ISRAEL JOURNAL OF
VETERINARY MEDICINE
DYNAMICS OF BITING ACTIVITY OF C. IMICOLA
KIEFFER (DIPTERA:CERATOPOGONIDAE) DURING
THE YEAR
Y. Braverman1, S. Rechtman2, A. Frish1, and R. Braverman3
Vol. 58 (23) 2003
1. Kimron Veterinary Institute, P.O.B. 12, 50250 Bet Dagan,
Israel
2. Tichon Reali Highschool, Rishon Le'Zion, Israel
3. Industrial Management Engineering, Ben Gurion University,
Beer Sheva
Summary
Collections from a bait calf yielded 520 C. imicola Kieffer. The calf’s back, in
particular the black haired patches, were highly preferred as landing and biting
sites. In only one out of six collection sites C. imicola were found in large
numbers. The crucial importance of vision in detecting the host by c. imicola and
other species was proved by using a variety of bait traps in Israel and Zimbabwe
he landing and biting activity of C. imicola were limited to twilight times, with
the largest peak occuring at sunrise. A constant ratio between parous and
nulliparous C. imicola females was found at sunset, while a different ratio was
found at sunrise. C. imicola constituted 98.5% of the Culicoides spp. collected at
Bet Dagan. The constant ratio between nulliparous and parous females C.
imicola, of 2:1 was obtained throughout the night hours. Numbers of C. imicola
peaked during the autumn. The flight activity of C. imicola in July-August
peaked between 3:00 am and 5:00 am. The peak hours varied from month to
month corresponding to changes in day length, temperature, and relative
humidity. Of all the meteorological parameters tested for their effect on
population density, the only correlation was found with temperature showing
numbers of C. imicola increasing between 17 and 25oC.
Introduction
The major species of Culicoides populations in the Middle-East have generally
two seasonal peaks: a small one in the spring and a larger one in autumn (1).
However in nightly suction light trappings throughout the year at Bet Dagan in
1982, only the autumn peak was detected (2). The hourly peak flight activity of
C. imicola was found by Nevill (3) in South Africa to band between 1.00 am and
3.00 am. No distinction was made in this study between the nulliparous and
parous components of the population. It was later found that females of different
physiological ages differ in their diurnal activity (4). Suction light traps can
provide only general information on the species composition within the attraction
range of the traps, but not on the activity of the biting population, its hourly
activity and physiological age. To obtain this information, studies using live
hosts (5) were carried out in various places in the world to identify which
Culicoides spp. bit different parts of the cow’s body. Culicoides brevitarsis
Kieffer, which is a close relative to C. imicola, prefers to bite the back of cattle
(6). It was therefore assumed that C. imicola has a similar preference. That C.
imicola prefers to bite cattle has been known for many years (7), but its biting
preference for various parts of the body has not been reported. The reported
biting activity times of medically important Culicoides spp. is at dusk and dawn.
Culicoides kingi Austen, a cattle feeder in southern Sudan, was found to have a
biting peak before sunset, twice as much as the peak before sunrise (8). It was
found in Alabama that Culicoides spp. prefer open fields for biting. The numbers
of biting midges collected from a sentinel calf in an open field were 2.5 fold
higher than those collected from a calf situated in a forest (9) and this might be
because a host is more visible in the open (10). Preferred meteorological
conditions for biting include: calm air or slight wind, high relative humidity and
temperatures around 200C (6).
This study was undertaken to identify the species of Culicoides biting cattle, the
preferred parts of the body, their diel landing and biting activity, and compare the
diel activity of the populations attracted to suction light traps with those attracted
to cattle. These data were correlated with weather conditions of temperature,
relative humidity, wind velocity and direction and cloud cover. The influence of
site location and housing of the host on the number of Culicoides collected was
also studied.
Introduction
Results
Discussion
back to top
Materials and Methods
The major study
was carried out at the
ground of the Kimron
Veterinary Institute
during 11 months
from 16.10.86 to
21.11.87. Male Israeli
Holstein calves were
used as baits. Seven
calves from 4 to 10
month old, standing
80 to 100 cm, length
150 to 200 cm and
weighing 100 to 300
kg were used. Most of
the collections were
done on a calf 6 to 10
month old, with
mainly black in
colour, with an initial
weight of 100 kg and
Fig. I Collection zones from the body of the bait calf
weighing 200 kg at
the end of the
experiment. There
were five collection
sites on the calf (Fig.
