The relative toxicity of hydrogen cyanide, chlorpicrin and ethylene oxide to the eggs, numphs and
adults of the common bedbug (Cimex Lectularius)
by Harold Gunderson
A THESIS Submitted to the Graduate Committee In partial fulfillment of the requirements for the
Degree of Master of Science in Entomology
Montana State University
© Copyright by Harold Gunderson (1935)
Abstract:
no abstract found in this volume THE RELATIVE TOXICITY OF HYDROGM CYANIDE, CKIlQRriCRIH ASD
ETHYLENE OXIDE TO THE EGGS, NYMPHS AND ADULTS
OF THE COMMON BEDBUG ( C teex L e c t u l a r l u s ) .
by
HAROLD GUNDERSON
2.
A THESIS
S u b m itted t o th o G rad u ate Committee i n
p a r t i a l f u l f i l l m e n t o f t h e re q u ire m e n ts
f o r t h e D egree o f M a ste r o f S c ie n c e
I n Entomology a t Montana
S t a t e C o lle g e
Approved*
I n Charge o f M ajor Ytork
Chairm an
Committee
/Z r /3 .
---^C h airm an U rad u ate Ccm m ltteeT
Bozeman, Montana
J u n e , 1935
r-u /ig
TABLE OF CONTESTS
Page
I
I n tr o d u c tio n
Acknowledgment • • • • • • • • • • • • • • • • • • * • • • • • • •
I
Review o f L i t e r a t u r e « • • • • • • • .
• • • • • • • • • • • • • • •
I
• • • • • • • • • • • • • • • * • • • • « « •
4
E x p erim en tal Metiiod
D is c u s sio n o f R e s u lts
6
C o n clu sio n s • • • * • • • • * • • • • • • • • • • • • • • • • « «
7
Suomary
7
• • • • • • • « • • • • • • • • • • • * • • • • « • » • •
L i t e r a t u r e C ite d
9
.siO
U
V
oa
5 0 4 8 6
THE RELATIVE TOZICITY OF HYDROGEJ CYAIIIDE, CHLORPICRIH ARD
ETHYLEHE OXIDE TO THE EGGS, EYm iS AKD ADULTS
OF THE COMMON BEDBUG ( C isex l e c t u l a r i u a ) .
IRTRODUCTIOR
Hydrogmi c y a n id e h a s b e e n u se d a s a s u c c e s s f u l fu m ig an t a g a i n s t
bedbugs f o r t h e p a s t tw e n ty - f iv e y e a r s , b u t v e r y l i t t l e w ork h a s b e e n done
t o d e te rm in e a c c u r a te ly t h e a c t u a l c o n c e n tr a tio n o f g a s n e c e s s a r y t o in s u r e
good r e s u l t s *
I t i s known t h a t a g r e a t d e a l o f g a s i s l o s t th ro u g h le a k a g e ,
a b s o r p tio n , end o t h e r w ays, b u t a s f a r a s c a n b e d e te rm in e d , no one h a s
fo u nd t h e l e t h a l c o n c e n tr a tio n o f g a s n e c e s s a r y f o r Cimex l e c t u l a r i u s , n o r
h a s t h e m edian l e t h a l c o n c e n tr a tio n b e e n d e te rm in e d .
E th y le n e o x id e and
c h l c r p i c r i n h av e come i n t o g e n e r a l u s e e s fu m ig a n ts o n ly r e c e n t l y , b u t
t h e i r grow ing p o p u l a r i t y makes s t u d i e s I n t o t h e i r e f f i c i e n c y d e s i r a b l e .
ACERORLEDGMMT
The w r i t e r w is h e s t o th a n k D o cto r A . L . S tr a n d f o r s u g g e s tio n
o f th e problem and f o r h e lp and c r i t i c i s m d u rin g t h e c o u rs e o f t h e w o rk ,
and D o c to r E . L . H a en isc h end P r o f e s s o r G. A . K a il f o r s u g g e s tio n s an d a i d
d u rin g t h e p r e p a r a t io n o f t h e p a p e r .
Ik
REVIEU OF LITERATURE
The f i r s t u s e o f h y d ro g en c y a n id e a s a fu m ig a n t a g a i n s t h o u seh o ld
i n s e c t s w as re c o rd e d b y Howard ( 7 ) , who s t a t e d t h a t K S r l a tt u se d hyd ro g en
c y a n id e a g a i n s t book l i c e i n 1398,
H e rric k (G) u se d h y d ro g en c y a n id e f o r i j ,
fu m ig a tin g d o r m ito r ie s and o b ta in e d e x c e l l e n t r e s u l t s .
