Cold hardiness of adult Asian citrus psyllid, Diaphorina citri (Homoptera: Psyllidae)

The survival of Diaphorina citri adults during the winter in Tsukuba (lbaraki, Japan) and under various low temperatures was investigated. When adults were released into a screened cage containing a potted Citrus unshiu tree in the field in Tsukuba, new generation adults emerged and reached a peak in late October. Rapid population decline was not observed by December 24 when daily minimum temperatures had decreased below 0 degrees C for 4 days and an extreme low temperature reached -3.9 degrees C. Adults died between December 25 and January 5, when daily minimum temperatures were continuously below 0 degrees C and an extreme low temperature reached -6.4 degrees C. When adults maintained at 15 degrees C on Murraya paniculata and C unshiu were transferred to the field in Tsukuba in mid-January and early February, they did not die immediately, even though the minimum temperature decreased below -4 degrees C on the first and third days after transfer. Mortality trends did not differ between D. citri maintained on M. paniculata and C. unshiu. When adults were exposed to temperatures decreasing at 1 degrees C/h, mortality rates were 58 and 89% at -10 and -11 degrees C, respectively. At a constant temperature of -6 degrees C, it took 4 hours to reach 50% mortality. At constant temperatures of 12.5 and 15 degrees C, psyllid adults on M. paniculata survived for more than 50 days. Mean adult longevity decreased as temperatures fell below 10 degrees C. With water alone and without water or leaves, the longest longevity (34 and 28 days, respectively) was observed at 12.5 degrees C. Mean adult longevity on M. paniculata under alternating temperatures Of 12.5 degrees C (12 h)/5 degrees C (12 h) was more than 50 days, longer than at a constant temperature of 10 degrees C (38 days). These results suggest that maximum and minimum temperatures are more important than the mean temperature in determining winter survival of the psyllid, and they would be able to survive the winter in areas where mean daily minimum and maximum temperatures of the coldest month are above 5 and 12.5 degrees C, respectively.