1). The caged animal
was moved to six
different sites to find
an appropriate
location rich with
Culicoides spp.
Collections were
made mainly with a
battery operated
asprirator (Housherrs'
Machine works, N.Y.
USA) and to a lesser
extent with a mouth
aspirator. For
illuminating the site
of collection, a head
lantern covered with
red cellophane to
avoid disturbance to
midges was used
(Type 1904 Y. Cell,
Justrite
Manufacturing,
USA). Time of
collection was from
half an hour before to
an hour post sunset
and sunrise. Each
collection continued
for 10 minutes and
was followed by a
break of 5 minutes.
The 90 minute
collections at the
calendar sunset and
sunrise were divided
into periods of 30
minute. Twenty-four
hour collections were
also made to
determine the exact
biting time.
The collected insects were put in saline solution containing detergent for
identification. Insects were categorized by species, sex, nulliparous and parous.
Suction light trap (11) situated in the center of the cowshed was also operate to
compare the composition of the population attracted to the suction light trap in
parallel with that collected from the calf. The second purpose was to determine
the seasonal activity and the third to determine the diel activity. For the last aim
the catch at each hour was sorted according to the above criteria.
Host detection: Data from a modified Magoon type (5) bait trap, a Davies trap
(12) and a Monks Wood suction black light trap, as described by Braverman et
al. (13) in Israel were utilized. In order to learn whether the midges enter the
Magoon traps and do not escape, a window frame from which the glass was
removed, was covered with strips of organdy cloth, smeared with castor oil and
placed inside the Magoon trap to catch the midges. Another type of trap baited
with a two week old calf weighing about 50 kg was operated fourteen times
between July 16 and December 31, 1978 in Ga'ash (32014'N 34049'E). The trap
was situated in an open field at the northeastern side of the village. The trap was
a square structure the four sides of which were each comprised of two
electrocuting grids (from Matador insect exterminator model 1220, Ga'ash
Lighting Co. Israel), from which the black light lamps were removed. The top of
the structure was covered with a plastic sheet. Insects had access to the calf
through the electrocuting grids. Bait trap data from Harare area, Zimbabwe were
also used based on lard-can traps (14); a trap designed by Turner (15) and
trappings by a version of the bed-net trap (16). Data on the last trap were reported
also by Braverman and Phelps (17).
Meteorological data: Minimum and maximum temperatures were taken in Bet
Dagan at the collection site near the bait animal. Temperatures, relative humidity
(%), cloud cover, wind direction, wind velocity and rainfall for other dates were
taken from the monthly data published by the Israel Meteorological Services. The
influence of these parameters on the collection from calf with a suction light trap
was examined.
Statistical analysis: The following tests were used: a. paired t test; b. c2 (Chi
square) and c. analysis of variance. The t and F tests were performed on
logarithmic transformed data.
Results
Collections from a calf. Fifty-two collections at six sites located at different
places on the farm were made. Of these, site no. V yielded 98% of all the
Culicoides specimens. Table 1 shows the numbers of Culicoides spp. collected at
the different sites. In the years 1981 to 1982, from January to December, suction
light traps were run in parallel at three sites of the animal compound, near a
stable, near a calf shed, and near a large cowshed. Comparison of Culicoides spp.
numbers collected from these sites show significant differences. At the first site,
during 6 light trappings, 1117 specimens of Culicoides spp. were caught versus
30 specimens of Culicoides spp. caught near the cow shed (P< 0.01). From the
calf shed, 1208 specimens of Culicoides spp. were caught during 3 light
trappings, as compared to 336 specimens of Culicoides spp. caught near the cow
shed. (P < 0.05). Thus, significant differences in Culicoides spp. numbers were
found between the various collection sites. This agrees with our findings from the
calf collections. Of the total number of Culicoides collected from a calf, 522
were C. imicola, 1 C. newsteadi Austen and 1 C. schultzei gp. Thus 95% of the
collected midges were found on the back and 5% were found on the flank of the
calf (Fig. 1). At both collection areas, most of the females were nulliparous, and
10% of the females collected from both areas were engorged (Table 2).
Culicoides imicola clearly preferred to land on the dark than the lighter areas of
the calf.
Table 1. Collection of Culicoides spp. from a calf in various sites within the
animal compound at Bet Dagan (1986/7).
Site
No.
