Mission Bntomologique O .i4 .S .T .O ,Ph,

a u p r e s d e 1 ' 0 . C ,C .G .E 2

1 he u s e of chemosterilants for vector control (1)

J. Hamon e t J. Mouchet

(1) @e document est bas6 sur un cuurs f a i t l o r s du Seminaire O.;:~.S i n t e r - r e g i o n a l s u r les m6thodes entomologiques d e

contr6ile d e s vecteurs' qui a e u lieu en U . R . S . S , en Septem-

bre - Octobre J.965, 11 e s t d i f f u s 6 car il paurrait Btre

u t i l e aux e n t o m o l o g i s t e s devant f a i r e d e s exposes s u r ce s u j e t darrs l e s pays d'affectation I1 c o n v i e n d r a i t alors d e completer l a b i b l i o g r a p h i e .

1,t 1

. - " c

// HE US? OF CHEPAOSTERILANTS POE VECTOR GdNTROL

++ by J. HANON ’ & J . iwC?UCHET

’“edical B n t o m o l o g i s t s

O f f i c e de l a Beche rche S c i e n t i f i q u e

& Technique Outre-Mer, P a r i s , F r a n c e .

!

e

i* ,i! MTRODUCTION . i

S i n c e a b o u t t w e n t y y e a r s many a r t h r o p o d s of medical and

v e t e r i n a r y i m p o r t a n c e have been k e p t u n d e r c o n t r o l by t h e u s e of L

s i d u a l i n s e c t i c i d e s , f o r t h e b e n e f i t of humm h e a l t h and Welf a r e .EU*. the m a s s . s p r a y i n g o f i n s e c t i c i d e s , e i t h e r for v e c t o r c o n t r o l O r d i -

sease e r a d i c a t i o n programmes, as w e l l as for a g r i c u l t u r a l and domes,

tic u s e s , has seleçted i n s e c t i c i d e - r e s i s t a n t p o p u l a t i o n s of various

v e c t o r s i n many areas o f t h e wor ld . Year a f t e r y e a r t h e number of r

s i s t a n t s p e c i e s and t h e i r d i s t r i b u t i o n i n c r e a s e s . Now, 60 t o 70 spe- c i e s af m e d i c a l and v e t e r i n a r y i m p o r t a n c e , b e l o n g i n g t o 9 ma jo r f a -

m i l i e § , a r e r e s i s t a n t t o o n e or s e v e r a l c h e m i c a l g r o u p s of r e s i d u a l

i n s e c t i c i d e s , and t h e i r o c c u r e n c e i s a v e r y s e r i o u s c o m p l i c a t i n g f -

t o r f o r t h e o r g a n i s a t i o n and development of many p u b l i c h e a l t h pro,

grammes (W.H.O., 1963 - COZ & al., i964 - P A C , 1964 - SHAM & STOPJB-

1964 - UNGUBIBALW, 1964). W.11.0. has s p o n s o r e d a c o o r d i n a t e r e s e a r c k

programme f o r t h e deve lopment and s c r e e n i n g o f nsw i n s e c t i c i d e s , O:

a w o r l d b a s i s ; t h e r e s u l t s of Fthich are v e r y p r o m i s i n g , b u t it shr

be anyway w i s e r t o bo n o t r e l y e n t i r e l y on one t y p e o f v e c t o r con-

t r o l and to i n v e s t i g a t e o the r v e c t o r c o n t r o l p o s s i b i l i t i e s t h a n i ~ 1 - 1

s e c t i c i d e s .

4. 0.E.S.T.CI.Pi. Team near O . C . C . G . B . , F.O.B. 171, Bobo-Dioulasso Upper Volta . O.R.S.T.B.%. , 70 - 7 4 Route d’Aulnay ,, 93 - Bondv , France ++

I

_ - 2 I n s e c t i c i d e s used f o r p u b l i c h e a l t h programmes are,, as a

rule, s e l e c t i v e t e x i c a n t s f o r i n s e c t s , w i t h a l o w o r modera t e mam- m a l i a n t o x i c i t y . However, t h e i r . . u s e m o d i f i e s more o r less t h e e n v i -

r o n m e n t a l c o n d i t i o n s and t h e g r e a t e r t h e t r e a t e d a r e a , t h e g r e a t e r

t h e i m p a c l on t h e env i ronmen t . p roreover , some o f t h e most w i d e l y

s p r a y e d i n s e c t - i c i d e s a re c h e m i c a l l y v e r y s t a b l e and d i s a p p e a r o n l y

s l o w l y f rom t r e a t e d p r e m i s e s , s o i l s , w a t e r c o u r s e s , " i d so' on. Conta-

m i n n t i o n r i s k s of t h e e n v i r o n m e n t b o l o n g s t o t w o major t y p e s : a B u t ~

and i m m e d i a t e i n t o x i c a t i o n s , easy t o d e t e c t and t o p r e v e n t , and l o n .

t e r m a c c u m u l a t i o n o f the most s t a b l e compounds; t h i s l a s t risk i s

l e s s ' e a s i l y de t ec t ed and n o t h i n g b u t t i m e c a n c l ea r t h e contamincl-

t e d a r eas and p e o p l e (DALE & QUINEY, 1 9 6 3 - HBYBS & a l . , 3.963 - HA- .

%ON & a l . , 1 9 6 5 ) . Up t o now t h i s s i t u a t i o n h a s n o t c a u s e d d i f f i c u l -

t i e s f o r human h e a l t h , t h e s p o r a d i c damages b e i n g r e s t r i c t e d t o t h e

most d'eveloped c o u n t r i e s and b e i n g ' % a i n l y i n d u c e d i n w i l d l i f e . Bowe-

v e r s u c h a s i t u a t i o n u n d e r l i n e s t h e n e c e s s i t y t o combine all a v a i l 2

b l e me thods o f v e c t o r c o n t r o l t o g e t t h e b e s t o f e a c h o f t h e m i n an

' i n t e g r a t e d c o n t r o l programme, and t o u s e r e s i d u a l i n s e c t i c i d e s o n l y

when and whore t h e y o f f e r the b e s t p r o s p e c t s of success , s o t o avoiCI

useless c o n t a m i n a t i o n o f t h e e n v i r o n m e n t . One o f t h e new deve lop i r ig

c o n t r o l procedure ' s is based on t h e ' m a s s release of s t e r i l i z e d males ,

. .

I

a.. 5

-.I t

!

t,

2, THIS THEORY OF VBCTQR CONTROL BY ';ASS RELEASE OF STERILIZED TiULEf

I n many v e c t o r s p e c i e s t h e f e m a l e is i n s e m i n a t e d o n l y on-

c e ' f o r i t s whole l i f e o r , when i n s e m i n a t e d s e v e r a l t i m e s , t h e f i rs t r e c e i v e d , b a t c h of s p e r m a t o z o a is t h e ma jo r o n e , o r the o n l y o n e ,

p loyed for e g g f e r t i l i s a t i o n . 'There a r e howeveir some e x c e p t i o n s (

.SOTE,' 2948.- W@A, 1963)

I f i t is p o s s i b l e t o re lease, i n a s t a b l e p o p u l a t i o n , a s

'many s t e r i l e males a s t h e r e a r e normal m a l e s , SO% of t h e v i r g i n fe--* i*

'males w B l l b e i n s e m i n a t e d by s t e r i l e males and e i ther s h a l l n o t l a v

e g g s , or s h a l l l a y s t e r i l e e g g s , w i t h Che r emote p o s s i b i l i t y to i n - U L

duce p a r t h e n o g e n e t i c deve lopmen t , The n e x t g e n e r a € i o n w i l l b e r e d u -

ced t o 50% o f t h e i n i t i a l gene ra t&,op , a n d , . i.f the number o€ relea-

sed s te . r i le males i s c o n s t a n t , 33% o n l y of t h e r e s u l t a n t f e m a l e s . . s h a l l g i v e a p r o g e n y , and s o o n , a l o n g a d e c r e a i n g e x p o n e n t i a l our-

ve, u n t i l t h e &apearance of t h e s p e c i e s . Thè s u c c e s s w i l l b e a c h i e ~

ved much q u i c k e r i€, from t h e b e g i n n i n g , t h e s t e r i l e malos outnumbc

. . , ,

3

by 'several times t h e no rma l males- (ICNSPEING, 1955) . \ , .

1 1

It s h o u l d be moro d i f f i c u x t t o g e t t h e spa& r e s u l t s by re-

lease of s t e r i l e females as t h e males c o p u l a t e many t i m e s d u r i n g

t h e i r f i r s t .days or weeks ,of l i f e and s h o u l d be a b l e anyway t o i n s o -

m i n a t e no rma l f e m a l e s . The mixed re lease o f ' bo th , s t e r k l e males and

f e m a l e s s low down t h e p r o c e s s , a p r o p o r t i o n o f Che s t e r i l e ma les

b e i n g d i v e r t e d from . t h e no rma l t o t h e s t e r i l e f o m a l e s . . a

S t e r i l e males, t o be c o m p e t i t f i v e w i t h no rma l o n e s , m u s t -

have a no rma l e x p e c t a t i o n of l i f e or, a t l e a s t , must be s e x u a l l y ac-

t i v e i n l a r g e numbers a s l o n g as t h e normal males, They m u s t a l s o

i n s e m i n a t e f e m a l e s w i t h a norma l amount o f s p e r m a t o z o a and a c c e s s o -

r y g l a n d s e c r e t i o n s # b e c a u s e t h e f e m a l e s w i t h empty o r p a r t i a l l y emp-

t y s p e r m a t h e c a e c o u l d a g r e e t o be i n s e m i n a t e d a s e c o n d t i m e , S t e r i l e

males must be a l s o p o t e n t i n s e m i n a t o r s , The d i f f i c u l t y t o f u l f i l l

a l l t h e s e c o n d i t i o n s i s a s e c o n r e a s o n Lor r e l e a s i n g a nupber of S t e r

r i l e males s e v e r a l times h i g h e r t h a n t h e e s t i m a t e d number of normal

ma les , t h e r a t i o of s t e r i l e t o n o r a a l m x l e s b e i n g , a t l e a s t 18 t o one ~

F i n a l l y s t e r i l e m a l e s m u s t be e v o n l y s c a t t e r e d among w i l d population

D i f f i c u l t i e s i n c r e a s e w i t h t h e n a t u r a l d e n s i t y of t h e v e c t o r popula-

t i o n , w i t h s p e c i e s e i t h e r w i t h dormant eggs a n d / o r w i t h m u l t i p l e i n -

s e m i n a t i o n s , and w i t h s h o r t f l i g h t - r a n g e s p e c i e s ,

