R e v i s t a d a S o c i e d a d e B r a s i l e i r a d e M e d i c i n a T r o p i c a l 1 7 ( 1 ) : 1 3 - 1 6 , J a n - M a r , 1 9 8 4
MORTALITY OF
DIPETALOGASTER M AX IM U S
(UHLER) IN RESPONSE
TO TEMPERATURE A N D HUMIDITY
Colin E. Johnson1, Elaine F. O akley1 and Philip D. M arsden2
O b s e r v a t i o n s w e r e m a d e o n t h e m o r t a l i t y o /D ip e ta lo g a s te r m a x im u s i n r e l a t i o n t o h u m i d i t y a n d t e m p e r a t u r e i n c o n t r o l l e d c o n d i t i o n s . T h e b u g s s u r v i v e d l o n g e r a t h i g h e r r e l a t i v e h u m i d i t i e s a n d a t l o w e r t e m p e r a t u r e s , b u t w h e n t h e s e r e s u l t s w e r e p l o t t e d a g a i n s t v a p o u r p r e s s u r e d é f i c i t , n o i n d e p e n d e n t t e m p e r a t u r e e f f e c t w a s s e e n . T h e r e s u l t s m a y b e e x p l a i n e d b y t h e f a s t e r d e p l e t i o n o f w a t e r r e s e r v e s a t h i g h e r v a p o u r p r e s s u r e d e f i c i t s . D . m a x im u s d i d n o t i n c r e a s e i t s r e s i s t a n c e t o w a t e r v a p o u r t r a n s f e r a t h i g h e r v a p o u r p r e s s u r e d e f i c i t s . I n o r d e r t o i n c r e a s e s u r v i v a l r a t e s w h e n D . m a x im u s i s u s e d f o r x e n o d i a g n o s i s i n f i e l d c o n d i t i o n s i t s h o u l d b e p r o t e c t e d a g a i n s t h i g h t e m p e r a t u r e s a n d l o w h u m i d i t i e s .
K e y w ords: D i p e t a l o g a s t e r m a x i m u s . M o rta lity . H u m id ity . T e m p e ra tu re .
X e n o d ia g n o s is o f C h a g a s ’ d is e a s e h a s b e e n ro u tin e ly a c c o m p lis h e d b y usin g first in s ta r n y m p h s o f th e bu g D i p e t a l o g a s t e r m a x i m u s (U h le r) (T ria to - m in a e ) ^ ^ 7. W h ile th is sp e c ie s is a m o re effec tiv e a g e n t fo r x e n o d ia g n o s is th a n th e p re v io u sly u se d
T r i a t o m a i n f e s t a n sh ig h e r m o rta lity w a s n o te d in D . m a x i m u s , a n d it w a s su g ge ste d^ th a t v a ria tio n s o f te m p e ra tu re a n d h u m id ity w ere inv olve d.
A lth o u g h u n d e r la b o ra to ry c o lo n y c o n d itio n s u n fe d first in s ta r D . m a x i m u s c a n su rv iv e fo r up to 1 20 d a y s 2, little in fo rm a tio n is a v a ila b le o n th e su rv iv a l o f th e s e bu gs in d iffe re n t c o n d itio n s o f te m p e ra tu re a n d h u m id ity .
T h e o b je c tiv e o f th is s tu d y w a s to im p ro v e su rv iv a l r a te s o f b u g s u se d in field c o n d itio n s fo r d ia g n o s is o f C h a g a s ’ d is e a s e b y s tu d y in g th e m o rta lity o f eggs a n d firs t in s ta r D . m a x i m u s in c o n tro lle d te m p e ra tu re s a n d hu m id itie s.