Date
I
October 22-31.86
0/4
0
II
October 22-31.86
0/4
0
III
June 20-July 10.87
1/4
2
IV
April 23-June 11.87
1/5
3
V
July 19-November 21.87
30/34
513
VI
October 6-15/87
3/3
6
Total
October 16.86-November 21.87
35/52
524
No. of positive collections /
total no. of collections
No. of Culicoidesspp.
collected
Table 2. Physiological age distribution of C. imicola gnats collected from the back
and sides of a calf (Bet Dagan, 1986/7).
Body zone
Total no. of
nulliparous
No. of engorged
nulliparous
Total no. of
parous
No. of
engorged
parous
Total
%
Back (1)
296
29
145
27
497
95
Side (2)
16
1
7
1
25
5
Others
(3,4,5)
0
0
0
0
0
0
Total
312
30
152
28
552
100
Diel activity peaks of C. imicola. Collections from a calf over 24 h showed
only two peaks, i.e. at sunrise and sunset. Of the 44 sunset collections, 38
yielded Culicoides spp. At sunrise, only 8 collections were made and 7 were
positive. The landing and biting activity occured from half an hour before till one
hour after sunset. According to the "t" test, the sunrise peak is significantly (P<
0.05) higher than the sunset peak (Table 3).
It was found that the proportions of nulliparous, engorged nulliparous, parous
and engorged parous of C. imicola, caught at sunset and sunrise, were similar at
both times. Statistical analysis (c2) for sunrise and sunset showed no significant
dependence between the four categories of female C. imicola and the time
periods of 30 minutes. This infers that the fixed proportions between nulliparous,
engorged nulliparous, parous and engorged parous are independent of the time of
collection.
Table 3. Numbers of C. imicola collected at sunset and at sunrise (Bet Dagan.
1986/7).
Date of
collection
Sunset
Sunrise
Hours of collection
No. of midges
Hour of collection
No. of
midges
July 19-20
19.20-20.50
0
5.30-7.00
12
August5-6
19.15-20.45
4
5.15-6.45
18
August 12-13
19.00-20.30
6
5.30-7.00
28
August 26-27
18.45-20.15
0
5.15-6.45
29
October 1-2
17.00-18.30
3
5.00-6.30
10
October 20-21
16.10-17.40
19
5.30-7.00
28
Total
32
Figure 2 and statistical analysis show that accumulatively at sunset similar
numbers of C. imicola were collected at the first [89] and third [83] time periods,
whereas in the second [197] time period higher numbers of insects were
collected. At sunrise accumulatively (Fig. 3), similar numbers were collected at
the first [78] and second [60] time periods, whereas smaller numbers [6] were
collected during the third time period. Statistical analysis for each of the
following categories: nulliparous, engorged nulliparous, parous and engorged
parous showed similar tendencies. Analysis by c2 showed that the proportions of
the numbers of C. imicola collected at each time of sunset and sunrise differed
from (P<0.01) 1:1:1.
Information on the biting activity of C. imicola could be derived from the
analysis of each time period at sunrise and sunset collections during July through
December (Fig. 4, 5, 6, 7). Figure 4 shows that the activity of the nulliparous C.
imicola at sunset is not stable over the season and is characterized by sharp rises
and falls. The following four major peaks are shown: second half of July, first
half of September, second half of October and second half of November. The last
peak is the highest and reflects the rise which occurred during the three collection
periods. The activity of the nulliparous C. imicola at sunrise showed moderate
changes compared with changes at sunset. The peak is in August after which
there is a moderate decline till October. In this month, there is a moderate rise in
125
the first and third time periods and a sharper rise in the second time period. The
activity of parous C. imicola during sunset (Fig. 6) is not fully expressed due to
the smaller numbers collected throughout the season compared with the activity
of the nullipars (Fig. 4).
The parous have three main peaks: first half of August, first half of September
and first half of November. The last peak is the longest and highest and reflects
the rise in numbers of C. imicola collected in the three time periods. Numerically
the peaks of the parous are smaller than those of the nulliparous. The activity
changes of the parous C. imicola at sunrise (Fig. 7) throughout the season were
more moderate than the changes during sunset (Fig. 6). The parous peak was in
August, similarly to the peak of the nulliparous (Fig. 5). Following the peak,
there was a moderate decline till October when there was a moderate rise in the
second and third time periods, versus a slow decline during the first time period.
