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Twenty Years of the Presence of Aedes albopictus in Italy
municipalities (out of 8,101), from coastal plains to inner lands, up to 600
Figure 1: Distribution of Aedes albopictus in Italy
metres of altitude. The current distribution of Aedes albopictus in Italy by
by Province, 2008
province is shown in Figure 1. The different intensity of colour indicates
five classes of numerical presence of infested municipalities within the
province. Italy is a long and narrow peninsula extending over the
46 °
Mediterranean Sea for about 10° latitude. Foci of Aedes albopictus are
No. of municipalities with
between 37° and 46° latitude north in areas with different environmental
Aedes albopictus foci
and climatic conditions. As a consequence, the seasonal dynamic of the
> 101
species varies greatly within the country in the four to five months of
2 3 71–100
QuickTime™ and a1
41–70
activity recorded, from the pre-mountainous northern limits of the Pianura
11–40
Padana to Rome, where the tiger mosquito is active the whole year.
26,27
1–10
No data
Aedes albopictus, as with other species that live in a wide distribution
area that includes different climatic zones, show a polymorphic
42 °
4
pattern with photoperiodic response, depending on genetic
characters.
8,27
In fact, although the populations of the species
established in the northern region of Italy show trophic activity lasting
five to seven months (generally May/June to October/November),
being fully sensitive to the short photoperiod that induces egg
diapause, those that move southward may be active for nine to 10
5
months or even for the whole year. The length of the activity of the
Aedes albopictus population that colonised Rome has been rising
7
6
slowly but constantly since their introduction, from eight months in
1998 to the whole year in 2003,
27,28
even if the populations active
37 °
during the coldest months of winter (December to February) are
strongly reduced with respect to activity during the summer.
28
During
winter the mild temperature of the capital city may have partially The different intensity of colour refers to the number of communities infested by Aedes
deselected those characters that induce egg diapause in the mosquito
albopictus within the respective province. The number of infested communities is divided into
five classes, from 1 to over 100, as shown in the legend. The circled figures 1–7 identify
population, allowing a small fraction of females that are less sensitive cities of particular interest, namely: 1 = Genova; 2 = Padova; 3 = Ravenna; 4 = Rome;
5 = Cagliari; 6 = Palermo; 7 = Messina.
to the photoperiodic response to extend their period of activity.
27
This
event, coupled with a certain degree of endophily, permits these cycle may last a week) and the availability of small containers,
females to rest and sometimes to lay eggs indoors, which may depending on the kind of housing, are the factors that contribute to
contribute to the reduced but constant activity for 12 months.
28
the massive reproduction of the species. In the southern regions the
scarcity of rain and the hot temperature (e.g. the city of Cagliari; see
Factors that Favour the Adaptation of Aedes albopictus to Figure 1, number 5) strongly limit the seasonal development of the
New Environments and Strategies of Survival species as occurs in most of the infested sites of the northern regions.
After 20 years of presence in Italy, Aedes albopictus may be considered Exceptions are some urban areas, such as those of two large cities in
a stable member of the Italian mosquito fauna. Its establishment has Sicily (Messina and Palermo; see Figure 1, numbers 6 and 7), where the
been due to the genetic characteristics of the species and to favourable local environmental and microclimatic conditions allow the local
environmental and climatic conditions, but also to human errors. populations of the species to reach high levels of abundance.
26
Most of the Aedes albopictus foci were detected following reports of The ability of the species to adapt to different, often unfavourable, new
an uncommon daytime biting mosquito when the colony was already environments is due to a complex set of genetic and behavioural
strongly established. Control intervention, often carried out by characteristics. These strategies are, in part, common to other species
unskilled personnel, did not succeed. In addition, the unawareness of belonging to the same genera
8
and may be summarised as follows: the
the local administrative and/or sanitary authorities about the wide range of hosts available for blood feeding, from birds to humans;
importance of the problem represented by this species led to its the capacity to complete a full blood meal very quickly, often taking
potential being underestimated. Furthermore, the impact that vector- several blood meals within the same gonothrophic cycle; females that lay
borne diseases have on the global sanitary problem in Italy, with eggs from the same batch over several days and over different containers;
respect to other important pathologies, has resulted in a poor some of the eggs laid during the summer do not hatch at the first wetting
allocation of public funds for dealing with the tiger mosquito. stimulus, nor sometimes in a second wet/dry spell;
29
the ability to colonise
unusual breeding sites, such as the catch basins of street drains, which
The climatic and environmental factors that may favour the are particular to Italy, where Aedes albopictus breed despite a water
establishment and seasonal abundance of the species are related to often rich in organic matter, in competition with Culex pipiens and/or
the amount of rain (in particular during the four warmest months of Culiseta spp. larvae; and after the maximum density reached during the
the year). The high relative humidity, together with the availability of early phase of colonisation, the species is able to self-reduce its entity,
green areas, allows the mosquitoes to have longer survival. The warm according to the trophic resources available in the area. Finally, further
temperature (in the hottest months of the summer the pre-imaginal evidence of this adaptability may also be expressed by behaviours that
EUROPEAN INFECTIOUS DISEASE 99
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