Feeding behaviour in young societies of the ant <Emphasis Type

Insectes Sociaux, Paris.
9
Masson,
Paris,
1979
1979, V o l u m e 26, n ~ 1, p p . 19-37.
FEEDING BEHAVIOUR IN YOUNG SOCIETIES OF THE
ANT T A P I N O M A E R R A T I C U M L. :
TROPHALLAXIS AND POLYETHISM
A. LENOIR (*)
Laboratoire de Psychophysiologie, Facultd des Sciences, Parc de Grandmont, F 37200 Tours
Regu le 15 mai 1977.
Accept6 le 22 n o v e m b r e 1977.
SUMMARY
The study of alimentary behaviour in newly f o u n d e d societies of ants Tapinoma
erraticum (Dolichoderinae) w i t h m a r k s on the gaster enabled us to classify the individuals
in terms of foraging and b r o o d care. There are 3 different g r o u p s : p e r m a n e n t foragers
(foragers in m o r e t h a n 80 % observations), i n t e r m i t t e n t foragers (between 20 to 80 %)
and nurses (less than 20 %). The behaviour of ants changes w i t h a g e : young ants are
nurses at first, t h e n they are i n t e r m i t t e n t foragers, and p e r m a n e n t foragers at last. Ants
less than one m o n t h old are called young ( u n d e r laboratory c o n d i t i o n s ) : 65 % of t h e m
are nurses, some are i n t e r m i t t e n t foragers (35 %). Ants m o r e t h a n one m o n t h old are
called old : 60 % are i n t e r m i t t e n t foragers, 30 o/~ p e r m a n e n t foragers and 10 % only nurses.
Young w o r k e r s become nurses very quickly (in a few days) b u t they are not active donocs
to other workers. After one montt{ m o s t of t h e m b e c o m e m e m b e r s of a pool of
unemployed ants able to forage and give food to the queen or larvae. Most of the
foraging is done by p e r m a n e n t foragers, older w o r k e r s . Individual development is very
variable, according to social pressure, if t h e r e are not enough old foragers, young ants
become foragers. This p h e n o m e n o n can be reversible.
RESUME
Le comportement a|imentaire dans les jeunes soci6t6s de la Fourmi
Tapinoma erraticum L. : trophallaxie et paly6thisme
L'observation des jeunes soci~t6s de F o u r m i s Tapinoma erraticum (Dolichoderinae)
a permis de classer les individus en fonction de leur activit6 darts l ' a p p r o v i s i o n n e m e n t du
nid, celui-ci est effectu~ par des ouvri6res sp6cialis6es: les pourvoyeuses. On reconnait
(*) This research was made in collaboration w i t h Mrs M. MEUDEC and the results
partly p r e s e n t e d during the meeting of the F r e n c h Section of I n t e r n a t i o n a l Union for
Study of Social Insects (Tours, m a r s 1976). I t h a n k Mrs M. GUASTAVINOfor translation.
20
A. L E N O I R
3 catdgories d'ouvri6res: les pourvoyeuses permanentes ; elles sont pourvoyeuses dans
plus de 80 % des observations et ne sont jamais nourrices, les pourvoyeuses
intermittentes (de 20 '% tt 80 %) qui peuvent 6tre simultandment pourvoYeuses et
nourrices de larves, enfin les nourrices strictes (moins de 20 % des observations) qui
s'occupent presque exclusivement du couvain.
Le comportement est en relation avec l'~ge: les ouvri~res sont d'abord nourrices,
ensuite pourvoyeuses interm6diaires et enfin pourvoyeuses permanentes. Les fourmis
agdes de moins d'un mois sont en grande majorit6 nourrices (65 %), quelques-unes sont
pourvoyeuses intermittentes (35 '%). Parmi les ouvri~res ~gdes de plus d'un mois 60 %
sont pourvoyeuses intermittentes, 30 % pourvoyeuses permanentes et 10 % restent
nourrices. Les jeunes ouvri~res deviennent en quelques jours de bonnes nourrices et
soignent activement les larves alors qu'elXes sont tr6s mauvaises donneuses envers les
autres ouvri~res. A partir d'un mois, la majeure pattie des ouvri6res entre dans un pool
d'individus disponibles selon les besoins de la eolonie, ils sont pourvoyeurs mais peuvent
aussi nourrir les larves ou la reine. La plus grande partie de l'approvisionnement est
assur6e par les pourvoyeuses permanentes qui sont de vieilles ouvri~res et peuvent
pr6senter une prdfdrence alimentaire marqu6e vers des aliments de type sucr6 ou protdique
L'6volution individuelle est tr~s variable, elle peut 6tre influenc6e par la pression sociale :
s'il manque des pourvoyeuses ~g6es et c'est le cas lorsque le nombre de jeunes ouvri~res
est sup6rieur ~ celui des ouvri~res ggdes, les jeunes de moins d'un mois peuvent devenir
momentan6ment pourvoy~uses.
INTRODUCTION
Division of l a b o u r a m o n g ants has been. k n o w n for a very long time.
T h o u g h s t u d i e s o f t h e i n d i v i d u a l b e h a v i o u r of a n t s a r e v e r y n u m e r o u s (WILSO,~
r e v i e w 1971, p. 163) n o s y s t e m a t i c s t u d y h a s y e t b e e n d o n e o n n e w l y f o u n d e d
colonies or fondations.
In the species studied, dissemination occurs when
t h e s w a r m i n g f e m a l e ( m a t e d q u e e n ) l o o k s f o r a h o l e to l ay h e r f i r s t e g g s i n
a n d ' t h e n t a k e s c a r e o f t h e m a l o n e . At t h e e n d o f t h e f i r s t s e a s o n t h e r e a r e
a f e w w o r k e r s t o h e l p t h e q u e e n to t e n d t h e b r o o d a n d s e a r c h f o r f o o d f o r
the young colony. The following year there are m o r e w o r k e r s b u t they can
b e still c o u n t e d in t e n s , a n d t h e i r n u m b e r w i l l s e l d o m r e a c h a " h u n d r e d .
W o r k e r s are always small. The colony does not p r o d u c e alates. We have
studied the structure of these embryonic societies by marking individuals.
S i n c e it is n o t e a s y t o f o l l o w s i m u l t a n e o u s l y m a n y i n d i v i d u a l s t h e g r o u p s
s t u d i e d w e r e o f b e t w e e n 10 a n d 30 a n t s .
I n this p a p e r w e discuss o b s e r v a t i o n s m a d e on the ant T a p i n o m a
e r r a t i c u m L. T h e b i o l o g y o f t h i s s p e c i e s h a s b e e n d e s c r i b e d b y M e u d e c
(1973 a).
MATERIAL
AND METHODS
Ants were reared in glass tubes, 30 centimeters long, with interior diameter of 1 cm.
One end of the tube was closed by cotton-wool and at the other end there was a water
supply (L~OlR 1973). Ants were fed on honey and on pieces of Tenebrio larvae.