Fig 2. Numbers of C. imicola aspirated from a calf from July to November in each
tertiary period of 30 minutes during sunset in 1987.
Fig 3. Numbers of C. imicola aspirated from a calf from July to November in each
tertiary time period of 30 minutes during sunrise in 1987.
Fig 4. Numbers of nulliparous C. imicola aspirated from a calf in each tertiary time
period of 30 minutes during sunset in 1987.
Fig 5. Numbers of nulliparous C. imicola aspirated from a calf in each tertiary time
period of 30 minutes during sunrise in 1987.
Fig 6. Numbers of parous C. imicola aspirated from a calf in each tertiary time
period of 30 minutes during sunset in 1987.
Fig 7. Numbers of parous C. imicola aspirated from a calf in each tertiary time
period of 30 minutes during sunrise in 1987.
The influence of meteorological factors on the biting activity of C. imicola
The comparison of the meteorological data with the numbers of collected
midges showed a significant association only with the daily maximum
temperature. The peak of activity occurred when temperatures were between 20
to 24oC and activity continued up to amaximum daily temperature of 34oC (Fig.
8). The regression equation on the association between the numbers of Culicoides
(tot) and the maximum temperature (t.max): tot = 82.04 - 2.30 * t.max. with r2 =
0.38 (P< 0.0008). No collections were made on rainy days.
Fig 8. Numbers of gnats aspirated from a calf plotted against the maximum
temperature.
Suction light trappings
a. The diurnal activity of Culicoides spp. as measured by
suction light trappings
Only few Culicoides spp. were caught during daytime
operation of suction light traps. Similarly 40 daytime
trappings at the animal compound of the Veterinary Institute
were carried out in 1978 to 1979, and only in 5 trappings
11Culicoides were caught: 6 C. imicola, 4 C. distinctipennis
Austen and 1 C. circumscriptus Kieffer.
In the present study, the suction light trap was operated
over 38 nights and Culicoides were caught each night.
Seven of the trappings were done in 1986. A total of 10,257
Culicoides spp. were caught, out of these 285 (2.75%) were
males. Seven species were caught (Table 5), the principal
one was C. imicola which constituted 98.5% of the catch.
These findings are parallel to the collection from the calf,
where C. imicola was also the principal species.
b. Average monthly catch of C. imicola
The numbers of C. imicola during April through
November 1987 grew gradually till the peak in September
Fig 9. Monthly abundance of C. imicola
(autumn). In October-November a marked decrease in their
numbers occurred (Fig. 9). Similar activity was seen in
1969, when the autumn peak continued over 4 months i.e.
August to November (Fig. 10).
c. The peak hours and the diem activity of Culicoides spp.
as measured by suction light trappings
Hourly night trappings were conducted in May to
November 1987 over 10 nights. The catch from each hour
was sorted and identified. A rise in the number of
Culicoides was found during the night and the sharpest
increase occurred in July-August between the seventh and
eighth hours of darkness (2:00-3:00). In May-June the peak
was between the eighth and ninth hour at 2.30 a.m. to 4.30
a.m.; in July to August, at 3.00 to 5.00 a.m.; 1.30 to 3.30
a.m. in October and 12.30 a.m. to 2.30 a.m. in November.
Following the peak, there was a sharp decrease at the
eleventh hour (of darkness) i.e. 5.00 to 6.00 a.m. in JulyAugust (Fig. 11).
The major component of the population was nulliparous
and parous females, whereas in decreasing order were:
engorged nulliparous, engorged parous and males.
Engorged females were caught throughout the night, with a
peak at the eighth and ninth hours. A significant (P <
0.0003) difference was found in the activity of the various
categories of females (nulliparous, engorged nulliparous,
parous and engorged parous) throughout the 12 hours of
night trapping.
d. The influence of meteorological factors on the flight
activity of Culicoides spp. as measured by suction light
trappings
By correlating the meteorological data with the number of
Culicoides spp. caught by the suction light trap throughout
the season, a significant (P<0.0001) association was found
only with the minimum daily temperature (Fig. 12).
Host detection: Using bait traps originally designed for
mosquitoes, between March to October 1978 at Bet Dagan
yielded only small numbers of Culicoides spp. (Table 6).
Fig 11. Numbers of gnats suction light trapped according to
five categories: M, males; P, parous; PE, parous
engorged; N, nulliparous; NE, nulliparous engorged.
