Grébaut, S.

Guillet, Pierre

Mouchet, Jean

Horizon / Pleins textes

WORLD HEALTH ORGANIZATION 
ORGANISATION MONDIALE DE LA SANTG 
WHO/VBC/77.678 
ENGLISH ONLY 
DDT RESISTANCE I N  SIMULIUM DAMNOSUM s.l. (DIPTERA, SmLIIDAE) 
IN WEST  AFRICA^ 
2 
i P. G u i l l e t ,  J .  
by 
3 Mouchet’ and S. Grébaut 
I n  West A f r i c a  Simulium damnosum s.1. may l o c a l l y  develop a h igh  l e v e l  of r e s i s t a n c e  
t o  DDT. A probable  r e l a t i o n s h i p  between such r e s i s t a n c e  and t h e  sometimes i n t e n s i v e  
a g r i c u l t u r a l  use  of DDT has  been e s t a b l i s h e d .  Although these  r e s i s t a n c e  phenomena a r e  ’ 
very  l o c a l i z e d ,  t hey  may have some repe rcuss ions  on t h e  ex tens ive  Onchocerciasis  Cont ro l  
Programme being c a r r i e d  o u t  by t h e  World Heal th  Organiza t ion  i n  West Af r i ca .  
DDT has  been wide ly  used i n  West Af r i ca  f o r  t h e  c o n t r o l  of b l a c k f l y  l a r v a e  of t he  
S. damnosum s.1. complex. e ‘i. _ I ’  
Between 1960 and 1971, i n  c o n t r o l  campaigns i n  t h e  Volta  bas in  a r e a ,  h igh  concen t r a t ions  
of DDT (0.1 ppm/30 min) were a p p l i e d  weekly t o  r i v e r s  (Le Berre e t  a l . ,  1964; 
Le Berre ,  1974). From 1970 onward t h e  t rea tment  supe rv i so r s  no ted  a q u i t e  marked decrease  
i n  t h e  e f f i c a c y  of  DDT on c e r t a i n  s t r e t c h e s  of wa te r  ( t h e  Comoé a t  FOlOn26, t he  lower 
Bandama). 
Phi l ippon & 
A t  K a i n j i  i n  N ige r i a  t h e  e f f e c t i v e  concen t r a t ions  of DDT doubled between 1961 and 1968, 
a s i g n  of a decrease  i n  t h e  s u s c e p t i b i l i t y  of t h e  l a r v a e  of S. damnosum s.1. (Walsh, 1970). 
. v  
I n  Ghana, on t h e  lower reaches  of the  Vol ta ,  Kuzoe & Noamesi ( i n :  Brown 6r P a l ,  1973) 
a l s o  noted  a decrease  i n  t h e  e f f i c a c y  of DDT and a decrease  i n  the  LC50 values  (ob ta ined  by 
t h e  method of Muirhead-Thomson, 1957). 
In Upper Vol ta ,  Quélennec 6 Vervent (1970) showed t h a t  i n  a r e a s  of onchoce rc i a s i s  
v e c t o r  c o n t r o l ,  S. harg reaves i  could r a p i d l y  develop r e s i s t a n c e  t o  DDT. 
Outs ide A f r i c a ,  r e s i s t a n c e  of  S imul i idae  l a r v a e  t o  DDT has been r epor t ed  i n  Japan 
w i t h  S. a o k i i  (Suzuki  e t  a l .  , 1963) and w i t h  S. omatum (Asahina e t  a l . ,  i 1966), i n  t h e  
Uni ted  S t a t e s  and Canada w i t h  S. venustum and S. fuscum (West; 1967; Jamnback & West, 1970). 
MATERIALS AND METHODS 
The methodology f o r  t e s t i n g  t h e  s u s c e p t i b i l i t y  of b l a c k f l y  l a r v a e  t o  i n s e c t i c i d e s  
proposed by Mouchet e t  a l .  (1977) w a s  s u c c e s s f u l l y  app l i ed .  
F i e l d  t e s t s  were c a r r i e d  o u t  e a r l y  i n  the  morning and i n  the  evening.  For each concen t r a t ion  
two ba tches  of 25  l a r v a e  of  s t a g e s  4 and 5 were used,  p laced  i n  g l a s s ’bowls  con ta in ing  250 m l  
of  preoxygenated d i s t i l l e d  water .  The t e s t s  were r epea ted  two t o  fou r  t imes ,  depending 
on t h e  number of l a r v a e  a v a i l a b l e .  The c o n t a c t  time w a s  t h r e e  hours  and m o r t a l i t y  w a s  
This  s tudy  w a s  suppor ted  by a g r a n t  from the World Heal th  Organiza t ion .  
Medical  en tomologis t  , ORSTOM.. 
Medical entomology t e c h n i c i a n ,  OCCGE. 1‘ 
Ce document ne constitue pas une publication. The issue of this document does not constitute 
abstracted or quoted without the agreement of r6sum6 ni d’aucune citation sans l’autorisation de 
the World Health Organization. Authors alone l’Organisation Mondiale de la Santé. Les opinions - 
are responsible for views expressed in signed exprimées dans les articles signés n’engagent, 
articles. 
3 &  
1 formal publication. It should not be reviewed, II h e  doit faire l’objet d’aucun compte rendu ou it 
que leurs auteQraR.S.T. 0. bvk. ~ w i s  DocumsnZairr: 
a s s e s s e d  by t o t a l l i n g  t h e  dead and dying l a r v a e  f o r  each c o n c e n t r a t i o n  ( h i g h  m o r t a l i t y ) .  
The d i l u t i o n s  were ob ta ined  from s t a n d a r d  e t h a n o l  s o l u t i o n s  s u p p l i e d  by WHO. 
Only t h e  t e s t s  i n  which t h e  temperature  remained between 20 and 25°C were taken i n t o  
accoun t .  By a n a l y s i n g  t h e  r e s u l t s  of 20 t e s t s  w i t h  temephos on S. damnosum S.S. and 
S. sirbanum, Grébaut & G u i l l e t  (1977) showed t h a t  w i t h i n t h e  20-25°C range and w i t h  a c o n t a c t  
t ime of t h r e e  hours  t h e  temperature  has  no s i g n i f i c a n t  e f f e c t  on t h e  r e s u l t s  of  t h e  t es t s .  
