| Temperature is an important factor influencing insect physiological characteristics such as growth, development, reproduction and survival. Capacity of tolerance against temperature stress combined with other factors determine the potential distribution and spreading. The introduction of Coccobius azumai Tachikawa to control the typical exotic invasive species Hemiberlesia pitysophila Takagi is an economical, sustainable, effective and common-used measure. This paper makes a comprehensive evaluation on the tolerance capacity of H. pitysophila and C. azumai against extreme temperature, which was embodied by the supercooling point, discriminating temperature (DT), semi-lethal sum of temperature (LST50) and mortality. The effects of host, latitude and altitude on tolerance of H. pitysophila were also evaluated. In addition, we predicted the potential distribution areas of H. pitysophila, C. azumai and their parasitism relationship by combining with regional climate characteristics, which theoretically had an important value for revealing adaptability of the exotic species to local niches and effectively control of H. pitysophila using C. azumai as a biocontrol agent. The main results were as follows:1 Seasonal variation in cold tolerance of the population of H. pitysophilaThe parameters of supercooling point (SCP), mortality exposed to designated low temperature (ME), discriminating temperature (DT) and semi-lethal sum of chill injurious temperature(LSCIT50) of H. pitysophila collected from different seasons were measured and compared in Quanzhou, Fujian Province, China from 2007 to 2008. The individual SCPs of this pest fluctuating from -22.4℃to -3.3℃were measured. Among all the developmental stages of the pest in each season, the winter female adults had the lowest mean SCP (-14.83℃), which was significantly lower than those of the summer female adults, the winter newly hatched nymphae and 1st instar nymphae. However, the mean SCPs of other developmental stages between winter and summer all showed no markedly differences. Experiments exposed to low temperature indicated that the parameters of ME, DT and LSCIT50 of the 1st instar nymphae, 2nd instar nymphae before sex differentiation, 2nd instar male nymphae after sex differentiation, female adults and entire population were all obviously lower in winter than in summer. A linear correlative analysis showed that there were significant positive correlations between the mean air temperature and the LSCIT50s of the 1st instar nymphae, 2nd instar male nymphae after sex differentiation and the entire population, but no significant correlations between SCPs and LSCIT50s at each developmental stage. These results suggest that there is a clearly seasonal adaptability independent of SCP and nearly correlative with air temperature in cold tolerance of H. pitysophila. The cold tolerance of this pest population seems to peak in winter and touch bottom in summer. The SCP isn't a reliable indicator for the cold tolerance of H. pitysophila.2 Effects of different host plants on the cold tolerance of H. pitysophilaThe supercooling point (SCP) and mortality of H. pitysophila exposed to a designated and regulated low temperature were measured, which feeded on the four different plants, Pinus massoniana, P. elliottii, P. taeda and P. thunbergii. Significant effects of plant on SCP of female adult were observed that the mean SCPs were 0.9～2.3℃higher on P. massoniana and P. thunbergii than on the other two plants. The mean SCP of the 2nd instar female nymphae after sex differentiation was 2.08℃higher on P. massoniana than on P. elliottii. However, a separate experiment showed no remarkable difference between the SCPs of the 2nd instar male nymphae after sex differentiation on the two plants. Another separate experiment of exposure to low temperature indicated that relations between low temperature and mortality of all the insect developing stages and the population on the two plants were all in accordance with a revised double-variable Logistic model. Nevertheless, the incipient sensitively low lethal temperature and mortality exposed at -20℃condition of these developing stages and the population were all lower on P. massoniana than on P. elliottii. The semi-lethal sum effective of chill injurious temperature (LSECIT50) of the population was lower on P. massoniana than on P. elliottii. These results suggest that the SCP and mortality of H. pitysophila exposed to low temperature can be significantly affected by host plants.3 Cold tolerance of H. pitysophila in different regionsThe supercooling points (Scps) and mortality of H. pitysophila exposed to designated low temperature were measured in different regions in China, including Xinyi, Guandong Province, Zhangzhou, Quanzhou and Changle, Fujian Province in the winter of 2007. The results showed that Scps of the female adults had significant differences among the four regions that the lowest mean Scps appeared in Changle, while the highest in Xinyi, whose difference reached 2.03℃. As exposed to low temperature of 10 to -20℃, the mortality of H. pitysophila was remarkably higher in Xinyi than in Changle and Quanzhou. However, the relationship between exposed low temperature and mortality of the population in Xinyi, Quanzhou and Chanle were all in accordance with double variable Logistic model, so were the five insect developing stages such as the 1st instar nymphae, 2nd instar nymphae before sex differentiation, 2nd instar females, 2nd male nymphae after sex differentiation and female adults. The semi-lethal sum effective of chill injurious temperature (LSECIT50) was also higher in Xinyi than in Quanzhou and