Fig 10. Monthly abundance of C. imicol
Fig 12. Numbers of gnats suction light t
minimum temperature.
Table 4. Distribution of the physiological stages of C. imicola collected at sunrise
and at sunset.
Time Period of Collections
Sunset
Nulliparous Nulliparous Parous Parous
engorged
engorged
1st
58
4
23
4
catch
%
65
4.5
26
4.5
2nd
124
10
51
12
catch
%
63
5
26
6
3rd
53
7
18
5
catch
Total
89
Nulliparous Nulliparous
engorged
37
5
Sunrise
Parous
Total
29
Parous
engorged
7
Nullipa
78
95
100
197
47.6
31
6.4
4
37
25
9
0
100
60
57
155
100
83
51.7
4
6.6
0
41.7
2
0
0
100
6
60
57
%
Total
%
1
64
235
64
8
21
5.5
22
92
25
6
21
5.5
100
369
100
67
72
50
0
9
6.25
33
56
38.8
0
7
4.95
100
144
100
64
30
60
Each collection lasted 90 minutes divided into three 30-min segments.
Table 5. Culicoides spp. light trapped at the veterinary institute in the years
1986/1987
Month/year
10/86
11/86
12/86
4/87
5
1
1
1
No. of trapping
operations
Species
Total No. of Average Total No. of Average Total No. of Average Total No. of Average Total No
males per night
males per night
males per night
males per night
ma
C. imicola
1389
28
277.8
124
0
124
6
0
6
C. schultzei gp
37
12
7.4
1
0
1
1
0
0.25
14
0
3.5
C. newsteadi
C. puncticollis
1
Becker
C.
circumscriptus
Total
1426
0
40
0.25
285.2
2
0
124
6/87
7/87
No. of trapping-
5
4
Species
Total
C. imicola
1076
No. Average Total
of
per night
males
35 215.2 1809
C. schultzei gp
4
0
0.8
C. newsteadi
1
0
0.2
C. puncticollis
14
0
2.8
C.
circumscriptus
C. obsoletus
Meigen
1
0
0.2
1
0
0.2
Total
1098
35
219.6
Month/year
14
1823
124
7
0
7
15
0
3
2
0
3.75
99
5
10/87
6
1
3
No. Average Total
of
per night
males
38 452.25 2826
No. Average Total
of
per night
males
67 471
740
No. AverageTotal
of
per
males night
21 740
1563
No.
of
males
41
5
0
3
0
3
14
3
14
2
14
4
0
1581
44
3.5
455.75
7
1.2
2
0
0.3
1
0
1
2835
67
472.5
758
23
758
11/87
Total
3
Total
2
9/87
43
8/87
No. of trapping
operations
Species
3
0.5
0
Month/year
91
No. of
37
Average
Total
N
C. imicola
C. schultzei gp
469
6
males
28
0
per night
156.3
2
C. newsteadi
C. puncticollis
16
0
5.3
10107
87
38
17
C. circumscriptus
4
C. obsoletus
C. cataneii Clastier
4
1
491
Total
28
163.6
10257
Table 6. Live and chemical baits used in various traps in order to catch Culicoides
spp. in Israel in 1978..
