ISRAEL JOURNAL OF
VETERINARY MEDICINE
Vol. 56 (3) 2001
THE INTERACTION BETWEEN CLIMATIC FACTORS
AND BLUETONGUE OUTBREAKS IN ISRAEL AND
THE EASTERN MEDITERRANEAN, AND THE
FEASIBILITY OF ESTABLISHING BLUETONGUEFREE ZONES
Y. Braverman1, F. Chechik2, B. Mullens3
1. The Kimron Veterinary Institute, Bet Dagan, Israel;
2. The Meteorological Services, Bet Dagan, Israel;
3. Department of Entomology, University of California, Riverside, CA, USA
Abstract
Israel has accumulated extensive information on bluetongue (BT) occurrence in sheep flocks and
sentinel cattle in various regions of the country for more than 30 years. Meteorological parameters had
not been independently correlated with the occurrence of BT over the entire period. Meteorological
parameters preceding years with high prevalence of bluetongue (1975, 1987, 1988 and 1994) (average
of 43 sheep flocks affected) were compared with those for years with little or no BT transmission
(1980, 1981, 1983 and 1992). Winters preceding high-BT seasons were significantly warmer; the
average maximum temperature of the coldest month was 2 to 3 0C higher, and the average
maximum and minimum temperatures were 1-20C higher. After extremely dry and
warm winters over the eastern Mediterranean, such as those of 1998 and 1999, single
cases of BT occurred in 1998 and none in 1999. Rainfall in BT outbreak years was
approximately normal, whereas winters preceding low-BT seasons were wetter (40%
more rainfall than average in the coldest month and 17% more winter rainfall overall).
BT outbreak years had significantly more winter days with maximum temperatures
higher than 13 or 180C (in the Inner-land and in the Arava regions, respectively), and more nights
with minimum temperatures > 50C. Average maximum temperatures below 16.50C for the coldest
winter month were associated with low-BT seasons, while winters with more than 18 days warmer than
180C were followed by high BTV transmission. In most parts of Israel except in mountains >700 m
above sea level, the average maximum temperature of the coldest winter month is >12.5 0C, which is
thought to enable the survival of BT viruses. Mountain areas also have fewer animals/km2 than lowland
areas, and more of these are BT-resistant ruminants such as goats. Two candidates for "safe zones"
with regard to export of ruminants and their products are proposed: the Arava Rift Valley and
mountains above 700 m. Bluetongue outbreaks are not known in these regions. The Arava is assumed
to be a particularly low-risk region because there are smaller numbers and presumed lower survival of
the principal vector, Culicoides imicola. The Arava Rift Valley is also beyond the Persian Trough air
stream, which seems to be connected with the introduction of BT vectors into Israel. These safe zones
might be exploited for export of animals and germplasm.
Introduction
Bluetongue (BT) disease affects wild and domestic ruminants and is widely distributed globally. Biting
midges of the genus Culicoides transmit bluetongue viruses, and the distribution and abundance of the
vector are thought to account for the seasonal and spatial distributions of BT (1). Several attempts have
been made to relate climatic factors to outbreaks and spread of BT in various regions (2, 3, 4). Walker
and Davies (5) found in Kenya that numbers of several dominant Culicoides species, including the
principal vector C. imicola (=pallidipennis) greatly increased after the rainy season. They postulated a
causal relationship between peak rainfall in April-May, peak numbers of Culicoides in May-June and
peak bluetongue prevalence in June-July. However, Davies (6) did not find that rainfall affected
serological conversion rates of sentinel cattle to BT viruses in Kenya. Wright et al. (4) related weather
variables to seroconversion in cattle to bluetongue in Alabama, USA; while the best predictors were
mean daily hours of wet vegetation (as the result of dew) and total rain days during the second weekly
period prior to sample collection. The most thorough studies have been done in Australia, where Ward
(3) studied 18 climatic variables: Daily maximum temperature and average annual rainfall best
explained the variability in the prevalence of BT. Subsequent modeling efforts (7) showed that spring
rainfall and minimum temperatures had the greatest effects on predicted transmission; periodic
disruptions (drought) introduced cyclic instability into the model, mirroring patterns that are sometimes
seen naturally.