TROPHALLAXlS AND P O L Y E T H I S M IN TAPINOMA
21
Each 'worker was m a r k e d using a technique developed in the l a b o r a t o r y : a tiny
nickel plate bearing a figure or a n u m b e r is stuck to the gaster (VERROrr and BARREAU 1974~.
During the operation the ants w e r e anaesthetized by CO2. For studying feeding behaviour
the groups w e r e starved for a period of 24 o r 48 hours. If this p e r i o d of s t a r v a t i o n is too
long, w o r k e r s begin to eat larvae, o r give eggs a n d young larvae to older larvae, w h i c h
could invalidates the results of food r e c r u i t m e n t experiments.
The experiment consisted simply in observing, using a binocular m i c r o s c o p e , the
exchanges of regurgitated food (trophallaxis) following the introduction of f o o d at the end
of the tube (a larva off Tenebrio and a drop of honey). All b e h a v i o u r related to
foraging and food-sharing has been n o t e d ; exchanges bet~veen foragers, o t h e r w o r k e r s
larvae, and the queen. E a c h trophallaxis was timed. Most of the time, observations did
not last m o r e t h a n half an hour, after w h i c h time, activity considerably diminished if
the need for food was not very strong.
The results are partly p r e s e n t e d as diagrams called " sociograms ". Trophallaxie
is shown as a r r o w s the head pointing t o w a r d the ant which receives food. This time
taken by foragers to feed on honey or Tenebrio is also r e p r e s e n t e d by an a r r o w whose
width thickness r e p r e s e n t s the length of time sharing lasted. A sociogram is the image
of the colony behaviour at one time ; it is a picture of a group which keeps on changing.
Each group is unique at a precise time. H o w e v e r some comparisons may b e carried out to
u n d e r s t a n d the different influences contributing to the structure of the society and the
development of individuals.
DESCRIPTION
OF T H E D I F F E R E N T
COLONIES
1 - - Colony B X (fig. 1)
Number of workers
TAPINOMA
colony
BX
o
old '~orkeri
9 youngworkers
\
l/1"15Jvll
.1r
Js|/
1~0 1~
18
19 20
24
26
28
.30 31
s.=,,l
1
2
~;l|O -
Fig. 1 . - N u m b e r of old and young w o r k e r s in colony BX. On each d a t e there was
an observation of half an hour. Young w o r k e r s hatched on July 14-15th.
Fig. 1. - - N o m b r e de vieilles ouvri6res et de jennes ouvri~res dans la colonie BX. A chaque
j o u r c o r r e s p o n d une observation de 30 ran. Les jeunes ouvri~res s o n t n6es le
14-15 juillet.
22
A.
LENOIR
This colony consisted, at the beginning, of 2 queens and 19 " o l d e r " ~vorkers. An
w o r k e r is any individual w h o s e age w e do not know, b u t w h i c h is dark
coloured and is at least 25 to 30 days old w h e n the experiment started. Young w o r k e r s ,
on the o t h e r hand, are newly h a t c h e d ants, and are less thai~ 30 days old w h e n the
experiment ends. We m a d e p r e m i m i n a r y observations every day during 3 days. As there
were m a n y p u p a e 10 w o r k e r s w e r e b o r n on July 14-15th. The colony w i t h young
workers was observed 13 times in 2 series : on July 18-19o20th and then every day b e t w e e n
July 24th and August 2rid. At the end of the experiment, young w o r k e r s w e r e j u s t a b o u t
15 days old. The n u m b e r of large larvae had increased by a factor of two ( f r o m 25
to 51), while the n u m b e r of young larvae and eggs has decreased (220 to 170) as m i g h t
be expected w h e n starvation lasts for a long time. Periodic egg p r o d u c t i o n b y t h e queen
may also play a role. No food had been given during the experimental period, except
w h e n observations were being made.
" older"
2 --
C o l o n y C B 1 (fig. 2)
Humber of workers
T A P ] HOMA
colony
CB
O old werkere
9 yeuag workers
,\
~4&s July
July
Au|oet
O~
Fig. 2. - - N u m b e r of old a n d young ~vorkers in colony CB. On each date theYe was an
observation of half an hour. 3 young 'workers h a t c h e d b e t w e e n July 4th and 8th,
9 others on July 14-15th. 6 old w o r k e r s were d r z w n back d o w n b e t w e e n the 15th
and 18th and m a n y others died.
Fig. 2. - - N o m b r e de vieilles ouvri~res et de jeunes ouvri~res dans la colonie CB. A chaque
j o u r c o r r e s p o n d une observation de 30 mn. 3 jeunes ouvri~res sont ndes e n t r e
le 4 et le 8 juillet, les 9 autres entre le 14 et le 15 juillet. 6 vieilles ouvri6res ont
dtd retir6es entre le 15 et le 18, et la plupart des autres sont mortes.
This colony 'was observed d u r i n g the same period as colony BX. It included one
queen, 14 old w o r k e r s and 3 young workers, 5 days old. Unfortunately m o s t of the old
w o r k e r s died during the course of the experiment (6 were removed bet~ween 15 and 18th
and the others died later). There w e r e no m o r e t h a n 3 old w o r k e r s left at the end.
The b r o o d had n o t changed very m u c h : 17 to 25 large larvae. The same data w e r e found
f o r young larvae and eggs in colonies BX and CB (220 to 170 for CB).
The two colonies w e r e collected in June 1973, before the experiment.
TROPHALLAXIS
3 ~- Colonies
T II
AND
POLYETHISM
IN TAPINOMA
23
to T VI
T h e s e five c o l o n i e s w e r e s t u d i e d a t t h e e n d o f t h e i r h i b e r n a t i o n p e r i o d in t h e
l a b o r a t o r y i n April. T h e r e f o r e , a t t h e b e g i n n i n g , t h e r e w e r e o n l y o l d e r w o r k e r s , b o r n
either during the summer time or the preceding autumn.
Six o b s e r v a t i o n s w e r e m a d e ,
BX
TAPINOMA
Fig. 3. - - Sociogram o f c o l o n y B X o n J u l y 27th. Q u e e n is m a r k e d n ~ 98. T r o p h a l l a x i s
a r e r e p r e s e n t e d like a r r o w s ' w h o s e h e a d p o i n t s t o w a r d r e c e i v i n g a n t o r larvae.
T h e i r t h i c k e n e s s is in r e l a t i o n w i t h t h e d u r a t i o n o f e x c h a n g e . T h e t i m e p a s s e d b y
f o r a g e r s to f e e d o n h o n e y o r Tenebrio is also r e p r e s e n t e d b y a n a r r o w .
0 to 50 s e c .....................................
50 to 100 sec.
100 to 200 sec.
M o r e t h a n 200 sec.
