Mosha, F.W.

Subra, Raymond

Horizon / Pleins textes

Salinity and breeding 
of Culex quinquefasciatus Say, 
Anopheles funestus Giles 
and Anopheles gambiae Giles sey~su stricto 
(Diptera : Culicidac) on the Kenya Coast 
Franklin W. MOSHA (l), Raymond SUBRA 0) 
Summary 
NewZy h,atched lnrvne of C. quinquefasciatus, An. funestus and An. gambiae S.S. were rea.red in different 
dilutions of sea. water. 11~aximum snlinities support@ full development for the larune were 30-40 yo sea wafer 
for C. quinquefasciatus and 20-30 o/O seau water for both An. funestus a.n.cl An. gambiae S.S. Possibilities of using 
sa.linity as a, mean of controllin, 0 these species are briefly discussed. 
Key words : Mosquitoes - Salinity - Preimaginal development - Kenya. 
Résumé 
SALINITÉ ET DÉVELOPPEMENT PRÉIMAGINAL DE Culex quin.quefa.sciatus SAY, Anopheles funestus GILES 
ET Arzophebes ganrbiue GILES SENSU STRICTO (DIPTERA : CULICIDAE) SUR LA COTE DU KENYA. Cetta étude a 
&é effectuée ci pa.rtir de la.wes de stade I de Culex quinquefasciatus, Anopheles funestus et Anopheles gambiae S.S.; 
qui ont été élevées da.ns différentes dilutions d’eau de mer. Le développement de C. quinquefasciatus étnit interrompu 
entre 30 et 40 y0 d ‘eau de mer. Pour An. funestus et An. gambiae S.S. la toléran.ce nmximum. se situ.a,it entre 20 
et 30 %. Les possibilittk d’utiliser la. sa.linisa.tion des gîtes la.rvaires comme moyen de lutte contre ces moustiques 
son.t bri&ement discu.tées. La salinisat.ion des @tes de C. quinquefasciatus serait réalisa,ble sur la côte du, Kenya 
et serait sans doute bien acceptée par les populations locales. Par contre les perspectives concernant An. funestus 
et An. gambiae S.S. semblent beaucoup plus limitées. 
tiots-clés : Moustiques - Salinité - Développement préimaginal - Kenya. 
, 
(1) The Internntion.al Centre of Insect Physiology and Ecology, P.O. Box 80804, Mombasa, Ken.ya. Present address : P.O. 
Box 8370, Moshi, Tanzania. 
(2) O.R.S.T.O.M. Medical En,tomologist, the international Centre of Insect Physiology and Ecology, P.O. Box 80803, Mombasa, 
Kenya. 
Cah. O.R.S.T.O.M., stk. Ent. méd. et Parusitol., vol. XXI, no 3, 1983 : 135-135 
136 li’. PV. Mosha, R. Subra 
Introduction 
Crrlt’.r quirrquefcLsciatrc~~ Say, An.opheles funestus 
(type form) Gilrs and An.. gnm bia.e complex Giles, 
arc the vectors of Bancroftian filariasis in East 
Africa. The anophelines are also vectors of human 
malaria. Along the East African toast, An. 
ganlbitre complex ronsists of three sibling species, 
namely ,&L. UWI’ZIS Donitz which breeds in brackish 
wat,er and -4,. gcrmbine (sensu stricto) and AIL. 
arabitvrsis Patton which breed in freshwater. 
Larvar of C. qrri?zqrcefrrscbBtzrs are found mainly 
in polluted waters of lrit latrines and septic tanks, 
whereas the anoplielines prefer unpolluted water. 
-1~. /‘unestus occurs in permanent and semi-perma- 
nent botlies of clrar watrr with emergent vegetation, 
and freshmater rnembers of the An. gambiae com- 
plex (-Arr. ga.tn bi0.e S.S. and 14.71. arcs biensis) in shallow 
open suri--lit ponds. 
Salini~y as a limiting fnctor in the breeding 
of c‘. qzrrnqlct?ftrscicttrts, AI~. funestus and fresh- 
water An. gamhiue hns not been well documented, 
but it is known to bas-e detrimental effects at high 
concentrations. The ability of C. quinquefasciatus 
to breed in brackish mater bas been reported 
by Macfie and Ingram (1916) and Dunn (1928) 
in West Africa but. the exact limits have net been 
recmded. 
BH. fumstns shows little tolerance for salt 
water. Jenson et al. (1947) ohserved that in 
Mauritins it occurred in salinities of less than 
0.2 y0 NaCl (equivalent to 6.4 y0 sea water), 