Movement of Culicoides species in Australia has been associated with northerly winds (8) and that in
Israel with a summer north-westerly wind system termed the Persian Trough (9). Most outbreaks of BT
in Israel occur from mid-summer (July) to the onset of cold winter temperatures (NovemberDecember) paralleling the activity of the Persian Trough and the buildup of large numbers of C.
imicola vectors (9) with high vectorial capacity (10, 11). Similar climatic factors prevail over the
eastern Mediterranean, and the situation in Israel should be representative of this area. The present
study was undertaken to elucidate which climatic factors, or combination thereof, determine BT
prevalence in Israel. We also investigated whether BT-free zones might exist in Israel.
Materials and methods
Data on BT outbreaks in sheep flocks were available from the Epidemiological Quarterly of the Israeli
Veterinary Services. Climate data were obtained from the Israeli Meteorological Service. The rainfall
data were regional averages taken from 22 meteorological stations (Table 1) whose distribution was
related to the size of the BT-affected area. i.e., more meteorological stations were included for a larger
affected area than for a smaller affected area. Data characterizing winter frost days and spring Sharav
days (Sharav day=a day with maximum temperature of 330C or more, and relative humidity at
1400 h of 25% or less) were taken from the Kefar Blum meteorological station, where
the probabilities for frost and Sharav days are high. This northern locality is
representative of the climate of the inland valleys.
Two types of analyses were conducted: linear correlations between BT outbreak frequencies in sheep
flocks versus selected climatic factors; and climatological comparisons of years with many BT
outbreaks (> 30) versus years with 0 to 1 BT outbreak. Correlations were examined between BT
outbreak frequencies (number of outbreaks) and climatic data over a 20-year period (1970-1989). The
following climatic factors were tested: 1. Seasonal (September-May) rainfall (mm); 2. Spring (MarchMay) rainfall (mm); 3. Number of nights between November and March during which the minimum
temperature was <50C; 4. Number of frost nights (November-March); 5. Number of consecutive frost
nights (November-March); 6. Number of consecutive nights (November-March) with temperature of
20C and below; 7. Number of spring (April-May) Sharav days; 8. Number of spring days with
maximum temperature of 350C and above; 9. The highest daily maximum temperature of the year. A
detailed analysis was done, to compare climatic factors prevailing before each of four years with many
BT outbreaks (>30) (1975, 1987, 1988 and 1994) versus climatic factors for four years with 0-1 BT
outbreaks (1980, 1981, 1983 and 1992). The values of each climatic factor in low-BT and high-BT
years were compared by t-test. It was assumed that extreme temperatures (very low or very high) and
drought prevailing in a certain year would reduce the number of surviving vectors in the following
year. Data for this analysis were taken from two meteorological stations: Kefar Blum in the north and
Bet Dagan on the central coastal plain, where the frequency of frosts and Sharav days is lower than in
Kefar Blum. For each of the four-year groupings, the following averages of meteorological parameters
were tested: 1. Average maximum temperature (0C) of the coldest winter month (December-March); 2.
Average maximum winter temperature; 3. Minimum winter temperature; 4. Number of days with
maximum temperature of 130C
or above in January-February; 5. Number of days with
maximum temperature of 180C or above in January-February; 6. Number of winter (DecemberMarch) nights in which the minimum temperature was 5 0C or below; 7. The average amount of rainfall
at 22 meteorological stations; 8. Spring (April 1 to June 15) maximum temperature; 9. Number of
Sharav days in the spring (March-May); 10. The average amount (mm) of spring rainfall as measured
at 22 meteorological stations.
Culicoides trapping: Where data were available, the numbers of Culicoides at the various localities
were related to specific regions or seasons. Collections were made in DuToit suction light traps (12)
equipped with mercury vapor lamps (HPW125 W-TS, Belgium). Bet Dagan, in the central Coastal
Plain served as a permanent trapping station, where Culicoides were collected either throughout the
summer or throughout the year. Collections at Bet Dagan were made at the byre of the Veterinary
Institute, the byre of the Volcani Center, or at both sites. At Bet Jann, Upper Galilee, 36 suction light
trap collections were made between August 25 and October 6, 1981. At En Kerem in the Judean Hills,
30 suction light trap collections were made between September and December 1978. At Yotvata in the
Arava Valley, two suction light trap collections were made in August 1982.
