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ABSTRACT FIELD TESTS OF MOLYBDENUM AND TUNGSTEN BAITS FOR TERMITE CONTROL Yoshio Katsuda, Koji Nakayama and Charunee Vongkaluang Molybdenum and tungsten compounds are slow acting to termites and show a high termiticidal efficacy. In our previous papers, we have already reported that those are useful as termiticidal ingredients of bait formulations. The demand for natural rubber is still on the increase. However some kinds of termites inhabiting rubber plantations damage rubber trees and pose a serious threat. To cope with this problem, we prepared bait stakes by having rubber tree chips impregnated with barium salts of molybdenum and tungsten compounds and then solidifying the mixture with phenolic-type adhesive. In field tests conducted at a rubber plantation in Thailand, the bait stakes were hit into the ground around each termite mound and the level of termite activities were observed at intervals. After one and a half years from the start of the test, it was confirmed that our bait formulations eventually eradicated termite colonies of Macrotermes and Odontotermes. Key words : Molybdenum, Tungsten, Bait, Rubber plantation, Termite control, 1. INTRODUCTION Macrotermes , Odontotermes Damages by termites pose serious problems in many countries. For example, termites often cause important damages to buildings in Japan. As main countermeasures, termiticides such as emulsifiable concentrate and oil formulations are sprayed on buildings and under the floor or surroundings thereof, or anti-termitic plastic sheets containing termiticidal ingredients are employed on the ground under the floor. Silafluofen (1-4) is regarded as an effective termiticidal ingredient, as it is characterized by excellent properties in all aspects of termiticidal activities, safety to mammals, chemical stabilities and so on. On the other hand, almost termiticides of other types such as pyrethroids, organo-phosphorus compounds and carbamates which can be used as spraying agents are difficult to be mixed with plastic resins due to instability in alkaline environment, being unsuitable for applications to building materials. In China, damages by termites that eat woods or destroy embankment become social concern, and in particular, the damage of embankment by Odontotermes formosanus, Odontotermes hainanensis, Globitermes, or Macrotermes is serious. These kinds of 1
termites make mud tubes under the embankment, and the river water in a flooded season sinks into the mud tubes, causing a threat of destroying the embankment. To preserve the embankment, eradication of termite colonies is indispensable, and conventionally bait formulations containing organic chlorine-based termiticides such as mirex have been employed for this purpose. However the use of these chemicals is banned because of residual toxicity and environmental pollution, making the development of new alternatives a pressing need. Molybdenum and tungsten compounds are slow acting to termites and show a high termiticidal efficacy. Since around the middle of 1980s, we had been engaged in development works of applying these inorganic compounds to bait formulations. Our first papers (5) on their mode of action suggested that the termiticidal effectiveness of molybdenum and tungsten compounds might be much more associated with the physiological depression caused by the accumulation of their oxides in the body, especially in the fat body, rather than with the influences on the symbiotic intestinal flagellates. After that, we proceeded with formulation studies and field tests aimed at practical use in Japan and China, and reported in our subsequent papers (6-8) that those compounds are useful as termiticidal ingredients of bait formulations. Rubber trees are planted mainly in Thailand, Malaysia, Indonesia and Sri Lanka, and are important as a source of supply for natural rubber whose demand is still on the increase. At rubber plantations of these hot and humid countries, there live many kinds of termites including Macrotermes and Odontotermes which cause damages especially by attacking roots of young rubber trees (until 7-8 years old). In case that rubber trees die all at once before the harvesting season of natural rubber resin, the damages become awfully serious for the exporting nations as well as producing farmers. Countermeasures taken for the damages in the past are only physical ones such as removing surface soil (about 40cm in depth). In consideration of these circumstances, we have conducted field tests of bait formulations containing molybdenum and tungsten compounds for termite control at rubber plantations in Thailand since July of 1999. This report deals with the test results and their high practicability of the bait formulations. 2. MATERIALS AND METHODS 2.1. Test materials The bait formulation served for field tests is shown in Table 1. An aqueous solution of sodium salts of molybdic acid and tungstic acid was impregnated uniformly in rubber tree chips, followed by the addition of an aqueous solution of barium chloride to cause formation and precipitation of slightly water-soluble barium salts of molybdic acid and tungstic acid. After drying, the mixture was hardened using phenolic-type 2
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Page 5 and 6: 3.2. Outline of observation results

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

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