Fig. 3. - - Sociogramme de la c o l o n i e B X le 27 juillet. L a r e i n e p o r t e le n ~ 98. L e s t r o p h a l laxies s o n t r e p r 6 s e n t 6 e s p a r d e s fl~ches d o n t la p o i n t e e s t dirig~e v e r s la f o u r m i
o u les l a r v e s r e c e v e u s e s . L e u r 6 p a i s s e u r e s t p r o p o r t i o n n e l l e h la d u r 6 e de 1'6change.
Le t e m p s p a s s 6 d a n s le m i l i e u e x t 6 r i e u r s u r le m i e l o u le Tenebrio e s t a u s s i repr6s e n t 6 p a r u n e fl6che.
0 ~ 50 s e c ..................................
50 ~ 100 sec.
100 ~ 200 sec.
> 200 sec.
A. LENOIR
24
at the rate of one a week, after a period of starvation of 48 hours, at the time of the
emergence of the first workers born from the -~vintering brood. This ~vas in MayJune 1974. Each colony had only one queen (in colony T II the queen died during the
third ~veek). ~I1 5 colonies had a small brood, never more than 50 l a r v a e .
The death rate xvas very high among older workers during the six w e e k s
observation, ~vhile there ~vere almost no deaths among young workers. The rate of death
varies between 82 % for T V and 27 % for T I I I . That is an average of 70 % for old
hibernating workers and 8,5 % for young workers 3 or 4 ~weeks old.
Typical behaviours
The observed behaviours have been described in Lasius niger (LENOIR 1974) and are
illustrated by figures 3 and 4.
CB
X~tutI |It
/
I
I
I
I
[]
I
~
I
I
i
I
g
f
1
I/x"
I/
/
I
Fig. 4. - - Sociogram of colony CB on August Ist.
(see symbols on fig. 3)
Fig. 4. - - Sociogramme de la colonie CB le 1.3 aofit.
(voir symboles fig. 3)
Foragers search for food at the end of the tube and return to the group of sedentary
ants to give them the liquids stored in their crops.
It is interesting to note that some foragers s h o w personal preferences either for
insects or for honey. They feed on honey or on Tenebrio more than 70 '% of observations.
The proportion of foragers sho~ving a marked alimentary preference is variable according
TROPHALLAXIS AND POLYETHISM
IN TAPINOMA
25
to the different colonies 75 % for BX, 50 % for CB, 10 to 30 '% for T I I - T V I . This
shows that there might be a speeialisation in the alimentary behaviour of some foragers.
This specialisation should be studied in the field or in an artificial nest with a larger colony.
Nurses feed larvae. They receive food from foragers or receivers which act then
as an intermediary.
Some workers are inactives when the sharing of food is concerned.
RESULTS
1
--
Individual development
At t h e e n d of t h e o b s e r v a t i o n s a n t s w e r e c l a s s i f i e d a c c o r d i n g t o t h e %
number of times they showed a foraging behav~our.
M o r e t h a n 80 % o f t h e t e s t s : P e r m a n e n t Foragers P F
F r o m 20 to 80 % : I n t e r m i t t e n t Foragers I F
U n d e r 20 % : N u r s e s N
1 - P e r m a n e n t Foragers PF
Permanent foragers may rest passively, but they stand near the entrance
o r o u t s i d e t h e n e s t . I t is n o r m a l l y a p e r m a n e n t f o r a g e r w h i c h d i s c o v e r s t h e
f o o d s o u r c e , c o m e s b a c k to t h e n e s t a n d r e c r u i t s n e s t m a t e s w i t h a r e c r u i t m e n t display. It may then become an Inactive. Half these ants are never receivers.
T h e o t h e r s a r e r a r e l y so. T h e r a t i o o f t i m e s p e n t f e e d i n g ( r e g u r g i t a t i n g ) /
r e c e i v i n g ( F / R ) is a l w a y s m o r e t h a n 5, u s u a l l y a s l a r g e a s 50 a n d m a y b e
i n f i n i t e w h e n n o r e c e i v i n g o c c u r s ( T a b l e I). T h e y d o n o t t e n d t h e b r o o d a n d
very seldom lick larvae or carry them.
T h e s e a n t s a r e n o t v e r y n u m e r o u s : 28 % o l d w o r k e r s in CB-BX, a n d 3 1 %
w i n t e r i n g ' w o r k e r s in T I I - V I ( T a b l e I I A). T h e y a r e alxvays o l d . O n l y
o n e e x a m p l e of a y o u n g w o r k e r s b e h a v i n g l i k e a p e r m a n e n t f o r a g e r ( t w i c e
s u c c e s s i v e t i m e s a f t e r e m e r g e n c e , i.e. 100 % o f t h t w o o b s e r v a t i o n s f o r t h i s
a n t ) h a s b e e n f o u n d , b u t it w a s n o t a c t i v e a n d d i d n o t s h a r e food, ( T a b l e I I B *).
I n o u r c o l o n i e s P F r e p r e s e n t e d 10 to 15 % o f t h e w o r k e r p o p u l a t i o n .
2-
I n t e r m i t t e n t Foragers I F
T h e s e a r e w o r k e r s w h i c h c a n f o r a g e if n e c e s s a r y , f o r e x a m p l e , to f e e d
young workers or brood. They can be characterised by an intermediate %
n u m b e r of f o r a g i n g b e h a v i o u r : 20 t o 80 % o f t h e o b s e r v a t i o n s . T h e y a r e
n u m e r o u s in t h e c o l o n i e s : 57 % o f h i b e r n a t i n g a n t s in T I I - V I , 67 % of o l d
w o r k e r s in CB-BX ( T a b l e I I A). T h e y r e p r e s e n t e d 47 % o f t h e t o t a l
p o p u l a t i o n of o u r c o l o n i e s ( T a b l e I I B).
T h o s e I F a r e w h a t w e d e s c r i b e d a s " d i s p o s a b l e " ( a v a i l a b l e ) in a
p r e l i m i n a r y w o r k w i t h Lasius (1974).
T h e y a r e e i t h e r m o r e i n c l i n e d to
forage outside or more inclined to rest inside tending the brood, as necessary.
They may be classified in 2 categories :
26
A. L E N O I R
Table I. - - S u m m a r y of characteristics of individuals in CB - BX colonies during 10 days
observation samples. Activities connected ~vith feeding larvae are not sho~vn.
Tableau I. - - R6sum6 des caract6ristiques individuelles des ouvri~res des colonies CB
et BX, ~tablies apr6s 10 j o u r s d'observations. Les activit6s associ6es /~ l'61evage de
larves ne sont pas quantifi6es.
