Current studies were focused on two important aspects of control programme for subterranian termites viz. delineation of nesting system of termites through radiotracers and dyes; and development of an effective bait for termite control.
In order to test Co-60 as a radiotracer for termites, laboratory studies were conducted. Over a period of four weeks, mortality caused by feeding on bait containing Cobalt-60 (30 microcurie) did not exceed 6% in Heterotermes indicola. Microtermes unicolor or Reticulitermes flavipes. The data on radiation distribution in different body parts of H. indicola after feeding on radioactive bait showed maximum radioactivity in gut (64.63%) followed by external contamination (26.81%), appendages (5.87%) and exoskeleton (2.92%). There was an evidence of transfer of radioactivity from the workers feeding on Co-60, to the unexposed recipient workers.
Radiotracers, lodine-131 and G01d-198 were used to study the nesting system of subterranean termites at three ecological sites. The radioactive bait used was readily acceptable for the termites. Application of the radiotracers at different foraging points H. indicola indicated the presence of five independent colonies. Use of 1-131 led to detection of more number of interlinked foraging points (6-7) while Au-198 detected up to three interlinked points. 1-131 was used to study the foraging territories of M. unicolor in an infested orchard. Although radioactive bait was removed by the termites, destination of the removed bait could not be detected. On the other hand, 1-131 detected the foraging of Odontotermes lokanandi on surrounding trees in an area of 200 m2. At another site in an area of bare ground formerly a fruit orchard which had been destroyed by M. unicolor, Use of 1-131 detected the interconnection of 17 points within an area of 85 m2.
Different concentrations of Nile blue A, Sudan red 7B, Fuchsin acid and Eosin gelblish were tested as dye markers for H. indicola. 0.25% Nile blue caused a negligible mortality (6%) and was retained in more than 50% of the termites for 4 months. Sudan red was also less toxic at lower concentrations (< 0.25%) but did not retain in the body of termites for more than 2 weeks. At 0.06% concentration, Fuchsin acid and Eosin caused 16-17% mortality. The mortality rate reduced at higher concentrations probably due to avoidance of feeding by termites. Fuchsin acid and Eosin did not retain in termite 2-3 days after termites fed on these dyes.
Colonies of H. indicola at the campus of Nuclear Institute for Food and Agriculture were delineated by Nile blue A and Sudan red 7B using mark-release-recapture technique. Tracing experiments indicated the presence of 6 colonies within the area with foraging sites of a single colony ranging from 1-16 covering an area of 10 to 108 meters. Some of the colonies were as close as 2.5 meter without an apparent linkage. Nile blue showed a long (105-382 days) retention time under field condition while Sudan red persisted for 14-42 days. Simultaneous use of 60th the dyes increased the tracing efficiency than using either of them separately.
Different constituents were tested to make bait that is acceptable and palatable for subterranean termite, H. indicola. The materials tested include termite body extract, agar and carbohydrates. Extracts of whole termites in different solvents were tested for attractiveness to H. indicola using crude body extract and Soxhlet extraction methods. Overall crude body extract elicited higher attraction response. Among the solvents tested, propanol extract showed a consistent attraction response. Among various carbohydrates tested, 3% glucose increased the H. indicola survival. Agar concentration @ 3% made the bait more palatable for H. indicola than 2 and 1 % agar.
Different compounds at six different concentration levels were tested to screen potential slow-acting toxicants. Among these compounds molybdophosphoric acid, zinc sulphate,-lead acetate, and cadmium chloride caused a low mortality rate that did not exceed 76% even at the highest concentration (0.5%) used. The second group including boric acid, sodium arsenate and mercuric iodide exhibited ELT 90 within 14 days, at least at one concentration. Behavioural observations indicated that among the three compounds in the second group, only boric acid (0.1 %) when offered in agar media allowed normal tunneling behaviour of termite. When boric acid was used against the field colonies of H. indicola, it led to a partial suppression of foraging activity.
In the laboratory studies, mirex (0.3%) when used in the bait caused 100% mortality in H. indicola and M. undicola in 7-8 days. Hydramethylnon (0.03%) took 16 and 10 days to kill 100% of H. indicola and M. unicolor respectively. Field application of mirex-treated bait led to a complete elimination of H. indicola activity within one month. Hydramethylnon suppressed the foraging activity of O. lokanandi by 90% within one month. Three to four month later, no foraging activity was recorded indicating the ultimate elimination of the colony.