Pupal Exuviae of Culex Pipiens L. (Diptera: Culicidae) Can be Utilised as a Non-Invasive Method of Biotype Differentiation

TL;DR

This study shows that DNA from discarded pupal skins of Culex pipiens mosquitoes can be used to identify their biotype without harming the adult mosquitoes, which is useful for studying their role in disease transmission.

Contribution

The study validates non-invasive DNA extraction methods from Cx. pipiens pupal exuviae for biotype differentiation.

Findings

DNA from pupal exuviae can be used for biotype identification up to 24 hours post-eclosion.

Direct real-time PCR had a lower amplification success rate compared to other methods.

Field-derived exuviae showed more variable results in DNA extraction and identification.

Abstract

Culex pipiens L. is a principal vector of zoonotic arboviruses in Europe, acting in both an amplification role in enzootic transmission between avian hosts and as a bridge vector between avian hosts and mammals. The species consists of two forms which are indistinguishable using morphological methods but possess varying ecological and physiological traits that influence their vector capacity. In this study we validate methods that can be used to extract trace DNA from single pupal exuviae of Cx. pipiens for use in molecular speciation of samples. These DNA extraction methods are compared using measurement of the total yield and successful identification using a real-time polymerase chain reaction (PCR) assay.

Genomic DNA was initially extracted from colony-derived individuals using an ethanol precipitation method, two commercially available DNA extraction kits: DNeasy® Blood & Tissue Kit (Qiagen, UK) and Wizard® SV Genomic DNA Purification System (Promega, UK) and a direct real-time PCR method. Time elapsed between eclosion and processing of pupae significantly influenced Cx. pipiens form identification as nucleic acid concentration and PCR amplification success decreased with increased time elapsed. Real-time PCR amplification success, however, was not shown to vary significantly between the three extraction methods, with all methods successfully identifying all samples, but the direct real-time PCR method achieved a lesser amplification success rate of 70% (n = 20 for each treatment). More variable results were produced when field-derived exuviae were used, with no significant difference in real-time PCR amplification success found across the four methods and a lower overall rate of successful identification of 55–80%.

This study shows that both colony and field derived Cx. pipiens pupal exuviae can be a useful non-invasive source of trace DNA permitting accurate biotype differentiation for at least twenty-four hours post-eclosion. The significance and utility of this technique in ecological and behavioural studies of Cx. pipiens is discussed and recommendations made for use according to experimental scenario.

The online version contains supplementary material available at 10.1186/s12575-024-00246-1.

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