Coleman ( 4 ) tras one o f t h e f i r s t t o d e te rm in e t h e r e l a t i o n ­
s h ip betw een t h e c o n c e n tr a tio n o f fu m ig a n t, tim e o f e x p o su re and i n s e c t
m o rta lity .
He i n v e s t i g a t e d t h e t o x i c p r o p e r t i e s o f h y d ro g en c y a n id e a g a in s t
s c a le i n s e c t s ,
h y d ro g en c y a n id e w as g e n e r a te d and p a s s e d th ro u g h a s e r i e s
o f p u r if y in g tu b e s i n t o a I o t y g a s j a r , l a w hich h i s e x p e rim e n ta l i n s e c t s
w ere p la c e d .
From t h i s fu m ig a tio n cham ber t h e g a s was w ith d raw n i n t o a
s o l u t i o n o f p o ta ss iu m h y d ro x id e , and t i t r a t e d w ith s i l v e r n i t r a t e t o d e te rm in e
t h e amount o f hydrogen c y a n id e p r e s e n t .
H is m easurem ent o f t o x i c i t y was
b a s e d on 100# m o r t a l i t y o b ta in e d o v e r p e r io d s o f fro m 15 t o 60 m in u te s .
Be
fo u n d t h a t a g r e a t d e a l o f hy d ro g en c y a n id e trsed i n a c t u a l fu m ig a tio n was
l o s t th ro u g h le a k a g e and t h u s h a d no a c t i o n upon t h e i n s e c t s .
a r e q u e s tio n a b le f o r tw o r e a s o n s .
E ls r e s u l t s
F i r s t , a 100# m o r t a l i t y i s t h e o r e t i c a l l y
u n o b ta in a b le , and u n d e r e x p e rim e n ta l c o n d itio n s , t h e e x a c t c o n c e n tr a tio n o f
g a s c a u s in g 100# m o r t a l i t y w ould b e h a r d t o d e te rm in e .
A lso t h e c o n c e n tr a tio n
o f £08 c a u s in g 100# m o r t a l i t y i n 15 m in u te s w ould b e much g r e a t e r th a n t h a t
c a u s in g t h e same m o r t a l i t y i n 60 m in u te s .
B l e f e r t and G a rris o n (1 1 ) d e te rm in e d t h e c o n c e n tr a tio n s o f a number
o f to x ic a g e n ts , iM c h c a u se d 100# m o r t a l i t y i n 24 h o u r s , u s in g h y d ro g en
c y a n id e a s a s ta n d a rd f o r com paring t h e t o x i c i t y o f o t h e r g a s e s .
They u s e d
m e te rs t o m easure and r e g u l a t e t h e flo w o f m ixed g a s end s i r i n t o a 5 - l i t e r
j a r , w hich s e r v e d a s a fu m ig a tio n cham ber.
p r e s s e d a s p e r c e n ta g e s .
L e th a l c o n c e n tr a tio n s w ere ex­
H ere a g a in t h e same o b je c t io n s p r e v a i l a s i n C olem an's
w ork.
S tra n d (1 4 ) com pared d i f f e r e n t m ethods o f d e te rm in in g r e l a t i v e
to x ic ity ,
Be d e te rm in e d t h e 6 -h o u r m ed ian l e t h a l c o n c e n tr a tio n s o f hydrogen
- 3-
c y a n id e , c h l o r p i c r i n end e th y le n e o x id e f o r t h e C onfused f l o u r b e e t l e
( T rib o lIu m c^onfusun D u v .).
He fo u n d t h a t i f t h e tim e o f ex p o su re en d th e
te m p e ra tu re d u rin g e x p o su re w ere k e p t c o n s ta n t, and o n ly t h e c o n c e n tr a tio n
o f t h e fu m ig an t v a r i e d , h e h a d a n i d e a l m ethod f o r com paring t h e r e l a t i v e
t o x i c i t y o f v a r io u s fu m ig a n ts .
By fo llo w in g S t r a n d 's m ethod, one may n o t
o n ly com pare t h e e f f e c t o f d i f f e r e n t a g e n ts on one s p e c ie s o f i n s e c t , b u t
a l s o have a b a s i s f o r t h e co m p ariso n o f a fu m ig a n t o n d i f f e r e n t i n s e c t s .