Colony
Worker
n~
PERMANENT FORAGERS
CB
22
00
BX
12
65
57
INTERMITTENT FORAGERS
CB
64
12"
56*
60*
BX
3
4
15
18
20
49
51
61
70
82
84
NURSES
CB
0*
7*
26*
33*
73*
91"
99*
90*
BX
X2
9*
13"
17"
24*
27*
49,*
55*
71"
77*
00"
%
foraging
F
R
F/R
100
100
100
100
90
9 530
3 920
5 830
7 540
1 210
0
440
0
0
150
30
40
20
20
50
70
30
30
40
30
60
50
50
70
40
880
200
530
140
60
440
0
810
200
1450
70
390
310
880
200
770
210
1 350
2 060
840
250
1400
1 410
1 000
560
30
580
380
380
610
1.1
0.95
0.4
0.06
0.07
1.8
0
0.57
0.2
2.6
2.3
0.7
0.8
2.3
0.3
10
0
0
10
0
0
0
0
10
0
0
0
0
0
0
0
0
0
0
240
40
20
80
490
0
50
90
0
0
30
0
0
760
10
0
0
0
0
3 110
1 880
1 160
3 110
2 110
1 140
1 440
1 140
800
860
1 740
1 750
1 500
1 030
250
310
970
1 270
1 610
0.07
0.02
0.01
0.02
0.2
0
0:03
0
0
0
0.02
0
0
0.7
0.004
0
0
0
0
% f o r a g i n g : % observations ~r
the
w o r k e r is forager.
F : total time feeding o t h e r w o r k e r or
queen (seconds).
R : total time receiving.
F/R: ratio Feeding/Receiving.
* : young ~vorker.
9
8
% f o r a g i n g : % des observations oh l'ouvri~re est pourvoyeuse.
F : t e m p s total pass6 h n o u r r i r d ' a u t r e s
ouvri6res ou la reine (secondes).
R : t e m p s total pass6 ~t recevoir de la
nourriture.
F / R : r a p p o r t activit6 de donneuse / actlvit6 de receveuse.
*: jeune ouvri~re.
TROPHALLAXIS A N D P O L Y E T H I S M I N TAPINOMA
27
a - S t r o n g l y i n c l i n e d to f o r a g i n g (50 to 80 % observations) (Table I)
These are ants w h i c h are observed m o s t l y outside the nest. They m a y
also be receivers, the ratio feeding/receiving is less than one (they receive
m o r e than they regurgite). They never or seldom lick brood. CB-BX w o r k e r s
3, 4, 51, 61, 70 and 82 were classified in this group (Table I).
b - N o t i n c l i n e d to 1oraging : these are foragers in less than 50 % observations.
Very often they leave the nest to forage only t o w a r d s the end of the period
of observation. Their activity is very v a r i a b l e : some are good donors. F / R
is in 7 cases out 9 (80 %) less than one for this g r o u p of workers.
The w o r k efficiency of foragers, m e a s u r e d by the total time during
which regurgitation occurs clearly s h o w s that p e r m a n e n t foragers are m u c h
m o r e active t h a n i n t e r m i t t e n t foragers.
3 - Nurses
These practically always r e m a i n inside the nest, n e a r the queen and
brood, or s t a n d on it, They lick larvae and eggs, they also move t h e m and
collect t h e m in piles. Nurses are very active receivers, They are rarely
foragers (see table I n ~ 0, 33 and X2 for 10 %) and if they are, they
regurgitate very little food. Thus F / R is a!ways smaller than 1, and very
often 0 or near (Table I). The n u r s e s somdtimes fed larvae d u r i n g the
observation period. This b e h a v i o u r takes place after a s h o r t period of
antennal stroking. During regurgitation the mandibles of the nurse are wide
open a r o u n d the head of the larvae. If the larvae are small, nurses grip
them between their forelegs to p u t the head of the larvae between their
mandibles.
4 - D e v e l o p m e n t o f b e h a v i o u r d e p e n d i n g on the age o f the a n t
Young ants, after hatching f r o m the pupae, are generally receivers only,
a n d in a few days they are able to feed brood. They b e c o m e nurses and
stand on b r o o d as has been described above. They are able to leave the
nest at 4-5 days of age and they b e c o m e foragers for one or two days.
W h e n they are one week old they m a y b e c o m e i n t e r m i t t e n t foragers, for
example 12, 56 and 60 in CB (Table I). This behaviour shows a great plasticity
and d e m o n s t r a t e s that the ethological g r o u p s I have d e t e r m i n e d ( p e r m a n e n t
foragers, i n t e r m i t t e n t foragers and nurses) provide a convenient classification.
that is not an absolute one, w h e r e all intermediaries exist.
A m o n g the older w o r k e r s very little difference can be noticed between
the 'wintering w o r k e r s and the w o r k e r s w h o s e age is unkno~vn but w h o are
definitely m o r e than 25 days old (Table I I A). We can thus consider that
a one m o n t h old ant is already old in the l a b o r a t o r y e n v i r o n m e n t . A m o n g
these individuals, a b o u t 30 % are p e r m a n e n t foragers, 60 to 70 % i n t e r m i t t e n t
foragers and 5 to 10 % nurses. I t m u s t be added that old nurses are very
b a d nurses as they do nothing, m o s t of the time, and very selddm regurgigate
A. LEIVOIR
28
T a b l e I1. - - F r e q u e n c y o f v a r i o u s e t h o l o g i c a l g r o u p s o f w o r k e r s
T a b l e a u II. - - F r 6 q u e n c e
ouvri~res.
des divers groupes
6thologiques
in r e l a t i o n w i t h
en relation
avec
l'~ge
age.
des
A - - A n t s of u n k n o w n a g e ( m o r e t h a n 25 d a y s o l d a t t h e b e g i n n i n g of t h e e x p e r i e n c e )
and wintering ants.
x2 = 0.008 n o t s i g n i f i c a n t ( w h e n g r o u p i n g I F a n d N)
~-~ 1.d.l., .05 = 3,84)
A-
F o u r r a i s d ' ~ g e i n c o n n u ( p l u s de 25 j o u r s a u d 6 b u t
hivernantes.
~'~ -- 0,008 n o n s i g n i f i c a t i f (en r e g r o u p a n t N et IF)
N
Total
1
5.5 %
18
100 %
5
27.8 %
12
66.7 %
Wintering
workers
Number
%
9
31
%
17
56.8 %
Mean
29.8 %
61.7 %
B
--
fourmis
IF
Number
%
--
et
PF
" Old " w o r k e r s
> 25 d a y s
B
de l ' e x p 6 r i e n c e )
3
10
%
29
100 %
8.5 %
B o t h old a n d w i n t e r i n g a n t s c o m p a r e d w i t h y o u n g a n t s .
x 2 = 30.157 P < .001 ( w h e n g r o u p i n g P F a n d IF)
(x2 1.d.l., .001 = 10.83)
* Young worker outside the nest but completly inactive.
x 2 a r e c a l c u l a t e d w i t h c o r r e c t i o n f o r c o n t i n u i t y o f Y a t e s (2 • 2 c o n t i n g e n c y t a b l e s ) .
C o m p a r a i s o n e n t r e f o u r m i s ~g6es o u h i v e r n a n t e s a v e c j e u n e s .
x -~ = 30,157 P < .001 (en r e g r o u p a n t P F et IF)
* J e u n e o u v r i 6 r e ~ l ' e x t 6 r i e u r d u nid, m a i s c o m p l ~ t e m e n t i n a c t i v e .
