Importance of Formic Acid in Various Ethological States of Oecophylla smaragdina (Fabricius) 55
Results and Discussion
The observation on an exposed nest revealed that
the polymorphic colony of Oecophylla smarag-
dina possessed winged males, winged females
and three types of apterous workers (major, inter-
mediate and minor). FA is present in the poison
gland seen in association with Dufour’s gland in
workers (Fig. 1 ).
Among different individuals of the colony,
worker castes possessed high content of FA but
the winged males and females possessed negli-
gible quantities of FA. Among the worker castes,
minor workers possessed very high content of FA
followed by intermediate and major workers. The
major share of FA of workers was in abdomen
but the head and thorax possessed negligibly low
content of FA. Head and thorax after repeated
washing in distilled water and subsequent esti-
mation of FA did not show any detectable quan-
tity. The developing stages such as larvae and
pupae had no traces of FA in their body (Table 1 ).
On estimating FA content of worker castes at
different time intervals, it was found that FA of
major workers showed a strong periodicity with
physical activity. In major workers, FA during
afternoon (1 pm) showed a 50 % elevation com-
pared with the contents at morning (7 am). The
amount of FA gradually decreased at evening
and reached at its initial amount (the content
at morning) at night. The intermediate workers
also showed a slight but significant elevation of
FA content at 1 pm but its fluctuation were not
prominent as in major worker (Fig. 2 ). The minor
workers did not show any significant fluctuation
in the content of FA during different time inter-
vals of 24 h cycle.
When the major workers were allowed to bite
on the body, most of them remained detached
from the site of bite and searched for new sites.
After three or four bites, each lasting less than
15 s, they did not show any interest in biting at
a new site. A small proportion of ants (less than
25 %) did not detached from the site of bite
and continued on biting for more than 25 min
and after that they became immobile. During the
course of bite, they intermittently constricted the
mandibles with a simultaneous spray of FA and
it was accomplished through forward bend of
abdomen. These ants when forcefully detachedTable 1 The content of formic acid in different individu-
als in O. smaragdina
Individuals Formic acid
Workers Major 9.7 ± 0.7
Intermediate 29.1 ± 2.3
Minor 43.7 ± 3.1
Major worker Head 0.63 ± 0.02
Thorax 0.1 1 ± 0.01
Abdomen 42.9 ± 3.6
Winged forms Males 1.27 ± 0.12
Females 1.23 ± 0.1 1
Developing forms Larva Nil
Pupa Nil
All values are mean ± SD of 4 observations ( n = 4). Val-
ues are expressed in mg/gm fresh tissue
indicates the values are significantly different. ( p < 0.01)
Fig. 2 Fluctuations of FA content of different worker
castes of O. smaragdina in 24 h cycle (All values are
mean ± SD, n = 4. Values are expressed in mg/gm fresh tis-
sue, Elevation of FA content in major and intermediates at
1 pm was significantly different from FA content at morn-
ing. p < 0.01, n = 4)Fig. 1 1 Poison gland, 2 Dufour’s gland