Evaluating preservation methods for identifying Anopheles gambiae s.s. and Anopheles arabiensis complex mosquitoes species using near infra-red spectroscopy

Abstract

BackgroundNear-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.MethodsIn 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.ResultsStorage 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.ConclusionNIRS 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.

Seeing Cellular Debris, Remembering a Soviet Method

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An Autoencoder and Artificial Neural Network-based Method to Estimate Parity Status of Wild Mosquitoes from Near-infrared Spectra

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Near‐infrared spectroscopy for metabolite quantification and species identification

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“…In this study, we investigate the accuracy of NIRS in determining metabolites levels by comparing the results to those obtained from a commercial assay kit. NIRS has been applied in noninvasive measurement of a variety of metabolites including blood glucose of patients with type I diabetes (Robinson et al, 1992), less invasive quantitative curately identify a range of species including Anopheles mosquitoes (Mayagaya et al, 2015), Zootermopsis termites (Aldrich, Maghirang, Dowell, & Kambhampati, 2007), Calliphoridae blowflies (Voss, Magni, Dadour, & Nansen, 2017), and Tetramorium ants (Kinzner et al, 2015). Morphologically, male D. melanogaster can be differentiated from male D. simulans by the shape of the genital arch genitalia, but females are difficult to identify and these taxa are considered sibling species.…”