field tests of molybdenum and tungsten baits - IRG. International ...

adhesive under low pressure and then the molding was cut to give bait stakes (15x
40x250mm).
Table 1 Bait formulation for field tests
Materials Contents
Na2MoO4・2H2O (MW:242)
Na2WO4・2H2O (MW:330)
BaCl2・2H2O (MW:244)
Rubber tree chips
Phenolic-type adhesive
13.0 % (5.2% as Mo)
5.0 (2.8% as W)
15
57~61
6~10
Total 100
2.2. Test methods
Ten and more termite mounds at Phuket Rubber Experiment Station were selected as
test sites. On April of 2002, 4-6 test bait stakes (15x40x250mm) were hit into the
ground around each mound, and stakes of rubber wood (40x40x300mm) were set on
the top of each mound and around it if necessary. Then the level of termite activities at
each mound were observed at intervals. In case that damages of test bait stakes and
wood stakes were found to be serious on the observation time of October of 2002, the
stakes were replaced for new ones and the tests were continued.
3. RESULTS AND DISCUSSION
3.1. Determination of bait formulations
Ahead of this field tests, bait formulations containing sodium salts of molybdic acid
and tungstic acid, not converted to barium salts, were tested. The result was
unsatisfactory, as water-soluble sodium salts leached out during the tests. Then we
prepared solid and hard baits by hardening with phenolic-type adhesive under high
temperature and high pressure, but the baits invited a reduction in bait feeding by
termites. For this field tests therefore, barium salt-based baits were prepared by
converting sodium salts to slightly water-soluble barium salts by ion exchange method,
being free from the danger of leaching out of active ingredients. Moreover, bait
feeding by termites was found not to deteriorate as the baits can be formed porously
under low pressure.
As base materials for baits, rubber trees were suited for termites in Thailand, although
favorable base materials in Japan and China were pine trees and eucalyptus barks or
bagasse respectively. This seems to indicate diversity in bait feeding according to
termites on the spot.
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