Abstract
Population trends of Thrips palmi KARNY on sweet pepper cultivated in vinyl-houses was investigated in Gobou-City, Wakayama Prefecture from 1985 to 1986. Seasonal changes in thrips density were similar in most of the vinyl-houses; the densities were low in winter but they increased through spring showing peak incidences in April or May. Fluctuation of the percentages of injured fruits delayed that of adult density on flower of the sweet pepper for 7-10 days because of larvae mainly infesting the fruits. Economic injury denisity for sweet pepper was estimated at 0.105 adults per flower or 4.4 adults per sticky trap per day assuming that economically permissible level of yield loss was 5% of the maximum yield.