Results
The average maximum temperatures of the coldest month (usually January) in Israel are shown in Fig.
1. Temperatures between 12.5 and 180C, which are thought to enable the survival of BT viruses in
vectors during winter (13) prevail over most of the country. The exceptions are hills above 700 m
(<12.50C) and the Arava and Jordan Valley (>180C). There was no correlation between the 10
individual climatological parameters and the numbers of BT outbreaks in sheep during 1970-1989
(Table 2). Temperatures in the four winters that preceded seasons with many outbreaks and those that
preceded seasons with no (or few) outbreaks are shown in Table 3. Seasons with many outbreaks were
preceded by winters in which the average maximum temperature of the coldest month was 2 to 30C
warmer (P=0.0009). In addition the average maximum and the average minimum
temperatures of the entire winter (December-March) were 1 to 1.50C warmer in
winters preceding high-incidence years (P=0.0061). High-incidence years were
preceded by winters (January-February) with more days in which the maximum
temperature was > 130C (P=0.0346) and >180C (P=0.0002). The number of spring Sharav
days was not useful to distinguish high-incidence from low-incidence years. Low incidence years were
preceded by wet winters, with 40% more rainfall on the average of the coldest month than those which
preceded by high-incidence years (and which had approximately normal rainfall) (P=0.0058). The
overall amount of rainfall in years without outbreaks was, on average, 17% higher than that in years
with many outbreaks. The data of Table 3 indicate that average maximum temperatures below 16.5 0C
in the coldest month of winter were associated with a low probability of BT outbreaks
in the following summer. Likewise, winters with more than 18 days with temperatures
above 180C were associated with a high probability of BT outbreaks in the following summer. The
mountains (700 m above sea level) had no reported BT outbreaks, and the Arava desert valley (e.g.,
Yotvata, 75 m above sea level) recorded only a single BT case during 1970-1989. These areas have
fewer Culicoides vectors than a typical BT area such as Bet Dagan (Table 4). Table 5 shows the
numbers of vectors, namely C. imicola, trapped in June, one month before the usual outbreaks of BT in
sheep. There were large differences in the numbers of Culicoides spp. at the two sites at Bet Dagan and
between the numbers collected in 1982 and in 1996. In the absence of a source of infection, even a C.
imicola population yielding 345 insects per night per trap at the Volcani Center in 1982 did not result
in a BT outbreak (Table 5). Table 6 shows the numbers of Culicoides spp. trapped nightly during the
BT-free season, i.e., winter of 1997/8. The numbers of the vector C. imicola ranged from 170 in
November 1997 to 6 in February and March 1998. The Rehovot District (Fig. 2), which includes Bet
Dagan, contains large numbers of reservoir animals, i.e., dairy cattle, it is not surprising therefore that
the BT virus is active in this area. In contrast parts of the Be'er Sheva District, which includes the flat
Arava, and the Jerusalem and Akko Districts, which are hilly and contains smaller numbers of cattle
that may serve as BT reservoirs.
Discussion
Climatic variables presumably influence BT spatial and seasonal distributions through modifications of
vector capacity and abundance. Vector capacity incorporates biting rates, vector survival, extrinsic
incubation (time required between ingesting the virus and becoming infective), and vector competence
(ability of the vector to become infected by the virus). Our analysis concentrated more on winter
climate parameters than on summer ones, since in the eastern Mediterranean summer parameters are
stable whereas the winter ones are variable (14, 15). The importance of winter was confirmed in a
recent study in Spain, where it was reported that C. imicola predominated in a zone with the highest
minimum and maximum temperatures during the winter (16). Both temperature and rainfall appear to
be significant.
Temperature: Temperature has a profound influence on several of these vector capacity components.
Our temperature analysis shows that, theoretically, BT virus types should be able to survive the
winters, at least in part, in infected insects throughout the entire country, except in the mountains above
700 m. Extrinsic incubation of BT virus in the vectors is temperature dependent: in the laboratory, C.
sonorensis, BT virus remained in a quiescent state for at least 22 days, but it replicated rapidly when
infected insects were exposed to higher temperatures (17). The virus is assumed to survive above a
temperature threshold of 12.50C (13), which is below the activity threshold for flight of C. imicola.