H is e x p e rim e n ta l m ethod d i f f e r e d b u t s l i g h t l y from t h a t u se d i n t h e e x p e r i­
m ents d e s c r ib e d h e r e i n .
He d e te rm in e d t h e c o n c e n tr a tio n o f h y d ro g en c y a n id e
p r e s e n t i n th e fu m ig a tio n cham ber b y a b s o rb in g t h e g a s i n p o ta ss iu m h y d ro x id e
and t i t r a t i n g w ith s i l v e r n i t r a t e .
Page (1 2 ) and L u b a ttl (9 ) e v o lv e d a m ethod f o r m e asu rin g t h e concen­
t r a t i o n o f hydrogen c y a n id e end e th y le n e o x id e p r e s e n t a t an y tim e d u rin g
a c t u a l fu m ig a tio n .
They u s e d a n e v a c u a te d f l a s k f i t t e d w ith a c a p i l l a r y
tu b e w hich c o u ld be b ro k e n o f f a t an y tim e b y c lo s in g a n e l e c t r i c c i r c u i t .
The a b s o rb e n t u se d f o r hydrogen c y a n id e was 50 c c . o f 0 .1 H sodium h y d ro x id e .
A t t h e end o f t h e ex p erim en t t h e sodium h y d ro x id e was t i t r a t e d w ith s i l v e r
n i t r a t e t o d e te rm in e t h e amount o f hyd ro g en c y a n id e a b s o rb e d .
f o r e th y le n e o x id e was magnesium c h l o r i d e .
The a b s o r b e n t
The c o n te n ts o f t h e f l a s k w ere
t i t r a t e d a t t h e end o f t h e e x p e rim e n t w ith d i l u t e sodium h y d ro x id e , u s in g
m eth y l o ra n g e a s a n i n d i c a t o r .
1!oor0 ( 1 0 ) , who was one o f t h e f i r s t t o u s e c h l o r p i c r i n , d e term in e d
t h e minimum l e t h a l d o se o f c h l o r p i c r i n n e c e s s a r y t o k i l l IOQ^ o f t h e I n s e c t s .
He u s e d t h e b e an w e e v il ( B ruchus o b te c tu s S . ) . t h e Angumols g r a i n m oth
Cg i fe lt r o Sa c e r e a l e l l a O i i v . ) , t h e In d ia n H eal m oth ( P lo d la in te rp u n c t a i l s
E b n .) , M e d ite rra n e a n f l o u r moth ( E p h o s tla fc u e h n le lla Z e l l . ) , and th e
Confused f l o u r b e e t l e ( T rlb o liu m c o n fu su n D w r.).
B e r tra n d , E rocq-R ouseeau and D a a s o n v ille ( l ) d e term in e d t h e to x ­
i c i t y o f c h l o r p i o r i n a g a in s t bedbugs ( £ . I e c t u l a r l u s ) and w e e v ils .
L in d g ren end Shepard (8 ) m o d ifie d S t r a n d 's e x p e rim e n ta l m ethod.
They found t h a t ch an g es i n h u m id ity c au se d th e m edian l e t h a l c o n c e n tr a tio n
o f c h l o r p i o r i n t o v a ry r a t h e r s i g n i f i c a n t l y f o r th e e g g s o f t h e C onfused
f l o u r b e e t l e ( I . c onfusum D u v .), b u t h a d no e f f e c t on t h e a d u l t s .
They a l s o
found t h a t changes i n h u m id ity had no e f f e c t on t h e m edian l e t h a l concen­
t r a t i o n o f e th y le n e o x id e f o r eggs and a d u l t s o f t h e b e e t l e .
B ro m (3 ) u s e d
a m ix tu r e o f c a rb o n d io x id e and e th y le n e o x id e t o fu m ig a te c o ck ro ac h es
( B l a t e l l a s p . ) and bedbugs (C . I e c t u l a r i u s ) .
B ase (S ) co n d u cted e x p erim en ts
w ith e th y le n e o x id e a s a fu m ig a n t f o r t h e bedbug (C . I e c t u l a r i u s ) .
e ^pesikental method
The a p p a r a tu s u s e d i n th e s e e x p e rim e n ts i s t h e S tra n d a p p a r a tu s a s
m o d ifie d b y L in d g ren and S hepard ( 8 ) .