Locality
Trap type
Trap position Bait
Bet Dagan
Modified
Magoon trap
Modified
Magoon trap
Modified
Magoon trap
On the ground 4-13 chickens
Period of
trappings
operations
March-June
Modified
Magoon trap
Modified
Magoon trap
Modified
Magoon trap
Modified
Magoon trap
Bet Dagan
Bet Dagan
Palmahim
Palmahim
Bet Dagan
Bet Dagan
Bet Dagan
Bet Dagan
Bet Dagan
Bet Dagan
Bet Dagan
Bet Dagan
Bet Dagan
Modified
Magoon trap
Modified
Magoon trap
Modified
Magoon trap
Modified
Magoon trap
Modified
Magoon trap
Modified
Magoon trap
Modified
Magoon trap
No. of trap
operations
Culicoides spp. t
9
4
On the ground 2 turkeys
August-September 3
0
On the ground 1 calf
March-June
12
2
C. circunscr
June
2
1
0
C. sp.
On the ground 1 calf
On the ground 1 calf and 2
turkeys
On the ground 1 sheep
June
4
0
June-September
12
0
On the ground 1 calf, 1 sheep
and
May-September
6
0
10
0
6
0
May-June
2
0
August
3
13
C. circumscr
4
2
C. imicola
3
C. circumscr
C. imicola
2-3 turkeys
On the ground 1 sheep and 1-2 July-October
turkeys
On the ground 4 kg dry ice
May-June
On the ground Ammonia
(NH4OH) 5%
Hung on pole Monks wood
inside the
suction black
modified
Magoon
traplight trap
Hung on pole
inside the
Monks wood
suction black
light trap with
dry ice
On the ground 1sheep and
Monks wood
black light trap
August
August
1
1
C. distinctipe
1
Bet Dagan
Bet Dagan
Bet Dagan
1
Davies (1973)
trap
Davies (1973)
trap
Davies (1973)
trap
Hung on pole
on tree
Hung on pole
on tree
Hung on pole
on tree
Palm dove
March-August
7
1
1
C. circumscr
Guinea pig
March-August
7
1
C. circumscr
3 kg dry ice
June-Julyt
2
1
C. circumscr
All Culicoides trapped were females.
Magoon trap baited with chickens caught four C. distinctipennis on March 28
and April 4. A frame with organdy cloth smeared with castor oil used in one
operation with the chickens did not collect any Culicoides. A calf used as bait
caught two C. circumscriptus and one unidentified Culicoides on March 21 and
April 17. A frame covered with organdy smeared with castor oil which was
operated three times with a calf did not catch Culicoides spp. Magoon trap baited
with a sheep, mixed hosts of a calf, a sheep and turkeys, sheep and turkeys; and
the attractants; 4 kg dry ice and 5% ammonia, yielded no Culicoides spp. An
organdy frame with castor oil was used three times together with dry ice failed to
trap any Culicoides. Monks Wood suction black light traps without any
additional bait, were operated 3 times inside the Magoon traps. In addition a
similar trap plus dry ice and another one together with a sheep were operated.
With these 16 C. circumscriptus, 8 C. imicola, 3 C. distinctipennis, 2 C. schultzei
gp., 1 C. newsteadi and 1 C. odiatus Austen were caught, i.e. five times more
than with animals alone as baits during eight months.
Davies trap baited with a palm dove (Streptopelia s. senegalensis) caught on
June 20, only 1 C. circumscriptus. On July 4, 1 C. circumscriptus was caught in a
trap baited with a Guinea pig. On July 20, Davies trap baited with dry ice, caught
1 C. imicola.
Only Culicidae and no Culicoides spp. were caught at the bait trap in Ga'ash.
In Zimbabwe (Table 7) lard can traps baited with a rabbit, two guinea pigs,
pigeon and dry ice, hung on trees in various positions and laid on the ground,
yielded no Culicoides spp. During the same period lard can traps baited with
chickens caught C. milnei Austen on two occasions. A single female was caught
on January 5, and three females were caught on May 3 on the castor oil smeared
funnel from which the carnivore protecting net on the opening was removed
(Table 7). Turners' (15) trap baited with a chicken caught Culicoides spp. on four
occasions: 30-31.3.77; 31.3.-1.4.77; 12-13.4.77 and 2-3.5.77. The catch on the
first date was the largest and comprised 25 C. imicola and 8 C. milnei. Three of
Turner's trap (15) of the four operations were conducted at a site richer in
Culicoides spp. In all four operations that yielded Culicoides spp., castor oil was
smeared on the strips of the muslin cloth and also on strips of muslin cloth that
were put over the chicken restrainer. The Culicoides specimens were actually
collected from the smeared cloth. Bed net trap baited with a calf caught 12
Culicoides specimens which is the largest number when compared to 6 and 2
Culicoides specimens caught in a similar device baited with human and sheep
respectively.
Table 7. Culicoides spp. collected in live and chemical baits used in various traps
in Harare area, Zimbabwe (1976-1977).