< I

The f i r s t known method of male s t e r i l i z a t i o n w a s based O P

gamma o r % - r a y i r r a d i a t i o n of l a r v a e o r pupae , wh ich i m p l i e s l a b o r a -

t o r y m a s s - r e a r i n g of t h e \ v e c t o r to contro l . The f i r s t w i d e - s c a l e

scheme o f v e c t o r c o n t r o l by m a s s r e l e a s e of s t e k i l i z e d males w a s Carp.

o u t a g a i n s t a p e s t of v e t e r i n a r y i m p o r t a n c e , t h e screw-worm Cochliomgc

i a homin ivorax which h a s a long f l i g h t - r a n g e (EI@~-iTG4!3l¿ & a l , , 2 9 6 5 ) h

The s u c c e s s of t h e screw-norm e r a d i c a t i o n , programme, f i r s t i r ì 1954

i n C u r a ç a o (laAU?ANOVEE &. a l . , 1955) and t h e n i n ~00,000 s q u a r e kilo- meters of t h e s o u t h e a s t e r n U n i t e d S ta tes d u r i n g E958 and 1959 t h r o u g F

t h e r e l e a s e o f more t h a n t w o ' b i l l i o n s o f s t e r i l e f l i e s (KTJIFLING,

19601, n o t o n l y s t i m u l a t e d w i d e i n t e r e s t i n i n s e c t c o n t r o l by m a l e

s t e r i l i z a t i o n and i n l a b o r a t o r y n a s s r e a r i n g o f p o s t s o f ecorlomic i m - p o r t a n c e (FAY &. al,, 1963 -, PWL:LAM & al,, l.963), b u t also i n ,Con t ro l

by s t 6 r i l i z n t i o n w i t h chemicals as w e l l a s by i r r F d i a t i o n

\

4

, The s t e r i l i z a t i o n by i r r a d i a t i o n r e q u i r e s c o s t l y i n s t a l l a -

t i o n s , n o t v e r y c a s i l y h a n d l e d i n f i e l d c o n d i t i o n s . E o r e o v e r many

w o r k e r s have s t ressed t h a t i r r a d i a t e d males have a s h o r t e r e x p e c t a -

t i o n o f l i f e and a re less c o m p e t i t i v e f o r matimg t h a n n o r m a l males ~

(SACCA, 1961,, Trusta domes. t iea - RAKAKRISWNAN & al,, 3.963, Culex p i -

p i e n s f a t i a a n s - I38RT?EBFRY & r!cCOVSEN, k.968, D r o s o p h i l a m e l a n o p a s t e r -

STAHLER & TEEZPAN, L963, Aedes a e g y p t i - COXEIZ-XBFI'EZ & a l . , $962 i3

1964 , Rhodnius p r o l i x u s ) , t h e s a f e t y marg in between t h e LOO% s te r i -

l i z i n g d o s e and t h e l e t h a l one b e i n g o f t e n v e r y narrow . Chemos te r i -

l a n t s o f f e r ; b e t t e r p r o s p e c t s of developixent and p r a c t i c a b i l i t y ( S C H -

MIDT & a l , , l.964) and t h e s c r e e n i n g of t h o u s a n d s o f c h e m i c a l s f o r

s t e r i l i z i n g p r o p e r t i e s a g a i n s t i n s e c t s begun some y e a r s ago i n l a b o -

r a t o r i e s o f the A g r i c u l t u r a l E e s e a r c h S e r v i c e o f U n i t e d S t a t e s ' D e -

,

I * r

' -, .

p a r t m e n t of A g r i c u l t u r e . 3 . THE CWBMQSTERIEANTS com?ourws .

3.1. C h e m i c a l n a t u r e and p r o p e r t i e s

C h e m o s t e r i l a n t s a re chemicals c a p a b l e of c a u s i n g s e x u a l

s t e r i l i t y ; t h e y p r e v e n t r e p r o d u c t i o n i n i n s e c t s or o t h e r o r g a n i s m s .

I n s e c t s c h e m o s t e r i l a n t s may a c t i n one o f t h e th ree fol low'& p r i n -

c i p a l ways : 1

- They may cause i n s e c t s t o f a i l t o p roduce ova o r spe rm ; - They may c a u s e t h e d e a t h o f sperm and o v a a f t e r t h e y have a l r e a d y

b e produced ; I

- They may i n j u r e s e v e r e l y t h e g e n e t i c m a t e r i a l i n t h e spe rm and

o v a and , . a l t h o u g h t h e spe rm and ova r ema in a l i v e and t h e sperm

r e t a i n f u l l m o t i l i t y , t h e z y g o t e s , if formed, do n o t c o m p l e t e de-

velopme'nt i n t o m a t u r e p rogeny e

The two f i r s t ways are n o t v e r y e f f i c i e n t for v e c t o r con-

t r o l a s norinal f e m a l e s c a n be i n d u c e d t o m a t e l a t e r on w i t h f e r t i l e z-

males i f t h e i r s p e r m a t h e c a e a r e empty , The t h i r d t y p e o f a c t i o u p re -

s q n t s t h e g r e a t e s t i n t e r e s t at t h e p r e s e n t t i m e and i s t h a t shown by

t h e s o - c a l l e d " r a d i o m i m e t i c " compounds . The s e l e c t i o n o f i n s e c t c h e m o s t e r i l a n t s h a s been g v i d e d ,

f rom t h e f i r s t b e g i n n i n g , by. the r e l a t i o n s h i p between compounds ef - f e c t i v e i n c a n c e r chemotherapy and m i t o t i c a g e n t s (SPd~TT-9: & al.$ A964

5

FAHUY &: FAHMY, 1964 - CHANC, TSAO & CHIHNG, 1.963). 0ther i n v e s t i g a -

t i o n s -have be'en c a r r i e d o u t w i t h compounds s i d i l a r w i t h no rma l i n s e c t

m e t a b b l i t e s wh ich c o u l d r ep lace these m e t a b o l i t e s and s t o p c e l l u l a r

deve lopment , Then some g u i d e l i n e s have been e s t a b l i s h e d . Xn s e l e c t i n g

c h e m i c a l and s t r u c t u r a l f e ' i t u r e s c h a r a c t e r i s t i c for c h e m d s t e r k l a n t s

amongst all t h e c a n d i d a t e compounds i n v e s t i g a t e d (2XSTICH & àl.,P965), 8 ,

The c h e m o s t e r d l a n t s c a n be c l a s s i f i e d i n t o * t w o main c a t e g o -

r i e s t h e a n t i m e t a b o l i t e s and t h e a l k y l a t i n g a g e n t s , which aqe a l s o ra-

d iomimet i e . Some o t h e r a g e n t s , a t t h e p r e s e n t time Mithou$ p r a c t i c a l

i m p o r t a n c e , c a n n o t be c l d a s s i f i e d fMOUCEEI' & RACEAU, A963 - &KENAGA,

11965,). The a n t i m e t a b o l i t e s , p u r i n e and p y r i m i d i n e a n t a g o n i s t s , a n t i -

f o l i c s , a re m a i n l y a c t i v e a g a i n s t f e m a l e i n s e c t s and t h e i r a c t i o n may

be of a t e m p o r a r y n a t u r e , The a l k y l a t i n g a g e n t s a r e m u t a g e c i c and da-

mage t h e g e n e t i c m a t e r i a l of ova and sperm b u t , g e n e r a l l y , do n u t i n -

h i b a t e l i v e s p e r m a t o z o a f o r m a t i o n ; t h e i r a c t i o n i s o f a more perma-

n e n t n a t u r e , The most p r o m i z i n g a l k y l a t i n g agents are t h o d e r i v a t i v e s

of a z i r i d i n e , some of them b e i n g u s e d s i n c e several . y e a r s i n t h o t e x -

t i l e i n d u s t r y and i n c a n c e r t h e r a p y , The commonly i n v e s t i g a t e d a z i r i -

d i n e , d e r i v a t i v e s , for i n s e c t c h e m o s t e r i l i z a t i o n , are now t h e fo.110-

wing ( f i g . í ) :

- Tepa = Aphoxide = t r i s ( I - a s i r i d i n y l ) p h o s p h i n e oxyde , - ] ' @ t e p a = F'etaphoxide = Fris ( 2 - m e t h y l - i - a z i r i d i n y l ) p h o s p h i n e oxyda

- T h i o t e p a = t r i s ( E - a z i r i d i n y l ) p h o s p h i n e s u l f i d e

- Aphola t e = 2, 2, 4, 6 , 6 , 6 , hexa ( l - u z i r i d i n y l ) 2, 4,.6, t r i p h o s -

I

pha 1, 3 , 5 , t r i a z i n e , I

The t o x i c o l o g i c a l r i s k s i n h e r e n t i n the m u t a g e p i c p r o p e r t i é s

of a l k y l a t i n g a g e n t s r e s t r i c t t h e i r s t u d y as i n s e c t . s t e r i l a n t s to l a -

b o r a t o r y e x p e r i m e n t s and t o v e r y l i m i t e d f i e l d trials u n d e r c l o s e SU-

p e r v i s i o n . However r e c e n t researches have shoxn t h a t some compounds,

EMPA (=hexamethylphosphoramide ) and HNM ' (=€IHM E H e m e l = hexnmethylme-

l a m i n e ) , s t r u c t u r a l l y similar r e s p e c t i v e l y t o Tepa and t o T r e t a m i n e

(= 3, 4 , 6 , t r i s ( l - a z i r i d i n y l ) S.triazine), b u t l a c k i n g a l k y l a t i n g

p r o p e r t i e s arid b e i n g of low t o x i c i t y t o m a m m a l s , s t i l l r e t a i n t h e p r c

p e r t y o f s t e r i l i z i n g i n s e c t s (CHABG & a l . , 3.964). Y e c a n hope t h a t

f u r t h e r i n v e s t i g a t i o n s w i l l d i s c o v e r i n s e c t s chemos$.er i lants more ac-

c e p t a b l e f o r p r a c t i c e t h a n t n o s e h i t h e r e o a v a i l a b l e , ' and researches