M A T E R I A L A N D M E T H O D S
E g g s o f D . m a x i m u s w ere c o lle c te d du rin g a p e rio d o f o n e w e ek from a la b o ra to ry c o lo n y m ain ta in e d a t th e N ú c le o d e M e d ic in a T ro p ic a l, U n iv e rs ity o f B ra sília . T h e o v ip o sitio n d a te w a s a p p ro x im a te d b y th e m e a n d a te ( 2 0 .1 0 .7 9 ) . T h e b a tc h w as s e p a ra te d in to g ro u p s o f 1 5 -2 0 eggs a n d e a c h g ro u p p la c e d in a
1. L a b o ra tó rio d e E c o lo g ia , D e p tP d e B io lo g ia V e ge ta l, U n iv e rs id a d e d e B ra sília.
2. N ú c le o d e M e d ic in a T ro p ic a l e N u triç ã o , U n iv e rs id a d e d e B ra sília .
R e c e b id o p a r a p u b lic a ç ã o e m 2 8 /1 1 /8 3 .
s e p a ra te g la ss b e a k e r w ith a m u slin co ve r. T h e grou ps w ere e q u a lly d is trib u te d b e tw e e n th e c o n tro lle d h u m id ity a n d te m p e ra tu re en v iro n m en ts .
C o m m e rc ia lly a v a ila b le in c u b a to rs (G riffin & G e o rg e L td ., L o n d o n ) w ere u se d to c o n tro l the te m p e ra tu re b e tw e e n a m b ie n t (2 5 ° C ) a n d 3 4 °C . In th is e q u ip m e n t, a ir h e a te d b y a th e rm o s ta tic a lly c o n tro lle d lig h t b u lb is a llo w e d to c irc u la te thro u g h the c h a m b e r. H u m id ity w a s c o n tro lle d se p a ra te ly in a s e rie s o f 3 0 c m d e s ic c a to rs , u sin g g ly c e ro l so lu tio n s o f d iffe re n t c o n c e n tra tio n s 11. A sm a ll q u a n tity o f c o p p e r s u lp h a te w a s a d d e d to th e so lu tio n s to a v o id the grow th o f m ou ld . T h e h u m id ity tre a tm e n ts w ere m a in ta in e d a t ro o m te m p e ra tu re . T h e g ly c erol so lu tio n s p e rm itte d a ra n g e o f b e tw e e n 3 0 a n d 1 0 0 % re la tiv e h u m id ity ( R H ) , a n d d ry silic a gel w a s u se d to p ro v id e a R H o f 2 0 % . A li th e e x p e rim e n ts w ere do n e in a sm all in s u la te d ro o m w h e re th e te m p e ra tu re m e a s u re d b y a th e rm o g ra p h v a rie d b e tw e e n 2 3 a n d 2 6 ° C du rin g te s t p e rio d ( M a rc h -J u n e 1 9 8 0 ).
T h e h u m id itie s w ere m e a s u re d usin g a fine w ire c o p p e r-c o n s ta n ta n th e rm o c o u p le p s y c h ro m e te r a n d a m illiv o ltm e te r1 a n d d id n o t v a ry sig n ific an tly d u ring th e e x p e r im e n t V a p o u r p re s s u re d e fic its (V P D ) (i.e. th e d iffe re n c e in w a te r v a p o u r p re ssu re be tw e e n the e v a p o ra tin g su rfa c e a n d th e e n v iro n m e n t) w ere c a lc u la te d a ss u m in g th a t th e a ir in c o n ta c t w ith th e w et su rfa c e is s a tu ra te d w ith w a te r v a p o u r. T h u s V P D = e s( T ) - e a w h e re e s(T ) is th e s a tu ra te d v a p o u r p re ssu re a t th e te m p e ra tu re T , a n d e a th e a m b ie n t v a p o u r p re ssu re . T h e b u g te m p e ra tu re s w e re a s s u m e d e q u a l to th e a m b ie n t C o n v e rs io n fro m re la tiv e hu m id ity to V P D m a y b e m a d e u sin g th e form ula:
V P D = e s( T ) .( l - R H /1 0 0 )
J o h n s o n C E , O a k l e y E F , M a r s d e n P D . M o r t a l i t y o /D ip e ta lo g a s te r m a x im u s ( U h l e r ) i n r e s p o n s e t o t e m p e r a t u r e a n d h u m i d i t y . R e v i s t a d a S o c i e d a d e B r a s i l e i r a d e M e d i c i n a T r o p i c a l 1 7 : 1 7 - 2 0 , J a n - M a r , 1 9 8 4
W h ile th e te m p e ra tu re o f th e h u m id ity se rie s w as m a in ta in e d c o n sta n t, it w as n o t p o ss ib le to k e e p the V P D c o n s ta n t in th e c o n tro lle d te m p e ra tu re c h a m b e rs. T a b le 1 sh ow s th e te m p e ra tu re and h u m id ity serie s use d.