The temperature  cannot t h e r e f o r e  e x p l a i n  t h e  wide v a r i a t i o n s  i n  s u s c e p t i b i l i t y  t h a t  a r e  
encountered.  I n  t h e  case of  DDT, however, i t  should be no ted  t h a t  t o x i c i t y  g e n e r a l l y  
drops as t h e  temperature  i n c r e a s e s  (Hadaway & Barlow, 1957; Fan Cheng & Richard,  i n :  
Brown 6, P a l ,  1973).  
I n  Ivo ry  Coast t h r e e  s u s c e p t i b l e  popu la t ions  o f  d i f f e r e n t  compositions were t e s t e d :  
S .  yahense on t h e  Goué a t  Wa (south-western Ivo ry  Coast ,  7'26'N, 8'10'W), S. s a n c t i p a u l i  on 
t h e  Bandama a t  T i a s s a l é  ( sou the rn  Ivo ry  Coast ,  5"56'N, 4"49'W), S. damnosum S . S .  and 
S .  sirbanum which predominate on t h e  Boa a t  Tjokoronidougou i n  t h e  d ry  season (north-  
w e s  t e r n  Ivo ry  Coast , 8 "41 ' N  , 7'"22 'W) . 
Within t h e  boundaries  of phase III of t h e  Onchocerciasis  Programme i n  t h e  Volta B a s i n  
Area,  f o u r  popu la t ions  of  S. damnosum S.S. and S. sirbanum w i t h  low s u s c e p t i b i l i t y  o r  
r e s i s t a n c e  t o  DDT were t e s t e d :  i n  Mali on the  Banif ing II (11°45'N, 7"lO'W) and on t h e  
Baoulé (12'301N, 6"50'W), i n  Benin on t h e  K i a t i k o  (10"18'N, 1 '22 'E) ,  and i n  Togo on t h e  
Sossoa (9"42'N, 1 '15'E).  
A r e s i s t a n t  popu la t ion  c o n s i s t i n g  mainly of S. soubrense w a s  t e s t e d  a t  Bouaflé on t h e  
Marahoué ( c e n t r a l  Ivo ry  Coast ,  7"N, 5'45'W). 
RESULTS 
Table 1 g ives  t h e  r e s u l t s  ob ta ined  w i t h  t h e  t h r e e  s u s c e p t i b l e  popu la t ions  t e s t e d  i n  
Ivo ry  Coast .  The correspondi,ng c o n c e n t r a t i o n - m o r t a l i t y  r e g r e s s i o n  l i n e s  a r e  p re sen ted  i n  
F igs  1 and 2 .  
I n  o r d e r  t o  compare t h e s e  r e s u l t s  w i t h  those ob ta ined  w i t h  r e s i s t a n t  p o p u l a t i o n s ,  t h e  
a r i t h m e t h i c  means of  t h e  LC50 and LCg5 va lues  were c a l c u l a t e d  (0.045 and 0.12 ppm 
r e s p e c t i v e l y ) .  
The popu la t ions  t e s t e d  on t h e  Bandama and Boa (March 1977) do n o t  d i s p l a y  s i m i l a r  suscep- 
t i b i l i t y  t o  those on t h e  Goué and Boa (March 1976).  
s u s c e p t i b l e  i n  view of  t h e  c o n c e n t r a t i o n - m o r t a l i t y  r a t i o  and t h e  L C ~ S / L C ~ ~  r a t i o s  (3 .3  and 
The s u b s t a n t i a l  v a r i a t i o n s  found i n  t h e  LCIOO va lues  w i l l  be no ted .  
Neve r the l e s s ,  t hey  are regarded as 
3 .4 ) .  
Table 2 g i v e s  t h e  r e s u l t s  ob ta ined  from popu la t ions  w i t h  low s u s c e p t i b i l i t y  o r  r e s i s t a n c e  
t o  DDT. The c o e f f i c i e n t  of r e s i s t a n c e  i s  t h e  r a t i o  between t h e  LCg5 observed and t h e  mean 
LCg5 i n  s u s c e p t i b l e  popu la t ions .  The corresponding r e g r e s s i o n  l i n e s  ( F i g s  1 and 2 )  have 
t h e  c h a r a c t e r i s t i c  appearance of DDT r e s i s t a n c e :  normal m o r t a l i t y  a t  low c o n c e n t r a t i o n s  and 
a ve ry  marked p l a t e a u  a t  h i g h  concen t r a t ions .  
Two l e v e l s  of resistance were found: 
a h igh  l e v e l  ( c o e f f i c i e n t  of r e s i s t a n c e  above 21) f o r  t h e  popu la t ions  o f  t h e  Banif ing 
L I  (Mali)  and t h e  Marahoué ( Ivo ry  Coas t ) ;  
a moderate l e v e l  ( c o e f f i c i e n t  of  r e s i s t a n c e  10.4) f o r  t h e  popu la t ions  of  t he  
K i a t i k o  (Benin) and t h e  Sossoa (Togo). 
DISCUSSION 
Up t o  now DDT r e s i s t a n c e  i n  S. damnosum s.1. has neve r  been c a t e g o r i c a l l y  proved. 
WHO/VBC/77.678 
Page 3 
The a g r i c u l t u r a l  use  of DDT i s  s t i l l  very widespread i n  West Af r i ca .  Consequent ly ,  
few d a t a  have been c o l l e c t e d  on t h e  b a s i c  s u s c e p t i b i l i t y  t o  DDT of S. damnosum s.1. 
On a more gene ra l  l e v e l ,  and w i t h i n  the  c u r r e n t  con tex t  of t he  ex tens ibe  Onchocerc ias i s  
Cont ro l  Programme i n  West A f r i c a ,  t he  mechanisms of t h e  development of  i n s e c t i c i d e  r e s i s -  
t ance  i n  S. damnosum s.1. a r e  c e r t a i n l y  a very  complex m a t t e r .  Two groups o f  opposing 
f a c t o r s  must be p a r t i c u l a r l y  involved .  
Fac to r s  favourable  t o  t h e  developement of r e s i s t a n c e :  t h e  very  s t r o n g  s e l e c t i v e  
p re s su re  e x e r t e d  by the  i n s e c t i c i d e s  because of t he  c o n s t a n t l y  i n c r e a s i n g  a r e a  
of  t h e  t r e a t e d  zones ( a t  p re sen t  one a r e a  a lone  i s  700 O00 km2) and the  f requency  
of l a r v i c i d e  t r ea tmen t  (once a week) on t h e  one hand and the  s h o r t  d u r a t i o n  of t h e  
development cyc le  (8-15 days) on the  o t h e r  hand. 