E rlenm oyer f l a s k s o f a p p ro x im a te ly
6 .4 l i t e r s c a p a c ity w ere u se d a s fu m ig a tio n cham bers.
Each f l a s k w as f i t t e d
w ith a ground g l a s s s to p p e r , th ro u g h w hich w ere c o a le d tw o g l a s s t u b e s , each
s u p p lie d w ith a s to p c o c k .
The h y d ro g en c y a n id e u sed i n t h e s e e x p e rim e n ts was o b ta in e d th ro u g h
t h e r e a c t i o n o f sodium c y a n id e w ith s u lp h u r ic a c i d i n t h e p re s e n c e o f w a te r .
The g a s was c o o le d i n a c o n d en sin g tu b e and c o l l e c t e d i n a f l a s k b u r ie d i n
ic e .
The r e s u l t i n g l i q u i d was r e d i s t i l l e d s e v e r a l tim e s u n t i l t h e f r e e z i n g
p o i n t o f p u re hy d ro g en c y a n id e was re a c h e d .
• 5»
The HCB m s m easured I n to t h e fu m ig a tin g f l a s k s a s a gas*
A gas
b u r e t t e c a l i b r a t e d I n 0 .0 1 c c . m s f i l l e d M t h m ercu ry and a le v e l in g b u lb
a tta c h e d *
The tu b e c o n ta in in g t h e l i q u i d c y a n id e m s a tta c h e d t o th e
b u r e t t e and e a r n e d g e n tly , t h e l e v e l i n g b u lb low ered and t h e g a s d r a m I n to
th e b u r e tte .
The p r e s s u r e m s e q u a lis e d , t h e volume o f g a s m easu red ,
te m p e ra tu re and p r e s s u r e re c o rd e d , and th e n t h e g a s m s draw n i n t o t h e
p a r t i a l l y e v a c u a te d f l a s k .
The w e ig h t o f g a s I n a g iv e n volume was de­
te rm in e d b y means o f t h e form ula* FV= g B I, w here P i s t h e a tm o sp h e ric
p r e s s u r e , V i s th e volume o f g a s , g i s w e ig h t o f g a s , M I s t h e m o le c u la r
w e ig h t o f t h e g a s , R i s t h e g a s c o n s ta n t; 8 2 ,0 8 c . e , a tm . p e r mol d e g .; and
I I s t h e te m p e ra tu re a t w hich t h e volum e o f g a s I s m e asu re d .
T h is fo rm u la
i s d e riv e d from t h e fundament a l g a s Issrs a n d . I n g e n e r a l. I s a c c u r a te t o
w ith in 5/Z.
I n o r d e r t o check t h e r e s u l t s o b ta in e d w ith t h i s fo rm u la , a g iv e n
volum e o f g a s m s a b so rb e d I n a s o l u t i o n o f p o ta ss iu m h y d ro x id e , and t i t r a t e d
w ith s i l v e r n i t r a t e .
The r e s u l t s ch eck ed w i t h i n 1 # .
C h lo r p lc r ln was m easured a s a l i q u i d w ith a m ic r o p ip e tte c a l i ­
b r a t e d I n 0 .0 0 1 cc*
E th y le n e o x id e m s m easured a s a g a s I n t h e same m y a s was
h y d rogen c y a n id e .
I t was assum ed t h a t th e e r r o r I n m e asu rin g w ould n o t
exceed 1 ^ .
The e g g s, nymphs end a d u l t s o f t h e common bedbug ( £ . J e c t u l a r i u s ) ,
w ere u s e d i n t h e s e e x p e rim e n ts .
w ere o f seco n d end t h i r d l n s t a r s .
The eg g s u s e d w e re two d ay s o ld ; nymphs
A ll s ta g e s w ere k e p t a t 27°C .
F o r e ac h
e x p erim en t betw een 25 and 50 i n d iv id u a ls o f e a c h s ta g e w e re u s e d , s in c e
T revan (1 5 ) showed t h a t t h e u s e o f l e s s th a n 50 t e s t I n d iv i d u a ls c a u s e s a
- 6-
c o n s id o ra b le e r r o r , b u t t h e u s e o f more th a n t h i s number c o n t r i b u t e s l i t t l e
t o t h e a c c u ra c y o f t h e e x p e rim e n t.