A t a b o u t five d a y in te rv a ls , th e g ro u p s o f eggs o r bu gs w ere c h e c k e d to d e te rm in e m o rta lity ra te s , a n d e a c h b a tc h w as w eighed. T h e le th a l tim e to 5 0 % m o rta lity (L T 5 0 ) o f th e h a tc h e d bu g s w a s m e a s u re d for e a c h tre a tm e n t.
R E S U L T S
1 ■ E g g s
T h e p e rc e n ta g e m o rta lity ra te s o f D . m a x i m u s in th e egg sta g e in v a rio u s c o n d itio n s o f te m p e ra tu re a n d h u m id ity a re sh o w n in T a ble 1. I t is n o t p o s sib le to d e m o n s tra te a n y e ffe ct o f te m p e ra tu re b e y o n d th a t o f in c re a sin g th e V P D . T h e m o rta lity o f egg s h e ld in co nditions o f y P D g r e a te rth a n 2 .0 k P a w a s significantly h ig h e r th a n th o se in lo w e r V P D (c h i-s q u a re d , p < l % ).
T a b le 1 - M o r t a l i t y r a t e s i n t h e e g g s t a g e o f D . m a x im u s h e l d i n v a r i o u s c o n d i t i o n s o f t e m p e r a t u r e a n d h u m i d i t y . T h e c o r r e s p o n d i n g v a p o u r p r e s s u r e d e f i c i t s a r e a l s o s h o w n ( V P D ) .
R e l a t i v e H u m i d i t y ( % ) T e m p e r a t u r e ( ° C )
2 0 32 6 2 74 10 0 25 28 3 0 32 34
V P D ( k P a ) 2.7 2 .3 1.3 0 .9 0 0 .8 1.4 1.9 2 .4 3.1
E g g M o r t a l i t y
(%)
4 0 5 15 10 15 15 10 10 25 502. F i r s t i n s t a r b u g s
A fte r ha tc h in g , th e m o rta lity ra te w a s low o r zero until an initial po in t w as re a c h e d w hen it in cre as e d ra pid ly . T h e tim e ta k e n to re a c h this p o in t v a rie d from a b o u t 8 0 d a y s a fte r o v ip o sitio n a t a V P D o f 0 .8 k P a to a b o u t 30 d a y s a t 3 .0 k P a , a n d no sig n ific a n t dife re n c e be tw e e n the h u m id ity a n d te m p e ra tu re C ontrols w a s found.
T h e m o rta lity (L T 5 0 ) w as p ro p o rtio n a l to th e V P D , as sho w n in F ig . 1. L in e a r re g re ssio n a n a ly sis sho w ed th a t 9 5 % o f th e v a ria n c e c o u ld b e e x p la in e d b y th is fac tor, a n d th ere w as no sig nifica nt difFerence b etw e e n the te m p e ra tu re a n d hu m id ity C ontrols. T h e un u su a lly high m o rta lity o b se rv e d a t z e ro V P D ( 1 0 0 % R H ) w a s ex c lu d e d from the an a ly sis , a n d w as p ro b a b ly du e to a p a th o g e n ic fungus.
T h e ra te o f w eight lo ss o f th e firs t in s ta r bu gs w a s v irtu a lly c o n s ta n t fo r e a c h tre a tm e n t, a n d lin e a r re gressio n a n a ly sis w as u se d to c a lc u la te th e m e a n ra te o f w eight loss. A s e x p e c te d , th e m o rta lity ra te s c a n be relate d w ith this rate (F ig . 2). T h e ra te o f w eig h t lo ss a t 3 4 °C w as m u c h g re a te r th a n a t o th e r te m p e ra tu re s .