6

a r e p r o g r e s s i n g a l o n g t h i s way (ASCHER, 1965 - FYE & a l . , 12965 - ICENAGPI, i965 - P A R I S H & AWTHUR, 3.965a - SHAIJ & RXVIBLLO, 19'62 - RISTICH & a l . 1 9 6 5 ) , b u t t o o o f t e n t h e most e f f i c i e n t new c h e m o s t e r i -

l a n t s are a l s o t h e most t o x i c f o r mammals . I

Used a s . d r y d e p o s i t s Tepa and M e t e p a d i s a p p e a r s r a p i d l y

by v o l a v t i l i s a t i o n , and t h e y are also a c t i v e l y s o r b e d o n ' porous . sur - f a c e s (DAME & .SCHMIDT, 1964) a T h i o t e p a is p r o b a l y s l i g h t l y l e s s vow

l a t i l e and h a s besen a c t i v e a g a i n s t f e m a l e Aedes aegprut i d u r i n g 23 U

d a y s a f t e r a p p l i c a t i o n a t t h e dosage of 400 mg/sq.moter on f i l t e r

p a p e r (EBWTRAM, l .964) . . In s o l u t i o n a l k y l a t i n g a g e n t s a re s l o w l y decomposed i n

. . ' i n a c t i v e compounds, Tepa and T e t e p a a r e more s t a b l e i n n e u t r a l or

- i n s l i g h t l y a l k a l i n e t h a n i n ac id s o l u t i o n s , Decomposi t ion r a t e s v a r y

d i r e c t l y w i t h t e m p e r a t u r e , b u t even a t 2 5 O C Y t h e h a l f - l i f e may a t t a i n

32 d a y s f o r Tepa and 72 d a y s f o r " e t e p a (BEROZA & BObtKOVBC, 1964 , i n

EERTXRM, 1964 a ) ,

However DATCB, WOODABD &. FOED (1964) stress t h a t , i n f i e l d

c o n d i t i o n s , Tepa s o l u t i o n s l o s s t h e i r e f f i c a c y i n t h r e e d a y s . I n s i d e i n s e c t s a l k y l a t i n g a g e n t s d i s t r i b u t e t h e m s e l v e s

q u i t e r a p i d l y i n t o a l 1 t i s s u e s , a s shown by DAKE & SCHMIDT (1964)

w i t h r a d i o l a b e l l e d V e t e p a i n mosqu i toes . Bu t t h e compounds a r e ra-

p i d l y e x c r e t e d and r e t a i n t h e i r s t e r i l i z i n g form no more t h a n 6 t o

8 h o u r s a f t e r t h e end o f t h e i n s e c t t r e a t m e n t (FLAPF 8 a l . , 1962)

3.2* B i o l o g i c a l a c t i o n of c h e m o s t e r i l a n t s i n l a b o r a t o r y expe- r i m e n t s ,

I n l a b o r a t o r y e x p e r i m e n t s c h e m o s t e r i l a n t s have i n d u c e d

* s t e r i l i t y i n a g r e a t v a r i e t y o f o rgan i sme (CRESSMAN, 1963 , a c a r i n a - BURDEPi & SMXTTLB, 1 9 6 3 , c o c k r o a c h e s - CBANG & CHIANG, 1 9 6 3 , moths - KEISER & a l , 1965, f r u i t - f lies ) i n c l u d i n g maminals (GA91?ES & KIMEWOUGH

A964) ' and t h e i r e f f i c a c y and l i m i t a t i o n s have been a s s e s s e d on some

of t h e major i n s e c t s o f m e d i c a l i m p o r t a n c e (SRITH, 1964) , Some com-

I -.+

' pounds a r e much more t o x i c for some s p e c i e s t h a n f o r o t h e r o n e s ,

and t h e o r d e r of e f f i c a c y o f c h e m o s t e r i l a n t s v a r i e s a c c o r d i n g t o

t h e s p e c i e s u s e d and t h e a p p l i c a t i o n method employed i n s c r e e n i n g

t e s t s (COUCS & a l , , 1963 a ) .

I - -

7

' C h e m o s t e r i l a n t s c a n be applies2 t o i n s e c t s by va r$ous me- t h o d s : d i p p i n g , d u s t i n g , t o p i c a l a p g l i s a t i o n , t a r s a l c o r ~ t a c t w i t h

t r e a t e d s u r f a c e s , a e r o s o l a d m i n i s t r a t i o n o r i n g e s t i o n o f t r e a t e d baiL

(Dk7'B, MOODAÄtB & FORD, 1964 - DkTLil! & SC-IKIDT, 1 9 6 4 - CEYSTAL, A 9 6 4 &

2.965) . P h y s i c a l b r o p e r t i e s v a r y i n g w i t h t h e compounds. s t a n d a r d i z e d a s s e s s m e n t t e c h n i q u e s c a n n o t be u s e d fol . a l l c a n d i d a t e compounds ;

however t h e m a j o r i t y of r o u t i n e a s s e s s m e n t s a r e done by o r a l a p p l i -

c a i i o n (GOUCK & al., 1963 a - CHANG, TSAO & CHIhHG, 1963) . ir

3.2 .L. E i o l o g i c a l a c t i o n o n v e c t o r s . ' r I d

3.3.1.1, ::ales . The s t e r i l i t y i n d u c e d by a p h o l a t e t r e a t m e n t of Aedes aegyp-

- t i l a r v a e i s c a u s e d by chromosomes damaging , w i t h d i l a t a t i o n s , l i n -

k a g e s , s p l i t t i n g 2nd s o o n ; t p C % S C have a norrnal s ize b u t p roduce

less s p e r m a t o z o a (j?kjC 1965 ) . EERTWAT!II ( 1 9 6 3 ) h a s found a c t i v e sperm

i n T h i o t e p a s t e r i l i z e d mates o f he . a e g y p t i , m a t i n g and i n s e m i n a t i o n

b e i n g s t i l l p o s s i b l e ; t h e s t e r i l i t y was c o m p l e t e i n t he d a y s f o l l o -

w i n g ' t h e t r e a t m e n t b u t l a t e r on some o f t h e i n s e m i n a t e d f e m a l e s gnve

e g g s w i t h n h a t c h r a t e o f 13%. S i m i l a r r e s u l t s have been o b t a i n e d in D r o s o p h i l a s t e r i l i z e d by T r e t a m i n e by FPliET,.!Y & FARPAY ( 1 9 5 4 ) and i n

nioles i n PAusca d o m e s t i c a s t e r i l i z e d by Tepa (SACCh & a1.1964 - SHEH C H I N CEUNC, 1965). Such r e s u l t s a re p r o b a b l y t h e consequence of t h e

g r e a t e r S u s c e p C i b i P i t y t o c h e m i c a l s of p o s t - q e i o t i c s t a g e s ( s p e r m ,

s p e r m a t i d s ) t h a n o f e a r l i e r p r e - m e i o t i c s t a g e s i n s p e r m a t o g e n e s i s .

11 is p d s s i b l e t h a t l o n g e r e x p o s u r e s t o - or i n c r e a s e d c o n c e n t r a t i o n r

of - t h e t o x i c a n t s c o u l d k i l l t h e p r i m a r y g e r m i n a l t i s s u e and e l i m i -

I

' n a t e a l l p o s s i b i l i t i e s o f r e c e v e r y . C h e m o s t e r i l i z e d m a l e s a r e n o t a lways as v i g o u r o u s and a b l e

t o c o p u l a t e t h a n t h e no rma l m a l e s (DAME & SCHXPDT, 1964 - .CRUSTAE,

1964) and t h e amount of sperm i s sometinzes i n s u f f i c i e n t , l e a v i n g t h e

f e m a l e s amenable t o f u r t h e r c o p u l a t i o n s w i t h no rma l males and s u b s e -

q u e n t f o r m a t i o n of f e r t i l e e g g s . (DAME, WOODARD & FORD, 1964). Howe-

ver, f o r p r a c t i c a l a p p l i c a t i o n ? c h e m o s t e r i l i z e d males a r e g e n e r a l l y

( b u t n o t a l w a y s ) c o m p e t i t i v e w i t h no rma l ma les (PRJEVOSH.& A l . , 1 9 6 4 *

LABRECQUE & al,, 1962 a- SHEN C R I CHANG, 1 9 6 5 ) and t h e s t e r i l e s p e r -

matozoa a c c o m p l i s h , a h i g h r a t e o f f e r t i l i z a t i o n g i v i n g u n f e r t i l e egg:.

e v e n when t h e y a r e mixed t o n o m m l s p e r m a t o z o a i n t h e female s p e r m a ~

theca (LBEItECQUBS & al., 1962 a). N e v e r t h e l e s s i n soine s p e c i e s , l i k e

8

Culex p . f a t i g a n s , < t h e s a f e t y margin between t h e s t e r i l i z i n g a n d t h e

' l e t h a l c o n c e n t r a t i o n s is v e r y nar row f o r t h e m a j o r i t y of t h e m o s t

pro in i s ing c h e m o s t e r i l a n t s (XULLA, 1964).

3.2.1.2, Females

I f t h e v e c t o r c o n t r o l programme i s based upon t h e r e l e a s e

of l a b o r a t o r y - b r e d i n s e c t s i t is n o t w o r t h w h i l e t o r e l e a s e s t e r i l i z e '

f e m a l e s , f i r s t because t h e i r i m p a c t on t h e spe rma tozoa a v a i l a b i l i t y

o f w i l d males w i l l be a l m o s t n i l , and s e c o n d l y because s u c h a p roce -

d u r e w i l l i n c r e a s e t h e s i z e o f . t h e b i t i n g s e c t i o n of p o p u l a t i o n . E u t ,

as w e s h a l l se@ l a t e r , c h e m o s t e r i l a n t s o f f e r w i d e r p r o s p e c t s t o vec-

t o r c o n t r o l o p e r a t i o n s t h a n i r r n d i z t i o n procedtares and , u n d e r some

r e s t r i c t i o n s , s h a l l p r o b a b l y b e u s e d i n t h e f u t u r e d i r e c t l y a g a i n s t

w i l d males and f e m a l e s ,

n

?

