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Jourml
of Arid
Emironment
(1981) 4, 123-129
Rainpools as breeding and dispersal sites of mosquitoes
and other aquatic insects in the Central Negev Desert
Ch. Dimentman*
& J. Margalitt
Accepted 15 August 1980
During a faunistic survey of temporary rainpools of the Central Negev,
the following mosquito species were found : Culiseh 1ongiareoIata
(Macquart), Culex laticinctus Edwards and Culex ad&i Kirkpatrick.
Physico-chemical
features
of the rainpools
were
recorded.
C.
hgzimeolata
breeding sites were found under a wider range of abiotic
conditions (temperature, conductivity, pH and various ions) than
those of the other species. The most restricted species was C. adairi.
Characteristics of the mosquitoes’ breeding sites-and the role played
by temporary rainpools in the distribution of mosquitoes across the
Negev Desert are discussed. A dispersal mechanism for aquatic desert
insects is proposed involving the use of temporary pools as stepping
stones to connect the oasis refuges.
Introduction
The structure and dynamics of the mosquito fauna from the Northern and Central regions
of Israel and the Sinai ,Peninsula were described and reviewed by Margalit & Tahori (1973,
1974). However, information on the mosquito fauna of the Negev, in Southern Israel, is
absent. The purpose of this paper is to provide some data on the mosquito fauna which
breeds in rainpools of the Central Negev and to characterize the breeding sites of each
species.
The Central Negev (see Fig. 1) is a winter rainfall desert. Most of the rainfall occurs
erratically between November and April. It varies from 28 to 168 mm per year with an
average of about 86 mm (Evenari et al., 1968). The mean monthly evaporation from an open
water surface is 50-70 mm in January and 200-240 mm in July. The mean annual evaporation
is about 1700 mm (Rosenan, 1970). M ean daily temperature for the coldest month (January)
is 10-S OC and for the hottest month (August) is 25 “C. Hot dry desert winds may raise the
daily maximum temperatures to 42 V’during
the late spring (Evenari et al.., 1968).
The Negev soils differ substantially from those in the Mediterranean region (Ravikovitch,
1969). The most abundant type of soil in the Negev is loess, which is transported to this
area- by winds and floods (Yaalon, 1966). Loess is a rich source of nutrients which play a
rcile in the Negev’s terrestrial and aquatic ecosystems.
Materials
and methods
Sampling the fauna and water from rainpools was conducted for three years, one to four
times per month, starting with the first flood at the beginning of winter and continuing until
the pools dried out in midsummer. Samples were taken by a 60 pm dip-net and preserved
l
Department
of Zoology, The Hebrew University of Jerusalem, Jerusalem, Israel.
of the Negev, Beer-Sheva, Israel.
t Department of Biology, Ben Gurion Univeisity
0140-l 963/M lo20123 + 07 $02.00/O
IO
0
1981 Academic Press Inc. (London) Limited
C. DI~IEN’I’~IXY
124
& J. MARGAI,I’I‘
in 4 per cent formafdehyde or 70 per cent alcohol. Identification generally follows the keys
of Kirkpatrick (1925), Rioux (1958), Scourfield & Harding (1958), Linnavouri (1960), Rylov
(1964) and Hartland-Rowe
(1968). Water samples from the rainpools were analysed for
calcium, sodium and potassium ions with an Eppendorf-Geratebau
flame photometer.
Eiectrical conductance at 25 OC was measured with an Electronic Switchgear Type MC1
Conductivity bridge. Hydrogen ion concentrations were determined with a Radiometer
24e PI-I meter. Chemical analyses for chloride and dissolved oxygen were conducted according
to procedures recommended by the American Public Health Association (1965). Water
temperatures were measured with either a thermistor or a minimum-maximum
thermometer.
Results
Distribution and abundance
Mosquito breeding sites were found in 19 temporary rainpools at nine localities. Duration
of the various rainpools fluctuated from one to eight months each year. The localities,
coordinates and latitudes of these pools are presented in Fig. 1 and Table 1. The most
prevaIent species was Culiseta Zongimeolata (Macquart), which was found in all the 19 pools.
Less abundant was C&x Zaticinctus Edwards, which was collected in three pools. CuZex
adairi Kirkpatrick was found, in this survey, in one temporary pool only. Later, during
1979, this species was found also in the permanent water body of En Orihot spring in the
same vicinity.
