15.10. 1975
Specialia
b e t w e e n t h e 2 y e a r s 6. I n 1970, f e m a l e s h a d r e a d y access f r o m t h e well to t h e o v i t r a p s v i a a n e x i t t r a p in t h e well lid, f r o m w h i c h t h e m o s q u i t o s were l i b e r a t e d o u t s i d e t h e well daily. H o w e v e r , in 1971, 1972 a n d 1973 m o s q u i t o s c o u l d o n l y l e a v e t h e well w i t h d i f f i c u l t y b e c a u s e t h e lid was sealed and the only access was t h r o u g h u n d e r g r o u n d c h a n n e l s 2 , * T h e c o n c l u s i o n t h a t t h e r e d u c e d r a f t collect i o n in 1971, c o m p a r e d w i t h 1970, is n o t a t t r i b u t a b l e to t h e effect of t h e t r a n s l o c a t i o n is s u p p o r t e d b y d a t a 6 s h o w i n g a p p r o x i m a t e l y c o n s t a n t n u m b e r s of r a f t s collected in t h e o v i t r a p s in 1971, 1972 a n d 1973, d u r i n g w h i c h p e r i o d t h e p r o p o r t i o n of t r a n s l o c a t e d r a f t s d e c l i n e d f r o m 8 0 % to less t h a n 1% (Figure). T h e r e s p o n s e to n a t u r a l s e l e c t i o n of a m a l e - l i n k e d t r a n s l o c a t i o n differs f r o m t h a t of a n a u t o s o m a l or X c h r o m o s o m e t r a n s l o c a t i o n w i t h a v i a b l e a n d fertile homozygote, where the translocation frequency would i n c r e a s e s p o n t a n e o u s l y if a c e r t a i n e q u i l i b r i u m is e x c e e d ed 1`2-t4. T h i s p r o p e r t y arizes f r o m n e g a t i v e h e t e r o s i s (i.e. t h e h e t e r o z y g o t e h a s less f i t n e s s t h a n e i t h e r h o m o z y gote) arid it does n o t a p p l y to t h e m a l e - l i n k e d case w h e r e t h e t r a n s l o c a t i o n h o m o z y g o t e c a n n o t exist. M a l e - l i n k e d t r a n s l o c a t i o n s could p e r s i s t in p o p u l a t i o n s , or e v e n s p o n t a n e o u s l y i n c r e a s e , in t h e f o l l o w i n g s i t u a t i o n s : 1. P e r m a n e n t a s s o c i a t i o n of t h e t r a n s l o c a t i o n w i t h g r e a t l y e n h a n c e d m a t i n g competitiveness~~ :Enhanced competi t i v e n e s s in t r a n s l o c a t e d m a l e s w a s f o u n d in a c a g e e x p e r i m e n t n , b u t t h i s w a s a p p a r e n t l y d u e to t h e c o n d i t i o n s u n d e r w h i c h t h e t r a n s l o c a t i o n m a t e r i a l for release w a s r e a r e d a n d w o u l d n o t t h e r e f o r e be e x p e c t e d to a p p l y in t h e p r o g e n y of r e l e a s e d m a l e s . 2. L i n k a g e of t h e t r a n s l o c a t i o n to a f a c t o r c a u s i n g s e g r e g a t i o n d i s t o r t i o n in f a v o u r m a l e s 15 17. T h i s s y s t e m could o n l y lead to i n c r e a s e in t h e t r a n s l o c a t i o n f r e q u e n c y if t h e t r a n s l o c a t i o n c a u s e d less t h a n 50% s t e r i l i t y ; o t h e r w i s e t h e o u t p u t of m a l e p r o g e n y f r o m d i s t o r t e r - t r a n s l o c a t i o n f a t h e r s w o u l d be s u b - n o r m a l and n a t u r a l selection would favour the n o r m a l m a l e - d e t e r m i n i n g c h r o m o s o m e . H o w e v e r , r e c e n t field c a g e t e s t s a t t h i s U n i t h a v e s h o w n t h a t i n t e g r a t i o n of sex-ratio distortion with translocations improves their a b i l i t y to s u p p r e s s a p o p u l a t i o n ' S . 3. A s s o c i a t i o n of t h e t r a n s l o c a t i o n w i t h a ' t r a n s p o r t s y s t e m ' b a s e d on n e g a t i v e heterosis. Cytoplasmic incompatibility m a y provide such a s y s t e m ~, a n d cage e x p e r i m e n t s 2~ h a v e s h o w n t h e o p e r a t i o n of t h e principle. H o w e v e r , a p o l y m o r p h i s m of c y t o -
1141
p l a s m i c t y p e s in I n d i a n C. /atigans p o p u l a t i o n s 21 a n d a t t e n u a t i o n of i n c o m p a t i b i l i t y w i t h a g e i n g of m a l e s 22 c a n c a u s e r e c o m b i n a t i o n of a t r a n s l o c a t i o n a n d t h e c y t o p l a s m i c t r a n s p o r t s y s t e m 2~ F u r t h e r s t u d i e s a r e required to determine whether, b y minimizing female r e l e a s e s a n d e n s u r i n g t h a t f e m a l e s h a v e m a t e d before release, t h e s y s t e m c o u l d a c h i e v e e f f e c t i v e p o p u l a t i o n control.
