Abstract
Traps baited with a sex pheromone lure were placed in two fields located in Pathum Thani Province in central Thailand to estimate the seasonal trend in population density of the diamondback moth, Plutella xylostella, over a two year periods. Although a large number of moths were captured all year round regardless of different climatic conditions such as dry and rainy seasons, the population density was clearly different between the two fields, indicating that the number of emerging moths varied form place to place even in the same season. The population density declined sharply with the harvest of cruciferous vegetables, and recovered several weeks after the harvest. Forewing length of male moths captured in Thailand were constantly short through the year and about the same size as those of males found only in mid-summer in Japan.
