A comparison was made of the probing behavior of reproductively diapausing winter-form pear psylla,Psylla pyricolaFoerster (Homoptera: Psyllidae), given access to leaves ofPyrus communiscv. Winter Nellis (pear, the sole reproductive host) andPrunus persicacv. Lovell (peach, a transitory host on which psylla do not reproduce). Winter-form pear psylla ingested predominantly from the phloem, xylem, and spongy parenchyma cells of pear and peach leaves. The elapsed time to first probe was significantly longer when insects were given access to peach than when given access to pear, yet the mean proportion of total probe time spent ingesting when various peach and pear leaf cell types were probed did not differ significantly, with the exception of spongy parenchyma cells. These results suggest that preprobe stimuli mediate discrimination between reproductive and transitory host plants by winter-form psylla. The possible sensory mechanisms underlying host acceptance and discrimination between leaf cell types by winter-form pear psylla, as well as the epidemiological implications of these data for pear decline, are discussed.