~ 
The l e v e l s  of  r e s i s t a n c e  mentioned h e r e  f o r  West Af r i ca  a r e  h i g h e r  than  those  r epor t ed  
by Suzuki e t  a l .  (op. c i t . )  ( c o e f f i c i e n t  of r e s i s t a n c e  = 12.8) and by West and Jamnback 6, 
West (op. c i t . )  ( c o e f f i c i e n t  of  r e s i s t a n c e  = 5-7) i n  p a l a e a r c t i c  and n e a r c t i c  b l a c k f l i e s .  
c1 It i s  a l s o  po in ted  o u t  t h a t  on t h e  Boa t h e  LCg5 inc reased  by a f a c t o r  of 2.7 i n  one y e a r ,  
i n d i c a t i n g  a p o s s i b l e  r e g r e s s i o n  of DDT s u s c e p t i b i l i t y .  
This  r e s i s t a n c e  i s  occur r ing  i n  t h e  b l a c k f l y  popu la t ions  of t h r e e  temporary r i v e r s  
None of t h e s e r i v e r s  had a t  w i t h  a low d i scha rge  and one permanent r i v e r ,  t h e  Marahoué. 
t h e  time e v e r  been s u b j e c t e d  t o  a b l a c k f l y  c o n t r o l  campaign. They f low through areas where 
c o t t o n  i s  i n t e n s i v e l y  c u l t i v a t e d ,  and each r a i n y  season t h e  c o t t o n  crop i s  t r e a t e d  w i t h  
8-10 kg of DDT pe r  h e c t a r e . ,  Some of  t h i s  DDT i s  c a r r i e d  away by t h e  r i v e r s  on t h e  account  
of t he  ve ry  s u b s t a n t i a l  run-of f .  The exposure of  S. damnosum s.1. larvae t o  low concen- 
t r a t i o n s  of  DDT f o r  s e v e r a l  months may be s u f f i c i e n t  t o  account  f o r  t h e  l e v e l  of r e s i s t a n c e  
mentioned. This  phenomenon i s  commonly observed among t h e  Cu l i c idae .  
Fac to r s  unfavourable  t o  t h e  development of  r e s i s t a n c e :  t h e  phenomena o f  d i s p e r s i o n  
and mig ra t ion ,  ve ry  marked i n  S. damnosum s.1,. females ,  caus ing  t h e  m a s s i v e .  
i n t r o d u c t i o n  i n t o  t r e a t e d  a r e a s  of  f e r t i l i z e d  females  from u n t r e a t e d  a r e a s .  
This  l e a d s  t o  d i l u t i o n  of any r e s i s t a n c e  genes p re sen t  i n  the  t r e a t e d  popu la t ion  
and keeps t h e  f requency  of such genes below a c r i t i ca l  th re sho ld .  This  phenomenon 
w a s  r e c e n t l y  s t u d i e d  from the  t h e o r e t i c a l  viewpoint  by Comins (1977).  
CONCLUSION 
The l e v e l  of s u s c e p t i b i l i t y  of S. damnosum s.1. l a r v a e  t o  DDT i s  on t h e  whole r a t h e r  
v a r i e d  and some c a s e s  of h igh  r e s i s t a n c e  have been r epor t ed .  Although s p o r a d i c  and 
l o c a l i z e d ,  t hese  cases  a r e  very  impor tan t  because they  d e f i n i t e l y  prove t h a t  S. damnosum s.1. 
has t h e  c a p a b i l i t y  t o  develop a c e r t a i n  l e v e l  of  DDT r e s i s t a n c e  f a i r l y  r a p i d l y .  
' 
0 
It i s  l i k e l y  t h a t  t h e  use  of DDT i n  t h e  Regional  Onchocerc ias i s  Cont ro l  Programme would 
have l e d  to' t he  appearance of widespread r e s i s t a n c e  t o  t h i s  i n s e c t i c i d e .  
doubt on t h e  a d v i s a b i l i t y  of u s i n g  DDT analogues i n  the  c o n t r o l  of S. damnosum s . l , ,  as 
. c r o s s - r e s i s t a n c e  phenomena a r e  common i n  t h i s  group of  i n s e c t i c i d e s  p a r t i c u l a r l y  i n  t h e  
biodegradable  analogues.  For example, a ve ry  h igh  l e v e l  of c r o s s - r e s i s t a n c e  i s  observed 
between OMS-1476 and DDT i n  t h e  Cu l i c idae  (Quiroga e t  a l . ,  1976) .  
This  c a s t s  g r e a t  
A t  p r e s e n t  t h e  on ly  group of i n s e c t i c i d e s  r e a l l y  s u i t a b l e  f o r  use  i n  o n c h o c e r c i a s i s  
c o n t r o l  i n  West A f r i c a  remains the  organophosphorus compounds; 
(unpubl ished document) have n o t  s o  f a r  recorded  any r educ t ion  i n  s u s c e p t i b i l i t y  t o  temephos 
i n  popu la t ions  t r e a t e d  r e g u l a r l y  f o r  more than f i v e  yea r s .  
G u i l l e t  6, Grébaut 
W HO/VBC/7 7 .6 7 8 
page 4 
REFERENCES 
Asahina,  S . , e t  a l .  (1966) I n s e c t i c i d e  r e s i s t a n c e  o f  t he  l a r v a e  of  S. ornatum, Jap .  J .  San. 
 ZOO^., 17, ( 4 1 ,  243-246 
Brown, A. W.  A. & P a l ,  R. (1973) Rés i s t ance  d e s  a r th ropodes  aux i n s e c t i c i d e s ,  Wld H l t h  Org. 
Monogr. Se r .  No. 38 
Comins, H. N .  (1977) The development o f  i n s e c t i c i d e  r e s i s t a n c e  i n  the  presence of  
m i g r a t i o n ,  J.  Theor. B io l .  , 64, 177-197 
Grébaut ,  S .  & G u i l l e t , .  P. (1977) S e n s i b i l i t é  B l ' A b a t e ,  a u  Chlorphoxim e t  a u  DDT des  
p o p u l a t i o n s  larvaires  du complexe S. damnosum dans l a  phase III du Programme de L u t t e  
c o n t r e  l 'Onchocercose dans l a  r ég ion  du Bassin de l a  Vo l t a ,  Doc. ronéo. I R 0  Bouaké, 
No. 9/0ncho/Rapp/77 , 24 pp . ,  m u l t i g r .  