Trap type
Position of the Bait
trap
Period of
trappings
No. of trap
operations
Culicoides spp. trapped1
Lard can
Hung
1 rabbit
horizontally on
tree vertically
and on the
ground
28.10.765.4.77
43
0
Lard can
Hung
2 guinea pigs 15.2-18.2.77
horizontally on
tree
3
0
Lard can
Hung on tree
horizontally
and vertically
Lard can
Turner, 1972
1 chicken
3.11.76-4.5.77 57
4
Hung
1 pigeon
horizontally on
tree
dry ice
28-29.10.76
1
0
18-19.1.77
4
0
Hung on tree 1 chicken
and on ground
11.3-5.5.77
20
37
C. inicola
16
C. milnei
Turner, 1972
Turner, 1972
18-19.3.77
1
0
Bed net
Hung
1 rabbit
horizontally on
tree
On the ground 1 sheep
22.12.7625.2.77
10
1
Bed net
On the ground 1 calf
14.3-24.3.77
7
1
7
3
1
1
Bed net
1
On the ground 1 human
4.3.-12.3.77
2
4
1
1
C. milnei
C. milnei
Ingram &
Macfie
C. pycnostictus
C. milnei
C. imicola
C. nivosus De
Meillon
C. zuluensis
De Meillon
C. minei
C. imicola
C. fulvithorax
Austen
All Culicoides trapped were females.
Discussion
a. The preference of Culicoides to the calf site
High numbers of Culicoides midges were aspirated on one out of six site
locations of the calf. At the same time the suction light trap caught Culicoides
spp. near five negative sites. This indicates the existence of a factor(s) that
hampers detection of the host by Culicoides. The known major host attraction
parameters are: temperature, humidity, scents and sight of the host. It is assumed
that host's temperature in summer was similar at all collection sites as all were
done at the same time, and mostly from the same calf. Site II, from which no
Culicoides spp. were collected, was close to a large cowshed and the midges
were probably attracted more to the animals in the cowshed emitting more
attractants. Even when the calf was put inside the same cowshed (site III), only
two Culicoides specimens were collected. Culicoides might be more attracted to
older and larger animals. At site IV, three Culicoides spp. were caught where the
calf was put inside a citrus grove. The trees might have hidden the host from the
midges. This finding is in accord with a study in Alabama (10) where it was
shown that 2.5 fold more Culicoides specimens were collected from a host
situated in a field than from one situated in a wooded area. Most Culicoides spp.
were collected from site V which was situated in an open area that could be seen
from most sides. Site VI, like site V, was situated in an open area and indeed
Culicoides spp. were collected from the bait animal in smaller numbers. The
smaller numbers of Culicoides specimens from site VI is probably due to the
distracting light from a lantern situated nearby, and/or air turbulence which
disturbs landing of the biting midges on the calf. In this case it seems that
visibility of the animal was the determining factor. In the negative sites, the trees
and/or animal houses shaded and obscured the calf from the Culicoides spp. The
fact that C. imicola preferred to land on the dark haired areas of the body,
avoiding the white ones, shows that even at twilight time and darkness the
midges like mosquites can distinguish between different light and/or temperature
intensities (18). Intense shadowing at the negative sites might have prevented the
Culicoides spp. from finding the calf. The fact that houses and trees interfere
with the orientation of Culicoides spp. to their hosts, can explain the seemingly
erratic transmission of bluetongue or other Culicoides-borne pathogens, when
one farm is infected while a nearby farm is not. It can be concluded that the
location of the animal house, related to its exposure to Culicoides spp., can
influence pathogen transmission by midges.
b. C. imicola preferred landing and biting sites on a calf
In collections made directly from the calf, the major species was C. imicola
which also constituted 98.5% of the Culicoides spp. population caught by the
suction light trap. It was found that C. imicola prefers to land and most probably
bite the back, especially the dark haired areas, and avoids the white ones.
Landing preference of C. imicola on the back was already described in a horse
(19). This finding strengthens the assumption that C. imicola behaves similarly to
the Australian species C. brevitarsis which also prefers to bite the dark areas
along the back of the cow (6).
c. The diel biting cycle of C. imicola
Many species of Culicoides prefer to bite mainly at crepuscular time (8,20).
Little information was published on the biting habits of C. imicola. According to
Braverman (19) a peak biting time occurs at sunset, sunrise was not previously
checked however. The present study shows a greater peak at sunrise than at
sunset.
d. The association between light intensity and C. imicola activity
Monitoring the numbers of C. imicola caught at each time shows an increase
towards sunrise or sunset confirming the finding that biting activity is associated
with changes in light intensity. At sun-rise, there is a sharp drop in the numbers
of collected midges with full daylight. The numbers of C. imicola collected at the
first and third time periods of sunset is similar probably because in the first time
period is too much light, and in the third time period it is too dark. Largest
numbers of C. imicola were collected at the second time period, when the highest
changes in light intensity occur.
e. Hourly flight activity of C. imicola as measured by a suction light trap
The peaks of activity observed in April-June, July-August, October and
November were similar to those found in South Africa (3).Temperature and
relative humidity (%) seemed to be the factors that determined the time of peak
flight activity of Culicoides spp. During the hottest months of July-August, the
air temperature drops only between 3.00 to 5.00 A.M to its optimum for
Culicoides spp. when there is the highest relative humidity.