Summary. P u b l i s h e d d a t a on a n e x p e r i m e n t a l release of Culex pipiens c a r r y i n g a m a l e - l i n k e d t r a n s l o c a t i o n are r e - e x a m i n e d a n d it is s h o w n t h a t t h e s t e a d y decline in t r a n s l o c a t i o n f r e q u e n c y a f t e r t e r m i n a t i o n of r e l e a s e s a g r e e s w i t h t h e o r e t i c a l e x p e c t a t i o n s , b e c a u s e of t h e s e l e c t i v e d i s a d v a n t a g e of t r a n s l o c a t i o n h e t e r o z y g o t e m a l e s . S y s t e m s b a s e d on n e g a t i v e h e t e r o s i s or m e i o t i c d r i v e are c o n s i d e r e d w h e r e b y it m i g h t be p o s s i b l e t o p r o l o n g t h e p o p u l a t i o n c o n t r o l w h i c h w o u l d be a c h i e v e d b y a s h o r t t e r m release. C. F . C U R T I S 28, 24
W H O / I C M R Research Unit on Genetic, Control o/Mosquitos, New Delhi (India), 2 June 1975.
12 A. S. SEREBROVSKII, Zool. Zh. 19, 618 (1940). la C. F. CURTIS, Nature, Lond. 218, 368 (1968). 14 ,'V[.VV'HITTEN,in Sterility Principle/or Insect Control or Eradication (I.A.E.A., Vienna 1971), p. 339. 15 W. A. HIGKEY and G. B. CRAIG, Genetics 52, 1177 (1966). is S. G. SUGUNAarid C. F. CURTIS, J. Commun. Dis., india 6, 102 (1974). ~7 T. L. SWEENY, Ph. I). Thesis. Univ. California, Los Angeles (1972). lS C. It. CURTIS, l(. l
Specialia
b e t w e e n t h e 2 y e a r s 6. I n 1970, f e m a l e s h a d r e a d y access f r o m t h e well to t h e o v i t r a p s v i a a n e x i t t r a p in t h e well lid, f r o m w h i c h t h e m o s q u i t o s were l i b e r a t e d o u t s i d e t h e well daily. H o w e v e r , in 1971, 1972 a n d 1973 m o s q u i t o s c o u l d o n l y l e a v e t h e well w i t h d i f f i c u l t y b e c a u s e t h e lid was sealed and the only access was t h r o u g h u n d e r g r o u n d c h a n n e l s 2 , * T h e c o n c l u s i o n t h a t t h e r e d u c e d r a f t collect i o n in 1971, c o m p a r e d w i t h 1970, is n o t a t t r i b u t a b l e to t h e effect of t h e t r a n s l o c a t i o n is s u p p o r t e d b y d a t a 6 s h o w i n g a p p r o x i m a t e l y c o n s t a n t n u m b e r s of r a f t s collected in t h e o v i t r a p s in 1971, 1972 a n d 1973, d u r i n g w h i c h p e r i o d t h e p r o p o r t i o n of t r a n s l o c a t e d r a f t s d e c l i n e d f r o m 8 0 % to less t h a n 1% (Figure). T h e r e s p o n s e to n a t u r a l s e l e c t i o n of a m a l e - l i n k e d t r a n s l o c a t i o n differs f r o m t h a t of a n a u t o s o m a l or X c h r o m o s o m e t r a n s l o c a t i o n w i t h a v i a b l e a n d fertile homozygote, where the translocation frequency would i n c r e a s e s p o n t a n e o u s l y if a c e r t a i n e q u i l i b r i u m is e x c e e d ed 1`2-t4. T h i s p r o p e r t y arizes f r o m n e g a t i v e h e t e r o s i s (i.e. t h e h e t e r o z y g o t e h a s less f i t n e s s t h a n e i t h e r h o m o z y gote) arid it does n o t a p p l y to t h e m a l e - l i n k e d case w h e r e t h e t r a n s l o c a t i o n h o m o z y g o t e c a n n o t exist. M a l e - l i n k e d t r a n s l o c a t i o n s could p e r s i s t in p o p u l a t i o n s , or e v e n s p o n t a n e o u s l y i n c r e a s e , in t h e f o l l o w i n g s i t u a t i o n s : 1. P e r m a n e n t a s s o c i a t i o n of t h e t r a n s l o c a t i o n w i t h g r e a t l y e n h a n c e d m a t i n g competitiveness~~ :Enhanced competi t i v e n e s s in t r a n s l o c a t e d m a l e s w a s f o u n d in a c a g e e x p e r i m e n t n , b u t t h i s w a s a p p a r e n t l y d u e to t h e c o n d i t i o n s u n d e r w h i c h t h e t r a n s l o c a t i o n m a t e r i a l for release w a s r e a r e d a n d w o u l d n o t t h e r e f o r e be e x p e c t e d to a p p l y in t h e p r o g e n y of r e l e a s e d m a l e s . 