Les • s o n t c a l c u l 6 s a v e c la c o r r e c t i o n de c o n t i n u i t 6 d e Y a t e s ( t a b l e a u d e c o n t i n g e n c e 2 • 2).
PF
IF
N
Total
Old ( ~ 25 d a y s )
and wintering
workers
Number
%
14
29.8 %
29
61.7 %
4
8.5 %
47
100 %
Young workers
( ~ 30 d a y s )
Number
%
1"
1.7 %
21
35.6 %
37
62.7 %
59
100 %
14.1%
47.2 %
38.7 %
Mean
PF : P e r m a n e n t f o r a g e r
IF : Intermittent forager
N : Nurse
PF : P o u r v o y e u s e p e r m a n e n t e
IF : Pourvoyeuse intermittente
N : Nourrice
TROPHALLAXIS AND P O L Y E T H I S M I N TAPINOMA
29
to larvae or care for t h e m ; for e.g. X2 in colony BX (Table I) o r 76 in T V.
This last ant died during t h e 4th week.
A m o n g y o u n g w o r k e r s the results are quite different. 65 % are nurses
and 35 % intermittent foragers (Table I I B ) . The difference b e t w e e n y o u n g
and old w o r k e r s is very significant (P < 0.001 with X 2). Here we see a
p h e n o m e n o n well k n o w n a m o n g a n t s : y o u n g e r ants are nurses at first and
then they become foragers. A p r o b l e m a t t r a c t e d our a t t e n t i o n : are the
p e r m a n e n t foragers the oldest w o r k e r s ? At p r e s e n t we c a n n o t a n s w e r this
question because some individuals m i g h t b e c o m e p e r m a n e n t foragers at once
or r e m a i n intermittent only for a s h o r t while, according to the social
environment.
2 --
Influence
of the hatching
of young
workers
The hatching of young w o r k e r s creates new needs for food in the colony
since these new ants are active receivers. If the food supply is not sufficient
they m a y leave the group to search for food. The total trophallactic activity
of the colony BX was low on July 9th, 10th a n d l l t h in the absence of y o u n g
workers. It increased greatly after the hatchin~ of the y o u n g a n d r e m a i n e d
at a high level, more than 4 or 5 times the starting level.
Figure 5 represents on the abcissa the n u m b e r o f y o u n g w o r k e r s a n d on
the ordinate the trophallactic activity of the w h o l e colony. The g r a p h clearly
shows a positive linear correlation (r = 0.770, P < .01).
Table i i I indicates the levels oF trophallactic activity ( m e a s u r e d in
seconds) for either foragers or receivers for one observation. We have
r e p o r t e d the durations of regurgitation for foragers, and receiving for
receivers. The animals are classified in g r o u p s : feeble activity ( f r o m 0 to
59 see), m e d i u m activity (from 60 to 199), high activity ( f r o m 200 to 599 sec)
a n d very intense activity (600 sec that is m o r e than 10 minutes).
Results are presented as a function of the ratio Y / 0 : n u m b e r of Young
w o r k e r s / n u m b e r of Old workers.
Y/0 = 0 : There are no y o u n g w o r k e r s and with m o d e r a t e starvation
(24 or 48 h) the trophallactic activity is generally very low.
Y / O < 1 : The n u m b e r of y o u n g w o r k e r s is smaller than the n u m b e r of
old ,workers. The activity of the colony is g r e a t e r but ranks at a m e d i u m
level (between 800 to 1 600 seconds, and one at 4 000). The y o u n g w o r k e r s
are not foragers.
--
If 'we look at table I I I A, we can see that the trophallactic activity of the
y o u n g is very high. They are active receivers, b u t there is a great variability
b e t w e e n individuals: 27 % show a feeble activity, on the c o n t r a r y 53,9 %
(38,5 % + 15,4 %) show a high or very intense activity. Foraging is done by
old w o r k e r s (Table 3 B, 2nd line).
A. L E N O I R
30
Trophallactic
activity
of the colony (s)
3oo
!=486 + 217 x
r = 0,?70
lOOO
TAPINOMA
1
2
Y/o <~ 1
1
u
:> !
Humber of youngworkers
Fig. 5. - - Correlation between total trophallactic activity of the various colonies and the
number of young workers.
r = 0.770 is significant ~vith P <~ 0.01.
Fig. 5. - - Corr61ation entre l'activit6 trophallactique totale des colonies et le nombre des
jeunes ouvri~res.
r = 0.770 significatif avec P <~ 0.01.
--Y/O
> 1: Y o u n g w o r k e r s a r e m o r e n u m e r o u s t h a n o l d , w o r k e r s a n d
t h e a c t i v i t y of t h e c o l o n y is m u c h h i g h e r . I n 70 % of cases t h e t o t a l a c t i v i t y
of t h e c o l o n y is s u p e r i o r to 2 000 s e c o n d s (25 m i n u t e s of t r o p h a l l a x i s f o r
30 m i n u t e s of o b s e r v a t i o n , w h i c h is p o s s i b l e b e c a u s e t h e r e a r e s i m u l t a n e o u s
e x c h a n g e s ) . W e h a v e o b s e r v e d t h a t i n this s i t u a t i o n y o u n g w o r k e r s b e c o m e
f o r a g e r s . Y o u n g w o r k e r s a r e s o m e t i m e s o n l y 4-5 days old, m o r e o f t e n t h e y
a r e 10 o r 15 days. T h e y o u n g w o r k e r s w h i c h r e m a i n r e c e i v e r s a p p e a r m o r e
a c t i v e t h a n i n t h e case Y / 0 < 1 ( T a b l e I I I A) : 27 % a r e v e r y a c t i v e as a g a i n s t
o n l y 15 % w h e n t h e r e a r e n o y o u n g f o r a g e r s b u t t h e X2 o b t a i n e d is 0.358
w h i c h is n o t s i g n i f i c a n t . Foraging is thus the w o r k o[ both young and old
workers. T h e l a t t e r a r e m u c h m o r e e f f i c i e n t s i n c e i n 24 o b s e r v a t i o n s 40 %
old w o r k e r s are very intense donors ~ h e n only 8 % young w o r k e r s are
( T a b l e ! I I B, l i n e s 3 a n d 4 - X 2 s i g n i f i c a n t w i t h P < 0.02).
TROPHALLAXIS AND POLYETHISM
IN TAPINOMA
31
Table III. - - Trophallactic activity (in seconds) of the individuals of colonies T II - VI,
for one observation (half an hour).
Ants are foragers (feeding) or receivers.
