云南丽江地区铁杉球蚜发生与环境因子的关系

Relationships of infestation of hemlock woolly adelgids,Adelges tsugae,with environmental factors in Lijiang Prefecture,Yunnan

铁杉球蚜Adelges tsugae Annand（Hemiptera：Adelgidae）是铁杉的主要害虫，在北美造成铁杉成片死亡。为有效地寻找控制铁杉球蚜的天敌，作者于2005年8—2006年12月，在云南省丽江地区的河源、牦牛坪、黑水河3个地点对铁杉球蚜的发生进行6次调查，统计不同树枝方位、不同树冠层次、不同取样地点、不同取样时间的铁杉球蚜的为害率。在多数情况下，铁杉北向和南向树枝上的球蚜为害率高于西向和东向；树冠下层的铁杉树枝上的球蚜为害率高于树冠上层；5月树冠上层球蚜为害率反而高于下层，树冠层次球蚜密度随着时间而变化的现象，与铁杉球蚜第2代发生高峰期相吻合。3个地点的每株树铁杉球蚜为害率平均为24．6％，河源的球蚜为害率又高于牦牛坪和黑水河。对来自3个地点的12块样地的每样地铁杉球蚜为害率与环境因子进行偏相关分析表明，坡向、年均相对湿度、年均降雨量与铁杉球蚜发生呈显著正相关。在调查铁杉球蚜的发生或采集球蚜天敌昆虫时，应在不同时间依据树枝方位和树冠层次来分别进行。在选择调查采集地点时，应以林区坡向、相对湿度、降雨量等环境因子为依据。

The hemlock woolly adelgid （HWA）, Adelges tsugae Annand （Hemiptera： Adelgidae）, is not a serious pest of hemlocks in China, but it has caused alarming mortality of hemlocks in Northeast America. Understanding to what degree hemlocks are infested with HWA in China should shed light on an ongoing investigation of natural enemies of HWA in China for the potential of biological control of HWA in North America. Our objectives were to know whether the HWA occurrence differed among cardinal directions, between crown heights, between generations （over time）, or among sites. We studied HWA in three different sites （each with 10 randomly selected trees） in Lijiang Prefecture, Yunnan Province, from August 2005 to December 2006, in reference to different environmental factors. Within a tree （each with 400 1-year foliage branches）, HWA occurred at higher percentages in the north- and southfacing directions; HWA infestation was usually more severe at the lower crown than the upper, but it was reversed in May when higher percentages of HWA were found on the upper crown of a tree. This seasonal difference in infestation between crown heights coincided with the onset of the new HWA generation. The infestation rate of 1-year foliage branches with HWA averaged 24.6% over the three sites, where Heyuan had higher HWA infestation than Maoniuping or Heishuihe. A correlation analysis with 12 plots （each with 10 randomly selected trees） from the three sites indicated that aspect （slope orientation）, average annual relative humidity, and average annual rainfall were positively correlated with the infestation rate of HWA at significant statistical levels, while temperature, altitude, slope degree, canopy closure, and tree height seemed to have little effect on HWA occurrence. Search for natural enemies should consider more efforts on the north- and south-facing directions of a tree and at lower crown height where HWA tend to be denser.