REDUCED COLD-HARDINESS OF PEAR PSYLLA (HOMOPTERA, PSYLLIDAE) CAUSED BY EXPOSURE TO EXTERNAL WATER AND SURFACTANTS

Overwintering pear psylla, Cacopsylla pyricola (Foerster), were misted with water or with one of several dilute solutions of water and surfa ctant, and then exposed to a range of subzero temperatures for 24 h. M isted psylla had significantly greater mortality than unmisted control s. Increases in mortality occurred at temperatures as warm as -6 degre es C, a temperature well within the range of conditions in the field. At extreme low temperatures (-18 degrees C) there was virtually no mor tality in the unmisted controls, whereas mortality approached or reach ed 100% in several of the misted groups. Temperatures necessary to kil l 50% of insects estimated for topically treated psylla ranged between -2.6 and -12.7 degrees C for surfactant-treated insects, and below -1 8 degrees C for water-treated or control insects. The possibility of u sing surfactants and water for control of overwintering pear psylla is discussed.