impaginato piccolo - Società Italiana di Parassitologia (SoIPa)

122
Fig. 2. Meteorological data collected in Rome during the
2007 (UCEA).
Study on winter eggs.
As implementation of the winter surveillance, a further
study was carried out from mid December 2007 to the
end of February 2008. Twenty strips from positive ovitraps
were selected weekly in order to evaluate a possible
hatching and, in case of positive response, the mean
rate of hatching. Selected strips were placed individually
for a maximum of 7 days into plastic trays (15 by 10
by 6 cm) containing 350 ml of dechlorinated tap water
at room temperature (18±1°C), and with a natural photoperiod.
In order to estimate the length of the larval
cycle (indoor and outdoor temperatures), a combinated
lab/semi-field study was performed. Batches of first
instar emerged larvae were placed in trays commonly
F. Severini et al. - Aedes albopictus in Rome
Rome, whole urban area
(data referred to the period of June-November)
used in our insectary for mosquito rearing (15 x 25 x 8
cm), containing one litre of dechlorinated tap water).
Half of the total trays were maintained in laboratory at
the same conditions above described, and the remaining
50% into an open greenhouse, where temperature
was 1-2 °C higher than outdoor. The bioassay was followed
up to the development of larvae to adults or to
the death of all the larvae used for the test.
Results and Discussion
From the analysis of the data showed in Tab. 1 it is
noteworthy that the population of the species reached
its maximum level of abundance during the first phase
of invasion/colonization of a new area. As showed in
column 3, the monitoring net (column 2) revealed
rates of positivity that increased almost constantly during
the first four years of colonization, reaching the
maximum level of abundance (peak) in 2002. After
that, a marked decrease was observed since 2003, corresponding
to a phase of stabilization, related to trophic
resources and/or breeding sites available. The number
of positive zone (column 4) followed the same
trend showing a marked decrease in the records
belonging to the forth and the fifth classes of eggs
abundance (101-300 and >301 eggs, respectively),
from 220 to 8 records and from 14 to 1 respectively. In
columns 3 and 6 is underscored the relationship
between yearly mean rate of positivity and mm of rain-
Table 1. Data from ten years of monitoring in Rome (1998-2007). Data come from a net of ovitraps that was implemented in
1998 (50 ovitraps) and gradually improved (650 ovitraps at present). Ovitraps are distributed on to the whole surface of the
urban area, on the base of the surface of the 19 Administrative Districts and about 300 further areas in which the town is
divided. Data were collected weekly. In this table are reported the mean values of the already discussed parameters, along
24 weeks per year, corresponding to the majority of the season favorable to the massive reproduction of Aedes albopictus
in Rome (June-November).
Housing
An example of single district mean
rate of positive ovitrap
(mean No. eggs/ pos.trap)
1 2 3 4 5 6 7 8 9
Year Monitoring
net No.
ovitraps
Mean rate
of positivity
(Seasonal
peak)
No. zones with at least one
weekly record to the IV or V
class of abundance
Max No
eggs/pos.
trap
Rainfall mm
(mean No
eggs/pos.trap)
Central
District
(Downtown)
Residential
District
(Low hills)
1997 Late summer, the first foci of Ae. albopictus were recorded in two opposite sites (NE-SW) of the urban area
Beginning of the phase of invasion
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
~ 50
~ 300
500
500
500
650
650
650
650
650
16,5 (34,4)
31,2 (63,5)
25 (47,1)
45,9 (86,2)
62,8 (87,6)
48,9 (74,2)
41,7 (81,1)
50,2 (73,2)
44,5 (69,4)
44 (82,4)
-
-
220
236
320
185
133
75
34
8
-
-
14
12
15
359
632
572
453
429
267 (16,1)
387,8 (43)
305,4 (28,2)
183,4 (27,7)
513,2 (22)
Foci of the species are reported in all 19 Districts
Beginning of the phase of stabilization
10
1
8
0
1
612
550
506
144
337
233 (25)
306,8 (12)
451,4 (17)
239,7 (13)
139 (11)
-
-
38 (21)
42 (24)
62,3 (30)
52,7 (26)
52 (22)
53,5 (16)
50,5 (13)
55 (10)
-
-
45 (27)
44,5 (19)
63,1 (39)
57,8 (25)
59 (26)
54,4 (19)
52 (14)
60,32 (11)
Outskirts
(Commercial
Centre)
-
-
36,5 (22)
54,5 (23)
68 (25)
52,2 (20)
59,8 (23)
57 (17)
52,5 (15)
57,1 (10)