When t r e a t e d w i t h i d e n t i c a 1 , a m o u n t s of c h e m o s t e r i l a n t s , f e -

ma les a re s l i g h t l y less susceptible. t h a n males, b u t i n c a g e e x p e r i -

ments and i n n a t u r a l c o n d i t i o n s w i t h t r e i t e d b a i t s , t h e i n d u c e d s te -

r i l i t y is g e n e r a l l y h i g h o r i n , f e m a l e s as t h e y i n g e s t more b a i t and

s o more. c h e m o s t e r i l a n t t h a n males (CRYSTAL, 1965 - SACCk & a l . ,1964) ,,

\

Wild-caught f e m a l e s m o s q u i t o e s , a l r e a d y in semiha tec l , are

s t e r i l i z e d by r e s t i n g on -tepa or t h i o t e p a t r e a t e d s u r f a c e s , e v e n when

f o l l i c u l e s are as deve loped as s t a g e V, a s chown by WEIDHAAS (1962)

w i t h k . q u a d r i m a c u l a t u s , and by BB$CTP\AN (1963) w i t h A . m e l a s Similar resp l t s have been o b s e r v e d i n l a b o r a t o r y c o n d i t i o n s w i t h A e .aea.vFt i ,

A m o l and u i p i e n s (BBRTWJ4, 1 9 6 d a ) . The s p e e d o f a c t i o n o f azl .

r i d i n e d e r i v a t i v e s on house a r 1 d . f r u i . t - f l i e s i s s l o w e r t h a n on mosqui-

toes. , s p e c i a l l y when f e m a l e s f l i e s a re old (SACCA &. a l . , 1964 - CEZAI'G

& CHPANG, 11964 - KBHSXR & a l . , 1,965). -. -

En t r e a t e d f e m a l e s t h e o v a r i a n development i s soon r n a r c h i c ,

e a c h f o l l i c l e s h a v i n g i t s own r a t o o f deve lopment , The amount of l a i d

e k g s Is o f t e n n e a r l y no rma l d u r i n g t h e f i r s t o v i p o s i t i o n , b u t d e c r e a -

se s h a r p l y i n the f o l l o w i n g o v i p o s i t i o n s due t o sor l !a t ic d e t e r i o r a t i o n

of o v a r i c l e s , and there i s no h a t c h i n g . a t l e a s t i n m o s q u i t o e s , dama-

g e s t o t h e s p e r m a t o z o a i n t h e s p e r m a t e c a e of t r e a t e d f e m a l e s seem t o

be t h e main r e a s o n f o r s t e r i l i t y of t h e f i r s t b a t c h o f e g g s l a i d afee I

. . . . : '

.. . -. I

P n

.

e x p o s u r e ; i n c o m p a r a t i v e e x p e r i m e n t s w i t h low d o s a g e s of chemo,stez-i.-

l a n t s t h e p e r c e n t a g e o f i n f e r t i l e e g g s i s f a r h i g h e r i f f e m a l e s are

l n s e m i n n t e d b e f o r e e x p o s u r e t h a n i f t h e y mate a f t e r e x p o s u r e (BERTRAY:',

1 9 6 3 ) . Oogenes i s c a n also b e i n h i b i t e d f rom t h e b e g i n n i n g i f f e m a l e s

a re exposed t o c h e m o s t e r i l n n t s s c o n a f t e r t h e i r emergence b u t s u c h a 1

s u s c e p t i b i l i t y o f t h e f o l l i c u l a r e p i t h e l i u m is r e s t r i c t e d t o t h e f i r s "

h o u r s o f l i f e ; later o n , t h e e f f e c t s of c h e m o s t e r i l a n t s on o v o g e n e s i s

are o n l y c o n s p i c u o u s on a l o n g t e r m b a s i s (EBWFXWX, 1963 - CRYSTAL,

So, w i t h v e r y e a r l y a p p l i c a t i o n s , t h e , number of d e p i s t e d e g g s i s re-

duced almost t o n i l , w h e r c a s w i t h t r e a t m e n t of o l d e r ' f e m a l e s t h e n w -

b e r o f m a t u r e e g g s i s n o r m a l , b u t t h e y do n o t h a t c h (CEYSTAE, 1965'

I963 - WBTDMAAS, 3.962 - DAME & FBZE), 1 9 6 4 - CEY§TkL & Ek@NANCB,1963), i'

-

3.2.1.3. L a r v a e . I n s e c t s c a n b e a l s o s t e r i l i z e d as . a d u l t s f o l l o w i n g t h e i r

t r e a t m e n % as l a r v a e or pupae by a l k y l a t i n g a g e n t s , bu't t h e m u r t a l i t y

is' g e n e r a l l y i n c r e a s e d a i m o u l t i n g and emergence p e r i o d s . Tepa and

t h i o t e p a seem t o be more p r o m i s i n g t h a n a p h o l a t e f o r ' s u c h usage . The

t r e a t m e n t of n a t u r a l b r e e d i n g p l a c e s c a n n o t be c o n s i d e r e d , as the "

comp'ounds are mutagen'ric, and s h o u l d be a p p l i e d a t s h o r t i r i t e r v a l s , bu*

larval t r e a t m e n t c o u l d be a method of c h o i c e f o r mass s t e r i l i z a t i o n

o f r e a r e d m o s q u i t o e s (DAXB, WOODAED & PORD, L964).

3.2.2. B i o l o g i c a l a c t i o n on t r a n s m i t t e d p a r a s i t e s . C h e m o s t e r i l a n t s c a n a c t a l o n g two ways on t r a n s m i t t e d pa-

r a s i t e s d u r i n g t h e s t e r i l i z a t l o n ' o f i n f e s t e d v e c t o r s . They c a n e i t h e

k i l l t h e p a r a s i t e s , or cause m u t a t i o n s o f t h e p a r a s i t e s i n t o ncws.tT

of d i f f e r e n t p a t h o g e n i c i t y . If f e m a l e s a re t r e a t e d b e f o r e becoming i n

f e s t e d , t h e a c t i o n o f c h e m o s t e r i l a n t s i s n i l a s t h e compounds d i s a p -

p e a r f rom t r e a t e d i n s e c t s i n t h e ' h o u r s f o l l o w i n g t h e i r a b s o r p t i o n , Up

t o now i n v e s t i g a t i o n s have been c a r r i e d o u t o n l y on m a l a r i a and f i l c . .

r i a l p a r a s i t e s

3 .2i .2 *.2* l ' a l a r i a p a r a s i t e s . S e v e r a l i n v e s t i g a t i o n s have been c a r r i e d o u t , a l l baaed on

k e . a e g y p t i and Plasmodium g a l l i n a c e u m . kLTi.i3API (1963), r e p o r t e d s u b s t a n t i a l , b u t v a r i a b l e r e d u c t i o n

o f m a l a r i o m e t r i c i n d i c e s ( b y a b o u t 8 5 % ) by e x p o s i n g t h e v e c t o r f o r 90

to 5,40mn t o 100 mg/m2 of t e p a , on g l a s s , immedria-4;d.y b e f o r e and a f t e

t h e i n f e c t i v e meal and a l s o , i n one o c c a s i o n , when s p o r o z o ï t e s had rea,..

ched t h e g l a n d s ,

Us ing d i f f e r e n t s t r g i n s o% t h e same mosqu i to and PlasmodiQam - 2nd t h i o t e p a , BBETI<AV, SRIVASTAVA 6c WSA??GI (f964) have g o t on t h e who-

l e s i r n i l a r r e s u l t s , b u t w i t h an a v e r a g e r s d u c t i o n i n m a l q r i a t r a n s m i s -

6 i o n o f 25% o n l y . The d e p o s i t u s e d was 400 mg t h i o t e p a / s q . m e t r e . Con-

t a c t s o f t h e m o s q u i t o e s w i t h t he ' t r e a t e d s u r f a c e for 1 or 2 h o u r s w a s

a l m o s t i n e f f i c i e n t , b u t b e t t e r r e s u ï t s were o b t a i n e d w i t h 3 h o u r s of

c o n t a c t . The a c t i o n of t h e c h o m o s t e r i l a n t seemed p a r t i c ' u l a r l y impor-

t a n t when t h e m o s q u i t o e s were exposed some h o u r s o n l y a f t e r t h e i n f e e .

t a n t blood-meal (when g a d e t o c y t e s become g a m e t e s ) , b u t l e s s e f f i c i e n t

l a t e r on . I n t h e most f a v o u r a b l e c o n d i t i o n s o n l y 9% o f t h e c h i c k e n s

w'ere i n f e c t e d by t h e t r e a t e d m o s q u i t o e s , w i t h 100% i n f e c t i o n s i n t h e

c o n t r o l s Elowever, a s e c o n d p e r i o d o f i m p o r t a n t s u s c e p t i b i l i t y of m a -

l a r i a p a r a s i t e s o c c u r e d 4 8 h o u r s a f t e r t h e i n f e c t a n t blood-meal , du-

r i n g t h e m e i o s i s i n c a r l y cocys ' t s (30% of c h i c k e n i n f e c t e d ) . When t h e

t r a n s m i s s i o n t o ch icken ' s o c c u r e d t h e t r a n s m i t t e d Plasmodium was rior- ma2 and c o u l d be f u r t h e r t r a n s m i t t e d by A e . a e g y p t i w i t h o u t m o d i f i c a -

t i o n of i t s E a t h o g e n i c i t y ; when o c e u r i n g t h e r e d u c t i o n df t r a n s m i s s i o n

i s not o n l y caused by t h e i n t e r r u p t i o n or d e c r e a s e o f o o c y s t grouwth

and s p o r o z o % t e s p r o d u c t i o n , b u t a l s o by t h e l o s s or e f f e c t i v e n e s s of

t h e s p o r o z o P t e s pr 'obably t h r o u g h g e n e t i c damages (ISEI3TRAP2, 1964 b )

The v e c t o r i n b o t h t h e s e expe rLr l en t s k a s been m O r e e a s i l y

s t e r i l i z e d t h a n t h e p a r a s i t e . < ,

3.2 .2.3 F i l a r i a l p a r a s i t e s . The o n l y e x p e r i m e n t d e a l i n g w i t h t h e a c t i o n o f c h o m o s t e r i -

l a n e s on f i l a r i a l p a r a s i t e s have been c a r r i e d ut by BEETL2.m (196.?1a),

w i t h BruP, ia p a t e i and Aedes t o g ~ i exposed f o r 1 t o 8 h s u r s t o (100 mg

t h i o t e p a / s q .M d e p o s i t s on glass . C o n t a c t o f A h o u r d o e s n o t change t h e s p e e d o f deve lopment

o f f i l a r i a l worms i n the m o s q u i t o , b u t 2 h o u r s and 3 h o u r s t s e x p o s u r e

s l q w s down t h e deve lopment of t h e p a r a s i t e which a p p a r e n t l y n e v e r r e a -

c h e s , t h e i n f e c t i v e s t a g e and d i e s i n the t h o r a c i c m u s c l e s . It must b e

n o t e d t h a t t h e c h e m o s t e r i l a n t dose r e c e i v e d by f e m a l e m o s q u i t o e s du-

r i n g quch e x p e r i m e n t s i s f a r h i g h e r t h a n t h e r e q u i r e d one' f o r s t e r i l i r

t i o n , * and i s s u f f i c i e n t t o k i l l 95% of t h e ma les i n t h e 24 h o u r s fo l - ' l o w i n g e x p o s u r e .