S h o rt ( < 1 h) e x p o su re tim e s a t te m p e ra tu re s a bo ve 45 °C are le th a l to th is spe c ie s. F ir s t in s ta r
D . m a x i m u s e x p o se d to b rig h t su n sh in e (to ta l s o la r ra d ia tio n = 1 0 0 0 W n T ^ ) a n d s h e lte re d fro m th e w ind
in a gla ss b e a k e r w ere fo u n d to d ie a fte r o n ly six m in u te s, p re s u m a b ly fro m te m p e ra tu re effects.
D I S C U S S I O N
T h e hig h c o rre la tio n b e tw e e n m o rta lity ra te s a n d v a p o u r p re s s u re d é fic it in u n fe d bu g s is p ro b a b ly d u e to th e d e p le tio n o f w a te r re se rv e s. T h e ra te o f w a te r v a p o u r d iffu sio n is e x p e c te d to b e p ro p o rtio n a l to th e v a p o u r p re s s u re dé fic it” ^ , a n d p ro v id in g th a t the re s is ta n c e to w a te r v a p o u r tra n s fe r re m a in s c o n s ta n t, b u g s w ill su rv iv e lo n g e r in m o re h u m id e n v iro n m e n ts .
M a n y in se c ts c a n in c re a s e th e ir re s is ta n c e w h en e x p o s e d to h ig h e r v a p o u r p re s s u re deficits® , b u t th is e ffec t w a s n o t o b se rv e d w ith D . m a x i m u s w he re re s is ta n c e h a d a te n d a n c y to d e c re a s e w ith v a p o u r p re s s u re d é f ic it T h e c o n s ta n t ra te o f w e ig h t lo ss o b s e rv e d in e a c h tre a tm e n t sh o w e d th a t th e re s is ta n c e to w a te r lo ss w as c o n s ta n t d u rin g th e e x p e rim e n t. A t 3 4 ° C w a te r loss w as 2-3 tim es th a t a t o th e r tem p e ra tu re s, su g e stin g d e c re a s e d c u tic u la r re s is ta n c e o r in c re a s e d s p ira c u la r openin g.
J o h n s o n C E , O a k l e y E F , M a r s d e n P D . M o r t a l i t y o /D ip e ta lo g a s te r m a x im u s ( U h l e r ) i n r e s p o n s e t o t e m p e r a t u r e a n d h u m i d i t y . R e v i s t a d a S o c i e d a d e B r a s i l e i r a d e M e d i c i n a T r o p i c a l 1 7 : 1 7 - 2 0 , J a n - M a r , 1 9 8 4
Ae
r**a)
F ig . 1 - T h e re la tio n s h ip b e tw e e n m o rta lity ra te ( L T 5 0 ) o f D . m a x i m u s a n d th e v a p o u r p re s su re d é fic it (V P D ). T h e
lin e a r re g re ssio n line is show n. T e m p e ra tu re c o n tro lle d (o ), h u m id ity c o n tro lle d (o).
10 0 —
to
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o
X I
6 0
-o
Lf >
2 0
-0,15 0 ,2 0 0 ,2 5 0 ,3 0 0 ,3 5 0,40
W L (m g d - )
F ig . 2 - T h e re la tio n s h ip b e tw e e n m o rta lity ra te (L T 5 0 ) o f D . m a x i m u s a n d th e m e a n ra te o f w eig h t lo ss p e r in s e c t in
e a c h g ro u p (W L ). T w o d a ta p o in ts w ere n o t in clud ed: fo r 1 0 0 % R H a n d 3 4 ° C (s e e te x t). T e m p e ra tu re c o n tro lle d (o), h u m id ity c o n tro lle d (o).
J o h n s o n C E , O a k l e y E F , M a r s d e n P D . M o r t a l i t y o /D ip e ta lo g a s te r m a x im u s ( U h l e r ) i n r e s p o n s e t o t e m p e r a t u r e a n d h u m i d i t y . R e v i s t a d a S o c i e d a d e B r a s i l e i r a d e M e d i c i n a T r o p i c a l 1 7 : 1 7 - 2 0 , J a n - M a r , 1 9 8 4
egg p ro d u c tio n from D . m a x i m u s in c o lo nie s. T r i a t o m a i r t f e s t a n s h a s b e e n sh ow n to p re fe r a te m p e ra tu re o f a re u n d 2 7 ° C 5 . V e ry high h u m id itie s m a y stim u la te p a th o g e n ic fun ga i a ttâ c k .