Seasonal occurrenceof the mosquito Zarvae
Mosquito larvae appeared several weeks after the rainpools were filled by the first flood,
usually at the beginning of the winter. Subsequent floods washed out all larvae from pools
located in seasonal river beds, i.e. Nahal Zafit, N. Hatira, N. Zin, N. Hawwa and Ma’ale
Zin (see Fig, 1). The populations were re-established two to three weeks after each flood.
Table 2 shows the months in which larvae of each mosquito species were found in the
rainpools during 1965 and 1968-69. C. Zongiareolata was the first species to appear in the
pools. Its Iarvae were found from December till July. However, in July the presence of these
larvae was restricted to the Ramalia pools. The second species to appear was C. Zaticinctus.
I
35000’
I
34050’
I
35010’
I -.
I k‘ .1
Nat$l
31”&
.*
Moshtibbe
Zaf
\
Sade
t
,-_.--_ 03
/’
,’
Noh_ol IjatlTa
\
#’
\
\
/‘
_-’
/’
/
I
En
,_a6
,’ Nohal
_ ljclwwu
30”4d
G
Mlshor
i
Figure
q
Study
haR@ot
IOkm
(L~I,~~I~I_J
Legend
0 Rainpool
@Spring
-*‘-Wadi
c
area
ELAT
VI
1. Map of mosquito breeding sites in the Central Negev Desert.
_
.
RAINPOOLS
Table
AS RREEDISG
SITES
OF hlOSQl~ITOES
125
1. Species composifion of mosquito lan~ae in rainpoo/s
Central ;Tegm Desert
of the
Mosquito
Location
Coordinates
Lat. N./Long.
INo. rn
the map Locality
Nahal
2
2
z
&fit
Mash’abbe
Sade
Altitude
(m)
S
4
+
+
+
31OOl’
35O13’
280-290
31° 00’
34O 48’
370-380
240-250
NahaI
Hatira
30° 56’
3S” 02’
Ma’ale
Zin
3o” 51’
34O 49’
390-W
3o” 51’
34O 45’
490-500
Nahal
Hawarim
Nahal Zin (Pools:
Borot Ramalia
Nahal
a-g)
(Pools:
a-b)
Hawwa
Mishor
haRuhot
(Pools:
a-d)
3o” 49’
34” 46’
480-500
30” 47’
34O 45’
520-530
30” 44’
. 34O 55’
600-620
3o” 40’
34O 49’
770-790
_
*
3
z
.B
U
%
3
9
E.
species
U
‘
.t=
2
In pool b only
During
the winter and spring its larvae were found
in the pool of Ma’ale
Zin
only.
Later,
in June, it was found in other pools also. The presence of the third species, C. adairi, was
much more restricted. Its larvae were collected each year in the pool of Ma’ale
April and May only.
Zin during
Physico-chemical conditions
Dbmmims of habitats
Mosquito larvae were found in rainpools of various sizes. Surface areas of these pools
ranged from 1 to 200 ma and depths from O-5 to 4.0 m.
Temperature
In most habitats the minimum
water temperatures during winter were 7.5-9.0 OC. Maximum
water temperature during spring and summer were 31.533.0 OC. The greatest diurnal
changes during spring were 10-12 “C.
a
Dizzolwed oxygen
Seasonal fluctuations of dissoIvec! oxygen usually range from 50-95 per cent saturation.
Values lower than f mg Oa 1-r were detected near the mud bottom almost every year
during the final stage of the pool’s existence. In contrast, supersaturation occurred, as a
result of intensive photosynthesis, during short periods in several pools.. Several diurnal
measurements of dissolved oxygen showed marked daily changes from 4-5 mg 02 I-1
before sunrise’ to 8-9 mg 02 1-l during the afternoon hours.
Table 2. Seasonal occurrenceof mosquito larvae in the rainpook during
196.5, 1968 and 1969
!+ies
’
Cdiseta longiareohata
CuJ.exlaticinctus
C&x a&i?+
I
I
Nov.
Dec.
Jan.
Feb.
Mar.
Apr.
+
-
+
+
+
+
.-
+
+
-
+
+
i-
May
+
+
-I-
Jun.
Jul.
