resistance. If mosquitoes old enough to transmit malaria are still being suppressed with available insecticides, is resistance potentially having less of an impact than often assumed? However, the poor performance of LLINs used in this study in Burkina Faso, is a cause for concern and requires urgent investigation.
authors.affiliation: Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK. jonescm@liverpool.ac.uk
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Jones
authors.forename: Antoine
authors.initials: A
authors.lastname: Sanou
authors.forename: Wamdaogo M
authors.initials: WM
authors.lastname: Guelbeogo
authors.forename: N'Fale
authors.initials: N
authors.lastname: Sagnon
authors.forename: Paul C D
authors.initials: PC
authors.lastname: Johnson
authors.forename: Hilary
authors.initials: H
authors.lastname: Ranson
mesh_terms: D000367:Age Factors; D000483:Alleles; D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development; D002050:Burkina Faso; D016172:DNA Fingerprinting; D005260:Female; D007303:Insect Vectors / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development; D007305:Insecticide Resistance; D057148:Insecticide-Treated Bednets; D007306:Insecticides / Q000494:pharmacology*; D009032:Mosquito Control / Q000379:methods*; D009570:Nitriles / Q000494:pharmacology; D048448:Phenylcarbamates / Q000494:pharmacology; D011722:Pyrethrins / Q000494:pharmacology
chemical_list: D007306:Insecticides; D009570:Nitriles; D048448:Phenylcarbamates; D011722:Pyrethrins; C017180:decamethrin; C007725:bendiocarb