B l i s s (2 ) showed b y s t a t i s t i c a l m ethods
t h a t a s low a s 10 in d iv id u a ls c o u ld b e u s e d w ith n o l o s s o f a c c u ra c y b e ­
tw een p e rc e n ta g e m o r t a l i t i e s o f fro m 58 t o 61$,
The t e s t i n s e c t s w e re p la c e d i n b o l t i n g c l o t h c a g e s , p u t i n t o t h e
fu m ig a tio n cham bers, w hich w e re th e n p a r t i a l l y e v a c u a te d , and t h e fu m ig an t
I n tr o d u c e d ,
The f l a s k s w ere th e n p la c e d a t 25°C . and l e f t f o r 5 h o u r s .
At
t h e end o f t h a t tim e t h e i n s e c t s w ere removed from t h e c a g e s and p la c e d i n
g l a s s v i a l s a t 27°C .
48 h o u r s .
M o r ta lity c o u n ts w ere made i n 24 h o u rs and a g a in i n
I n a l l c a s e s i t was fo u n d t h a t t h e m o r t a l i t y d id n o t change
a f t e r <,4 h o u rs .
Ko c o r r e c t i o n was n e c e s s a r y s in c e none o f t h e c o n t r o l s d ie d .
The fu m ig a te d eggs w ere p la c e d a t 27°C. w ith c h e c k s , and in s p e c te d e v e ry
day.
Normal bedbug eg g s k e p t a t 27°C . h a tc h i n 5 d a y s, so no c o u n ts w ere
made a f t e r t h e e x p i r a t i o n o f t h a t tim e .
The p e rc e n ta g e m o r t a l i t y was c a lc u ­
l a t e d b y means o f A b b o t f s fo rm u la . J L Z J L t10Q) s w here x i s t h e p e r c e n t
h a tc h i n t h e c h ec k and y t h e p e r c e n t h a tc h i n t h e t r e a t e d l o t .
DISCUSSIOII OF RESULTS
From th e s e r e s u l t s i t w i l l b e se e n t h a t t h e t h r e e fu m ig a n ts u sed
h e r e d i f f e r g r e a t l y I n t h e i r a c t i o n upon t h e d i f f e r e n t s ta g e s o f t h e common
b ed bug.
TABLE I .
F iv e -h o u r M edian L e th a l C o n c e n tra tio n s f o r Eggs, Eynphs and
A d u lts o f Clmex l e c t u l a r i u s .
Fum igant
Hydrogen c y a n id e
C h lo r p ic r in
E th y len e o x id e
Hggs-M^ . / l i t e r
0 .1 0 7 5 mg,
0 .2 1 7
mg.
Nymphs-Hf;./ l i t e r
0 .3 1 9 mg.
2 .1 8 0 mg.
I e S l mg.
Adult s - M g . / l i t e r
0 .3 3 2 5 mg.
0 ,5 8 2 mg.
1 .8 8
mg.
- 7-
From a n I n s p e c tio n o f f ig * 2 i t may b e se e n t h a t no m edian l e t i i a l
c o n c e n tr a tio n o f c h l o r p i e r i n c o u ld b e d e te rm in e d f o r t h e e g g s o f C. l e c t u l a r i u s .
a lth o u g h i t seems t o l i e betw een 5 .0 and 6*0 mg. p e r l i t e r .
The nymphs and
a d u lts a p p e a r t o b e two o r t h r e e tim e s a s s u s c e p t i b l e t o c h l o r p i e r i n a s th e
eg g s.
H ydrogen c y a n id e and e th y le n e o x id e a p p e a r t o h av e n e a r l y t h e same
t o x i c i t y t o t h e eggs o f t h e bedbug, b u t a lm o st 6 tim e s a s much e th y le n e
o x id e i s needed t o pro d u ce 50# m o r t a l i t y i n nymphs and a d u l t s a s com pared
t o h ydrogen c y a n id e .
COKCLUSIOKS
From a n in s p e c tio n o f th e r e s u l t s o b ta in e d i n th e s e e x p e rim e n ts ,
i t i s in d ic a te d t h a t hy d ro g en c y a n id e i s a b e t t e r fu m ig a n t f o r a l l s ta g e s
o f jC. I e e t u l a r l u s th a n e i t h e r e th y le n e o x id e o r c h l o r p i e r i n .
E th y le n e o x id e
■would b e p r e f e r a b l e t o c h l o r p i e r i n b e c a u se o f i t s a c t i o n on t h e eggs o f t h e
bedbug.
