title: Evaluating preservation methods for identifying Anopheles gambiae s.s. and Anopheles arabiensis complex mosquitoes species using near infra-red spectroscopy.
abstract: BACKGROUND
  Near-infrared spectroscopy (NIRS) has been successfully used on fresh and RNAlater-preserved members of the Anopheles gambiae complex to identify sibling species and age. No preservation methods other than using RNAlater have been tested to preserve mosquitoes for species identification using NIRS. However, RNAlater is not the most practical preservative for field settings because it is expensive, requires basic laboratory conditions for storage and is not widely available in sub-Saharan Africa. The aim of this study was to test several cheaper and more field-friendly preservation methods for identifying sibling species of the An. gambiae complex using NIRS.
  
  
  METHODS
  In this study we describe the use of NIRS to identify sibling species of preserved An. gambiae s. s. and An. arabiensis. Mosquitoes of each species were placed in sample tubes and preserved using one of the following preservation methods: (i) refrigeration at 4°C, (ii) freezing at -20°C, (iii) drying over a silica-gel desiccant, (iv) submersion in RNAlater at room temperature, (v) submersion in RNAlater at 4°C, and (vi) submersion in RNAlater at -20°C. Mosquitoes were preserved for 1, 4, 10, 32 or 50 weeks before they were scanned.
  
  
  RESULTS
  Storage at 4°C was the only preservation method that, up to 32 weeks, did not result in significantly lower predicted values than those obtained from fresh insects. After 50 weeks, however, refrigerated samples did not give meaningful results. When storing for 50 weeks, desiccating samples over silica gel was the best preservation method, with a partial least squares regression cross-validation of >80%. Predictive data values were analyzed using a generalized linear model.
  
  
  CONCLUSIONS
  NIRS can be used to identify species of desiccated Anopheles gambiae s.s. and Anopheles arabiensis for up to 50 weeks of storage with more than 80% accuracy.
authors.affiliation: Ifakara Health Institute, P.O. Box 53, Ifakara, Tanzania. vmayagaya@ihi.or.tz.
authors.forename: Valeriana Simon
authors.initials: VS
authors.lastname: Mayagaya
authors.affiliation: Ifakara Health Institute, P.O. Box 53, Ifakara, Tanzania. ajohn@ihi.or.tz.|London School of Hygiene & Tropical Medicine, Keppel Street, WC1E 7HT, London, UK. ajohn@ihi.or.tz.
authors.forename: Alex John
authors.initials: AJ
authors.lastname: Ntamatungiro
authors.affiliation: Ifakara Health Institute, P.O. Box 53, Ifakara, Tanzania. smoore@ihi.or.tz.|Swiss Tropical & Public Health Institute, Soccinstraße 57, 4002, Basel, Switzerland. smoore@ihi.or.tz.|University of Basel, Petersplatz 1, 4003, Basel, Switzerland. smoore@ihi.or.tz.
authors.forename: Sarah Jane
authors.initials: SJ
authors.lastname: Moore
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, GA, 30329, USA. bew5@cdc.gov.
authors.forename: Robert Andrew
authors.initials: RA
authors.lastname: Wirtz
authors.affiliation: Engineering and Wind Erosion Research Unit, USDA ARS Centre for Grain and Animal Health Research, Manhattan, KS, USA. floyd.dowell@ars.usda.gov.
authors.forename: Floyd Ercell
authors.initials: FE
authors.lastname: Dowell
authors.affiliation: Ifakara Health Institute, P.O. Box 53, Ifakara, Tanzania. mmaia@ihi.or.tz.|Swiss Tropical & Public Health Institute, Soccinstraße 57, 4002, Basel, Switzerland. mmaia@ihi.or.tz.|University of Basel, Petersplatz 1, 4003, Basel, Switzerland. mmaia@ihi.or.tz.
authors.forename: Marta Ferreira
authors.initials: MF
authors.lastname: Maia
mesh_terms: D000818:Animals; D000852:Anopheles / Q000145:classification*; D003890:Desiccation; D007303:Insect Vectors / Q000145:classification*; D011309:Preservation, Biological / Q000379:methods / Q000662:veterinary*; D058428:Silica Gel; D019265:Spectroscopy, Near-Infrared / Q000379:methods / Q000662:veterinary*
chemical_list: D058428:Silica Gel