while in the laboratory trials full development 
up to the adult. stage occurred only in bowls with 
0.3 9;” NaCl jequivalent~ to 9.6 0/0 sea water) 
and below. 
Salt. t,olerance studies on An. garnbiaa comples 
bave mainly dealt, with the salt water species, 
namely -4~ IH~YUS and &. melas Theobald 
(Muirhead-Thomson, g 951 ; Giglioli, 1964 ; Mosha 
and Mutero, 1982). However, little attention 
has been paid to the other members of the An. 
gam biue comples. In divising salinity tolerance 
test. t,o difl’erentiate between An. melas ad 4.m 
ganrbiiw s.l. in West Africa, Ribbands (1944) 
reportecl that, t.hP maximum concentration in 
which ,&z. garnl&re s.l. underwent complete deve- 
lopment. from egg to adult under laboratory con- 
ditions was 37.5 y0 sea water (= 11.9 g NaCl/ 
lare). Smith and Vail (1959) observed that in 
the South Pare area of N.E. Tanzania, An. gambiu.e 
s.l. WRB breeding in water with 0.13-8.95 o/. chloride 
concentration (equivalent to 0.7 - 47.1 oh sea water). 
They also found that recentty hatched larvae 
survlved in chloride concentrations equal to 30 % 
sea water for S hours but died within 7 l/2 hours 
at. 34 o/. sea water. P.aterson (1964) recorded 
an LC,, of 52.9 and 45.0 o/O sëa water for labora- 
tory colonies of first instar larvae of An.. garnbiae 
s.s. (Kisumu strain) and An. arabiensis (Mozam- 
bique strain), respectively. 
The present studies were aimed at determin- 
ing the ranges of salinity (sea water dilutions) 
supporting full development of the three vector 
species. The knowledge gained should contribute 
to a better underst.anding of seasonal and spatial 
dist,ribution of C. qzcillqlsefasricrtus, An. funestus 
and An.. gnmbiae complex in coastal areas, and 
form a basis for planning their control by using 
salinisation met.hotls. 
Materials and methods 
The newly hatched larvae of C. qui?bqu.efasciatus, 
An. funestus and An. gambiae S.S. used in these 
experiments were hatched from eggs laid by 
wild caught female mosquitoes collected from the 
Kenya South Coast. The larvae were reared 
in 4 replicates of 25 larvae each in 250 ml clilutions 
of 0, 5, 10, 30 and 40 o/. sea water in distillecl water 
(100 yo sea water = approximately 31.35 g NaCl/ 
litre). Since preliminary t.ests had shown that 
the larvae of the tbree species could not develop 
in salinities higher than 40 o/. sea water, higher 
salinities were unnecessary. 
The media were placed in glass bowls of 
450 ml capacity with a depth of 5 cm in t.he centre. 
The larvae were fed on K Farex n » baby food 
solution, and maint,ained up to the ad& stage 
in an insectary with t.emperatures ranging between 
26.0-29.5%. 
Results 
Percentage survival up to the aclult stage 
of C. qu,inquefascintus, An.. funestus and An. gambia,e 
S.S. in different dilutions of sea water is shown 
in Table 1. Maximum salinities supporting full 
development for the larvae were 30-40 yo sea water 
for C. qu.il~quefasciatu.s and 20-30 o/. sea water 
for both An. fzLn.estus and An. garnbiae S.S. 
No significant differences were observed in 
larval survival rates at salinities of O-20 yo sea 
water for C. quinquefasciatus an-d 5-10 o/o sea water 
Cah. O.R.S.T.O.M., sér. Ent. méd. et Parasitol., vol. XXI, no 3, 1983 : 135-13s 
Salinity arrcl breeding of C. quinquefasciatus An. funestus and An. gamhiae .y.~. 137 
for An. fun.estus and An. ga.mbia.e S.S. The diffe- 
rentes in survival rates were statistically significant 
at salinity ranges 20-30 o/. sea water for An. funestus 
and An. gambiae S.S. (Table 1). 
The time talren for full development hy 
A n. gambiae S.S. and An. funestus was the same 
in a11 the different dilutions of sea water used. 