+
+
-
+
-
126
C. DI~IENT~IXN
5
Culiseta
10
& J. MARGXLIT
15
20
Water
temperature
30
35
(OC)
1
longiafeolaio
Culexlaticinctus
I
Cutex adairi
i
0.50
I
I
I.00
I*50
Specific
Culissta
25
I
I
Z-00
conductivity
2.50
ot
25’C
(mmho)
longiareolaia
Culcx laficincfus
Culcx ado/r/
I
100
150
Co2+
Culisefa
longiorrola
concentration
(mg/l)
fa
Culex laficincfus
I
r-
Culex adairi
I
50
I
I
100
150
No+
Culiscfa longiareolafo
I
Culex laticinctus
_
I
I
200
250
concentration
I
300
( mg
/I
)
Culcx adairi
Culex faticinctus
Culsx udairi
IB
I
Presence
of morqui to lorvac
Water
present
in pool
mosquito
;
larvae
obacnt
Figure
2. Some_physico-chemical characteristics of mosquito breeding sites in the rainpools
of the Central Negev.
.
Electrical conductivity
Specific conductivity increased, due to evaporation, from 0.22 mmhos immediately after
the formation of several rainpools, to l-88-2.12 mrnhos just before the pools dried up.
Calcium, sodium, potamkn and chloride ions
Increased conductivity reflected the rise of total ion concentration during the life span of the
rainppols. The ranges of the various ions (expressed as mg l-1) were as follows: Ca+ l :
S-104; Na+ : 34-297; I(+ : 4-104; Cl- : 17-396.
Hydrogen ion cmcen~trations
The lowest pH value detected in the rainpools was 7.35 and the highest 9.9. The diurnal
changes varied from 0.2 to 0.9 pH units.
RAINPOOLS
Table
3. Fauna
AS BREEDING
SITES
associated nkith mosquito larvae
Cen f ral l’<egev
127
in rainpools
of the
Corisidae :
Crustacea :
Branchipodidae
S’igara lateralis
S. morginata
S. hoggarica
Branchiptts schaqfferi
Daphnii&e
OF 3IOSQUITQEs
:
Notonectidae :
Daphniu maLynn
D. atkGrsoni
D. pulex
LVotonecta mactrlata
Anisops vavia
Chydoridae :
Dytiscidae:
Alona quadrangularis
Hydroporus
Cyclopidae :
Acanthocyclops bicuspidatzrs
Microcyclops mimrtus
Cypridae :
(?)
Hydrophilidae :
Unidentified specimens
Chironomidae :
Chironomus sp.
Eucypris sp.
A4mphibia :
Insecta :
Libellulidae :
Bufonidae :
Ol-thetrum sp.
Bufo viridis
Figure 2 shows the ranges of temperature and specific conductivity, as well as levels of
calcium, sodium, potassium and hydrogen ions from the breeding pools of the three
mosquito species.
Fauna
associated with the mosquito larvae
The temporary pools contained two faunistic elements. The first consists of various species
of-crustaceans which hatch soon after the pools fill. These species, most of which are plankton
grazers, are dominant in the pools during winter. The second group consists of various
species of insects and one amphibian species, all of which are immigrants from permanent
waters. The invasion of these species starts rather early, but this group becomes dominant
in the rainpools only during spring and early summer. Most of the immigrants are carnivorous,
e.g. the larvae of Libellulidae, Dytiscidae, Notonectidae and Hydrophilidae or omnivorous,
e.g. the tadpoles of Bufo uiridis. A list of animals found together with mosquito larvae in
rainpools of the Central Negev is given in Table 3.
Discussion
Environmental characteristics of the breeding sites
This study elucidates some abiotic features of mosquito breeding sites in the Central Negev.
C+zketa ZongiareoZata was found breeding in rainpools ‘with a wider range of physicochemical conditions and a longer period of seasonal occurrence than the other two species.
Thus, it appears to be a eurythermal and to some extent euryhaline and euryionic species.