While C. imicola may be collected on warm winter evenings, its minimum temperature for flight is 17180C (18). It has been suggested in other subtropical areas that are within its wide range, that winter
persistence of infected C. imicola provides at least a partial means of over-wintering for BT viruses
(19, 20).
Developmental rates, and, therefore, the generation interval of a multivoltine insect such as C. imicola,
are considerably shorter at higher temperatures (see, e.g., 21), which might enable population densities
to increase more quickly. In winter larvae of C. imicola do not hibernate, but develop at a slower pace,
so that higher winter temperatures might lead to a larger spring generation. The length of the
gonotrophic cycle, particularly the time required from blood ingestion to egg development, is also
much shorter at higher temperatures, provided they are below the upper threshold limits (22). Thus
individual vectors should feed more often, increasing opportunity for transmission over a defined time
period. These factors would act to encourage BT activity at higher temperatures. Indeed Rawling et al.
(23) suggested that the presence of C. imicola in Iberia is favoured by high summer temperatures,
possibly in conjunction with the seasonal low relative humidity. No significant relationships between
the presence of C. imicola and winter temperatures and relative humidity were found. On the other
hand, it is expected that daily survival would be lower at higher temperatures, such as those prevailing
in the Arava. The fact that the preferred climatic conditions for reaching peak populations of C. imicola
always occur everywhere in Israel in the autumn (September- November), when night temperatures are
lower and relative humidity is higher than in the summer, reflects a different situation from that in
Spain (23). The prevailing high winds in the Arava probably regularly suppress the host-seeking
activity of C. imicola and increase their mortality, as was suggested previously (24, 25). However,
Braverman et al. (11) found that C. imicola collected in light traps in the Coastal Plain, where
temperatures are more permissive maintained a high parity level (stage survival) during the mid
summer and early fall months. Survival between blood meals was actually highest in August on the
Coastal Plain (Bet Dagan).
Our analysis suggests that warm winters, which encourage survival in C. imicola, precede periods of
substantial BT transmission. This could be a result of reduced mortality and higher overwintering
populations of the vector but, except for the Bet Dagan area, we lack concurrent long-term vector
monitoring data to substantiate this. The above suggestion does not mean that BT outbreaks will
actually occur after every warm winter; the very dry and warm winters of 1998 and 1999 were
followed by summers with few BT outbreaks only in 1998. C. imicola is essentially an African species,
more adapted to high temperatures than low ones. Warm spring Sharav days had no detectable
influence on BT occurrence, probably because winter-induced C. imicola mortality had already
occurred and preceded the Persian Trough air stream that starts in the 2nd half of June and is believed
to introduce BT-infected vectors (9).
Rainfall: Because the immature stages of C. imicola are found in areas of damp or wet manure/organic
soil, one might assume that rainfall would have a major positive influence on vector population
densities. A recent study used the Normalized Difference Vegetation Index (NDVI), a satellite-derived
measure of photosynthetic activity, to evaluate relative abundances of C. imicola (24). Abundances
were positively correlated with the average and minimum NDVI (NDVImin), an index which is
strongly correlated with total annual rainfall. In the eastern Mediterranean the rainy season is limited to
the winter, and our analysis suggests that very wet winters result in reduced BT transmission the
following summer. An important reason for this is that heavy rains inundate and erode the breeding
sites of C. imicola. Ample rainfall-independent development sites for C. imicola are found near water
troughs, etc., in and around livestock yards (26, 27). Unlike the situation in Morocco and Iberia (24)
grass-covered wet sites were found to be poor biotopes for C. imicola. Irrigated fields and horticultural
crops in Israel are also not dependent on rainfall, and provide breeding sites for C. schultzei gp. and
other species (not C. imicola). The negative influence of rainfall is more likely due to the fact that
wetter winters are also much cooler, which may reduce vector survival. A contradictory phenomenon
was found in South Africa regarding C. imicola and African horse sickness (AHS) outbreaks. It was
found that a spell of drought succeeded by heavy rainfall was followed by AHS epizootics (28).