Hadaway, A. B.  6, Barlow, F. (1957) The i n f l u e n c e  o f  temperature  and humidity upon the  
a c t i o n  of i n s e c t i c i d e .  I. During t h e  p o s t  t reahr ,ent  p e r i o d ,  Ann. t r o p .  Med. P a r a s i t . ,  
- 51 ,  187-193 
Jamnback, H. & W e s t ,  A. S. (1970) Decreased s u s c e p t i b i l i t y  of b l a c k f l y  l a r v a e  t o  
P.P.'DDT i n  New York S t a t e  and E a s t e r n  Canada, J .  econ. Ent . ,  63, ( I ) ,  218-221 
Le Ber re ,  R.  , Ovazza, M.  6, Juge ,  E .  (1964) R é s u l t a t s  d 'une campagne l a r v i c i d e  c o n t r e  
1 S .  damnosum Theobald ( D i p t e r a ,  S imul i idae )  en Afr ique de l ' O u e s t ,  Proc.  1 2 t h  I n t .  Cong. 
E n t .  London, p .  811 
Mouchet, J .  e t  a l .  (1977) Méthodologie pour t e s t e r  l a  s e n s i b i l i t é  aux i n s e c t i c i d e s  des  
larves de Simulium damnosum, Cah. ORSTOM, s é r .  Ent.  méd. P a r a s i t o l . ,  15, ( I ) ,  55-66 
Muirhead-Thomson, R. (1957) Labora to ry  s t u d i e s  on the  r e a c t i o n  o f  - Simulium l a r v a e  t o  
i n s e c t i c i d e s .  II. The r e a c t i o n  of  Simulium damnosum l a r v a e  t o  DDT, Amer. J .  t r o p .  
Med. Hyg., - 6 ,  920-934 
P h i l i p p o n ,  B. & Le Ber re ,  R. (1974) R é s u l t a t s  a c q u i s  e t  o r i e n t a t i o n  a c t u e l l e  des  r eche rches  
dans l a  l u t t e  c o n t r e  l e  v e c t e u r  de l 'Onchocercose humaine en Afr ique Occ iden ta l e  
francophone (Côte d ' I v o i r e ,  Haute-Volta,  M a l i ) ,  Proc.  3rd.  I n t .  Congr. P a r a s i t o l . ,  
Munich, 2, 990-991 
Quélennec, G .  Q Vervent ,  G. (1970) Mesure de l a  s e n s i b i l i t é  aux i n s e c t i c i d e s  des  l a r v e s  
de s i m u l i e s  ( D i p t e r a ,  S i m u l i i d a e ) ,  Cah. ORSTOM, sér.  Ent .  Med. Pa ras i to l . ,  8 (11, 
21-43 
Qu i roga ,  M. e t  a l .  (1976) Ac t ion  d ' u n  analogue du DDT (OMS 1476) s u r  des  souches de 
moust iques s e n s i b l e s  e t  r é s i s t a n t e s a u  DDT, Cah. ORSTOM, sér. Ent.  Med. P a r a s i t o l . ,  2 
( 2 ) ,  89-92 
Suzuki ,  T. , I t o ,  Y .  6, Harada, S. (1963) A r e c o r d  of  black f l y  l a r v a e  r e s i s t a n c e  t o  DDT 
i n  Japan  (Simulium (odagmia) a o k i i ) ,  J ap .  J .  Exp. Med. , 33 (1) , 41-46 
Walsh, J .  F. (1970) Evidence of  reduced s u s c e p t i b i l i t y  t o  DDT i n  c o n t r o l l i n g  Simulium 
damnosum ( D i p t e r a ,  S imul i idae )  on t h e  r iver  Niger ,  Bul l .  Wld H l t h  Org. , 43, 316-318 
West, A. S. (1967) The s u s c e p t i b i l i t y  o f  b l a c k f l i e s  t o  DDT i n c l u d i n g  f i e l d  r e s i d u e s ,  
WHO I n f .  c i r c .  Insect. r e s i s t . ,  6, 14 pp. 
WHO/VBC/7 7.6 78 
page 5 
Loca l i ty ,  
river , 
country 
Lc50 
PPm 
Species  Date LCg5 
PPm 
Range of 
LC 100 
13.05.77 0.037 
~ 
Gauthier  F a l l s ,  
Bandama, 
Ivory  Coast 
S. s a n c t i p a u l i  29.03.77 0.053 0.18 0.25-0.50 
>5.7 
32.8 
6.7 
>2 1 
10.4 
5.2 0.62 1.25-2.50 
TABLE 1. CHARACTERISTIC VALUES OF POPULATIONS SUSCEPTIBLE TO DDT 
c 
? +  '.r Rat i o  
LC9 5 
c*- 
Lc50 
c 
~~ 
Wa, Goué, 
Ivory  Coast 
0.058 0.06-0.12 4- 1.5 - 
3.4 
1.6 
3.3 
S. yahense 
~ 
S .  damnosum s. s. 
T j okoronidougou , S. sir banum 
Boa, Ivory Coast S. soubrense 
S. s a n c t i p a u l i  
Ar i thmet ic  mean 
~ 
0.064 0.02-0.1 
0.175 0.25-0.50 
0.12 I 2.8 O. 045 
TABLE 2. CHARACTERISTIC VALUES OF POPULATIONS RESISTANT TO DDT 
LClOO 
Rat io  I Coef f i c i en t  Loca l i ty ,  
r i v e r  , 
country 
a 
r e s i s t a n c e -  , 
Species  
S. damnosum 
S. sirbanum 
S. damnosum 
S. sirbanum 
S. soubrense 
dominant 
S. damnosum 
S. s i r b a n m  
s.  damnosum 
S. sirbanum 
43 I 10.4 Sossoa 
Togo 
1.25 I B1.25 9.11.76 10.029 
>2.5 1 '2.5 325.5 1 ' > 2 1  Banif ing II 
Ma li 18.02.77 0.098 1 
~ 
0.44 
Bouaf l é  
Marahoué 
Ivory  Coast 
Kia t iko  
Benin 
Taouba 
Baoulé 
Ma li 
18.02.76 
3.11.76 O. 038 
0.092 14.02.77 
a 
- R a t i o  of LCg5 of r e s i s t a n t  populat ion t o  LCg5 of suscep t ib l e  populat ion.  
. . . .  - t .  ... 
% .  
