A detailed study of the nests, population ecology and developmental pathways of the fungus growing termites with hypogeal nesting system was carried out over a period of 5 years (1986-1990). Greater part of the studies concerned Odontotermes obesus (Rambur) the results are presented under chapters I, II and III.
NEST: Two elevated strips of the land between grassy plots (Ridge I) and between cultivated land (Ridge II) were selected for estimating nest density.
Nest density of the fungus growing subterranean termites belonging to the. genus Odontotermes was estimated as 60.69/hectare and 50.58/hectare on ridge I and ridge II, respectively. On ridge I, O obesus was abundant. On ridge II, O. gurdaspurensis Holmgren and Holmgren and O.guptai Roonwal and Bose were equally abundant (50% each).
Odontotermes Obesus was recorded making mounds as well as hypogeal nests in Lahore. A total of 12 hypogeal nests were opened. The nest consisted of a number of chambers. The circumference of the chambers in different nests ranged between 9 cm and 108 cm. The royal chamber was located 35 cm 75 cm below ground level and its circumference varied between 108 cm and 266 cm in different nests. Royal chambers were provided with vertical shafts filled with fungus combs, except in Nest No. 12, in which no shafts were present. The total number of chambers in the 12 hypogeal nests varied from 38-82, whereas, fungus occupied chambers numbered 5-45 in different nests.
Occurrence of fungus occupied chambers in different seasons was also recorded. Nests opened during summer months had significantly more (P<0.05) fungus occupied chambers than those opened in winter, fall and spring.
Odontotermes obesus-affected soils (nest soil and galleries soil) generally had significantly higher (P<0.05) amounts of total soluble salts (%). HCO3, CL. Na+,K+ and Phosphorus than the adjacent soil The pH and amounts of Ca++ Mg++ and Nitrogen was however not significantly different (P<0.05) in the nest, galleries and adjacent soil. The amounts of micronutrients (Zn, Cu, Fe, Mn) are higher in galleries soil and adjacent soil than those in the nest soil.
As regards microclimate of the nest,O obesus maintained 20.0°C-28.7°C temperature in the fungus occupied chambers, whereas in unoccupied chambers temperature slightly fluctuated with the atmospheric temperature. During winter, temperature in fungus occupied chambers was 1.3°C-6.8°C higher than the ambient temperature, whereas in spring the temperature of the fungus occupied chambers and unoccupied chambers was not much different from the ambient temperature.
Relative humidity inside the fungus occupied chambers of the nests ranged between 76.2% and 88.3% and was significantly higher (P<0.05) than the atmospheric humidity.
Comparison of the different nests was also made taking into consideration morphometric variations detected in the soldiers of 0 obesus collected from different nests. There was significant variance (P<0.05) component for all the parameters studied for soldier caste collected from different nests. Relationships of different parameters with one another was also studied.
POPULATION ECOLOGY The population density of 0 obesus in hypogeal nests estimated by volumetric method fluctuated between 2,188 and 1,65,749 individuals per nest (547/m2 to 41,437/m2).
Diurnal and seasonal fluctuations in population density/foraging activity of subterranean termites in a specified grassland plot were also studied. Termite foraging population varied during morning, noon and evening times in response to atmospheric temperature and relative humidity variations. Extreme temperature conditions inhibited foraging activity. At low temperature conditions (7.5°C - 18.0°C) during November to March, poor termite activity was noticed in the field at morning time and termite foraged more at noon time during these months. During summer months when atmospheric temperature at (35.0°C - 40.5°C), there was noon poor termite activity at noon time and higher termite population was recorded at morning time when atmospheric temperature ranged 19.5°C-31.0°C.
Termite population collected during morning time showed increase with an increase in atmospheric temperature and the relationship was positive and significant (Regression Co-efficient 2.95, (P<0.05) Similar results were obtained with atmospheric humidity at the morning time.
There was decrease in termite population /foraging .with increase in atmospheric temperature at noon time. The relationship between the two variants was negative and non-significant (Regression co-efficient -0.057, P<0.05). The relationship between relative humidity and termite population at noon' time was positive but non-significant (Regression co-efficient 0.29, P>0.05).