2. L i n k a g e of t h e t r a n s l o c a t i o n to a f a c t o r c a u s i n g s e g r e g a t i o n d i s t o r t i o n in f a v o u r m a l e s 15 17. T h i s s y s t e m could o n l y lead to i n c r e a s e in t h e t r a n s l o c a t i o n f r e q u e n c y if t h e t r a n s l o c a t i o n c a u s e d less t h a n 50% s t e r i l i t y ; o t h e r w i s e t h e o u t p u t of m a l e p r o g e n y f r o m d i s t o r t e r - t r a n s l o c a t i o n f a t h e r s w o u l d be s u b - n o r m a l and n a t u r a l selection would favour the n o r m a l m a l e - d e t e r m i n i n g c h r o m o s o m e . H o w e v e r , r e c e n t field c a g e t e s t s a t t h i s U n i t h a v e s h o w n t h a t i n t e g r a t i o n of sex-ratio distortion with translocations improves their a b i l i t y to s u p p r e s s a p o p u l a t i o n ' S . 3. A s s o c i a t i o n of t h e t r a n s l o c a t i o n w i t h a ' t r a n s p o r t s y s t e m ' b a s e d on n e g a t i v e heterosis. Cytoplasmic incompatibility m a y provide such a s y s t e m ~, a n d cage e x p e r i m e n t s 2~ h a v e s h o w n t h e o p e r a t i o n of t h e principle. H o w e v e r , a p o l y m o r p h i s m of c y t o -
1141
p l a s m i c t y p e s in I n d i a n C. /atigans p o p u l a t i o n s 21 a n d a t t e n u a t i o n of i n c o m p a t i b i l i t y w i t h a g e i n g of m a l e s 22 c a n c a u s e r e c o m b i n a t i o n of a t r a n s l o c a t i o n a n d t h e c y t o p l a s m i c t r a n s p o r t s y s t e m 2~ F u r t h e r s t u d i e s a r e required to determine whether, b y minimizing female r e l e a s e s a n d e n s u r i n g t h a t f e m a l e s h a v e m a t e d before release, t h e s y s t e m c o u l d a c h i e v e e f f e c t i v e p o p u l a t i o n control.
Summary. P u b l i s h e d d a t a on a n e x p e r i m e n t a l release of Culex pipiens c a r r y i n g a m a l e - l i n k e d t r a n s l o c a t i o n are r e - e x a m i n e d a n d it is s h o w n t h a t t h e s t e a d y decline in t r a n s l o c a t i o n f r e q u e n c y a f t e r t e r m i n a t i o n of r e l e a s e s a g r e e s w i t h t h e o r e t i c a l e x p e c t a t i o n s , b e c a u s e of t h e s e l e c t i v e d i s a d v a n t a g e of t r a n s l o c a t i o n h e t e r o z y g o t e m a l e s . S y s t e m s b a s e d on n e g a t i v e h e t e r o s i s or m e i o t i c d r i v e are c o n s i d e r e d w h e r e b y it m i g h t be p o s s i b l e t o p r o l o n g t h e p o p u l a t i o n c o n t r o l w h i c h w o u l d be a c h i e v e d b y a s h o r t t e r m release. C. F . C U R T I S 28, 24
W H O / I C M R Research Unit on Genetic, Control o/Mosquitos, New Delhi (India), 2 June 1975.
12 A. S. SEREBROVSKII, Zool. Zh. 19, 618 (1940). la C. F. CURTIS, Nature, Lond. 218, 368 (1968). 14 ,'V[.VV'HITTEN,in Sterility Principle/or Insect Control or Eradication (I.A.E.A., Vienna 1971), p. 339. 15 W. A. HIGKEY and G. B. CRAIG, Genetics 52, 1177 (1966). is S. G. SUGUNAarid C. F. CURTIS, J. Commun. Dis., india 6, 102 (1974). ~7 T. L. SWEENY, Ph. I). Thesis. Univ. California, Los Angeles (1972). lS C. It. CURTIS, l(. l
