DEGRADATION OF TERMITICIDES AND ITS EFFECT ON PERFORMANCE AGAINST THAILAND ECONOMICALLY MOST IMPORTANT SUBTERRANEAN TERMITE, COPTOTERMES GESTROI WASMANN (ISOPTERA, RHINOTERMITIDAE) .2. INDOOR AND OUTDOOR EXPOSURE IN ABOVE GROUND SITUATION

Experiments were conducted to evaluate the chemical degradation and th e change of termiticidal performance of three synthetic pyrethroids (c ypermethrin, fenvalerate and permethrin), the silane (silafluofen) and the organophosphate (chlorpyrifos) treated wood blocks after certain periods of indoor and outdoor exposure in above ground situation. From the mass losses of untreated wood blocks, the outdoor weathering seem ed to be more severe than the indoor weathering. Natural weathering co nsisting of ultraviolet irradiation and other unspecified variables ex erted less effects on the recovery rates and the termiticidal effectiv eness of all chemicals than when buried in soil. All chemicals at ever y concentration provided good termiticidal performance (less than 3% w ood consumption of treated blocks) even after 24 months' indoor weathe ring, but only 6 months' for outdoor weathering. Chlorpyrifos degraded more rapidly than the other termiticides in both indoor and outdoor w eathering. Among the synthetic pyrethroids, cypermethrin showed the hi ghest resistance to natural weathering, providing termiticidal perform ance even at the lowest concentration up to 12 months' exposure, follo wed by permethrin and fenvalerate. Silafluofen seemed to be the most s usceptible to outdoor exposure among termiticides other than chlorpyri fos, and lost its effectiveness in every concentration within 12 month s. Although the results of bioassay suggest the possibility of these c hemicals as alternative termiticides against the economically most imp ortant subterranean termite, Coptotermes gestroi Wasmann in Thailand, the higher concentrations are recommended for long-term protection in outdoor above ground situation.