An. pmbiae S.S. took an average of 9 days and 
An. funestes 19 days. The average period for 
C. q1cinqrtefasciatu.R was 9 days in all dilutions 
within the ranges O-20 o/. sea water, but 12 days 
at 30 o/O sea mater. 
TABLE 1 
Percent survival rate of newly hatched larvaeû to adult stages of C. qzLiBqzzefascintzzs, An. fzrnestzrs and =In. gnmbiae S.S. in different 
dilutions of sea water. 
- 
Percent survival 
C. quinquefasciatus A7z. fzcnestus 1171. gankbiae S.S. 
0 73b 67C 
5 6Ob 43d 
10 68” 49”d 
20 67” 6 
30 6 0 
40 0 0 
5 Total of 100 larvae of each species tested at each concentration. 
e to b Larval survival rate figures bearing the same superscripts irithe same column are not statistically different from one 
another (P ) .05, using Bonferroni Chi-square test. for O-20 y& sea water concent.rat.ions). 
Discussion 
The results from laboratory observations show 
that larvae of C. quinquefascia~tus, An. funestus 
and An. ga.m,biae S.S. are not tolerant to high 
saIinities, suggesting a possibility of their control 
by increasing the salinity of their respective 
breeding sites. Under natural conditions, even 
in coastal areas, salinity in the larval habitats is 
normally not suffkient~ly high to reduce the breed- 
ing of C. quinquefa,sciatus. An analysis of the 
breeding water from 12 yo (4/42) of the pit latrines 
in a shoreline village on the south Kenya toast 
showed low salinities of 2.6-6.0 o/. sea water during 
neap low tides and 5.3-7.9 o/. sea water during 
spring high tides. T~US, even in such breeding 
sites it would be necessary to raise salinity above 
the level found t.olerant by C. q&quefasciatus. 
Such a control method involving the addition of 
domestic salt into pit latrines would most probably 
be quite acceptable to local people since they have 
been practicing it for many years in the belief 
that it lowers pit latrine water level. Domestic 
sait is also cheap and readiIy avaiIabIe in many 
coastal villages from local cottage industries where 
it is made by boiling sea water. 
The low tolerance to salinity shown by An. 
funestus and An.. gant bine observed during the 
present studies may to a large extent be respon- 
sible for their rery low densities in coastal shore- 
line villages as recently observed by McMahon 
et al. (19SI) and Mosha and Mutero (19S2). A~L 
gambiae S.S. could thust be controlled by directing 
high tide water to its semi-permanent breeding 
sit.es, but this method seems to be limited because 
of high cost and the rislr of colonization of these 
sites by the bracliish water species dn. merus. 
ACKNOWLEDGEMENT 
We are most grateful to the United Nations Environ- 
ment Programme for funding this project through t.he 
International Centre of Insect Physiology and Ecology. 
Our sincere acknowledgement. are also extended to &f.essrs. 
J. Otieno, RE. Ngumah, L. Odongo and R. Musyoki for 
their fleld assistance. Lastlg me would like to t.hank 
Dr. M. W. Service for his comments on the manuscript 
and Dr. P. Ruvuna for his assistance in the statistical 
analysis. 
Man.uscrit reçu azz Service des Éditions de 1’O.R.S.T.O.M. 
le 6 octobre 1985 
Cah. O.R.S.T.O.M., s8r. Ent. nu%. et Parasitol., vol. XXI, no 3, 1983 : 135-138 
F. W. Mosha, R. Subrn 
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Salinity and breeding of Culex quinquefasciatus Say, Anopheles funestus Giles and Anopheles gambiae Giles sensu stricto (Diptera : Culicidae) on the Kenya Coast

Salinity and breeding of Culex quinquefasciatus Say, Anopheles funestus Giles and Anopheles gambiae Giles sensu stricto (Diptera : Culicidae) on the Kenya Coast

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