Utah State University Extension
Pear psylla (Cacopsylla pyricola), a western Europe native, is a very small sap-feeding insect and is considered the most serious insect pest of pear in the United States. Serious infestations can stunt, defoliate, and even kill trees. Psylla feeding produces copious amounts of sticky honeydew that can cause fruit russetting.
Alston, Diane and Murray, Marion, "Pear Psylla (Cacopsylla Pyricola)" (2007). All Current Publications. Paper 928.