99,’ 
99 
98 
95 
90 
80 
70 
60 
50 
40 
30 
20 
10 
5 
2 
091 
I t 
/ 
/ 
/ 
/ 
1 
0 
/ 
/ 
/ / 
/ C +  
Fig. I 
DDT Susceptible populations 
1 - Goue - Ivory Coast - 13.05 .77  
2 - Bandama - Ivory Coast - 29 .03 .77  
DDT Resistant populations 
- 9.11 .76  A, Sossoa - Togo 
B - Banifing II- Mali - 18.02.77 
C - Marahoué - Ivory Coast- 18.02.76 
w 
2,50 PPm 0,05 0,l o o25 0,SO 1,25 
0,Ol 402 
% 
99,! 
O,’ 
99 
98 
95 
90 
80 
70 
60 
50 
40 
30 
20 
10 
5 
2 
- 
0,Ol 0,02 0,05 OJO 0925 450 1,25 2,50 PPm 
D 
3 
t 
I 
I 
Í 
4 r ’  
Fig. II 
DDT Susceptible populations 
3 - Boa- Ivory Coast - 9.03.76 
4 - Boa - Ivory Coast - 15.03.77 
DDT Resistant populations 
D- Kiatiko - Benin - 3.11.76 
E- Baoule - Mali - 14.02.77 
H 
r ?  
O 


DDT resistance in Simulium damnosum s.l. (Diptera, Simuliidae) in West Africa

Grebaut, Serge

Name not available

DDT resistance in SIMULIUM DAMNOSUM s.l. (DIPTERA, SIMULIIDAE) in west Africa

- 97 - 
WORLD HEALTH ORGANIZATION 
ORGANISATION MONDIALE DE LA SANTG 
v 
DDT RESISTANCE I N  SPNLIUM 'DAMNOSUM S.l. (DIPTERA, SIMULIIDAE) 
IN WEST  AFRICA^ 
, by 
2 3 and S. Crebaut P. Gui l l e t , '  J. Mouchet 
In West Af r i ca  Simulium damnosum 8.1. may l o c a l l y  develop a h igh  l e v e l  of r e s i s t a n c e  
t o  DDT. 
a g r i c u l t u r a l  use of DDT has been e s t ab l i shed .  
very loca l i zed ,  they may have some repercuss ions  on t he  ex tens ive  Onchocerciasis Control 
Programne being c a r r i e d  ou t  by the  World Health Organization i n  West Africa.  
A probable r e l a t i o n s h i p  between such r e s i s t a n c e  and the  sanetimes i n t e n s i v e  
Although these  r e s i scance  phenomena a r e  
DDT has been widely used i n  West Af r i ca '  f o r  t h e  con t ro l  of b l ack f ly  l a rvae  of the 
S. damnosum s.1. complex. 
Between 1960 and 1971, i n  c o n t r o l  campaigns in  the  Volta bas in  a r e a ,  high concent ra t ions  
of DDT (0.1 ppm/30 min) were a p p l i e d  weekly t o  r i v e r s  (Le Berre e t  a l . ,  1964; 
Le Berre, 1974). 
in the e f f i c a c y  o f  DDT on c e r t a i n  s t r e t c h e s  of water  ( t h e  Comoé a t  Folonzo, t he  lower 
Bandama). 
Philippon & 
From 1970 onward the  t rea tment  supe rv i so r s  noted a q u i t e  marked decrease  
A t  Ka inJ i  i n  Niger ia  t h e  e f f e c t i v e  concent ra t ions  of DDT doubled between 1961 and 1968, 
a s ign  of a decrease  i n  the  s u s c e p t i b i l i t y  of t he  l a rvae  of S. damnosum s.1. (Walsh, 1970). 
In Ghana, on the  lower reaches  of the  Volta,  Kuzoe 6 Noamesi ( i n :  Brown 6 P a l ,  1973) 
a l s o  noced a decrease  in t he  e f f i c a c y  of DDT and a decrease  in che LC50 va lues  (obta ined  by 
che method of Xuirhead-Thomson, 1957). 
In Upper Volta,  Quélennec & Vervent (1970) showed t h a t  i n  a r e a s  of onchocerc ias i s  
vector c o n t r o l ,  S.  hara reaves i  could r ap id ly  develop r e s i s t a n c e  t o  DDT. 
Outside Af r i ca ,  r e s i s t a n c e  of Simuliidqe l a rvae  t o  DDT has been r epor t ed  in Japan 
v i&h  S. a o k i i  (Suzuki e t  a l . ,  1963) and wi th  S. ornatum (Asahina e t  a l . ,  1966), i n  t he  
United S t a t e s  and Canada wi th  S. venustum and S. fuscum (West, 1967; Jamnback 6 West, 1970).  
MATERIALS AND METHODS 
The methodology f o r  t e s t i n g  the  s u s c e p t i b i l i t y  of b l ack f ly  l a rvae  t o  i n s e c t i c i d e s  
proposed by Mouchet e t  a l .  (1977) was success fu l ly  appl ied .  
F i e ld  t e s t s  were c a r r i e d  o u t  e a r l y i n  themorningand i n  the  evening. Fo reachconcen t r a t ion  
The t e s t s  were repea ted  two t o  four  times, depending 
two batches of 25 Larvae of s t a g e s  4 and 5 were used, placed i n  g l a s s  bowls conta in ing  250 ml 
of preoxygenated d i s t i l l e d  water .  
on t h e  number of l a rvae  ava i l ab le .  The con tac t  time was three  hours and m o r t a l i t y  was 
' This s tudy  was supported by a g r a n t  from the World Health Organization. 
Medical en tomologis t ,  ORSTON.. 
Medical entomology t echn ic i an ,  OCCGE. 
The issue of th i s  documant does not constitute 
formal publication. It should not be reviewed. 
abstracted or Quoted without the agreement Of 
the World Health Organization. Authors alone 
are responsible for view6 expresead in signed 
articles: que-leurs auteure. 
,, 
Ce 'document, ne constitua pae une  publication, 
Il ne doit faire l'objet d'aucun compte rendu ou 
rBsum6 ni d'aucune citation sans I'autorisation de 
'l'0,rganisation Mondiale de la Santd. Les opinions 
exprim6es dans les articleri sign& n'engagent '' 
ORSTOM Fonds Documentaire 
Cote : 6 
I $ 93 Mo c 29 53$ 
1 
- 98 - 
asses sed  by t o t a l l i n g  the  dead and dying l a rvae  f o r  each concen t r a t ion  (h igh  m o r t a l i t y ) .  
The d i l u c i o n s  were obta ined  from s t anda rd  e thano l  s o l u t i o n s  supp l i ed  by WHO. 
