Exotic and Invasive Weed Research Unit, USDA/ARS, Reno, NV, USA.
Oecologia. 2011 Mar;165(3):605-16. doi: 10.1007/s00442-010-1859-y. Epub 2010 Dec 14.
The success of biological control programs is rarely assessed beyond population level impacts on the target organism. The question of whether a biological control agent can either partially or completely restore ecosystem services independent of population level control is therefore still open to discussion. Using observational and experimental approaches, we investigated the ability of the saltcedar leaf beetle [Diorhabda carinulata (Brullé) (Coleoptera: Chrysomelidae)] to reduce the water use of saltcedar trees (Tamarix ramosissima Ledeb.) in two sites (Humboldt and Walker Rivers) in Nevada, USA. At these sites D. carinulata defoliated the majority of trees within 25 and 9 km, respectively, of the release location within 3 years. At the Humboldt site, D. carinulata reduced the canopy cover of trees adjacent to the release location by >90%. At a location 4 km away during the first year of defoliation, D. carinulata reduced peak (August) stem water use by 50-70% and stand transpiration (July to late September) by 75% (P = 0.052). There was, however, no reduction in stem water use and stand transpiration during the second year of defoliation due to reduced beetle abundances at that location. At the Walker site, we measured stand evapotranspiration (ET) in the center of a large saltcedar stand and found that ET was highest immediately prior to D. carinulata arrival, dropped dramatically with defoliation, and remained low through the subsequent 2 years of the study. In contrast, near the perimeter of the stand, D. carinulata did not reduce sap flow, partly because of low rates of defoliation but also because of increased water use per unit leaf area in response to defoliation. Taken together, our results provide evidence that in the early stages of population expansion D. carinulata can lead to substantial declines in saltcedar water use. The extent of these declines varies spatially and temporally and is dependent on saltcedar compensatory responses along with D. carinulata population dynamics and patterns of dispersal.
生物防治计划的成功很少在目标生物的种群水平影响之外进行评估。因此，生物防治剂是否能够独立于种群水平控制，部分或完全恢复生态系统服务仍然存在争议。本研究采用观测和实验方法，调查了盐柳叶甲（Diorhabda carinulata (Brullé)）（鞘翅目：叶甲科）减少美国内华达州洪堡河（Humboldt River）和沃克河（Walker River）两个地点盐柳树木用水量的能力。在这两个地点，D. carinulata 在释放地点 25 和 9 公里范围内的大多数树木在 3 年内被完全取食。在洪堡河地点，D. carinulata 使释放点附近的树冠覆盖率减少了超过 90%。在取食的第一年，离释放点 4 公里的地方，D. carinulata 减少了 50-70%的峰值（8 月）茎部水分利用量和 75%的林分蒸腾量（7 月至 9 月下旬）（P = 0.052）。然而，由于该地点的甲虫数量减少，在取食的第二年，茎部水分利用量和林分蒸腾量并没有减少。在沃克河地点，我们测量了一个大型盐柳林分中心的林分蒸散量（ET），发现 ET 在 D. carinulata 到达之前最高，随着取食急剧下降，在随后的 2 年研究中一直保持低位。相比之下，在林分的周边，D. carinulata 并没有减少树木液流，部分原因是取食率低，但也因为叶面积的单位用水量增加以响应取食。总的来说，我们的研究结果提供了证据表明，在种群扩张的早期阶段，D. carinulata 可以导致盐柳树木用水量的大幅下降。这些下降的程度在空间和时间上是不同的，并且取决于盐柳树木的补偿反应以及 D. carinulata 的种群动态和扩散模式。