.l

12

3.2.3 . "f ie tabol is in and b i o l a g i c a l a c t i o n on mammals ,

The mammalian and i n s e c t m e t a t o l i s m of c h e m o s t e r i l a n t s h2.s

been r e c e n t l y i n v e s t i g a t e d by u s i n g p h o s p h o r u s 32 l a b e l l e d :Fetepa

(PLAPP & al., 1962) and T h i o t e p a (?ARISSIs & AE333UR, 1965 b ) a p p l i e d

t o l a b o r a t o r y r o d e n t s and t o s e v e r a l s p e c i e s o f e c o n o m i c a l l y impor-

t a n t i n s e c t s . Ke tepa i s v e r y r a p i d l y e x c r e t e d as s u c h , and i s a l S Q

e x c r e t e d a f t e r m e t a b o l i z a t i o n , one major breakdown p r o d u c t b e i n g prc

b a b l y p h o s p h o r i c a c i d ; d e g r a d a t i o n and e x c r e t i o n are c o m p l e t e w i t h i n

48 h o u r s of a d m i n i s t r n t i o n . I n i n s e c t s T h i o t e p a i s a p p a r e n t l y meta-

b o l i z e d i n t o Tepa , t h e n e x c r e t e d ; i n r o d e n t s T h i o t e p a i s e x c r e t e d p a r

t l y a f t e r m e t a b o l i z a t i o n i n t o Tepa , p a r t l y u n d e r t h e forni of weter- s s l e n b l e h y d r o b l i t i c p r o d u c t s .

The t o x i c h a z a r d s of c h e m o s t e r i l a n t s have been r e c e n t l y i n - v e s t i g a t e d and summarized by ßARPIES (i964), G R I F E S & 1LIMBXOUGI-l ( 1 9 6 4 )

and by HAYES ( 1 9 6 4 ) .

The p r e s e n t c o n c l u s i o n s a r e o f v e r y t empora ry n a t u r e a s ne?'

compounds a r e d i s c o v e r e d e v e r y y e a r , some of them h o t b e l o n g i n g t o

t h e p r e v i o u s l y i n v e s t i g a t e d c h e m i c a l g r o u p s . X o r e o v e r , minor c h e m i c a l

s u b s t i t u t i o n s c a n t r a n s f o r m a compound of low mammalian t o x i c i t y i n

a n o t h e r one f a r more t o x i c , And t h e two main c a t e g o r i e s i n t o which

a re c l a s s i f i e d t h e c h e m o s t e r i l a n t s do n o t c o r r e s p o n d t o s p e c i f i c phy.

s i o l o g i c a l a c t i o n , b u t t o l a r g e c h e m i c a l or b i o l o g i c a l g r o u p s , a l k y l

t i n g a g e n t s and a n t i m e t a b o l i t e s . So , na e x t r a p o l a t i o n of t h e t o x i c o -

l o g i c i n v e s t i g a t i o n s a l r e a d y c a r r i e d o u t s h a l l n o t be p e r m i s s i b l e to

d e a l w i t h new c q q " n c l s ( D A R N E S , 1964 - HAYES' 8 9 6 4 ) . 'C

On a whole a l k y l a t i n g a g e n t s a r e f a r l e s s c a r c i n o g e n i c t h a n

e x p e c t e d by t h e w o r k e r s u s i n g them as t o o l s i n c a n c e r r e s e a r c h . Human

b e i n g s i n c a n c e r t h e r a p y have s u p p o r t e d O, 6mg T h i o t e p a l k g ( i n . t h r e e

s u c c e s s i v e d o s e s of @,2mg/kg) and T h i o t e p a can be t o l e r a t e d w i t h a s

h i g h d o s e s as 10-40 mg a week, w i t h some v a r i a t i o n i n i n d i v i d u a l SUS-

c e p t i b i l i t y . T r e t a m i n e h a s been u s e d up t o d o s e s o f 1 5 - 2 5 mg i n i t i a "

l y and t h e p 2,5-5 9ng w e e k l y , b u t some p a t i e n t s c a n ' o n l y s u p p o r t 1/10

c f t h e s e amounts w i t h o u t bone marraw d e p r e s s i o n . On r a t s , wh ich a re p r o b a b l y l e s s s u s c e p t i b l e t h a n humans

t o Some of t h e a c t i o n s o f a l k y l a t i n g a g e n t s , f i v e d a i l y d o s e s of O$!

kg o f T h i o t e p a r e n d e r e d m a l e s s t e r i l e f o r f i v e weeks , and T r e t a m i n e

312

g i v e n a s .doses of 10,0!5mg/kg o v e r a p e r i o d of 3 0 d a y s gave . t h e same re

s u l t s ; s u c h r a t s r ema ined f u l l y a c t i v e and m o b i l e , s e x u a l l y a c t i v e ,

and t h e i r spe rma tozoa have been o b s e r v e d t o p e n e t r a t e t h e ovum of t h e

female, b u t w i t h o u t r e s u l t i n g progeny. These e f f e c t s of T h i o t e p a and

T r o t a n i n e on f e r t i l i t y are c o m p l e t e l y r e v e r s i b l e (JACKSON, FOX & C R A I G ,

1959 - BOCH & JBCXSON, 1 9 5 9 ) . I

S u s c e p t i b i l i t y of r a t s i s v e r y v a r i a b l e , and 00 are t h e

damages t o t h e s p e r m a t o g e n e s i s Fghich a re compr i sed between s l i g h t

damage &o t h e sperm and c o m p l e t e d e s t r u c t i o n o f t h e s e m i n i f e r o u x e p i -

t h e l i u m , % i o t e p a ancl T r e t a m i h e , " a l t h o u g h non p e r s i s t a r i t 'in t h e tis-

sues, h a v i n g some c u m u l a t i v e a c t i o n (JACKSON, FOX & CRAZG, 1961).

, a

c + .,

1 ,

During e x p e r i w ? n t a t i q n s w i t h r a t s , G A I N E S & KIP4~BROUGB(1964) I

h ave o b s e r v e d t h a t Metepa and Aphola t e , i n one a d m i n i s t r a t i o n i n t h e

d i e t , a re a b o u t as t o x i c than.DDT and t h a t Tega i s a b o u t as t o x i c t h a n

d i e l d r i n e ; Tepa and Meteya a r e aLso t o x i c if i n t r o d u c e d by de rmic ap-7

p l i c a t i o n s ; i n s u c h c o n d i t i o n s t h e CL 50, i n mg/kg is o f 1 3 6 . f ~ o r "etc-

pa and 37 f o r Tepa . When r a t s r e c e i v e d d a i l y small d o s e s o f Metepa

i n t h e i r , d i e t (5m.g/kg/day) t h e g e n e r a l c o n d i t i o n of t h e a n i m a l s ,wqs '

good, b u t a c i lmu la t ive a c t i o n o f t h e c h e m o s t e r i l a n t c a u s e d a t r o p h y of t e s t i s i n 77 dkys ( i n 55 d y a s when t h e d a i l y d o s e was LO mg/kg') - and

i n 297 d a y s w i t h 2,5mg/kg; l o w d o s e s as 1,%5 mg/kg/day were apparenti.

nbk harrrif ul. The damage t o tes t is were t o soke e x t e n t - r e v e r s i b l e , b u t

t h i s a spec t h a s n o t y e t been a d e q u a t e l y s t u d i e d . When t h e $nale s te r i -

l i C y i s n o t c o m p l e t s ' s o m e reduc-Cion i n . t h e number of b a b i e s o c c u r s ,

b u t t h e i r further deve lopmen t seems p e r f e c t l y n o r m a l , w i t h o u t any e'f-

f e c t o f p a r e n t treatment. : .on t h e i r p o t e n t i a l i t i e s and s u r v i v a l . The c h e m o s t e r i l a n t s which a r e now i n v e s t i g a t i o n have n'ot

shown' ahy s i g n of c a r c i n o g e n i c a c t i v i t y . They exe r t ori m a m m a l s : a b o u t

t h e same e f f e c t s t h a n un i n s e c t s and , a t low d o s a g e s , have a h i g h l y

s p e c i f i c and l o c a l i z e d a c t i o n on the d e v e l o p i n g s p e r m of mammals. It

i s o n l y a t f a r h i g h e r d o s a g e s than ' t h e s e compounds d e p r e s s t h e bone

marrow a c t i v i t y (BkRP.JBS, 1964 - NAYES', 1964 . H W A h a s a s t e r i l i m i n g a c t i o n a t c a n c e n t r a t i u n s , 5 0 t i m e s

h i g h e r t h a n Tepa , b u t i t s . C L 5 0 for r a , t s i s a s h i g h a s 2600 t o 6404

mg/kg a g a i n s t o n l y 37mg/kg for Tepa . B e s i d e s , WMFA has no mu-tagenic

and ' c a r c i n o g e n i c p r o p e r t i e s .

13

Tepa , Metepa, T h i o t e p a and A p h o l a t e a r e more t o x i c , t h a n

t h e commonly used i n s e c t i c i d e s . They a re q u i c k l y m e t a b o l i z e d and ex-

c re ted w i t h o u t a p p a r e n t a c c u m u l a t i o n i n t h e o rgan i sm; however , t h e y

seem t o e x e r t a c u m u l a t i v e e f f e c t when r o u t i n e l y a b s o r b e d , and may

s t e r i l i z e human b e i n g s a t d o s a g e s wh ich a r e n o t h a r m f u l if o n l y be-

h a v i o u r and su r -v iva l a r e t a k e n i n a c c o u n t . So i t seems u n t h i n k a b l e

t o u s e t h e compounds now a v a i l a b l e f o r i n d o o r h o u s e - s p r a y i n g or f o r

e x t e n s i v e t r e a t m e n t of b r e e d i n g p l a c e s ( E A R N B S , 1564 - WkYES,í964). 3.2.f-1. P o s s i b i l i t i e s o f r e s i s t a n c e t o c h e m o s t e r i l a n t s .

HkZkUD and a l (1964) have i n v e s t i g a t e d t h e p o s s i b i l i t y t o

s e l ec t a s t r a i n of A e . a e g y p t i r e s i s t a n t t o Apho la t e s t e r i l i ’ s a t i o n

by l a r v a l e x p o s u r e . I n s t a n d a r d i z e d r e a r i n g and t r e a t m e n t c o n d i t i o n s

t h e p e r c e n t a g e of s t e r i l i t y h a s d e c r e a s e d f rom 96% t o 46% i n h - g e n e -

r a t i o n s w i t h 5 ppm Apho la t e i n b r e e d i n g w a t e r , and f r o m 100% t o 72%

An 6 g e n e r a t i o n s w i t h 1 5 ppm A p h o l a t e . So Ae .aegyp t i seems a b l e t o

d e v e l o p Some r e s i s t a n c e t o A p h o l a t e , w i t h a d e c r e a s e of e f f i c a c i t y

o f 4 t o 5 t i m e s . 3 . 3 . P o s s i b l e u s e o f c h e m o s t e r i l a n t s for i n s e c t c o n t r o l ,

. A s i v a i l a b l e q n o w t h e c h e m o s t e r i l a n t s compounds c a n e i t h e r

r e p l a c e s t e r i l i z a t i o n by gamma r a d i a t i o n s , on l a b o r a t o r y - b r e d vector : .

f o r s u b s e q u e n t r e l e a s e , o r be u s e d t o s t e r i l i z e w i l d p o p u l a t i o n s .

