LONGEVITY OF SOIL TERMITICIDES WEATHERED FOR 3-4 YEARS IN THAILAND UNDER IN-SITU OBSERVATION AND LABORATORY BIOASSAY USING COPTOTERMES GESTROI WASMANN

Longevities of several soil termiticides against chlorinated hydrocarb ons mere evaluated with field-exposure tests and laboratory bioassays of weathered termiticide-treated soils. Field-exposure tests were cond ucted at three test sites in Thailand with the ground stake test (GST) and the modified ground board test (MGBT). Residual anti-termite acti vity was assayed for tunneling activity according to the Japanese stan dardized method using the most economically important Thai termite spe cies, Coptotermes gestroi Wasmann. Because of the reduced anti-termite activity in the soil treated with chlorpyrifos after short-term weath ering, an application of chlorpyrifos for termite control was consider ed useless for long-term protection in Thailand. Laboratory bioassay c ombined with field weathering was considered the most reliable method to determine the longevity of soil termiticides in a tropical country such as Thailand. Among the alternatives tested, permethrin (2.0%), al pha-cypermethrin (0.3%), and bifenthrin (0.1%) were promising consider ing their longevity. Concerning the field weathering procedure, the MG BT was considered preferable to the GST for better simulation of the s lab-on-concrete structures of Thailand and its well-suitability agains t C. gestroi.