Wind patterns:
It is as yet unclear to what extent the BT virus overwinters in vectors in
Israel, as opposed to overwintering in vertebrate reservoirs, exploiting seasonal
animal movement (limited to the Bedouin's flocks, who raise non-susceptible
animals), or potential seasonal introduction via airborne vectors. The local air stream
in the Arava valley flows from the Dead Sea southward through the Red Sea region.
Constant winds between 20:00 and 23:00 h have a velocity of 15 km/h, and this might
actually suppress flight activity, prevent biting during the main feeding hours and
result in increased mortality of C. imicola (25, 29). The detrimental effects of high
wind speeds on C. imicola are due to desiccation, prevention of feeding and physical
removal. High wind speeds have the potential to move insects considerable distances
quickly, but this is difficult to demonstrate. Despite this, one may consider the
potential influence of the air stream on vector introduction into the two candidate
regions we propose as BTV-free zones.
Candidate bluetongue-free zones:
Based on historical BT records, the disease is basically
unknown in two regions of Israel-mountainous areas and the Arava Desert (30).
Mountainous regions above 700 m, although in the path of the Persian Trough
airstream (15), have several characteristics that suggest they will remain BTV-free for
at least the near future. First, numbers of C. imicola are relatively low, and substantial
overwintering is unlikely. Animal densities are relatively low (Fig. 2), and species
composition is dominated by goats, mainly of the Mamber breed, and local sheep
breeds, mainly Awassi, which are fairly resistant to BT (31, 32) and are not preferred
hosts for the vector, C. imicola (33). This area is likely to remain BT-free until more
susceptible ruminants are introduced. Higher standards of living might result in the
introduction of more cattle and European sheep breeds, which could, in turn, result in
more BT transmission. This would be especially true for dairies, which provide
disproportionately suitable developmental sites for the vector. The Arava Desert also
has a relatively small number of C. imicola. The growing numbers of dairies in this
area are likely to increase vector numbers, but very high summer temperatures also
should result in poor survival of the vectors and thus maintain low vector capacity
(11, 36). The Arava Desert should be investigated thoroughly to check whether it is a
valid BTV-free area. The indication of probably being BTV-free is supported by the
fact that in the Southern Arava serological survey in sentinel cattle showed that they
have been free of BTV at least 13 years (30). However, this region may also serve as
a source of C. imicola innoculum for more northerly regions in spring and early
summer, particularly after winter mortality in those cooler climates, and given the
prevailing wind patterns. The density of C. imicola in the Arava will rise with the
growing numbers of new dairies there but, as the Arava is beyond the Persian Trough
system (15) and because of the supraoptimal temperatures prevailing in the summer,
the survival of the C. imicola population may be too low for transmitting BT (11, 36).
Probably an additional limiting factor, for the survival of C. imicola at present is the
scarcity of carbohydrate sources. This might change as the areas of irrigated crops and
trees increase in the future. Therefore, the Arava should be considered as a probable
BT-free safe zone, at present.
Routine monitoring of the vector C. imicola is advisable, particularly near animals, in these proposed
BTV-free zones. Trap collections are highly variable and, therefore, must be interpreted cautiously. On
the assumption that light trap collections in some way approximate biting rates, it is possible
approximately to relate collections to risk, pending more definitive research. Holbrook (35), for
example, reported no observed BT transmission to sentinel sheep at light trap collections below ca. 3540 C. sonorensis females/trap. From our extensive observations at Bet Dagan, where BT often occurs
(but seasonally), DuToit light trap collections in cow sheds of ca. 345 C. imicola or above tend to be
associated with BT outbreaks. If vector populations of such magnitude exist in an area when BT
viruses are introduced by some means, substantial transmission might be expected. In simulation
studies of African horse sickness in Spain, it was found that during an outbreak the proportion of
infected C. imicola never exceeded 3% and that below a threshold of ca. 11,000 C. imicola per host no
outbreaks occurred (23). Further studies would be useful to refine this rough figure and relate it to
specific fluctuations in vector capacity components.