S t e r i l i z a t i o n by c h e m i c a l s would be s i m p l e r and c h e a p e r

t h a n by gamma r a d i a t i o n s and t h e f a c i l i t i e s r e q u i r e d wou lc b e innore

r e a d i l y movable . Morsover , t h e m a l e s t r e a t e d w i t h c h e m o s t e r i l a n t s

are f a r more c o m p e t i t i v e t h a n t h e i r r a d i a t e d o n e s (IJj31CDdAkS &. SCH7AIDT3

. 1963), b u t t h e g e n e r a l l i m i t a t i o n s of t h e methods would b e t h e same

t h a n w i t h s t e r i l i t y i n d u c e d by i r r a d f a t i o n ,

The g r e a t a d v a n t a g e of t h e c h e m o s t e r i l i s a n t s i s t h e i r pos-

s i b l e a p p l i c a t i o n t o w i l d p o p u l a t i o n s . I f t h e y c o u l d be s a f e l y ap-

p l i e d t o n a t u r a l p o p u l a t i o n s , c o n t r o l o r e v e n e r a d i c a t i o n would be

+ r e a l i z e d by i n d u c e d . , s t e r i l i t y _I w i t h o u t t h e n e c e s s i t y o f r e a r i n g and

r e l e a s i n g l a r g e numbers o f i n s e c t s . If w i l d ma les a s w e l l as w i l d

f e m a l e s c o u l d be t r e a t e d t h e d e c r e a s e of n a t u r a l p o p u l a t i o n s wc;uld

be v e r y s h a r p , a l a r g e p r o p o r t i o n of t h e no rma l m a l e s i n s e m i n a t i n g

s t e r i l e f e m a l e s and many norma l f e m a l e s b e i n g mated by s t e r i l e malee

1,

9r ;

1 14

(KNZPZIMG, L962). Up t o now, t h e a d m i n i s t r a t i o n o f c h e m o s t e r i l a n t s i n Che a d u l t f o o d o r on r e s e i n g p l a c e s seems t o be t h e o n l y p r a Q t i -

ca l -me thqc l for f i e l d u s e and i s de,pendant o f t h e a d j u n c t i o n of power-

f u l and s e l ec t ive a t t r a c t a n t s (LIU, 1962 - ROCKING, 1963 - STEINER ¿%

a l . , 1961 - LBOSFE, 1962 - KESBIP & a l . , 195G - BRUkJN, WEST & LOCKLBY,

1 9 6 1 ) which c o u l d c o n t e r a c t t he r e p e l l e n t e f f e c t o f some of t h e che -

m o s t e r i l A n t s ( " I ,

C A & a l . , 1965) and a t t r a c t &n h i g h p r o p o r t i o n of 4 t i

' t h e n a t u r a l p o p u l a t i o n s . *$

O t h e r s d e v e l o p m e n t s i n t h e u s e of c h e m o s t e r ï l a n t s a w a i t

t h e a s s e s s m e n t ' o r d i s c o v e r y o f new compounds w i t h o u t t o x i c h a s a r d s for mammals . I .

4. F I E L D EXFBi3l?&BIvTS H I T H CIIEr;iOSTERILiiNTS . F i e l d e x p e r i m e n t s w i t h c h e m o s t e r i l a n t s have been res t r ic -

t e d *to a few a n a l l t e s t s t o e x p l o r e p o s s i b l e methods of a p p l i c a t i o n

and e v a l u a t i o n , m a i n l y w i t h h o u s e - f l i e s , b u t some o f t h e r e s u l t s of .-the f i e l d e x p e r i m e n t s c a r r i e d o u t . w i t h g a m m a - i r r a d i a t i o n s t e r i l i z e d

m a l e s g i v e also u s e f u l i n f o r m a t i , o n s on t h e p r a c t i c a l problems, t o sol--

ve ; .

4.1. Anopheles q u a d r i m a c u i a t u s \

A. q u a d r i m a c u l a t u s males, f rom t h e l a b o r a t o r y c o l o n y of O r l a n d g , have been s t e r i l i z e d e i the r by i r r a d i a t i o n , o r by e x p o s u r e

t o c h e m o s t e r i l a n t s ( c o n t a c t w i t h Tepa dr oral a d m i n i s t r a t i o n of Apho-

l a t e ) . The' s t e r i l i z e d males were s e x u a l l y p o t e n t and g a v e a h i g h r a -

t e o f f e r t i l i z a t i o n of w i l d f e m a l e s i n laboratory c b i i d i t i o n s , b u t the:T

were u n a b l e t o p e r f o r m t h e saine d u t i e s when r e l e a s e d amongst t h e ' . n a -

t u r a 1 p o p u l a t i o n of 8. q u a d r i m a c u l a t u s , Yhen t h e e x p e r i m e n t was du-

p l i c a i ' e d , u s i n g as s t e r i l e males, t h e k r a a t e d p rdgeny o f w i l d ' c a u g h t

females, t h e r e l e a s e d m a l e s s u c c e e ü e d t o ' i n d u c k s t e r i l i t y i n w i l d

f e m a l e s . S o i t i s p r o b a b l e t h a t t h e i n i t i a l ' f a i l u r e w a s n o t d u e t o

c h e m o s t e r i l a n t - i n d u c e d d e c r e a s e i n sexuzl l c o m p e t i t i v e n e s s , b u t t o

c h a n g e s o f beAaviour d u r i n g c o l o n i z a t i o n and to b a s i c i n a b i l i t y o f

y e a r s - l o n g c o l o n i z e d m o s q u i t o e s t o mate i n f i e l d c o n d i t i o n s w i t h W i l d a

females o f t h e same speagcs(DkME, WOODkiZD, FORD & WEXDHAAS, 1964)

'

, . I

. .

15

4.2. eausca domestica

The r e su l t s of o n l y ' f o u r f i e l d e x p e b i m e n t s car r ied o u t i n

F l d i d a a n d i n I t a l y , each b a s e d on a d i f f e r e ' n t c h e m o s t e r i l a n t i n

cohnmeal b a i t ( w i t h s u g a r , d r y m i l k and d r y egg a d d e d ) , have been y e t

p u b l i s h e d , as w e l l as t w o cage -expe r imen t s s i m u l a t i n g n a t u r a l cond i - t i d n s .

HÁPJSBNS & GRANBTT (1965) h a v e compared, i n two c a g e s of a b o u t s e v e n cubic metre each, t h e deve lopmen t of t w o c o l L n i e s o f hou-

se f l i e s w i t h l a r v a l b r e e d i n g medium a l w a y s a v a i l a b l e , b a i t s t r e a t e i

w i t h 2% A p h o l a t e b e i n g i n t r o d u c e d i n one, of t h e c a g e s twice a week.

The A p h o l a t e t r e a t e d c a g e has Lroducea , i n two sets of e x p e r i m e n t s ,

10 t o 40 f b 4 d less h o u s e - f l i e s t h a n t h e c o n t r o l c a g e ,

Dur ing a second se t of e x p e r i m e n t s , c a r r i e d o u t along t h e

same l i n e s t h a t t h e above o n e s , ZAPISENS (l.965) h a s i n v e s t i g a t e d t h e

r ' e l a t iw effect iveness o f Apholnte u n d e r t h e form ejttier of 2% tren-

t e d b a i t s , o r of i m p r e g n a t e d cords, and of both combined, w i t h variou,

rythma of a p p l i c a t i o n , a g a i n s t s u s c e p t i b l e and i n s e c t i c i d e m r e s i s t a n t

h o u s e - f l i e s . T r e a t e d b a i t s , i n t r o d u c e d a t week ly i n t e r v a l s , gave m8rL

t h a n 90% c b n t r o l a n d , i n c o m b i n a t i o h w i t h impre 'gnated c o r d s , e r ad ica -

t e d . the c a g e d p o p u l a t i o n s , Cords i m p r e g n a t e d with a s y r u p a6 72% Aph'

l a t e wepe less e f f i c i e n t , g i v i n g only 57% c o n t r o l , I n s e c t i c i d e - r e -

s i s t n n t > h o u s e - f l i e s were as e a s i l y anenabl"e t o c o n t r o ' l w i t h Aplìolate

as t h e s u s c e p t i b l e o n e s ,

\

EABWISCQUPI & al, (1962) have a s s e s s e d t h e e f f i c a c y , of b a i t s I

w i t h 0 , 5 $ Tepa, on garbage dumps in one o€ t h e F l o r i d a k e y s , w i t h

once a week a p p l i c a t i o n d u r i n g n i n e s u c c e s s i v e weeks, . The i s l a n d Was

r e l a t i v e l y i s a l a t e d and a n o t h e r dump, s i t u a t e d a t a b o u t 5 0 , k m f rom

t h e t r e a t e d one ,was u s e d as a o n t r o l . The h o u s e - f l y qnd s e c o n d a r y S C r e x + ;

Worm (Cochl iomya m a c e l l a r i a F.) d e n s i t i e s were e s t i m a t e d i n t h e most

i n f e s t e d a r eas , by t h e g r i d method, ,The s t e r i l i t y of f e m a l e s was i n v e r

t i g a t e d week ly on r e p r e s e n t a t i v e s a m p l e s of t h e house-fly p o p u l a t i o n .

House fly p o p u l a t i o n s were r e d u c e d from 47 p e r g r i d t o O w i t h i n 4

weeks and ehe p r o p o r t i o n of e g g masses (from f e m a l e s c o l l e c t e d o n , dump) c o n t a i n i n g a t l e a s t one v i a b l e egg was r e d u c e d from 100% $0 107 w i t h i n 5 weeks, and t h e p e r c e n t h a t c h among al& eggs l a i d Was r e p u c e t

to 1% w i t h i n 5 weeks , A f t e r t r e a t m e n t s were d i s c o n t i n u e d t h e p e r c e n t

" L

I

..