3 A : time during w h i c h young w o r k e r s are receiving food f r o m foragers.
x2 = 0.358, 1 d.1. P > .90
3 B : time during w h i c h young o r old w o r k e r s are giving food to receivers. There
are 3 situations in relaiton w i t h the ration Y/O (young / old w o r k e r s ) : Y/O = 0
(only old w o r k e r s ) Y/O < 1 less young t h a n old, and Y/O > 1 m o r e young t h a n
old workers.
x2 b e t w e e n old w o r k e r s = 28.957, 3 d.l., P < .001
x~ b e t w e e n young and old w o r k e r s w h e n Y/O > 1 = 6.402, 1 d.l., P < .02
x2 are calculated w i t h two groups : feeble + m e d i u m a n d high + very intense
activity (correction for continuity of Yates has b e e n u s e d for 2 • 2 contingency
tables).
Tableau III. - - Activitd trophallactique (en secondes) des individus des colonies T II
T VI, p o u r une observation de 30 nan. Les fourmis s o n t douneuses o u receveuses:
3 A : Activit6 de receveuse des jeunes ouvri6res nourries p a r les pourvoyeuses.
x~ = 0,358 P > .90
3 B : Activit6 de douneuse des pourvoyeuses jeunes oll ~gdes suivant le r a p p o r t Y/O
( n o m b r e de jeunes ouvri~res / h o m b r e d'ouvri6res ~gdes).
Y/O = 0 : u n i q u e m e n t des vieilles ouvri6res
Y/O < 1 : m o i n s de jeunes ouvri~res que de vieilles
Y/O > 1 : plus de jeunes ouvri~res que de vieilles
x' e n t r e vieilles ouvri~res = 28,957 P < .001
x2 e n t r e jeunes et vieilles q u a n d Y/O > 1 = 6,402 P < .02
Les x2 sont calculds el1 r e g r o u p a n t faible + m o y e n n e activitd et f o r t e + trSs forte
activitd et en utilisant la correction de continuitd de Yates p o u r les tableaux de
contingence 2 • 2.
Workers
Situation
3A
60-199
200-599
> 600
Total
see.
see.
sec.
feeble
medium
high
very
intense
%
5
19.2 %
10
38.5 %
4
15.4 %
26
100 %
Number
%
Y/O > 1 18
32.7 %
2
3.6 %
20
36.4 %
15
27.2 %
55
I00 %
Number
%
Y/O < 1
Young receivers
0-59
7
27
see.
3B
old
Y/O = 0
41
78.8 %
7
13.5 %
2
3.8 %
2
3.8 %
52
I00 %
Number
%
Foragers
old
Y/O < I
27
50.9 %
10
18.9 %
12
22.6 %
4
7.5 %
53
100 %
Number
%
young
Y/O > 1 27
56.25%
6
12.5 %
11
22.9 %
4
8.3 %
48
100 %
Number
%
old
9
28.1%
3
9.4 %
7
21.9 %
13
40.6 '%
32
100 %
Number
%
(giving)
I t i s p o s s i b l e t o c o n c l u d e t h a t w h e n Y / 0 < 1 t h e r e a r e n o y o u n g foragers.
W e h a v e n o t e d o n l y o n e e x c e p t i o n d u r i n g 26 o b s e r v a t i o n s (4 % ) .
On the
o t h e r h a n d , x v h e n Y / 0 > 1, young w o r k e r s b e c o m e foragers a f t e r a o n e d a y
s t a r v a t i o n p e r i o d ( n o e x c e p t i o n d u r i n g 13 o b s e r v a t i o n s ) .
This phenomenon
A. LENOIR
32
is p r o b a b l y t e m p o r a r y a n d r e v e r s i b l e : y o u n g w o r k e r s "which h a v e l e f t t h e
n e s t to f o r a g e b e c o m e n u r s e s a g a i n a f t e r a f e w d a y s (as in CB). T h e f o r a g i n g
b e h a v i o u r is i n f l u e n c e d b y s o c i a l p r e s s u r e s : w h e n t h e r e a r e m a n y " w o r k e r s
o r v e r y f e w o l d f o r a g e r s t h e r e is a c h a n g e i n t h e b e h a v i o u r o f y o u n g
i n d i v i d u a l s . T h i s p h e n o m e n o n is a social regulation of behaviour.
3 -- Effect of the forager mortality
I n t h e c o l o n y B X , t h e f o o d r e q u i r e m e n t s w e r e v e r y h i g h d u e to t h e
p r e s e n c e o f y o u n g w o r k e r s -which w e r e v e r y a c t i v e r e c e i v e r s in t h e f i r s t d a y s
after emergence.
T h e n e e d s "were e a s i l y s u p p l i e d b y t h e p o o l o f o l d
intermittent foragers which efficiently furnished the nest. The total number
o f f o r a g e r s p a s s e d f r o m 4 t o a m a x i m u m o f 17 ( a l t o l d - w o r k e r s e x c e p t o n e ,
and 2 young ~vorkers).
T h i s p h e n o m e n o n is s h o w n o n f i g u r e 6 w h i c h
Trophalfactlc activity ol the colony [s)
T A P] N 0 M A
40G
300(
9r U
200~
9
,~
;
T
8
1 :
0,126
100<
i
l
[ , I
I
2
i 4
6
Tr ouhiliactlc activity Of the colony (s}
Number of foragers-
4000
3000
ex
2000
t.=0754
1000.
y--,86 -(. 2 6 i X
,i
I
1
2
I
!
4
I
~
6
I
I
8
I
I
tO
i
I
t
I
t
T2
14
Number of foragers
Fig. 6 . - Correlation between total trophallactic activity and number of foragers in
colonies CB and BX.
CB : r no significant.
BX : r significant ~vith P < 0.01.
* young ,,vorkers forage (see text).
Fig. 6. - - Corr61ation entre l'activit6 trophallactique totale et le nombre de pourvoyeuses
darts Ies colonies CB et BX.
CB : r non significatif.
BX : r = 0.754 significatif avec P < 0.01.
* : jeunes ouvri~res pourvoyeuses (volt texte).
TROPHALLAXIS AND P O L Y E T H I S M I N TAPINOMA
33
r e p r e s e n t s the t o t a l trophallactic activity of the colony (in s e c o n d s ) as a
function on the n u m b e r of foragers. There is a v e r y significant c o r r e l a t i o n
(r = 0.754, P < .01).
F o r the colony CB w e m u s t go b a c k to Figure 2 : m o s t of the old
foragers died a f t e r a few days. T h e r e w a s one p e r m a n e n t f o r a g e r w h i c h died
w h e n y o u n g w o r k e r s e m e r g e d f r o m the pupae. 6 old w o r k e r s w e r e r e m o v e d
on July 18th, 4 others in the following days. I n d i v i d u a l 00 a n d 4 b e c o m e
p e r m a n e n t f o r a g e r s and 22 soon joined them. The linear f u n c t i o n b e t w e e n
trophallactic activity a n d foraging w a s not f o u n d again in colony CB
(r = 0.126). I t w a s even o b s e r v e d t h a t during the 10th day, 2 y o u n g w o r k e r s
w e n t foraging a n d 5 on the 18 th day (fig. 6). 2 y o u n g w o r k e r s only w e n t
out on the 19th day and then the p h e n o m e n o n s t o p p e d (see p a r a g r a p h on Y/0).