T w o studies® m a d e in th e n a tu ra l h a b ita t o f D . m a x i m u s sh ow th a t th e b ug s a re a ttra c te d to p o te n tia l h o s ts in the o p e n e v e n in c o n d itio n s o f b rig h t su nsh in e w h e n th e ro c k s a re h o t to to u c h a n d m a y a p p ro a c h th e le th a l te m p e ra tu re . E v e n th o u g h th e se co n d itio n s a p p e a r u n fa v o u ra b le , th e y d o n o t p re v e n t the bu gs from se a rc h in g fo rfo o d , a n d th e s h o rt su rviv a l tim e s o f un fe d bu gs m a y e x p la in th is b e h a v io u r.
S U M Á R IO
O b s e r v o u - s e a m o r t a l i d a d e d o D ip e ta lo g a s te r m a xim us e m r e l a ç ã o à t e m p e r a t u r a e u m i d a d e , e m c o n d i ç õ e s c o n t r o l a d a s . O s t r i a t o m i n e o s s o b r e v i v e r a m m a i o r t e m p o e m u m i d a d e s r e l a t i v a s m a i s a l t a s e e m t e m p e r a t u r a s m a i s b a i x a s , m a s q u a n d o e s t e s r e s u l t a d o s f o r a m d i s t r i b u í d o s g r a f i c a m e n t e e m c o n d i ç õ e s d e b a i x a p r e s s ã o , n e n h u m e f e i t o f o i v i s t o , i n d e p e n d e n t e m e n t e d a v a r i a ç ã o d e t e m p e r a t u r a . O r e s u l t a d o p o d e s e r e x p l i c a d o p e l a e v a p o r a ç ã o m a i s r á p i d a d e á g u a n a s c o n d i ç õ e s d e b a i x a p r e s s ã o . O D . m a xim u s n ã o a u m e n t a s u a r e s i t ê n c i a q u a n d o s e i n j e t a v a p o r d e á g u a e m a m b i e n t e s d e b a i x a p r e s s ã o . P a r a a u m e n t a r a s o b r e v i d a d o D . m a x im u s q u a n d o u s a d o p a r a x e n o d i a g n ó s t i c o e m c o n d i ç õ e s d e c a m p o é c o n v e n i e n t e p r o t e g ê - l o d a s a l t a s t e m p e r a t u r a s e b a i x a s u m i d a d e s .
P a la v ra s -c h a v e s : D i p e t a l o g a s t e r m a x i m u s . M o rta lid a d e . U m id a d e . T e m p e ra tu ra .
A C K N O W L E D G E M E N T S
T h e a u th o rs w o uld like to th a n k P ro f. A lu iz io P r a ta for pro v id in g the e x p e rim e n ta l m a te ria l. D r. B arry M o s e r a n a ly s e d som e o f th e d a ta a n d D r. C . J . S cho fie ld he lp e d in the p re lim in a ry ex p e rim e n ts . T h e e q u ip m e n t u se d in th e s tu d y w a s b o u g h t u sin g re s e a rc h fu nd s p ro v id e d b y F I N E P a n d T h e B ritish C ou n c il. W e w ould like to th a n k D r. A . B o sw o rth fo r m ak in g c o n stru c tiv e c ris tic is m s to a n e a rlie r m a n u sc rip t.
R E F E R E N C E S
1. B a rre to A C , M a rs d e n P D , C u b a C C , A lv a re n g a N J .
E s tu d o p re lim in a r so b re o em p reg o de D i p e t a l o g a s t e r
m a x i m u s (U h le r, 1 8 9 4 ) (T ria to m in a e ) n a té c n ic a d o
x e n o d ia g n ó s tic o e m fo rm a c rô n ic a d a d o e n ç a de C h a g a s. R e v is ta d o In s titu to d e M e d ic in a T ro p ic a l d e S ã o P a u lo 20 : 1 8 3 -1 8 9 , 1 97 8.