. /

c - e*

. 1 - I . ..

b I , -

I6

v i g b i l a t y r a p i d l y r e t u r n e d t o normal . Dur ing t h e e n t i r e p e r i o d o f

t h e e x p e r i m e n t v i a b i l i t y o f eggs f rom f e m a l e s from t h e c o n t r o l dump

ranged from 65 t o 99%. Xe w a s n o t p o s s i b l e i n t h i s e x p e r i m e n t t o as-

sess w h a t p r o p o r t i o n of t h e f e m a l e s w a s s t e r i l i z e d by f e e d i n g o n t h e

b a i t and what p r o p o r t i o n by m a t i n g w i t h s t e r i l e ma les . B l o w f l y c o u n t s

in t h e treated area was a l s o r e d u c e d marked ly toward t h e end of t h e

te.st, b u t all c a p t u r e d females oviposited freely on f r e s h m e a t and

a l l t h e egg mas9 Were v i a b l e ; p r e v i o u s - e x p e r i m e n t s have shown in the

past t h a t blow f l i e s a r e d i f f i c u l t t o c o n t r o l w i t h d r y g r a n u l a r i n -

s e c t i c i d e b a i t .

I ' " *

7

+

LABEECQUE & a1.(1963) have c a r r i e d o u t an e x p e r i m e n t w i t h

0.5% ndetepa b a i t s i n a p o u l t r y f a r m n e a r O r l a n d o , i n a n o n - i s o l a t e d -.

s i + u q t i o n . B a i t s were d i s t r i b u t e d o n c e a w e e l c d u r i n g 9 weeks and thm

twice a week. The d e n s i t y of house f l i e s w a s d r a s t i c a l l y r e d u c e d . The

hatching ra te of e g g masses w a s r e s p e c t i v e l y decreased 2,6 timesd, f h e n

5 . i t i m e s . Vale f e r t i l i t y was not s e r i o u s l y a f f e c t e d by t h e w e e k l y ap-

p l i c a t i o n of the b a i t s , b u t d e c r e a s e d t o 22% of the norma l when b a i t s

were d i s t r i b u t e d 5 times a week

I

c -

I

SACCA L STBELA (1964) have assessed t h e e f f i c a c y of syrup sprays, $ n c l u d i n g 1% of m a l t e x t r a c t : a5 a t t r a c t a n t , and f rom 0 , 0 6 2 5

t o O,% of Tepa,. on garbage dumps of s e v e r a l i t a l i a n towns . A h i g h

s t e r i l i t y r a t e was o b s e r v e d o n e hour a f t e r t h e a p p l i c a t i o n , e v e n w i t h

t h e l o w e s t c o n c e n t r a t i o n o f Tepa; a l t h o u g h m a l e s b e t h e o r i c a l l y more

s u s c e p t i b l e t o Tepa t h a n f e m a l e s , the h i g h e s t ra te of s t e r i l i t y has

been o b s e r v e d in f e m a l e s , p r o b a b l y b e c a u s e males a re less a t t r a c t e d

to g a r b a g e dumps and a l s o b e c a u s e i n f e m a l e s t h e male- induced Sterili-

ty adds i t s a c t i o n t o t h e i n t r i s i c female s t e r i l i t y , The f e r t i l i t y - p a -

t e r e t u r n e d to normal i n t h e days following the t r e a t m e n t , t h r o u g h

m i g r a t i o n s and n a t u r a l p o p u l a t i o n r e p l a c e m e n t helped by t h e r a p i d

Tepa h y d r o l y s i s . 4 i t h o n e , and t h e n &wo, w e e t l y a p p l i c a t i o n s of t h e

Tepa s p r a y on the g a r b a g e dump, 'and the i n s e c t i c i d e treatment of t h e

n e i g h b o u r i n g farms, t h e h o u s e f l y p o p u l a t i o n has been s t r o n g l y de-

p r e s s e d ; but d e s p i t e t h e i n s e c i i c i d e a p p l i c a t i o n t h e f l y p o p u l a t i o n

has q u i c k l y r e c o v e r e d a f t e r t h e c e s s a t i o n of t h e Tepa s p r a y i n g .

8 . ,

. -

I '

3.7

' a,4.3, C u l e x t a r s a l i s . , LEUALLEN & a l r (1965) have s t u d i e d . t h e e f f i c i e n c y of Aphv-

' late a p p l i e d t o a L l n a t u r a l b r e e e d i n g - p l a c e s of C u l e x t a r s a l l l s i n

small oases i s o l a t e d ' i n a desert of San Diego County; C a l i f o r n i a .

- A p h o l a t e was u s e d a t t h e c o n c e n t r a t i o n o f 7 5 ppm;with t h r e e a p p l i -

% c a t i b n s w i t h i n 22 d a y s . The n a t u r a l C . ta rsa1 is p o p u l a t i o n w a s only t e m p o r a r i l y d e p r e s s e d and z e t u r n e d to i t s p r -e - t r ea tmen t l e v e l 2.0- days

a f t e r t h e ' l a s t Apho la t e a p G l i c a t i o n . The f a i l u r e i3 a t t r i b u t e d to t h e

s u r v i v a l of w i l d f e m a l e s d u r i n g t h e w h o l e - l e n g t h of e x p e r i m e n t

4.4, O b s e r v a t i o n s c o l l e c t e d d u r i n g some o f t h e f i e l d - t e s t s c a r -

ried o u t w i t h e r a d i a t i o n - s t e r i l i z e d males . F o u r f i e l d exper i in 'en ts , t h r e e d e a l i n g ' w i t h m o s q u i t o e s and

one w i t h blow f l i e s , based on release o f r a d i a t i o n - s t e r i l i z e d males are v e r y i n t e r e s t i n g , KXHSHfaAMUkTHY & a l . (1963) ' h a v e worked w i t h

C u l e x p . f a t i & a n s ; in I n d i a , The r e s u l t s were n o t s a t i s f a c t o r y , p a r Z l y

b e c a u s e t h e number of released males 'Was n d t s u f f i c i e n t , g h r t l y be-

c a u s e the human p o p u l a t i o n d i d n o t a g r e e t o t h e release o f ' a n y mos-

q u i t o , even male and s t e r i l e .

.

PAOX'LAI? & a l . (1962) have released s t e r i l e males of Ae.aep.yp

-.c ti i n two areas of P e n s a c o l a ne ighbourhood , F l o r i d a , of a b o u t 1 squa-

re k i lometer . They used two n e a r b y u n t r e a t e d a r eas is c o n t r o l . The

e x p e c t e d r a t i o o f s t e r i l e t o no rma l males ( re leased a s p u p a e ) G a s of

. 47 : 1 to f70.0S6' : 1 i n t h e f i r s t a r ea$ and of 27:l t o %48:9 i n t h e s e c o n d area, E s t i m a t i o n of n a t u r a l p o p u l a t i o n s of Ae .aegyypti " w a s ba-

sed on a c t u a l c o u n t s of l a r v a e e v e r y second week; e x c e p t f 8 r ' s a m p l e s

col,lec.tecl for i d e n t i f i c a t i o n , l a r v a e w e r e c o u n t e d a n d r e t u r n e d t o

t h e i r original b r e e d i n g p l a c e s , F i e l d cd l l ec t ed e g g s , o b t a i n e d by li- n i n g f o r m e r l y i n f e s t e d r e c e p t a b l e s w i k h p a y e r t o w e l s , w e r e c o u n t e d

and submerged i n a 34-hour-old m i x t u r e of 8 , l g b r e w e r ' s y e a s t and

0,1 g g round dog chow i n o n e l i t e r of water ; e a c h h a t c h i n g t e s t was

c o m p l e t e d i n t h e week f o l l o w i n g egg c o l l e c t i o n ; l a rvae were i d e n t i -

f i e d and c o u n t e d . I n area 1 t h e releases have r e d u c e d , b u t f a i l e d t o

e r a d i c a t e , n a t u r a l p o p u l a r i o n s of ke . a e g v p t i ; i n area 3 the~"re1eases.

of s t e r i l e males f a i l e d t o r e d u c e t h e n a k u r a l p o p u l a t i o n . The r a t e

of egg h a t c h i n g , on t h e a v e r a g e , w a s only GO % of the nörmal i n the f i r s t area, b u t w a s $12 7% of t h e n o r m a l i n ,the s e c o n d are-a. Amongst t'

18 , I I <

r e a s o n s f o r f a i l u r e + a r e t h e g r e a t e r age of s t e r i l e m a l e s , r e b d

once a week and c o m p e t i t i v e o n l y some d a y s w i t h t h e norm21 w i l d ma-

l e s emerg ing e v e r y day , and t h e p o s s i b l e l i m i t e d d i s p e r s i o n o f % t h e

s t e r i l e m a l e s from t h e l i m i t e d d i s t r i b u t i o n o f i r r a d i a t e d pupae ,

, I ;

WEIDEAAS & a l . (1962) have r e l e a s e d 1.500 s k e r i l e m a l e s 'of

A , q u a d r i m a c u l a t u k p e r week and p e r s q . km, d u r i n g 11 months , i n t e n d i f f e r e n t s i t u a t i o n s on i s l a n d s o f 5 s q . km. of t h e Lakes Okeechobes

and P a n a i o f f k e e , F l o r i d a .

* _

Another a rea was u s e d as a c o n t r o l , To d e t e r m i n e i f t h e s e s t e r i l e males c a u s e d any r e d u c t i o n o f , or ' s t e r i -

l i t y i n , n a t u r a l p o p u l a t i o n s , t h e number bf a d u l t A , q u a d r i m a c u l a t u s

i n r e s t i n g s t a t i o n s , and t h e v i a b i l i t y o f e g g s from f e m a l e s c o l l e c -

t e d Eron t h e s e r e s t i n g s t a t i o n s were f o l l o w e d i n t h e r e l e a s e and

check a reas . The releases d i d n o t c o n c l u s i v e l y i n d u c e any s t e r i l i t y

An'wil& f e m a l e s bu t p e r h a p s when t h e n a t u r a l p o p u l a t i o n O E one islaEd W a s i n t h e s e a s o n a l d e c l i n e . F a i l u r e was a t t r i b u t e d t o t h e l a c k of b a s i c knowledge of t h e b i o l o g y and b e h a v i o u r o f A . q u a d r i c u m u l a t u s (

d

4

>

I

which i s , "en p a s s a n t " , one of t h e b e s t known amer i can m o s q u i t o e s

and i n t h e d i f f e r e n c e i n b a s i c b e h a v i o u r of c i ; l on ized and w i l d mos-

q u i t o e s o f t he ' same s p e c i e s . DOTJNEZLY (1964), h a s a t t e m p t e d t o c o n t r o l t h e Elow f l y &- \ a

' c i l i a s e r i c a t a o n one small i s l a n d of t h e e a s t e r n c o a s t of E n g l a n d ,