I t w a s concluded t h a t only old workers can quickly become permanent
foragers. Y o u n g w o r k e r s are able to help t e m p o r a r e l y in the s e a r c h for
food b u t c a n n o t i m m e d i a t l y t a k e the place of p e r m a n e n t f o r a g e r s if they
disappear.
4 --
Discussion
and
conclusions
I - Age polyethism in Tapinoma
The s t r u c t u r e of the society a n d division of l a b o u r c o r r e s p o n d s to k n o w n
models. Differences in b e h a v i o u r depend on the age of the a n t s : young
ants are n u r s e s a n d older ones foragers:
Y o u n g e r w o r k e r s usually r e m a i n motionless on the brood, n e a r the queen.
W h e n t h e i r p i g m e n t a t i o n is c o m p l e t e d (in two or t h r e e days) t h e y b e c o m e
very active r e c e i v e r s a n d feed larvae. W h e n they are 10-15 days old they are
good nurses. The m a t u r a t i o n o f ' t h e d o n o r b e h a v i o u r in r e l a t i o n w i t h o t h e r
w o r k e r s is very slow a n d even if they b e c o m e f o r a g e r s p r e m a t u r e l y their
activity is always l o w e r t h a n the activity of older foragers. This f a c t suggests
t h a t r e g u r g i t a t i o n is not the s a m e f o r a w o r k e r as f o r a larvae y o u n g e r
w o r k e r s are good donors to larvae a n d b a d d o n o r s to o t h e r w o r k e r s .
One r e a s o n could be that in young w o r k e r s the glands (esp. p o s t p h a r y n g e a l
glands) are still active a n d there m i g h t be t r a n s f e r r e d m o r e g l a n d u l a r
secretions r a t h e r t h a n r e g u r g i t a t e d c r o p content. NAARMAN(1963) on Formica
and MARKIN (1970) on Iridomyrmex humilis h a v e s h o w n t h a t s u b s t a n t i a l
a m o u n t s of g l a n d u l a r secretion are t r a n s f e r r e d w i t h r e g u r g i t a t e d m a t e r i a l s to
queens a n d small larvae. BUSCHINGERa n d KLOFT (1973) could find out similar
situations in colonies of Monomorium pharaonis (L.). Thus y o u n g w o r k e r s
tending the queen (s) as " H o f s t a a t " serve like a screen against p o i s e n o u s
baits t r a n s f e r r e d b y regurgitation of crop content.
From the 3rd or 4th week (or earlier according to social p r e s s u r e as will
be discussed later) a11 the w o r k e r s f o r m a pool of available individuals doing
34
A. LENOIR
n o t h i n g for m o s t of the time. They a r e able to feed the brood, to f o r a g e o r
both. We h a v e called these wol;kers i n t e r m i t t e n t foragers. This p h e n o m e n o n
has a l r e a d y b e e n o b s e r v e d in Lasius niger (LENOIR 1974) a n d SUDD (1967 p. 161)
m e n t i o n s this point. I t is not k n o w n if these w o r k e r s " doing n o t h i n g " a r e
also f o u n d in the field w h e r e t h e y m i g h t b e doing t a s k s i m p o s s i b l e in a n
artificial nest. S u d d thinks t h a t this is a general p h e n o m e n o n as it is also
o r d i n a r i l y o b s e r v e d in bee hives.
--After
t h a t s o m e individuals b e c o m e p e r m a n e n t foragers.
They are
p r o b a b l y the oldest ants ( p a r t i c u l a r y o v e r w i n t e r i n g ones). These w o r k e r s
are n o t n u m e r o u s b u t they are very b u s y a n d s u p p l y m o s t of the colony food.
T h e y m a y specialise in sweet diet (honey) w h i c h they quickly s h a r e w h e r e a s
t e m p o r a r y f o r a g e r s often p r e f e r a m e a t diet (Tenebrio) k e e p i n g tile
h a e m o l y m p h i n store in their crop. SCHNEIDER (1972) p o i n t e d o u t t h a t in
Formica polyctena large quantities of f o o d t a k e n u p b y s o m e individuals m a y
r e m a i n in the crop, unregurgitated. This k i n d of specialization has a l r e a d y
b e e n studied in this s p e c i e s : KILL (1934) has o b s e r v e d t h a t s o m e individuals
a r e h u n t e r s a n d others collect honeydew.
OTTO (1958) d i s c o v e r e d t h a t
h o n e y d e w collectors are smaller t h a n h u n t e r s . HORSTMANN(1973) c o n f i r m e d
the existence of these specialists in the foraging area. This is also f o u n d in
Camponotus w h e r e w o r k e r s collecting n e c t a r a r e l a r g e r t h a n honeyde~v
collectors (GOTWALD 1968). I n o u r e x p e r i m e n t a l foundations, w o r k e r s are all
s m a l l individuals, a n d specialization m i g h t be linked w i t h age only ( b u t the
size of w o r k e r s has not b e e n m e a s u r e d ) . I t is difficult to c o m p a r e age
p o l y e t h i s m in Tapinoma erraticum w i t h the results of OTTO (1958) in Formica
polyctena as w e only o b s e r v e d small colonies w h e r e the passage f r o m one
t a s k to a n o t h e r is certainly very easy. The t e m p e r a t u r e of o u r nests (25~
p r o b a b l y a c c e l e r a t e d the r a t e of d e v e l o p m e n t .
Otto has p o i n t e d out t h a t the p a s s a g e f r o m inside the nest to outside
the nest is a f f e c t e d a f t e r the 45th day. I n o u r t u b e nests t h e r e is no definite
b o r d e line b e t w e e n those 2 regions, Tapinoma w o r k e r s o f t e n stay n e a r the
place w h e r e the queen and the b r o o d are. We have chosen the tiine w h e n
the w o r k e r s begin to c o m e outside the b r o o d a r e a a n d explore the e x t r e m i t y
of the t u b e w h e r e food is g i v e n ; they b e c o m e i n t e r m i t t e n t foragers, a n d
c a n b e c o m p a r e d w i t h Formica w o r k e r s doing outside tasks.
I n the genus Myrmica 3 species h a v e b e e n studied : Myrmica scabrinodis
a n d Myrmica ruginodis (WEIR 1958 a, b) a n d Myrmica rubra (BRIAN 1974).
I n Myrmica it h a s b e e n k n o w n for a long t i m e t h a t pale y o u n g w o r k e r s are
n u r s e s a n d t h a t they change into f o r a g e r s as t h e y d a r k e n a n d age (EHRHARDT
1931). Weir recognised three w o r k e r j o b s : nurses, d o m e s t i c s a n d foragers.
The % t i m e s p e n t b y w o r k e r s on b r o o d , n e a r b r o o d a n d a w a y f r o m brood,
the b r o o d r e a r i n g efficiency a n d nest-building capacities xvere observed.
