Predicting Phenology of Pear Thrips Emergence in Pennsylvania Sugar Maple Stands

Abstract

Spring emergence of adult pear thrips, Taeniothrips inconsequens was monitored with 20-cm emergence traps in five sugar maple sites across Pennsylvania in 1990 and six sites in 1991 and 1992. Arnold’s least variability method and the standard error of prediction method were used to estimate the best start date x base (air) temperature combination among all combinations of 0–15 degrees C. and January 1 to March 1 for heating degree day (HDD) requirements to first and 50% emergence. The results suggest that HDD’s predict pear thrips emergence no better than average Julian date and that emergence is not temperature dependent, an interpretation inconsistent with previous studies of pear thrips and other thrips species. More likely, the relevant measure for thermal summation is soil temperature near the surface, where adults overwinter, rather than air temperature. Also, cessation of pear thrips overwintering may depend on a chilling requirement followed by thermal summation to promote development to emergence. Both possibilities should be explored through additional analyses and experiments.