MSc

Termites (Insecta: Isoptera) are eusocial insects living in a highly
organised and small to large extent of communities in different ecosystems. A
termite colony has morphologically and functionally distinct caste system which
includes functional reproductives / ‘royal pair’ of king and queen, sterile soldier
and worker castes and the immature stages or nymphs along with other inquiline
species of organisms.
The present investigation on the ‘Biodiversity of the termite (Isoptera)
fauna in crop environments’ was undertaken in a few selected crop environments
in the instructional farm area of the College of Horticulture at Vellanikkara
during 2010-11. The main objectives of the study were to identify the composition
of the termite fauna up to the family/ genus level in mango, cashew, cocoa and
coconut crop environments, elucidation of their feeding nature, behaviour,
association and their mound forming characteristics and to prepare a primary
termite colonisation map in the selected plantation and orchard systems in this
tract.
A preliminary survey was conducted by transect walk throughout the
instructional farm area of the campus to select the termite prone plantation and
orchard systems for the study. The soldier castes of termites were sampled from a
unit area of 200 sq. m each from different crop environments and kept under
preservation. The soldier castes from earthen mounds were collected by a special
“Glue trap technique” designed and standardised for the purpose by the author
through 20 numbers of encounter samplings per unit area of observation. The
soldier castes were identified based on the standard keys (Bose, 1984; Roonwal
and Chhotani, 1961 and Sornnuwat et al., 2004) with reference to their
characteristics of head capsule, mandibles and pronotum. The diversity pattern of
termite genera in different agro ecosystems in Vellanikkara were assessed by
using various diversity indices. Based on these information, a preliminary termite
colonisation map was prepared by depicting the distribution, spread and
colonisation density of the identified termite genera in the selected crop
environments. The morphometry of the aerial mounds along with some of the
physical properties of the termitarial soils were also determined. The influence of
temperature and humidity on the termite colonisation process was also observed.
A total of nine termite genera under two families were identified in
Vellanikkara. Out of this, seven termite genera viz., Odontotermes,
Procapritermes, Dicuspiditermes, Homallotermes, Microtermes, Microcerotermes
and Nasutitermes were under the family Termitidae, while, Heterotermes and
Coptotermes were coming under the family Rhinotermitidae. Odontotermes was
found to be the most dominant genus in all the selected crop environments
accounting for about 62.03 per cent of the total genera identified from the
Vellanikkara tract. The least present genus was Coptotermes which constituted
only 1.27 per cent among all the identified genera. Based on the distribution,
spread and colonisation density, a primary termite faunal distribution map was
prepared in selected systems.
The genera viz., Odontotermes, Microcerotermes, Nasutitermes,
Heterotermes and Coptotermes were identified as wood feeders while,
Procapritermes, Dicuspiditermes, Homallotermes and Microtermes were
observed as soil/ humus feeders.
Various diversity indices were worked out for the faunal distribution of the
termites in this tract to find out their relative dominance, spread and evenness in
its distribution. The genus richness of the termite genera at Vellanikkara tract was
found to be 9 and the value of Simpson- Yule diversity Index (D) was found to be
2.44 and that of the Shannon- Weiner Diversity Index (H) was found to be 1.38.
The Evenness Index (E) when worked out was found to be 0.63 and the Berger
Parker Dominance Index (d) for the genus Odontotermes was found to be 0.62.
When different systems were compared, the genus richness was found to
be the highest in cashew plantation with a value of 6 while, the mango, cocoa and
coconut systems were having a value of 3 only. The D value of 4.65, H value of
1.64 and the E value of 0.92 was found to be highest in cashew plantation, which
indicated that the cashew system was supporting maximum generic diversity of
the termites with a more evenness in its distribution. The values of these indices
were found to be the lowest in cocoa which indicated that the cocoa based systems
was having the lowest diversity and very low evenness in the distribution of
various genera. The mango and coconut based systems were having intermediate
values with these indices. The “d” value indicating the dominance of the
particular termite genus viz., Odontotermes was found to be the highest in the
cocoa based system with a value of 0.75 and the least in cashew with a value of
0.33.
The mean density of the mounds in mango, cashew and cocoa based
systems varied only slightly indicating their relative uniform distribution. The
mean number of buttresses or young mounds ranged from 5- 7 per mound
formation. The mean height of the mounds present in all the three systems showed
only very slight variation, but there was difference in the mean basal
circumference of the mounds in the three systems. Accordingly, the mean external
volume (above ground) of the mounds in cubic centimetres was found to be the
highest in cocoa and least in mango based systems. Statistical analysis of the data
revealed that there was no significant difference in the relative per cent increase in
the external volume of the mounds in cocoa plantation, while, there was
significant difference in the change of volume as observed in July’10- Aug’10 and
Jan’11- Feb’11 in mango and cashew based systems implicating the degree and
period of termite activity within the termitaria.
Regarding the physical properties, the soil colour of the mounds and of the
adjacent soil during the wet season was found to be dark reddish brown as per the
visual comparison through the standard Munsell colour chart. However, the colour
of the mound soil and of the adjacent soil during the dry season was found to be
brown and dark reddish brown, respectively. Particle size distribution in the soil
samples of the termitarial mounds from the three crop environments viz., mango,
cashew and cocoa based systems showed no significant difference among them.
But within the same crop systems, the clay content of the mound soil was
observed to be increasing by 10-12 per cent while, the sand content was
decreasing by about 10-15 per cent. There was not much variation in silt content
between the mound soil and adjacent soil. However, gravel was found to be
totally absent in the mound soil as compared to the adjacent soils.
When the temperature and relative humidity were recorded and compared
between inside and outside of the mounds, it was found out that both temperature
and relative humidity inside the mounds were significantly higher than that of the
external environment which prove that the termites have to essentially maintain
their homoeostasis with respect to the internal ambience for their survival and
other activities irrespective of the external ambience.
To conclude, the study reveals that the Vellanikkara tract is diverse in the
faunal distribution of termites with nine genera under two families and five
subfamilies with a dominant mound dwelling genus viz., Odontotermes in all the
crop environments of mango, cashew, cocoa and coconut systems. The
identification of the termite genera can very well be undertaken based on head
capsule and mandibular characteristics of the soldier caste by collecting them
easily by the newly designed method of “glue trap technique” by the author. The
termites colonize these systems without any major environmental or resource
degradation and thereby their role may be further investigated for the eco
restoration and conservation activities.