Aedes albopictus abundance and phenology along an altitudinal gradient in Lazio region (central Italy).

BACKGROUND

The Asian tiger mosquito Aedes albopictus (Skuse 1894), which is native to Southeast Asia, is among the top 100 invasive species worldwide and one of the most troubling vector species. It has become established in more than 20 European countries. Since its arrival in Italy in the 1990s, the species has colonized all the regions of the country, up to an altitude of 600 m. Nevertheless, no thorough investigation has ever been performed to confirm or extend its elevation limit (EL) in Italy.

METHODS

To define the EL of Ae. albopictus and analyse its phenology along an altitudinal gradient, we carried out an investigation by means of ovitraps placed in Lazio region, central Italy. Sampling was performed on a weekly basis in 13 villages within five 200-m altitudinal ranges [0-1000 m above sea level (asl)], with the addition of higher localities to the species range whenever the species was recorded in the highest range.

RESULTS

Aedes albopictus has colonized sites well beyond its known EL, with established populations at 900 m asl and positive ovitraps recorded at 1193 m asl. The relationship between egg abundance and elevation was described by an exponential decay regression, which predicted an EL for oviposition at 1015 m asl. In the active season, egg-laying started earlier at low altitude and ended earlier within the highest altitudinal range. Aedes albopictus abundance and activity period (number of days active) decreased, respectively, by 95% and 34% from the lowest to the highest altitudinal range.

CONCLUSIONS

Using data from the present study, the altitudinal limit of Ae. albopictus in central Italy was updated from 600 to 900 m asl. In addition, established populations were predicted to exist up to 1015 m asl. Considering that up to 99.5% of Lazio region's inhabitants could potentially be affected by Aedes-borne virus outbreaks, the surveillance area for Ae. albopictus should be expanded accordingly. However, our results also indicate that Ae. albopictus surveillance programs need to be revised in order to harmonize the resources earmarked for these with the altitudinal changes in the phenology of this species.