Only the  t e s t s  in which the  temperature remained between 20 and 25°C were taken i n t o  
account.  
S. sitbanum, Grébaut & G u i l l e t  (1977). showed t h a t  w i t h i n t h e  20-2SoC range and wi th  a con tac t  
time of t h r e e  hours the  temperaturd. 'has no s i g n i f i c a n t  e f f e c t  on t he  r e s u l t s  of t he  t e s t s .  
The temperature cannot t he re fo re  exp la in  the  wide v a r i a t i o n s  in s u s c e p t i b i l i t y  t h a t  are 
encountered. In the  case  O E  DDT, however, i t  should be noted t h a t  t o x i c i t y  g e n e r a l l y  
drops a s  t he  temperature inc reases  (Hadaway & Barlow, 1957; Fan Cheng & Richard,  i n :  
Brown IS P a l ,  1973). 
In Ivory Coast t h ree  s u s c e p t i b l e  popula t ions  o f  d i f f e r e n t  compositions were t e s t e d :  
By ana lys ing  the  r e s u l t s  of 20 t e s t s  w i th  temephos on S. damnosum S.S. and 
S. yahense on t he  Coué a t  Wa (south-western Ivory  Coast,  7'26'N, 8'lOtW), S.  s a n c t i p a u l i  on 
t h e  Uanddma a t  T i a s s a l é  ( southern  Ivory  Coast,  5'56'N, 4°49'W), S. damnosum 6.s. and 
S. sirbanum which predominate on the  Boa a t  Tjokoronidougou in the  d ry  season (north- 
western Ivory Coas t ,  8'41'N, 7.22'W). 
Within the  boundaries of phase III of the Onchocerc ias i s  Programme in  the  Volta Basin 
Area, four  popula t ions  OP S. damnosum S.S. and S. sirbanum wi th  low s u s c e p t i b i l i t y  o r  
r e s i s t ance  t o  DDT were t e s t e d :  i n  Mali on the Banifing II (1 lQ45 'N,  7'10'W) and on t he  
LIaoulG (1lo30'N, 6'50'W), i n  Benin on the  Kia t iko  (10°18'N, 1°22'E),  and i n  Togo on the  
Sossoa (9'42'N, 1'15'E). 
A r e s i s t a n t  population c o n s i s t i n g  mainly of S. soubtense was t e s t e d  a t  Bouaflé on the  
Marahoué ( c e n t r a l  Ivory Coast,  7 " N ,  5'45'W). 
RESULTS 
Table 1 g ives  the  r e s u l t s  ob ta ined  wi th  the  th ree  suscep t ib l e  popula t ions  t e s t e d  i n  
Ivory Coast. 
F igs  1 and 2.  
The corresponding concen t r a t ion -mor ta l i t y  r eg res s ion  l i n e s  a r e  presented  in 
In  o rde r  t o  compare these  r e s u l t s  w i t h  those obta ined  wi th  r e s i s t a n t  popula t ions ,  the  
a r i thmechic  means O E  the  LC50 and LCg5 va lues  were c a l c u l a t e d  (0.045 and 0.12 ppm 
r e s p e c t i v e l y ) .  
The popula t ions  t e s t e d  on t he  Bandama and Boa (March 1977) do n o t  d i sp l ay  similar suscep- 
t i b i l i t y  t o  those  on t he  Cou6 and Boa (March 1976). 
s u s c e p t i b l e  i n  view of the  concen t r a t ion -mor ta l i t y  r a c i o  and the  L C C J ~ / L C ~ ~  r a t i o s  (3.3 and 
3.4).  
The s u b s t a n t i a l  v a r i a t i o n s  found i n  the  LCloo va lues  w i l l  be noted. 
Never the less ,  they a r e  regarded a s  
Table 2 gives  the  r e s u l t s  ob ta ined  Prom popula t ions  wi th  low s u s c e p t i b i l i t y  o r  r e s i s t a n c e  
t o  DDT. 
LCg5 i n  s u s c e p t i b l e  popula t ions .  
t he  c h a r a c t e r i s t i c  appearance O P  DDb.resistance: 
il very marked p l a t eau  a t  h igh  concen t r a t ions .  
mo l e v e l s  of r e s i s t a n c e  were Eound: 
a high l e v e l  ( c o e f f i c i e n t  o f  r e s i s t a n c e  above 21) f o r  t he  popula t ions  o f  the  Banffing 
The c o e f f i c i e n t  of r e s i s t a n c e  is t he  r a t i o  between the  LCg5 observed and the  mean 
The corresponding r eg res s ion  lines (F igs  1 and 2)  have 
normal m o r t a l i t y  a t  low concen t r a t ions  and 
' 
If (Mali)  and the Marahoue ( Ivory  Coas t ) ;  
a moderate l e v e l  ( c o e f f i c i e n t  of r e s i s t a n c e  10.4) f o r  t he  popula t ions  o f  the  
Kia t iko  (Benin) and the  Sossoa (Togo). 
DISCUSSION 
Up to now DDT r e s i s t a n c e  in S. damnosum s.1. has never been c a t e g o r i c a l l y  proved. 
I 
WHO/VBC/~~. 678 
Page 3 
The l e v e l s  of r e s i s t a n c e  mentioned he re  €o r  West Af r i ca  a r e  h igher  than those repor ted  
by  Suzuki e t  a l .  (op. c i t . )  ( c o e f f i c i e n t  of r e s i s t a n c e  = 12.8) .and by West and Jamnback & 
Vest (op. c i t . )  ( c o e f f i c i e n t  of r e s i s t a n c e  = 5-7) i n  p a l a e a r c t i c  and n e a r c t i c  b l a c k f l i e s .  
I t  is a l s o  poin ted  o u t  t h a t  on the  Boa the  LCg5 i nc reased  by a f a c t o r  of 2.7 i n  one year ,  
Ind ica t ing  a poss ib l e  r eg res s ion  o f  DDT s u s c e p t i b i l i t y .  
This r e s i s t ance  is occur r ing  in the  b l ack f ly  popula t ions  o f  t h r e e  temporary r i v e r s  
v i t h  a low d ischarge  and one permanent r i v e r ,  t he  Marahou6. 
the time ever  been sub jec t ed  t o  a b l ack f ly  c o n t r o l  campaign. 
cotton is i n t e n s i v e l y  c u l t i v a t e d ,  and each r a i n y  season the co t ton  crop is t r e a t e d  wi th  
8-10 kg of DDT per hec tare .  Some of  t h i s  DDT is c a r r i e d  away by the  r i v e r s  on the  accounc 
of the very s u b s t a n t i a l  run-off.  The exposure of S. damnosum s.l. l a rvae  t o  low concen- 
t r a t ions  of DDT f o r  s e v e r a l  months may be s u f E i c i e n t  t o  account f o r  the  level  of r e s i s t a n c e  
mentioned. This phenomenon is commonly observed among the  Cul ic idae .  