2. B a rre to A C , P r a ta A R , M a rs d e n P D , C u b a C C , T rig u e ira C P . A s p e c to s bio ló g ic o s e c ria ç ã o e m m a s s a de
D i p e t a l o g a s t e r m a x i m u s (U h le r, 1 8 9 4 ) (T ria to m in a e ).
R e v is ta d o In s titu to de M e d ic in a T ro p ic a l d e S ã o P a u lo 23 : 1 8 -2 7 , 1 98 1.
3. C u b a C C , A lv a re n g a N J , B a rre to A C , M a rs d e n P D , C h ia rin i C . N u e v o s es tú d io s c o m p a ra tiv o s en tre
D i p e t a l o g a s t e r m a x i m u s y T r i a t o m a i n f e s t a n s en
x e n o d ia g n ó s tic o de la in fec c ió n c h a g á s ic a c rô n ic a h u m a n a . R e v is ta d o In s titu to de M e d ic in a T ro p ic a l de S ã o P a u lo 2 0 : 1 4 5 -1 5 1 , 1 97 8.
4. C u b a C C , A lv a re n g a N J , B a rre to A C , M a rs d e n P D ,
M a c e d o V , G a m a M P . D i p e t a l o g a s t e r m a x i m u s
( H e m ip te ra , T ria to m in a e ) fo r x e n o d ia g n o s is o f p a tie n ts
w ith se ro lo g ic a lly d e te c ta b le T r y p a n o s o m a c r u z i
in f e c tio a T ra n s a c tio n s o f th e R o y a l S o c ie ty o f T ro p ic a l M e d ic in e a n d H y g ie n e 73: 5 2 4 -5 2 7 , 19 79.
5. D i L u c ia n o V S . O rie n ta tio n o f T r i a t o m a i n f e s t a n s
(H e m ip te ra : R e d u v iid a e ) to en v iro n m e n ta l te m p e ra tu re s. J o u rn a l o f M e d ic a i E n to m o lo g y 20 : 4 4 6 -4 5 4 , 198 3.
6 . E d n e y E B . W a te r b a la n c e in la n d a rth ro p o d s. S pringe r- V e rlag , B erlin, p. 2 8 2 , 1 97 7.
7. M a rs d e n P D , B a rre to A C , C u b a C C , G a m a M D , A c k e rs J. Im p ro v e m e n ts in ro u tin e x en o d ia g n o s is w ith
firs t in s ta r D i p e t a l o g a s t e r m a x i m u s (U h le r, 1 8 9 4 )
(T ria to m in a e ). T h e A m e ric a n J o u r n a l o f T ro p ic a l M e d ic in e a n d H y g ie n e 28 : 6 4 9 -6 5 2 , 19 79.
8. M a rs d e n P D , C u b a C C , A lv a re n g a N J , B a rre to A C .
R e p o rt o n a fie ld c o lle c tio n o f D i p e t a l o g a s t e r m a x i m u s
(H e m ip te ra . T ria to m in a e ) (U h le r, 1 8 9 4 ). R e v is ta do In s titu to de M e d ic in a T ro p ic a l d e S ã o P a u lo 21: 2 0 2 - 2 0 6 , 19 79 .
9. M o n te ith J L , C a m p b e ll G S . D iffu sio n o f w a te r v a p o u r th ro u g h in te g u m e n ts - p o te n tia l c o nfu sio n. J o u r n a l o f T h e rm a l B io lo g y 5: 7 -9 , 19 80 .
10. R y c k m a n R E , R y c k m a n A E . E p iz o o tio lo g y o f
T r y p a n o s o m a c r u z i in so u th w e s te rn N o r th A m e ric a .
P a r t X : T h e b io s y s te m a tic s o f D i p e t a l o g a s t e r m a x i m u s
in M e x ic o (H e m ip te ra : R e d u v iid a e ) (K in e to p la s tid a : T ry p a n o s o m id a e ). J o u r n a l o f M e d ic a i E n to m o lo g y 4: 1 8 0 -1 8 8 , 19 67 .
11. S la v ík B. M e th o d s o f stu d y in g p la n t w a te r re la tio n s. E c o lo g ic a l stu d ie s vol. 9. S p rin g e r-V erla g , B erlin, p. 4 4 9 , 1 9 7 4 .