Acknowledgements
We are obliged to Dr. E. Rapaport of the Veterinary and Animal Health Services, Afula for providing
the data on outbreaks of BT in sheep, to Dr. A. Gnizi and Mrs M. Zarchi of the Volcani Centre for
performing the statistical analysis and to Dr. M. Van Ham of the Israeli Veterinary and Animal Health
Services, Bet Dagan for providing the figures on farm animal abundance in the various districts.
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Tables
Table 1: Stations from which precipitation data were taken for the BT study
Locality
Altitude above ground (m) Latitude N'
Longitude E'
Akko
15
320 55'
350 05'
Ein haHorsh
18
320 23'
340 56'
Galed
180
320 33'
350 04'
Ma’abarot
20
320 22'
340 54'
Bet Dagan
30
320 00'
340 49'
Yavne
20
310 54'
340 46'
Qiryat Eqron
50
310 52'
340 48'
Elon
300
330 03'
350 13'
Moshav Meron
941
330 00'
350 23'
Nazareth-Elit
460
320 42'
350 19'
Ramat David
80
320 41'
350 12'
Mizra
99
320 40'
350 17'
Afula
60
320 36'
350 17'
Tavor
145
320 41'
350 24'
Atarot
757
310 52'
350 13'
Kibbutz Hazerim
190
310 13'
340 36'
Beer Sheva
280
310 15'
340 48'
Golan Exp. Station
940
330 07'
350 48'
Gadot
100
330 01'
350 37'
Kefar Blum
75
330 10'
350 36'
Deganya Alef
-200
320 43'
350 34'
Tirat Zevi
-220
320 25'
350 32'
Table 2: Coefficient of correlation between number of BT outbreaks in sheep flocks in Israel in the
years 1970-1989 to selected climatic factors at Kefar Blum
Meteorological parameter
Coefficient
of the
linear
correlation
*Amount (mm) of rainfall, September through May
0.063
*Amount (mm) of spring (March-May) rainfall
-0.240
Number of frost nights (<00C) between November and March
0.154
Number of consecutive frost night between November and March
0.154
Number of consecutive nights in which the minimum temperature
was ²2 0C between November and March
0.070
Number of nights between November and March in which the
minimum temperature was ²50C
-0.052
The winter minimum temperature between November and March
-0.118
Number of Sharav days in spring (April 1 through June 15)
-0.136
Number of days in the spring in which the maximum temperature was >35?C
0.099
The annual maximum temperature
-0.441
*Average from 22 meteorological stations
Table 3: Comparison of the meteorological features at two localities of years with many bluetongue
outbreaks in sheep flocks to poor bluetongue years
Years with bluetongue epizootics (>30 flocks)
Year
Bet Dagan
75
87
88
94
Average
18.0
17.5
18.7
18.0
Kefar Blum
75
87
88
94
Average
17.5
16.8
Meteorological
parameter
Average maximum
temp. of the coldest
month (Dec.-Mar)
17.9
16.3
17.2
16.1
Average winter
maximum temp.
(Dec.-Mar.)
19.3
19.0
18.5
19.9
19.2
18.2
18.5
17.5
19.5
18.4
Winter minimum
temp. (Dec.-Mar.)
1.1
1.9
2.0
3.5
2.1
0
0
0
0.6
0.2
Total days in Jan.-Feb.
with maximum temp.
of 130C and above
56
58
57
59
58
54
55
50
57
54
Total days in Jan.-Feb.
with maximum temp.
of 180C and above
27
38
22
47
34
16
34
24
31
26
*Average seasonal
rainfall (mm)
523
643
599
384
537
523
643
599
384
537
23
34
17
4
19.5
41
48
26
33
37
Maximum spring
temperature (1 Apr-15
Jun)
37.2
39.4
43.2
41.2
40.3
37.9
39.4
40.9
38.0
39
Number of Sharav
days
7
2
5
6
5
10
8
10
20
12
Total days in winter
(Nov-Mar) with min.
temp. of 50C and
below
*Average rainfall in Mar-May (mm)
Years with no bluetongue epizootics (0-1 flock)
80
81
83
94
Average
75
87
88
94
Average
Average maximum
temp. of the coldest
month (Dec.-Mar)
16.8
16.7
14.9
18.7
18.0
16.3
17.2
16.1
17.5
16.8
Average winter
maximum temp.
(Dec.-Mar.)