The populations density/ foraging activity upto a depth of 45 cm during the summer evenings was found to be less than in the evenings of winter months due to higher temperature, resulting into downward movement of the termites. Therefore, the relationship between tile two variables was negative but non-significant (Regression co-efficient -0.186; P<0.05). The relationship between relative humidity and number of termites was positive but non-significant (Regression co-efficient 0.281, P>0.05)
Vertical distribution of termites showed that there was higher termite population / foraging activity in upper 15 cm layer of the soil than at lower depths (i.e.30 cm and 45 cm). Analysis of variance showed significant differences in termite populations at different depths (F.,7.97, df. 2:33; P<0.05).
In addition to the studies carried out on termite population density/foraging activity in the grassland field, population density/foraging activity in agricultural crops was also studied.
Biomass of the termite populations recovered different subterranean nests of 0.obesus ranged between 8.12 gm and 404.85 gm (i.e. 2.03 gm/m2 and 101.21 gm/m2).Maximum live biomass was recovered for nest No. 9. Biomass proportions (%)of various castes were: soldiers, 1.18%-22.43%; workers, 7.97%-92.11% and undifferentiated nymphs, 0.00-90.85%.
Caste composition of the 12 subterranean nests of O, obesus was studied. The proportions of soldiers, workers and nymphs varied in differer1t months of the year. During March, the workers constituted 90.51 of the total population.
Later in the year i.e., in the month of November the proportions of soldiers increased to 27.0%. and in the month of April the nymphs were most abundant (94.9%).
Feeding preferences of three fungus growing termite species were studied. Cedrus deodara was found highly resistant to O, gurdaspurensis whereas Pinus gerardiana was highly resistant to O. guptai and O, obesus,
Monthly variations in feeding preferences of 0, obesus were also studied. The analysis of variance of the 12 months data revealed that there were significant differences (P<0.05) in the feeding on different woods, but the amount of woods consumed in different months was not significantly different (P>0.05).
Eleven species of woods were tested for their natural resistance against Microtermes mycophagus (Desneux), Tectona grandis was found highly resistant and Populus euamericana highly palatable.
Studies on the effects of volume and position of stakes on feeding by O, obesus O, gurdaspurensis. O, guptai and M, obesi revealed that the. feeding on stakes was related to their volumes and positions in the soil. Feeding on the surface area was less in 50%. or completely buried stakes than those resting on soil surface. The absolute weight of wood eaten increases with the volume but the percent of weight loss might. decrease especially with those stakes with large volumes. Both absolute as well as percent weight loss decreases as the stakes are more deeply buried in the soil.
Effect of different temperature conditions on natural resistance of C. deodara was also studied. Termites ate more from the blocks which were dried at 100°C or 125°C indicating that timber loses its resistance quality at higher temperatures.
Swarming behaviour of 0 obesus, M, mycophagus, M, obesi and M, unicolor was observed during the swarming seasons of 1987 and 1988. Amongst the four fungus growing termites, 0, obesus was recorded as the most abundant among the fliers at the study site during 1987. Maximum swarming was witnessed on July 26, 1987 when the atmospheric temperature was 23.4°C and relative humidity, 88.3%. During 1988,M. unicolor was the most abundant species and the maximum swarming occurred on June 23,1988 at 27.9°C atmospheric temperature and 88.4% relative humidity. As O obesus showed maximum swarming on a cooler night (23.4°C), and M. unicolor on a relatively hot night (27.9°C), temperature conditions might have played an effective role in bringing about the reproductive isolation in different termite species. Frequency of the observed swarms was maximum between 8.00 to 8.30 P.M. Maximum number of total alates, however, were collected between 7.30 to 8.00 P.M.
DEVELOPMENTAL PATHWAYS Developmental pathways of O. obesus based on the collection brought from the nest, were studied. It was found that workers in colony were of two types (major workers and minor workers) differing only in minor details unlike those of the genus macrotermes. However, after second instar larva they can be easily differentiated, as they have different mandibular size and shape (not pattern). Detailed studies on caste differentiation of a field colony of O. Obesus revealed that major and minor workers develop from third instar larva. Both major and minor workers after their differentiation from third instar larva pass through three successive instars to become an adult sclerotized major or minor worker. There were many qualitative and quantitative changes from third instar larva to the adult workers. Biometrically all the instars of major worker and minor worker were significantly different in all the characters studied. However, for the total body length third instar major worker was not significantly different from worker.
The origin of pre-soldier takes place from third instar minor worker larva. The pre-soldier after five significantly different instars develops into a soldier. It is in the last moult that rectangularly oval head characteristic of the species appears.
The origin of alate line takes place from second instar larva. The nymph after five instars developed into alate. Biometrically all the instars were significantly different.