B r i a n h a s classified w o r k e r s , on the basis of t i m e s p e n t o n / o f f b r o o d into
n u r s e s (>t 2), f o r a g e r s (~< 0.5) a n d i n t e r m e d i a t e s ( < 2, > 0.5). Activities
T R O P H A L L A X I S AND P O L Y E T H I S M I N T A P I N O M A
35
c o n n e c t e d w i t h b r o o d are : standing on b r o o d , g r o o m i n g a n d f e e d i n g small,
w o r k e r - b i a i s e d larvae, a n d chewing prey. Activities c o n n e c t e d w i t h foraging
are standing a w a y f r o m brood, exploring a n d collecting food. Pale w o r k e r s
usually n u r s e a n d d a r k one usually forage o r b e h a v e as i n t e r m e d i a t e s , b u t
t h e r e are exceptions. B r i a n thinks t h a t i n t e r m e d i a t e s s e e m to c o r r e s p o n d
w i t h domestic. Weir r e g a r d e d the d o m e s t i c s as a mobile r e s e r v e of foragers.
I t is interesting to see t h a t o u r conclusions are similar, for t w o o t h e r species
Lasius niger (LENOIR 1974), a n d T a p i n o m a erraticum in this study. We
p r o p o s e to call d o m e s t i c s or i n t e r m e d i a t e s , i n t e r m i t t e n t foragers b e c a u s e
t h e y r e p r e s e n t a pool of available individuals.
2 - Individual d e v e l o p m e n t and interindividual variation
OTTO (I958) has already p o i n t e d out t h a t s o m e Formica p o l y c t e n a 'workers
pass to t h e outside t a s k s w i t h o u t feeding the brood, w h e n s o m e o t h e r s on
the c o n t r a r y did not leave the nest b e f o r e they w e r e 80 days old. Such
a n interindividual v a r i a t i o n has also b e e n o b s e r v e d in this studies, b o t h
f o r the activity a n d for individual d e v e l o p m e n t .
The activity of ants of the s a m e age o r of the s a m e class of age w h e n it
is not k n o w n exactly is v e r y variable. S o m e y o u n g w o r k e r s t e n d the larvae
(feed, lick a n d displace) w h e n others r a r e l y o r ' n e v e r do so a n d j u s t stay on
the brood, they are all called nurses in as m u c h as they do n o t c o m e out
of the nest.
Variability is also v e r y i m p o r t a n t .between w o r k e r s f o r t r o p h a l l a c t i c
activity as has b e e n s h o w n in T a b l e I I I . The h e t e r o g e n e i t y of r e s p o n s e
b e t w e e n individuals of a g r o u p h a s recently b e e n d e m o n s t r a t e d in the
olfactive i n t e r a t t r a c t i o n (VERRON 1973) a n d l o c o m o t o r activity (VERRON 1974)
f o r Lasius niger, a n d in the car.rying b r o o d (MEtlDEC 1973 b) f o r T a p i n o m a
erraticum.
I n d i v i d u a l d e v e l o p m e n t is linked to age, but, in a g r o u p of w o r k e r s of
the s a m e age, s o m e c o m e outside the nest early, others are n u r s e s for a
longer time. F o r e x a m p l e in colony CB, 2 w o r k e r s h a t c h e d on "July 4th, n ~ 12
b e c o m e i n t e r m i t t e n t f o r a g e r on 18th a n d n ~ 56 only on 27th (23 days old).
Of the 9 w o r k e r s h a t c h e d on July 14-15th, 3 b e c o m e i n t e r m i t t e n t foragers
on 27th a n d 6 w e r e still nurses on August 2nd. I n colony T I V 3 w o r k e r s ,
only 4-5 days old, b e c o m e i n t e r m i t t e n t foragers. The d u r a t i o n of the nursing
stage is v e r y variable, f r o m 4-5 days to 2-3 w e e k s in general, a n d s o m e t i m e s
m o r e ( u n d e r l a b o r a t o r y conditions). This variability is influenced b y social
regulation.
3 - Social regulation
This is v e r y i m p o r t a n t , even in a small colony. I t o c c u r s w h e n the
f o r a g e r s die o r w h e n t h e r e are not enough older w o r k e r s to feed the
colony b y the early d e v e l o p m e n t of foraging a n d d o n o r b e h a v i o u r in y o u n g
36
A. L E N O I R
a n t s . W h e n t h e r a t i o Y o u n g / O l d w o r k e r s is m o r e t h a n one, s o m e y o u n g
w o r k e r s m a y leave t h e n e s t a n d b e c o m e i n t e r m i t t e n t f o r a g e r s ( c o l o n i e s T I I VI). T h i s c h a n g e of b e h a v i o u r is s o m e t i m e s r e v e r s i b l e : a f t e r a f e w d a y s or
one day only, y o u n g workers ceased their task a n d become nurses a g a i n w h e n
e n o u g h f o o d w a s p r o v i d e d ( c o l o n i e s CB-BX).
T h e a c c e l e r a t i o n of t h e d e v e l o p m e n t of the b e h a v i o u r of y o u n g a u o r k e r
h a s a l r e a d y b e e n r e p o r t e d xvhen t h e r e a r e n o o l d w o r k e r s b y EHRHARDT (1931)
i n M a n i c a rubida, DOBRZANSKA (1959) i n F o r m i c a sanguinea, CHAUVIN (1969)
i n F o r m i c a p o l y c t e n a , a n d w e h a v e o f t e n o b s e r v e d it i n L a s i u s n i g e r ( w o r k i n
p r o g r e s s ) . G r o u p s of y o u n g w o r k e r s of t h e s a m e age v e r y q u i c k l y o r g a n i s e
t h e m s e l v e s i n t o n u r s e s a n d f o r a g e r s . T h e p r e s e n c e of a few o l d e r w o r k e r s
is s u f f i c i e n t to p r e v e n t t h e m o d i f i c a t i o n of b e h a v i o u r o r a t l e a s t t o l i m i t it,
as w e see i n t h e s e s t u d i e s . T h i s is p e r h a p s c o n n e c t e d w i t h t h e i n f l u e n c e of
o l d e r w o r k e r s o n t h e d e v e l o p m e n t of o v a r i e s of y o u n g w o r k e r s . OTTO (1958)
e s t a b l i s h e d i n F o r m i c a p o l y c t e n a t h a t o v a r i e s c o m e to m a t u r i t y f r o m t h e 10th
t o t h e 30th d a y a n d t h e n d e g e n e r a t e , w h e n t h e a n t s leave t h e n e s t . W o r k e r s
which were kept w i t h o u t older ones did not develope ripe ovaries.
The
p r e s e n c e of o l d e r w o r k e r s i n f l u e n c e s t h e o v a r i a n a c t i v i t y of t h e y o u n g w h i c h
b e c o m e foragers w h e n the ovaries degenerate. If there are no older ~vorkers
t h e r e is n o o v a r i a n d e v e l o p m e n t a n d s o m e w o r k e r s m i g h t b e c o m e f o r a g e r s
directly.
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