Ecological characterization and molecular differentiation of Culex pipiens complex taxa and Culex torrentium in eastern Austria.

Carina Zittra,Eva Flechl,Thomas Zechmeister,Michael Kothmayer,Heidemarie Rossiter,Hans-Peter Fuehrer,Simon Vitecek

doi:10.1186/s13071-016-1495-4

Abstract

BackgroundCulex pipiens complex taxa differ in behaviour, ecophysiology and epidemiologic importance. Despite their epidemiologic significance, information on genetic diversity, occurrence and seasonal and spatial distribution patterns of the Cx. pipiens complex is still insufficient. Assessment of seasonal and spatial distribution patterns of Culex pipiens forms and their congener Cx. torrentium is crucial for the understanding of their vector–pathogen dynamics.MethodsFemale mosquitoes were trapped from April–October 2014 twice a month for a 24-h time period with BG-sentinel traps at 24 sampling sites in eastern Austria, using carbon dioxide as attractant. Ecological forms of Cx. pipiens s.l. and their hybrids were differentiated using the CQ11 locus, and Cx. pipiens forms and their congener Cx. torrentium using the ACE-2 gene. Differential exploitation of ecological niches by Cx. pipiens forms and Cx. torrentium was analysed using likelihood ratio tests. Possible effects of environmental parameters on these taxa were tested using PERMANOVA based on distance matrices and, if significant, were modelled in nMDS ordination space to estimate non-linear relationships.ResultsFor this study, 1476 Culex spp. were sampled. Culex pipiens f. pipiens representing 87.33 % of the total catch was most abundant, followed by hybrids of both forms (5.62 %), Cx. torrentium (3.79 %) and Cx. pipiens f. molestus (3.25 %). Differences in proportional abundances were found between land cover classes. Ecological parameters affecting seasonal and spatial distribution of these taxa in eastern Austria are precipitation duration, air temperature, sunlight and the interaction term of precipitation amount and the Danube water level, which can be interpreted as a proxy for breeding habitat availability.ConclusionsThe Cx. pipiens complex of eastern Austria comprises both ecologically different forms, the mainly ornithophilic form pipiens and the mainly mammalophilic and anthropophilic form molestus. Heterogeneous agricultural areas as areas of coexistence may serve as hybridization zones, resulting in potential bridge vectors between birds and humans. Occurrence, seasonal and spatial distribution patterns of the Cx. pipiens complex and Cx. torrentium and the presence of hybrids between both forms were quantified for the first time in Austria. These findings will improve the knowledge of their vector–pathogen dynamics in this country.

Highlights

Culex pipiens complex taxa differ in behaviour, ecophysiology and epidemiologic importance
The complex is considered to consist of seven taxa: Cx. quinquefasciatus Say, Cx. pipiens pallens Coquillet, Cx. australicus Dobrotworsky & Drummond, Cx. globocoxitus Dobrotworsky and the nominal species, Cx. pipiens L., comprising two genetically and ecologically distinct forms: Culex pipiens f. pipiens, which is repeatedly described and examined as ornithophilic, diapausing, anautogenous, and eurygamous, whereas Culex pipiens f. molestus is interpreted as mammophilic, autogenous, and stenogamous [1,2,3,4]
Cx. pipiens f. pipiens represented with 87.33 % of the total catch (n = 1289) the most abundant species in all provinces, followed by hybrids between Cx. pipiens f. pipiens and Cx. pipiens f. molestus (5.62 %, n = 83), Cx. torrentium

Summary

Introduction

Culex pipiens complex taxa differ in behaviour, ecophysiology and epidemiologic importance. Molestus is interpreted as mammophilic (and especially anthropophilic), autogenous, and stenogamous [1,2,3,4] Both forms are known to hybridize in areas of coexistence [5, 6], potentially resulting in bridge vector populations presumed to feed mostly on birds, and on humans [4]. The absence of stable morphological determination characters and sympatric occurrence in some Culex species resulted in incomplete or erroneous data on spatial and seasonal distribution of these taxa [28]. This clearly necessitates detailed scrutinization of the ecology of Culex species, including Cx. pipiens complex taxa. Only males or larvae of Cx. pipiens forms and Cx. torrentium can be distinguished reliably (by either the structure of the phallosome on the hypopygium [29, 30] or chaetotaxy [31]), but neither males nor larvae are of major interest in strictly epidemiological studies

Methods

Results

Discussion

Conclusion