Response of Liriomyza trifolii to cold acclimation and differences of cold tolerance among different populations.
Objective: The response of the major invasive pest Liriomyza trifolii to cold acclimation and the cold tolerance of three geographical populations (Wuhan City, Hubei Province; Haikou City, Hainan Province; Anqing City, Anhui Province) were studied to provide references for the potential colonization of L. trifolii in high latitudes of China. Method: The pupae and adults of L. trifolii population in Hainan were exposed to low temperatures of -12, -14, -16, -18, -20, -22 and -24°C for 30 min, and the temperature with a survival rate of 15%-30% was selected as the recognition temperature. The L. trifolii pupae and adults were put at 5°C for 1-6 h or 12°C for 1-6 d, and then put at the recognition temperature for 30 min to detect the survival rate. The undomesticated pupae and adults were also placed at the recognition temperature for 30 min as a control, and the difference in low-temperature survival rate after cold acclimation was compared. Besides, five target temperatures were set at 0, -5, -10, -15, and -20°C, respectively, and the pupae of three geographical populations were exposed to the target temperatures for 2 h, the difference of survival rate was studied. Finally, the supercooling point (SCP) of pupae of three geographical populations was measured by supercooling point tester. Result: When theL. trifolii pupae and adults were exposed to -20°C for 30 min, the survival rates were 15.0%, 19.6%, and 21.0%, respectively. Therefore, -20°C was determined as the cold acclimation recognition temperature of L. trifolii. The cold tolerance ofL. trifolii pupae and adults was improved after rapid cold acclimation at 5°C, and the adults responded more positively to rapid cold acclimation. The effect of cold acclimation for 1 h and 2 h was the best, and the effect of rapid cold acclimation decreased gradually until disappeared with the extension of exposure time. Within 6 days, the cold tolerance ofL. trifolii pupae and adults was improved by low-temperature exposure at 12°C for different periods, and there was little difference in cold tolerance after cold acclimation for different periods. Besides, under the low-temperature exposure of 5, 0 and -5°C, there was no significant difference in the survival rate of pupae between the Hainan population and Anhui, Hubei populations, but under the low-temperature exposure of -10, -15 and -20°C, the pupa survival rate of Hainan population was significantly lower than that of Anhui and Hubei populations. The SCP of pupae in the Anhui and Hubei populations was significantly lower than that in the Hainan population. Conclusion: The cold tolerance of L. trifolii can be enhanced by cold acclimation, which may be one of the reasons why L. trifolii gradually spread to high latitudes in China. The cold tolerance of the Hubei and Anhui populations is stronger than that of the Hainan population. The results are helpful to predict the overwintering distribution area of L. trifolii in China and guide its monitoring, early warning, and prevention and control.