Changle. This paper indicates that H. pitysophila can adapt to low temperature, and the cold tolerance might become stronger with the latitude rising.4 Extreme temperature tolerance of H. pitysophila at different altitudesCold tolerance and heat tolerance of at altitudes of 80, 251, 391, 510 and 725 m were measured and compared by the indices of supercooling point (Scp), mortality and semi-lethal temperature (LT50). The results showed that there were remarkable differences among Scps of female adults at different altitudes that the lowest Scp appeared at the altitude of 391 m, while the highest at 251 m. It was an increasing trend in mortality as the exposed low temperature declining, and no survivals existed at -25℃. When exposed to the low temperature of 0～-10℃, mortalities of H. pitysophila were significantly affected by altitudes.. Its lowest LT50 of low temperature appeared at the altitude of 391 m. It was an increasing trend in mortality as the exposed high temperature rising, and no survivals existed at 45℃. The altitude also significantly affected the pest's mortality exposed at high temperature conditions, and its highest LT50 of high temperature appeared at the altitude of 391～510 m.. This study suggests that the extreme temperature tolerance of this pest had no linear relationship with altitudes.5 Seasonal variation in heat tolerance of H. pitysophilaBy means of the heat exposure methods, the mortality and semi-lethal sum of high injurious temperature (LSHIT50) of H. pitysophila among different seasons and developmental stages were analyzed and compared, and its the heat tolerance and seasonal adaptability were also synthetically evaluated. The results showed that the 2nd instar nymph before sex differentiation, the 2nd instar female nymph after sex differentiation and the entire population had significantly higher heat tolerance in summer than in other seasons, and appeared to a clearly seasonal adaptability characteristics. The lethal high temperature might be fluctuated around 45℃, thus it had the potential to spread southward and to make more bad damages. However, this seasonal adaptability to heat had no remarkable relationship with the three climate factors of mean air temperature, extreme high temperature and rainfall.6 Seasonal variation in cold tolerance of C. azumaiThe parameters of supercooling point (SCP), mortality exposed to designated low temperature and semi-lethal sum of chill injurious temperature (LSCIT50) of the chalcid adults collected from different seasons were measured and compared in Quanzhou, Fujian Province, China during 2007 to 2008. Mean SCP values of female adults from spring, summer, autumn and winter were -13.7559,-11.9700,-12.7936 and -13.6000℃, respectively, and spring and winter female adults had all a significantly lower value than summer female adults. Mean SCP values of male adults from spring, summer and autumn were -15.3917,-13.8400 and -13.2143℃, respectively, and the value was significantly lower from spring than from summer and autumn. Additionally, mean SCP values of female adults were all markedly lower than those of male adults in spring and summer, while was equivalent in autumn. Experiment of exposure to low temperature suggested that none of female adults from any seasons survived at -15℃. However, mortality of female adults was clearly lower in spring than in summer at 0℃, and than in summer and autumn at -5℃and -10℃. The relationships between sum of exposed to low temperature and mortality of female adults from each season were all highly fitted to revised Logistic model. Significant differences were observed between LSCIT50s of female adults estimated by this model from different seasons. Mean LSCIT50 of spring female adults was significantly lower than those of summer and autumn female adults. Its SCP and LSCIT50 seemed to decease with decrease in seasonal extreme low air temperature and increase in seasonal extreme difference in air temperature, and its LSCIT50 also seemed to decease with SCP decreasing. These results suggested that there is an obvious adaptability to seasonal variation of air temperature in cold tolerance of C. azumai adults; in the wild, autumn may be an important duration for increasing its cold tolerance by acclimation of seasonal low extreme air temperature and high extreme difference in air temperature.7 Seasonal variation in heat tolerance of C. azumaiThe heat tolerance of C. azumai was analyzed and compared in different seasons through exposure to high temperature method. The results showed that there was an increasing trend of mortality in the parasitoid of female adults from each season with the rising of exposed temperature. However, significant death differences were observed among different seasons when the parasitoids exposed to 39～40.5℃, and the mortality of summer female adults seemed to be the lowest. The results for the indices of the lower limited sum of effective heat injurious temperature (LLSEHIT) and the semi-lethal sum of heat injurious temperature (LSHIT50) showed that the sequence of heat tolerance in female adults in various seasons was summer >autumn>spring, and a clearly seasonal adaptability to heat was proved. The monthly mean air temperature and seasonal extreme high temperature might be the main causes of this adaptability. A separate experiment showed that the extreme high temperature was 41℃either in female or male adults. Whereas, mortality in male adults displayed higher mortality than that in female adults when exposed to 39～40.5℃, which indicated that the female adults had higher heat tolerance than male adults. |
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