It has a very wide distribution, extending from the .Azores in the west, through the
Ethiopian region, Pakistan, and India t6 Central Asia (Stone et al., 1959). Among the three
species, CuZex Zuttiizcf~ is in an intermediate position, regarding the above physicochemical parameters, as well as seasonal occurrence and abundance. Its general distribution
is not so wide as that of C. longiareolata, ranging from the Canary Islands through the
Mediterranean to Somali and Arabia (Stone et al., 1959). The data represented in Fig. 2
show that Culex ad&i iarvae have not been found in temperatures lower than 25 “C. This
may indicate that C. &zX
is a thermophilic species. Compared to the other two species,
C. adaiki has a much more restricted distribution, ? smaller number of breeding sites with
a narrower range of physico-chemical conditions, and a shorter period of occurrence in
I
I
,
I
I
CC‘.T~J~JJ~TT~IAS
12s
s: J. ~IXRGAI,I’I’
of Israel and Egypt. -Ycvertheless, we cannot say that C. adairi is a true stenoecic
appearance of C. nl/ai~i in the Xegev may be because this region is
on the peripherv
of the distriblltional
area lvhere potential habitats are limited. $Iayr (1966)
has also noted that such periphcr-al habitats may not offer optimal living conditions.
Larvae of dragonflies, and of se\-era1 families of n-ater beetles such as Dytiscidae and
Hydrophilidae, are ‘mosquito destro;-ers’ (Kirkpatrick, 1925). These predators were found
in rainpools together with the mosquito larvae (see Y‘able 3). During winter the number of
predators in the rainpools is verl- low, and the large biomass of potential prey consists of
dense populations of crustacean entomostracans, as well as mosquito larvae. As a consequence,
it is unlikely that predation exerts more than a minor influence on the mosquito larvae in
winter. In contrast, during late spring and early summer, the density of predators increases
while the prey biomass becomes relatively small. A severe reduction in the populations of
all three mosquito species was observed on several occasions during the spring and summer.
This reduction appears to be a result of predation.
rainpools
species. The ‘stenoecic’
Dispersal
mechanism of aquatic insects in the h’esev
It is reasonable to assume that temporary pools are used as stepping stones for passage of
aquatic insects, including mosquitoes, from one region to another. Based on this assumption,
and on the findings of this survey, we suggest a solution to several problems connected with
mosquito
distribution
in this area. The
presence
of C&x
Zaticincttts at En Kadeis
in North
(1925). In the absence of information on the occurrence of C.
laticinctus in the Negev, he hypothesized that this species was brought to En Kadeis by
travellers from Palestine, in water skins. The findings of the present study suggest that
the temporary waters of the Negev form links in a potentially connected chain, between the
C. Zaticinctus population of Israel and that of the springs in the vicinity of En Kadeis. Thus,
there is no need to explain the presence of C. Zaticinctus in En Kadeis as a result of human
activity. It will be of interest to check if this type of migration is also applicable to Saharian
or other deserts.
Another aspect of mosquito distribution in the Central Negev has to do with Culex adairi.
This species is also known from Egypt and French Equatorial Africa (Stone et al., 1959).
Rioux (1958) considers the species to be a Saharan relict. In Egypt C. adairi was found
breeding in four temporary rainpools in the Eastern Desert (Kirkpatrick,
1925). Since this
species has been found breeding in temporary pools, the question arises where or how does
it pass the dry season. Kirkpatrick (1925) suggested that C. adairi probably aestivates in the
adult stage, but there is nothing to support this hypothesis. However, recently we have
identified larvae of this species that were found in the Negev, in a permanent spring, En
O&hot (Fig. 1) b) 7 employees of the Nature Reserve Authority. This spring is located
about 21 km southeast of the temporary pool, ,Ma’ale Zin, which bears a breeding population
of C. adairi.‘AIthough we still do not yet have enough information on the permanent presence
of C. adairi during the whole year at En Orihot or any other spring, we can hypothesize
that this species inhabits permanent water bodies, from which it invades the temporary
7pools. If this is indeed the case, it is probable that C. adairi does not aestivate at all.
To summarize, we suggest that temporary pools together with permanent water bodies
create a combined ecoIogica1 system, enabling the mosquito fauna to inhabit the Negev
and other arid regions. Temporary pools in this ecological system are used as intermediate
stations that facilitate the penetration of mosquitoes to arid zones. On the other hand,
permanent water bodies create refuges in the dry seasons and dispersal centers after the
filling of temporary pools.
Sinai
puzzled
Kirkpatrick
We wish to thank Dr H.
and F. D. Por for their
suggestions.
M. C. Warburg,
R. Galun
Bromley and Professors C. S. Crawford,
and their subsequent
valuable
critical reading of this manuscript
_
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