18.3
18.8
17.0
19.9
19.2
18.2
18.5
17.5
19.5
18.4
Winter minimum
temp. (Dec.-Mar.)
1.0
2.5
0.2
3.5
2.1
0
0
0
0.6
0.2
Total days in Jan.-Feb.
with maximum temp. of
130C and above
59
58
45
59
58
54
55
50
57
54
Year
Total days in Jan.-Feb.
with maximum temp. of
180C and above
15
17
11
47
34
16
34
24
31
26
*Average seasonal
rainfall (mm)
728
608
686
384
537
523
643
599
384
537
Total days in winter
(Nov-Mar) with min.
temp. of 50C and below
28
24
42
4
19.5
41
48
26
33
37
Maximum spring
temperature (1 Apr-15
Jun)
42.0
37.2
36.6
41.2
40.3
37.9
39.4
40.9
38.0
39
Number of Sharav
days
12
2
1
6
5
10
8
10
20
12
*Average rainfall in
Mar-May (mm)
121
79
129
48
94
121
79
129
48
94
Table 4: Numbers of Culicoides spp. suction light trapped in the mountain and Arava areas, i.e.,
bluetongue free zones versus Bet Dagan zone where bluetongue prevails
Locality, region
(longitude and
latitude)
Beit Jann, Upper
Galilee
(320 58'N 350 22'E)
Altitude
(m)
Month/year
920
8-10/81 ;
Location of
trap:
host/breeding
site
goats
Average no. of Culicoides
spp. per night/per trap
Average no. of Culic
spp. per night/per trap
Dagan
<1 C. obsoletus; <1 C.
imicola
47 C. imicola; 6 C. sc
gp.;
<1 C. circumscriptus;
5 C. distinctipenn
<1 C. schultzei gp
7 C. circumscriptus;
cataneii;
<1 C. cataneii
<1 C. puncticollis; <
newsteadi;
1 C. obsoletus
Ein Kerem (Agr.
School), Judean Hills
(310
660
9/78
cows
<1 C. sp.
46'N 350 10'E)
Yotvata, Arava Valley
3 C. imicola; <1 C.
newsteadi
75
8/82
cows
95 C. imicola; <1 C.
;
131 C. imico
C. distinctipennis
5 C. schultzei gp; 1
cataneii
<1 C. newsteadi; <
circumscriptus
629 C. imicola; 74
(290
obsoletus;
53'N 350 03'E)
<1 C. schultzei gp
11/82
cows
72 C. imicola; 4 C. schultzei
gp.;
schultzei gp;
26 C. distinctipennis;
newsteadi;
<1 C. obsoletus; 1
circumscriptus
10 C. imicola; 8 C. sch
gp
>1 C. distinctipennis;
newsteadi;
<1 C. obsolet
C. circumscriptus
Table 5: Average numbers per night, per trap of Culicoides spp. suction light trapped in two sites at
Beit Dagan, Rehovot district in June, a month before the bluetongue season
Bet Dagan, Veterinary Institute
Bet Dagan, Volcani Center
Animal compound
Year
1982
8 C. obsoletus
>3 C. imicola
<1 C. cataneii
<1 C. newsteadi
<1 C. puncticollis
<1 C. circumscriptus
experimental dairy farm
Year
1982
345 C. imicola
10 C. schultzei gp
8 C. circumscriptus
6 C. distinctipennis
5 C. newsteadi
2 C. cataneii
<1 C. obsoletus
<1 C. puncticollis
1996
17 C. imicola
<1 C. circumscriptus
1996
18 C. imicola
<1 C. circumscriptus
Table 6: Numbers of Culicoides species per night per trap in the winter of 1997/98
(November 1997-March 1998)
Month
No. of trappings/no. of traps
Species
11/97
7/4
170 C. imicola
7 C. schultzei gp.
12/97
8/4
38 C. imicola
1.5 C. schultzei gp.
<1 C. puncticollis
1/98
5/4
10 C. imicola
<1 C. schultzei gp.
<1 C. puncticollis
2/98
9/4
6 C. imicola
<1 C. schultzei gp.
<1 C. circumscriptus
3/98
9/4
6 C. imicola
<1 C. schultzei gp.
<1 C. circumscriptus