Emergence of Pear Thrips (Thysanoptera: Thripidae) and its Relation to Foliar Damage

Abstract

Adult emergence of pear thrips, Taeniothrips inconsequens (Uzel), from soil in forests predominating in sugar maple, Acer saccharum Marshall, was monitored, using 7.6- cm-diameter traps, at sites in north central, northeastern, central and southwestern Vermont from 1989 to 1991. The onset of emergence ranged from 2 April to 15 May, but generally occurred in mid-April in all regions. We measured the number of thrips in soil in September and how many emerged in the spring, and monitored the timing and rate of emergence to determine if damage could be predicted from these factors. Thrips density in the soil was not consistently correlated with damage, making it an unreliable predictive measure. A correlation between thrips damage and the timing or duration of emergence was also not detected. The number of thrips per emergence trap was positively correlated with damage in all study years, and from this correlation the predicted number of thrips per trap for moderate damage to occur was 18 in 1989, 13 in 1990 and 8 in 1991. Annual fluctuations in the threshold number of thrips required for damage could limit the use of thrips emergence data for predictive purposes.