I n r e f u t a t i o n o f t h e id e a t h a t t h e eg g s o f an i n s e c t a r e th e m ost
r e s i s t a n t s t a g e , i t w as found t h a t th e y a r e t h e l e a s t r e s i s t a n t t o some o f
th e fu m ig a n ts p se d h e r e . . These e x p erim en ts te n d t o d is p ro v e t h e th e o r y
t h a t a second fu m ig a tio n o f ECB i s n e c e s s a r y t o k i l l t h e e g g s o f t h e common
b ed b u g .
In f a c t , i t Is q u ite th e re v e rs e .
A second fu m ig a tio n m ig h t b e
n e c e s s a r y t o k i l l th e a d u l t s .
SUiaiAEY
E xp erim ents a r e d e s c r ib e d and r e s u l t s re c o rd e d f o r t h e e f f e c t o f
- 8-
hydrogen c y e n id e , c h l o r p l c r l n and e th y le n e o x id e upon t h e e g g s , nymphs and
a d u l t s o f t h e common bedbug (C , l e c t u l a r l u a ) .
c o n c e n tr a tio n o f e ac h fu m ig a n t m s d e te rm in e d .
The 5 -h o u r m edian l e t h a l
I t i s s h a m t h a t HCN h a s &
g r e a t e r t o x i c a c t i o n a g a i n s t a l l s ta g e s o f t h i s i n s e c t th a n e i t h e r e th y le n e
o x id e o r c h l o r p l c r l n ,
9*
LITERATimE CITED
(1 )
B e r tra n d , B rocq-R oueseau, an d D f-ssom rille*
1919* D e s tr u c tio n o f t h e bedbug (_£• l e c t u l a r l u s ) w ith
c h lo r p ic r in * C.R.hebdomTAcsd* S c i 1 6 9 11059-1061*
(2 )
B l i s s , C .I .
1935» The c a l c u l a t i o n o f t h e d o sag e — m o r t a l i t y curve*
Ann* AppaB lo l.2 2 1134-167*
(3 )
Brown, E*W*
1933* C arboxide gas* a new i n s e c t i c i d a l fu m ig an t f o r c o ck ro ac h es
and b e d b u g s, U .S .N av.M ed.B ul.31, N o,3 :2 5 3 -2 6 8 .
(4 )
Coleman, G.A,
1911. M ethods o f d e te rm in in g th e t o x i c i t y o f h y d ro c y a n ic a c i d
gas* Jour,E co n ,E h t* 4 t5 2 8 -E 3 1 *
(5 )
B ase , A,
1932*
(6 )
F u r th e r c o n tr ib u tio n s t o t h e know ledge o f e th y le n e o x id e
a s a n i n s e c tic id e # A r t* b io l,R eich sam t*Land.u*Forstw *
2 0 , No*2*
H e r r ic k , G.W.
1907* F u m ig atio n w ith h y d ro c y a n ic g as f o r bedbugs*
C an .E n t.3 9 :3 4 1 .
(7 )
Howard, L*0*
1907* H ydrocyanic a c id g a s a g a i n s t h o u se h o ld I n s e c ts *
UeSaDeA, C ir» 4 6 , 8*8»
(8 ]
L in d g re n , D .L . and S h ep ard , H .E ,
1932* The in f lu e n c e o f h u m id ity o n t h e e f f e c t i v e n e s s o f c e r t a i n
fu m ig a n ts a g a i n s t t h e eggs and a d u l t s o f T rlb o llu m
confusum Duv.
J o u r . E c o n ,E n t.2 5 :2 4 8 -2 5 3 .
(9 )
L u b a t t i • O .F .
1932* D e te rm in a tio n o f e th y le n e o x ide* J o u r.S e e * CheaeInd*
51*362 T - 367 T*
(1 0 ) M oore, %a*
1918*
F u m ig atio n w ith c h lo r p ic r in *
J o u r . Eco n .E n t.11«357-362.
(1 1 ) K l e f e r t , I*E* and G a rris o n , G.L*
1920* EK perim ents on th e t o x i c a c t i o n o f c e r t a i n g a se s on
i n s e c t s , s e e d s an d £ungi* U .S .D .A .B u l.8 9 3 .
(12) P a g e , A.B*p*
1932* The m easurem ent o f g a s c o n c e n tr a tio n s f o r t h e c o n tr o l o f
fu m ig a tio n . Jour*Soc*Chem*Ind*51 *369 T - 374 T*
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