The tre'ated area w a s o f a b o u t 2 , 5 s q . k m w i t h an e s t i m a t e d p o D u l a t i o n

of 2.000 w i l d males Of t h e blow f l y . The releases were c a r r i e d o u t 4 -

t o 5 months a y e a r , d u r i n g 2 y e a r s , and t h e s t e r i l e m a l e s were overw-

he lming t h e w i l d ones. Th& f a i l u r e . o f t h e e x p e r i m e n t is p a r t l y a t t r i -

bu ted $0 d e n s i t y - d e p e n d a n t f a c t o r s r e e s t a b l i s h i n g t h e no rma l d e n s i -

t i e s when t h e n a t u r a l p o p u l a t i o n W a s d e c r e a s i n g , a n d t o a p o s s i b l e

f o c a l d i s t r i b u t i o n o f n a t u r a l p o p u l a t i o n s , t h e seer i le males b e i n g

l e s s numerous t h a n no rma l o n e s i n s u c h f o c i . I

<r It c o u l d be a l s o i n t e r e s t i n g t o u n d e r l i n e here that t h e '

m e l o n f l y , Dacua c u c u r b i t a e , h a s been r e c e n t l y e r a d i c a t e d . f r o m R o t a ,

' l a r i a n a I s l a n d a , by relaase of a b o u t 260.000.030 of r a d i o - s t e r i l i z e d

males and f e m a l e s i n t e n months. The i s l a n d has a s u r f a c e o f a b o u t

92 sq, kin. Females o f D. c u c u r b i t a e are known f o r m a t i n g ' s e v e r a l ti-

m e s . d u r i n g t h e i r l i f e , * h a v e a l o n g f l i g h t r a n g e , b u t c o n g r e g a t e i n

h o s t p l a n t a t i o n s . Releases were p r e c e d e d by r e d u c t i o n of the n a t u r a l

-

~

_I _- . .- . _. . .. . ... , . .~

., c

b

. ' . 19 p o p u l a t i o n t h r o u g h m a l a t h i o n - t r e a t e d b a i t s (STEIfJBR & a l , , 1965) I

~ t ' (

5, DISCUsSXOk AND CONCLUSIONS - ' r . . . 1 i

C h e m o s t e r i l a n t s c o n s t i t u t e a new c l a s s of vec tor c o n t r o l

a g e n t s which o f f e r p r o m i s i n g p o s s i b i l i t i e s f o r t h e f u t u r e , b u t need

more s t u d i e s before becoming o p e r a t i o n a l . ' A c c o r d i n g t o t h e a v a i l a b l e p u b l i s h e d knoniedge t h e best

known compounds are n o t s a f e f o r f i e l d sca le use, b u t i n s p e c i a l

c o n d i t i o n s . They a re n o t c h e m i c a l l y very s t a b l e , which i n some as-

p e c t s has t h e a d v a n t a g e t o a v o i d r e s i d u a l c o n t a m i n a t i o n of t h e e n v i -

ronment , b u t decreases t h e p o s b i b i l i t i e s of l a r g e scale u s e o'f the?,

compounds. The s a f e t y Margin between t h e s t e r i l i z i n g d o s a g e s , arid t h e l e t h a l one is not a lways v e r y w i d e , a l t h o u g h much more t h a n w i t h

i r r a d i a t i o n p r o c e d u r e s . S t e r i l e m a l e s are not a lways c o m p e t i t i v e w x t h

t h e no rma l males and somet imes t h e s t e r i l i t y i n b o t h sexes, may b e of

B t e m p o r a r y n a t u r e ., Hew compounds s h a l l p e r h a p s of f e r b e t t e r p r o s p e c + . . but t h e y are still t o be d i s c o v e r e d a n a ' w e must n o t f o r g e t t h a t o,ne

of our m o s t potent r e s i d u a l i n s e c t i c i d e s was one of t h e f i r a t disco-

vered ones; it c o u l d be t h e same for c h e m o s t e r i l a n t s *

, .

If c h e m o s t e r i l a n t s are t o be osed as s u b s t i t u t e of i r r a - d i a t l i o n , t o t r e a t l a b o r a t o r y - b r e d vec to r s f o r f u r t h e r release i n na-

tural p o p u l a t i o n s , a good d e a l must b e l e a r n e d on e c o l o g x , b e h a v i o u r

d i s p e r s a l , p o p u l a t i o n dynamics , d e n s i F i e s and g e n e L t i c s of n a t u r a l po

p u l n t i o n s of a l l vec to r s c o n c e r n e d (BHHCB, 1963 - KNIPLIPIG, i963), ,

and. t h e methodology of mass c a l o n i z a t i o n of c o m p e t i t i v e s t r a i n s mus!'

be e l a b o r a t e d f o r t h e m a j o r i t y of p e s t s and vectors

I f c h e m o s t e r i l a n t s a r e to be used i n an o r i g i n a l approach ,

to i n d u c e d i r e c t l y s t e r i l i $ y i n w i l d p a p u l a t i o n s t h e y must p r o b a b l y

be a s s o c i a t e d t o p o w e r f u l b a i t s o r a t t r a c t a n t s , and n t t h e p r e s e n t

c time v e r y few p e s t s bu h y u s e f l i e s c a n t e c o n t r o l l e d by e f f i c i e n t

"', w a n t to e x p l o i t t h e full p o s s i b i l i t i e s of c h e m o s t e r i l a n t s (HOCI~I'?G,

h \

t reated b a i t s . Much m o r e is t o be learned abaut a t t r a c t a n t s i f b w e ,

k963). However, i n some c i r c u m s t a n c e s , t r e a t e d t r a p s v i t h p e r i o d i c

r e l e a s e c o u l d o f f e r . an e f f i c i e n t way t o deal with species d i f f d c u l t

t o c o l o n i z e b u t o c c u r i i i g In n a t u r e a t low d e n s i t i e s l i k e . tse-tse f? i

C h e m o s t e r i l a n t s , l i k e o t h e r chemicals , are m e t a b o l i z e d

i n t o i n a c t i v e compounds i n s i d e i n s e c t s , and w e c a n e x p e c t f i e l d de-

ve lopment of c h e m o s t e r i l a n t - r e s i s t a n p o p u l a t i o n s of v e c t o r s , as w e observed f o r i h seck ic ides . T h e r e i s a l r e a d y one l a b v r a t o r y o b s e r v a -

\

t i o n on a p h o l a t e r e s i s i a n c e lin A e , a e g y p t i . I I r i -

I -

- .

. . I. .

Vector c o n t r o l a c t i v i t i e s s h a l l . p r o b a b l y be s l o w l y modi-

f i e d by t h e deve lopment of c h e m o s t e r i l a n t s , bu these a g e n t s w i l l mo * re s u p p l y a d d i t i o n a l p o s s i b i l i t i e s O P c o n t r o l t h a n r e p l a c e t h e a l r .

dy a v a i l a b l e - methodes and compounds. T h e i r i n t e l l i g e n t u s e . r e q u i r e s 1

thks t h e c o l l e c t i o n bf basic i n f o r m a t i o n s on t h e v e c t o r p o p u l a t i o n s

and s h a l l h e l p t o d e v e l o p i n t e g r a t e d c o n t r o l p r o c e d u r e s

I

, /

- _ _

I ' 8

._ i

c *

IBL IOGRAPHSB

21

ALDlAN ( R J J ,) 1963 ,- The e f f e c t s of Tepa on Flasmodium g a l l i n a c e u m Aedes a e g y k t i , AinrJ.Hyg. , 77, 221 - 237 ,

ASCHBX (K.K.S .) , 1964.y A, review of c h e m o s t e r i l a n t s apd o v i p o s i t i o n - i n h i b i t o r s in i n s e c t s . %orla' l iev.Fest C a n t r o l , 3 , ' 7-26 ,

ASGHEE ( K . K . S . ) , 2 9 6 6 , - O v i p o s i t i p n - i n h i b i t i n g a g e n t s : a s c r e e n i n g f o r s i m p l e model ' s u b s t a n c e s e

8 - 1 1 . I n t e r n i t i o n a l 'FeBi C b h t r o l , 7 ,

BARNES 9964.- R symposium on c h e m o s t e r i l a n t s i n p e s t and vec- ~ to r c o n t r o l . 1 1 1 . Tox ic hazards and t h e u s e of i n s e c t chemos-

EAUMHOVER ( A . H . ) , GfiAHA? (k,.J.)~~HOPKING (D.B.)3 IYEW ( W . D . ) , DUDLEY

t e r i l a n t s , T r a n s .R,Soc . t r o p .Lyed.Hyg 0 , - 9 58 327 7 334 --'i3 TmR(B0Ao)

(F.H.) & BUSHLAND (K.C. ) ,1955 .- Screw-worm c o n t r o l t h r o u g h t b e release of s t e r i l i z e d f l i e s . J.econ.Bnt'. , 48, 462 - 466

3ESTRAY ( D , S ,), 1963,- O b s e r v a t i o n s on t h e c h e m o s t e r i l a n t e f f e c t of an a l k y l a t i n g a g e n t , Th iopepa , on w i l d c a u g h t Anopheles gambine va rme laa (Theo . ) i n G a n b i a , West Africa and on l a b o r a t o r y b r e d A.g ,melas and Bedes a e g y p t i (L . ) T r a n s .AC .Soc . trop .I ed .Kyg., _. 5 7 , 332 335

BEBXFtAM ( D , S , ) , 1964 a . - A symposium on c h e m o s t e r i l a n t s i n F e s t and v e c t o r c o n t r o l . 1 . E n t o m o l o g i c a l and p a r a s i t o l o g i c a l a s p e c t s of vector c h e m o s t e r i l i z a t i o n . T r a n s .R.Soc , t r o p .:'ed .pI.vp, -, 58 296 - 317

BERTRAPeC ( D . S . ) , %SIG4 b o - C h e m o s t e r i l i z a t i o n e f f e c t s on malaria para- s i t e s i n m o s q u i t o e s . P r o c .Ist .Int .Congr , P a r a s i t o I Rome, S O U S

p r e s s e . BI33TRAM (D .5 , ) SKSVASTAVI! (S.C .) & 84ShNGI (A .S ) , 1964 .- Transmis-

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CKA PIG

CHANG

22

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f

* CRYSTAL (1, ~ ~ ~ ' . ) &kLLACPTANCB ( L . E . ) , 1963.- The m o d i f i c a t i o n ' of r e p r o - . .' d u c t i o n i n i n s e c t s " t r e a t e d w i t h a l k y l a t i n g - a g e n t s . 1, I n h i b 4 T

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23

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I f i

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t

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t P

6 . -I

25

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26

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