In November the temperature between 3.00 am and 5.00 am is too low for
flight activity and therefore the optimum for flight is between 00.30 anm and
2.30 am. For C. sonorensis in southern California it was found that the peak
flight activity in October and November occurred at 0-3 h after sunset (21). At
this time of the year, relative humidity is high throughout the night. A constant
hourly ratio of nulliparous and parous female Culicoides was found throughout
the sampled nights. This was in contrast to the different patterns of hourly flight
activity in the various categories of females reported elsewhere (4). Constant
hourly ratios between nulliparous and parous for each night sampled were
similarly found throughout the insect season. In this study, as in previous ones (2,
4) it was found that the ratio of parous C. sonorensis and C. imicola was greater
towards the end of the season. The unmatched peaks of the suction light trap and
the direct collection from the calf indicated that the two trapping methods collect
different populations of the same species. The non-biting population of C.
imicola in the suction light trap has a different flight peak than the biting
population collected from the calf.
f. Host detection The paucity of Culicoides spp. entering the modified Magoon
and Davies (12) traps together with the absence of Culicoides in the castor oil
frame inside the modified Magoon trap eliminates the possibility that Culicoides
spp. might have entered the trap and eventually found their way out. Also the
visible attraction source, i.e. Monks Wood suction black light trap, positioned
inside the modified Magoon trap, caught five times more Culicoides spp. than
those caught during the entire period by animals and chemicals used as baits,
demonstrates the significance of sight in host detection. Indeed showing the
importance of sight for host detection by mosquitoes, enabled Klowden and Lea
(22) to construct their bait trap with a transparent Plexiglass cover. These
findings show that Culicoides spp. actually see the animals in their host detection
trials. In Zimbabwe the lard can bait trap which hid the animal prevented its
detection by Culicoides spp. Three out of four C. milnei, probably attracted by
the smell of the chicken bait, were picked off the castor oil smeared on the
opening of the trap. The only bait trap used in the entire study, especially
designed for trapping Culicoides spp. was Turners' (15) trap. In Virginia, Turner
caught eight Culicoides species with no details on the numbers trapped (15).
While in 21 catching operations, carried out in Zimbabwe, between March-May
1977, only 37 C. imicola and 16 C. milnei were caught (15). Out of the total 53
Culicoides specimens at least 18 were collected from castor oil smeared surfaces
of the trap. There is an indication that some of the Culicoides spp. found their
way out and it is evident that the trap was not effective in trapping the Culicoides
spp. in the study area. The Magoon bed net trap with each of the three baits
collected only few Culicoides spp. Though castor oil was not used in this case it
is assumed that the small numbers of Culicoides spp. caught was due to the
midges not detecting the bait, rather than their entering and escaping through the
opening. The least attractive bait was a sheep and the most attractive was a calf
luring 6 times more Culicoides midges than the sheep. This host preference was
previously recorded (7, 13).
g. The effect of meteorological factors on Culicoides spp. activity
Relative humidity, wind velocity and direction and cloud cover are known to
exert influence on Culicoides spp. activity, but no such influences were detected
in this study. This might be due to not collecting meteorological data at the
collection sites and not at the times of collections and trappings.
h. Importance of the findings
Biting time activity of Culicoides spp. is short and limited to sunrise and sunset.
As C. imicola prefers the back of the animal, it can be simply controlled by clock
operated foggers installed on turntables and programmed to spray a repellent
during the biting time periods. Back dusters or smearers of repellents can also be
used. Such control methods might minimize the risk of contracting Culicoides
borne pathogen in bovine insemination and ova collecting centers as well as
livestock exporting farms. Host detection by Culicoides imicola seems to depend
primarily on sight. Culicoides rarely penetrate shaded closed barns. At times of
outbreaks of Culicoides-borne diseases such as bluetongue, Akabane, African
horse sickness and bovine ephemeral fever, susceptible animals housed in a close
barn (not a shed) will be relatively protected.
LINKS TO OTHER ARTICLES IN THIS ISSUE
References
1.