None of these  r i v e r s  had a t  
They flow through a r e a s  where 
The a g r i c u l t u r a l  use o f  DDT is s t i l l  very widespread i n  West Afr ica .  Consequently, 
few data  have been c o l l e c t e d  on the  bas i c  s u s c e p t i b i l i t y  t o  DDT o f  S.  damnosum s .1 .  
On a more genera l  l e v e l ,  and wi th in  the  c u r r e n t  con tex t  of the ex tens ive  Onchocerc ias i s  
Control Programme in  West Af r i ca ,  the  mechanisms o f  the  development of i n s e c t i c i d e  resis- 
tance i n  S. damnosum s.1. a r e  c e r t a i n l y  a very complex matter. W o  groups of opposing 
fac tors  must be p a r t i c u l a r l y  involved. l i 
Factors  favourable  t o  the  developement OE r e s i s t a n c e :  the  very s t rong  s e l e c t i v e  
pressure  exe r t ed  by the  i n s e c t i c i d e s  because of t he  cons t an t ly  inc reas ing  a r e a  
of the t r e a t e d  zones ( a t  p re sen t  one a r e a  a lone  is 700 000 km2) and the  frequency 
of l a r v i c i d e  treatmenc (once a week) on the  one hand and t h r  s h o r t  du ra t ion  o f  t he  
development cyc le  (8-15 days) on t he  o t h e r  hand. 
Fac tors  unfavourable t o  the  development of r e s i s t a n c e :  t he  phenomena o f  d i spe r s ion  
and migra t ion ,  very marked i n  S .  damnosum s.1. females,  caus ing  t h e  massive 
in t roduc t ion  i n t o  t r e a t e d  a r e a s  of f e r t i l i z e d  females from un t rea t ed  a reas .  
T h i s  l eads  t o  d i l u t i o n  of any r e s i s t a n c e  genes present  i n  the  t r e a t e d  popula t ion  
and keeps the  frequency of such genes below a c r i t i c a l  th reshold .  This phenomenon 
was r e c e n t l y  s t u d i e d  from the  t h e o r e t i c a l ,  viewpoint by Comins (1977). 
CONCLUSION 
6 "*' 
The l e v e l  of s u s c e p t i b i l i t y  of S.  damnosum s.1. l a rvae  'to DDT is on t he  whole r a t h e r  
varied and some cases  o f  high r e s i s t a n c e  have been repor ted .  
l oca l i zed ,  these  cases  a r e  very important because they d e f i n i t e l y  prove t h a t  S.  damnosum s.1. 
has the c a p a b i l i t y  t o  develop a c e r t a i n  l e v e l  o f  DDT r e s i s t a n c e  f a i r l y  rap id ly .  
Although sporad ic  and 
It i s  l i k e l y  t h a t  the  use  of DDT i n  the  Regional Onchocerc ias i s  Cont ro l  P rograme  would 
have l e d  t o  the  appearance of wfdespread r e s i s t a n c e  t o  t h i s  i n s e c t i c i d e .  This c a s t s  g r e a t  
doubt on the  a d v i s a b i l i t y  of u s ing  DDT analogue? i n  the  c o n t r o l  of S. damnosum s a l . ,  a s  
c ros s - r e s i s t ance  phenomena a r e  common i n  t h i s  group of i n s e c t i c i d e s  p a r t i c u l a r l y  i n  the  
biodegradable analogues.  
between OMS-1476 and DDT i n  the Cul ic idae  (Quiroga e t  a l . ,  1976). 
For example, a very high l e v e l  O E  c ross - r e s i s t ance  i s  observed 
A t  p re sen t  t he  on ly  group o f  i n s e c t i c i d e s  , r e a l l y  s u i t a b l e  l o r  use  Ln onchoce rc i a s i s  
con t ro l  i n  Ves t  Af r i ca  remains the  organuphosphorusb%$ompounds; 
(unpublished document) have n o t  so f a r  recorded any reduct ion  i n  s u s c e p t i b i l i t y  t o  temephos 
i n  popula t ions  t r e a t e d  r e g u l a r l y  f o r  more than f iveAiyears .  
G u i l l e t  & GrBbaut 
i *  1 
6 - 
- 100 - 
U HO/VBC/7 7.6 78 
page 4 . 
REFERENCES 
Asahina,  S . , e t  a 966) I n s e c t i c i d e  r e s i s t a n c c  of the  l a rvae  o 
243-146 
S. omatum, Jap .  .Í. Sa-. 
Brown, A. W. A. 6 Pal, R. (1973) Res is tance  des a r thropodes  aux i n s e c t i c i d e s ,  Wld Hl th  Org. 
MonoEr. Ser.  No. 38 
Ccmins, H. N. (1977) The development of i n s e c t i c i d e  r e s i s t a n c e  in the  presence o f  
mig ra t ion ,  J. Theor. Biol. ,  64, 177-197 -. i 
Crfbau t ,  S. & G u i l l e t ,  P. (1977) S e n s i b i l i t e  B l 'Abate, au Chlorphoxim e t  au DDT des 
popula t ions  l a r v a i r e s  du complexe S. damnosum dans la phase III du Programme de Lu t t e  
c o n t r e  L'Onchocercose dans la reg ion  du Bassin de la Volta,  Doc. roneo. I R 0  Bouakb, 
No. 9/0ncho/Rapp/77, 24 pp., mu l t ig r .  ~- 
Hadawav. A. B. & Barlow, F. (1957) The i n f l k n c e  o f  temperature and humidity upon the  - .  - .  
a c t i o n  of i n s e c t i c i d e .  I. During the  pos t  t r e a t n e n t  per iod ,  Ann. t rop .  Med. P a r a s i t . .  
2, 187-193 
Jamnback, H. &West, A. S.  (1970) Decreased s u s c e p t i b i l i t y  of b l ack f ly  l a rvae  t o  
P.P.'DDT in New York S t a t e  and Eas t e rn  Canada, J. econ. Ent.. ,  63, (I), 218-221. 
