Duration times of the immature stages of Cacopsylla pyri L. (Hom., Psyllidae), estimated under field conditions, and their relationship to ambient temperature

The duration of the immature stages of Cacopsylla pyri L. was studied under field conditions by artificially infesting pear branches on several dates during the year. The duration of the egg stage decreased from winter to sum mer, as the season progresses and temperature rises, and slightly increased in September. it ranged from 27.4 to 6.7 days. The same trend was observed in the duration of the first three larval stages (L1-3) which ranged from 18.8 to 10.3 daps. For eggs deposited during the period February-August the duration of the last two larval stages (L4-5) ranged from 17.5 to 12.1 day s. However, the duration of L4-5 developed from eggs deposited in September and which give rise to winter-form adults were the longest observed. The r ate of egg development was related to average ambient temperature with a hi ghly significant linear relationship. This relationship indicates that the egg stage requires a constant number of 158.9 (SD = 5.0) of day-degrees abo ve an average temperature of 2.31 degrees C to complete development. The ra te of development both of L1-3 and L4-5 were related to average ambient tem perature with curvilinear relationships. These relationships indicate a pro portional increase in the developmental rate as temperature rises between 1 0-22 degrees C. At the higher average temperatures that occurred in the sum mer experiments (24-27 degrees C) the acceleration of development of L1-3 i s reduced and the developmental rate of L4-5 decreases. The developmental r ates of L4-5 developed from eggs deposited in September did not follow the established relationship with temperature and they were lower than those in the other periods of the year with the same average temperature.