First report of the invasive mosquito species Aedes koreicus in the Swiss-Italian border region

In 2012 and 2013, an entomological survey of Aedes albopictus, the Asian tiger mosquito, was carried out in the border region of southern Switzerland and northern Italy, using ovitraps. In July 2013, besides A. albopictus already known to the region several unusual eggs were recovered.; A total of 548 seemingly different eggs were found within three communities: Chiasso (Switzerland), and Como and Brunate (Italy). Proteomic diagnostics based on matrix-assisted laser desorption/ionization mass-spectrometry (MALDI-TOF MS) and morphological identification of one reared adult revealed the presence of at least 18 A. (Finlaya) koreicus (Edwards, 1917) specimens. A. koreicus is a species native to Southeast Asia and is competent to transmit Japanese encephalitis and potentially other arboviruses, as well as the dog heartworm Dirofilaria immitis. While new to Switzerland, this invasive species has previously been reported from Belgium, north-eastern Italy and European Russia.; This is the first report of the introduction of this exotic mosquito species into Switzerland and Lombardy, Italy, suggesting the range of A. koreicus is expanding in Central Europe. As A. koreicus is competent to vector pathogens its establishment imposes a risk to public and veterinary health. From a technical point of view, the presence of A. koreicus alongside A. albopictus requires careful analysis and reliable diagnostics. As a diagnostic tool the use of the recently developed MALDI-TOF MS approach has proofed to be a very useful approach, particularly since hatching rates of A. koreicus seem to be low, making identification by classic morphology difficult, if not impossible

Surveillance and control of Aedes albopictus in the Swiss-Italian border region: differences in egg densities between intervention and non-intervention areas

BACKGROUND: Aedes albopictus, the Asian tiger mosquito, originates from the tropical and subtropical regions of Southeast Asia. Over the recent decades it has been passively spread across the globe, primarily through the used tyre trade and passive transportation along major traffic routes. A. albopictus is a proven vector for many arboviruses, most notably chikungunya and dengue, with recent outbreaks also in continental Europe. In southern Switzerland, in the Canton of Ticino A. albopictus was spotted for the first time in 2003. Since then the local authorities have implemented a control programme based on larval source reduction. Despite these efforts, mosquito densities have increased over the last decade, casting doubts on the effectiveness of such larval control programmes. METHODOLOGY/PRINCIPAL FINDINGS: The Italian communities just across the Swiss-Italian border lack a control programme. This motivated us to compare the intervention and the non-intervention areas side by side in an attempt to find evidence for, or against, the effectiveness of larval A. albopictus control. Using ovitraps and a randomised sampling scheme, we examined the seasonal and spatial abundance of A. albopictus in sylvatic and urban environments across the Swiss-Italian border in 2012 and 2013. In the urban environments of the non-intervention area, egg densities were 2.26 times higher as compared to the intervention area. In the sylvatic environments, as compared to the urban environments, egg densities were 36% in the intervention area and 18% in the non-intervention area. CONCLUSIONS/SIGNIFICANCE: Though alternative explanations are also valid, the results support the hypothesis that the Ticino intervention programme does have an impact. At the same time the data also suggest that current larval interventions fall short in gaining full control over the mosquito, calling for the evaluation of additional, or alternative, approaches. Ideally, these should also consider inclusion of the neighbouring Italian communities in the surveillance and control efforts

Altitude range of trap positions.

<p>The boxplots show the distribution of the altitude above sea level for the 140 ovitraps in each of the two areas. The boxes represent the interquartile distances (IQD), while the centrelines through each box show the medians. The dots indicate outliers and the whiskers extend to the extreme values of the data, calculated as ±1.5 x IQD from the median.</p

Temporal distribution of <i>Aedes albopictus</i> in the Swiss-Italian border region.

<p>The numbers of <i>A</i>. <i>albopictus</i> eggs found in the ovitraps are shown as sums over all 70 traps for each combination of environment and area. In the calendar week 38 in 2013, an unusually high number of ovitraps was dysfunctional (e.g. traps were found turned over, damaged or missing; <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0004315#pntd.0004315.s001" target="_blank">S1 Table</a>), explaining the sudden drop in the curve for the non-intervention area in the urban environment.</p

Effects of “area” and “environment” on average egg counts.

<p>The difference in average egg counts between the urban and sylvatic environments in the intervention area was half the difference between the environments in the non-intervention area. Note that the average egg numbers represent the mode from the back-transformed coefficients.</p