Le Berre,  R. ,  Ovazza, M.  6 Juge ,  E. (1964) Resu l t a t s  d 'une campagne l a r v i c i d e  con t r e  
S. damnosum Theobald (Dip te ra ,  S imul i idae)  en Afr ique  de L'Ouest, Proc.  12th I n c .  Cong. 
Enc. London, p. 811 
Mouchet, J. e t  a l .  (1977) Mfthodologie pour t e s t e r  la s e n s i b i l i t e  aux i n s e c t i c i d e s  des 
l a r v e s  de Simulium damnosum, Cah. ORSTOM, ser. Ent. m6d. P a r a s i t a l . ,  2, (I), 55-66 
Muirhead-Thomson, R. (1957) Labora tory  s t u d i e s  on the  r e a c t i o n  of Simulium l a rvae  t o  
i n s e c t i c i d e s .  II. The r e a c t i o n  of Simulium damnosum la rvae  t o  DDT, Amer. J. t rop .  
Med. Hyg., 5 ,  920-934 
' Phi l ippon ,  B. & Le Berre ,  R. (1974) R e s u l t a t s  acqu i s  e t  o r i e n t a t i o n  a c t u e l l e  des recherches  
dans l a  l u t t e  con t r e  l e  vec teu r  de l 'Onchocercose humaine en Afr ique  Occidenta le  
francophone (Cate d ' I v o i r e ,  Haute-Volta, Ma l i ) ,  Proc. 3rd. I n t .  Connr. P a r a s i t o l . ,  
Munich, 2 ,  990-991 
QuPlennec, C. & Vervent,  G. (1970) Mesure de l a  s e n s i b i l i t e  aux i n s e c t i c i d e s  des l a r v e s  
de s imul i e s  (Dip te ra ,  S imul i idae ) ,  Cah. ORSTOM, ser. Ent. Med. P a r a s i t o l . ,  a ( I ) ,  
2 1-43 
Quiroga ,  H. e t  a l .  (1976) Action d'un analogue du DDT (OMS 1476) s u r  des  souches de 
moustiques s e n s i b l e s  e t r e s i s t a n t e s a u  DDT, Cah. ORSTOM, s6 r .  Ent.  Med. P a r a s i t o l . ,  fi 
(21, 89-92 
Suzuki,  T., I t o ,  Y. & Harada, S. (1963) A r eco rd  of black f l y  l a r v a e  r e s i s t a n c e  t o  DDT 
in Japan (Simulium (odagmia) a o k i i ) ,  Jap .  J .  Exp. Med., 2 (11, 41-46 
Walsh, J. F. (1970) Evidence of reduced s u s c e p t i b i l i t y  t o  DDT i n  c o n t r o l t i n g  Simulium 
damnosum (Dip te ra ,  S imul i idae)  on t he  r i v e r  Niger,  Bull .  Wld Hl th  Org., 43, 316-318 
West, A. S. (1967) The s u s c e p t i b i l i t y  of b l a c k f l 4 r s  t o  DDT inc luding  f i e l d  r e s idues .  
WHO I n f .  c i r c .  I n s c c t .  resist., a, 14 pp. 
TABLE i. CHARACTERISTIC VALUES OF POPULATIONS SUSCEPTIBLE TO DDT 
LC50 LCg5 Range o f  
Loca lit y , 
r i v e r  , S p e c i e s  Date 
c o u n t r y  3 PPm PPD LClOO 
13.05.77 0.037 0.050 0.06-0.12 . I  I L I  I S. yahenae Wa, G o d ,  Ivory  C o a s t  
G a u t h i e r  F a l l s ,  
Bandama, 
Ivory  C o a s t  I. 
9.03.76 0.036 0.064 0.02-0.1 S .  damnosum S.S. Tjokoronidougou,  S.  si rbanum 
Boa, I v o r y  Coas t  S.  soubrense  I i l l1 15.03';77 0.052 0.175 0.25-0.50 S. s a n c t i p a u l i  .'I 
Arithmetic mean I ' I  10.045 10.12 I 
1 
Rat io - 1  
1: 1 2.8 
TABLE 2 .  CHARACTERISTIC VALUES OF POPULATIONS RESISTANT TO DDT 
Loca l i t  y , 
r i v e r ,  S p e c i e s  
coun c r  y 
Date Lp,50 Lc95 
PPm PPm 
9.11.76 0.029 1.25 Sossoa S. damnosum 
Togo S. s i rbanum 
B a n i f i n g  II S.  damnosum 
Mali S .  s i rbanum 
Bouaf 16 
Elarahoué 18.02.76 0.44 r2.5 
Ivory C o a s t  
K i a t i k o  S. damnosum 
Benin S. si rbanum 
Taouba 
Eaoulé 
18.02.77 0.098 >2.5 
s. 
dominant  
3.11.76 0.038 1.25 
'. 
S .  si rbanum 
14.02.77 O.Ô92 0.62 
n a l i  L .  
'Ratio of LC95 of r e s i s t a n t  popula t ion ,  t o  LCg5 o f  s u s c e p t i b l e  popula t ion .  
1.25-2 -50 
I % -  
, ,, i ./ ! 
! l .  
I ' -  .i. 
I" ." 
.. 
% 
99,s 
99 
98 
95 
90 
80 
70 
60 
50 
- 40 
30 
20 
10 
5 
2 
41 
- 
.-* - I  
. DDT Susceptible populatiorrs A ,  / 
1 - Goué - Ivory Coast - 13.05 e 77 
2 - Bandama - Ivory Coast - 29.03.77 
DDT Resistant populations 
A -  Sossoa - Togo - 9 .11 .76  
B - Banifing II, Mali - 10.02.77 
C - Marahoue - Ivory Coast, 18.02.76 
/ 
C +  
-m 
090 1 402 0,05 0,l o 025 450 125 250 PPm 
% 
99,9 
99 
98 
95 
90 
80 
70 
-60 
50 
40 
30 
*m 
10 
5 
2 
091 
Fig.lI 
DDT Susceptible popu,ations 
H 
o n  3 - Boa- Ivory Coast - 9.03.76 % E  
2G 
G E  
4 - Boa - Ivory Coast - 15.03.77 
H H  
H O  o z  z a r  
DDT Resistant populations 
H z m D- Kiariko - Bénin - 3.11.76 v) 
E- Baoulk - Mali - 14.02.77 
0,Ol O P  0,05 OJO (325 0,SO 1,25 2,50 PPm 
I I I I I '  I I'." U 


DDT resistance in Simulium damnosum s.l. (Diptera, Simuliidae) in West Africa

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