松突圆蚧种群耐寒性的季节变化

采用过冷却点、低温暴露死亡率、冷识别温度和致死中低温累积等指标评价不同季节松突圆蚧的耐寒性.结果表明:各季节松突圆蚧的过冷却点波动在-22.4～-3.1 ℃之间,以冬季雌成虫的平均过冷却点最低(-14.83 ℃),显著低于夏季雌成虫、冬季1龄若虫和初孵若虫(P＜0.01),但其它发育阶段在冬、夏季之间均无显著差异;冬季1龄若虫、2龄性分化前若虫、2龄性分化后雄若虫、雌成虫和种群总体在-20～0 ℃下的死亡率、冷识别温度和致死中低温累积均明显低于夏季;1龄若虫、2龄性分化后雄若虫和种群总体的致死中低温累积与季节性平均气温均呈显著正相关(R＞R0.05=0.950,n-2=2),但各发育阶段的过冷却点与其致死中低温累积的相关性均未达显著水平.松突圆蚧冬季种群耐寒性最强,夏季种群最弱;该虫耐寒性的这一季节适应性并不依赖于过冷却点,而与气温的季节变化密切相关.

Seasonal variation in cold tolerance of the population of pine armored scale, Hemiberlesia pitysophila Takagi (Homoptera: Diaspididae)

The pine armored scale, Hemiberlesia pitysophila Takagi is a dangerous pine forest pest which mainly attacks needle leaves, cones and twigs of various evergreen pines, and has led to great damage in south China since early 1980s. The parameters of supercooling point (SCP), mortality exposed to designated low temperature (ME), discriminating temperature (DT) and median lethal sum of low temperature (LST_(50)) of the pest collected in different seasons in Quanzhou, Fujian Province, China from 2007 to 2008 were measured and compared. The results showed that individual SCP of this pest fluctuated from -22.4 ℃ to -3.1 ℃. Among all the developmental stages of the pest in every season, winter female adults had the lowest SCP with the mean value of -14.83 ℃, which was significantly lower than those of summer female adults, winter newly hatched nymph and 1~(st) instar nymph (P＜0.01). However, SCPs of other developmental stages in winter and summer all showed no markedly differences (P＞0.05). Experiments exposed to low temperature indicated that the parameters of ME, DT and LST_(50) of 1~(st) instar nymph, 2~(nd) instar nymph before sex differentiation, 2~(nd) instar male nymph after sex differentiation, female adults and population were all obviously lower in winter than in summer. A linear correlative analysis showed that there were significantly positive correlations between seasonal mean air temperature and LST_(50)s of 1~(st) instar nymph, 2~(nd) instar male nymph after sex differentiation and the pest population (R＞R_0.05=0.950,n-2=2), but no significant correlations between SCPs and LST_(50)s in each developmental stage (R＜R_0.05=0.950,n-2=2). Therefore, it is concluded that the cold tolerance of H. Pitysophila population seems to peak in winter and drop in summer. The adaptability to low air temperature in winter may be independent of SCP, but is nearly correlative with seasonal mean air temperature.