外来入侵杂草传统生物防治的生态风险及其防范对策

长期大量实践说明，引进天敌防治外来入侵杂草的传统生物防治方法是治理外来入侵杂草的一条切实可行的有效途径，但对其潜在的生态风险——对本土生物的直接或间接不良影响不容忽视。利用传统评价方法预测候选天敌的生态风险存在缺陷，主要表现在：（1）寄主专一性测定过分依赖室内进行的生理寄主范围测定结果，对生态寄主范围（实际寄主范围）问题重视不够，后者指在新环境中的一系列物理和生物条件下的寄主利用预测；（2）在生理寄主范围测定中，过分依赖完成生长发育的可能性，对行为、遗传性状以及系统发育关系重视不够；（3）在风险评估中，过多强调对经济作物的风险，而对自然生态系统的风险重视不够。对此，建议：（1）鼓励对已释放的天敌进行回顾性跟踪研究，从而为杂草生物防治实践提供生态学理论支撑；（2）在运用生物防治手段对付外来入侵杂草实践中，建议采用“有害推论”的预防性原则，以避免在面临入侵生物重大威胁时草率做出释放天敌的决策；（3）在评估候选天敌风险中重视生态效应的风险评估。

Ecological risks and their control in classical biological control of weeds

The .classical biological control is a viable, effective strategy and approach to control alien invasive weeds as manifested by numerous successes in the long history of classical biological control. However, introduction of non-native biological control a- gents from their native region can pose potential direct or indirect ecological risks to non-target native organisms, which calls for nec- essary alertness. There exist flaws in the conventional practices in assessment of potential risks of biological control agents, which are manifested by： （,1） host specificity testing depends mostly on physiological （fundamental） host range testing in the lab, but less on ecological （realized） host range testing which is a prediction of host use under the range of physical and biotic conditions in the n~w environment; （2） the physiological host range testing mostly relies on the ontogeny in the lab, but less on behavioral and genet- ic characteristics; （3） the risk assessment pays more attention to non-target plants of economic importance but less on organisms in natural ecosystems. To reduce the risks in conventional practices of biological weed control, it is suggested that： （ 1 ） retrospective ecological studies of released natural enemies should be encouraged, so as to provide theoretical support for the risk assessment of releasing bioldgical control agents; （2） for the application of biological control approach to management of alien invasive weeds, it is recommended that adoption of ＂harmful until proven safe＂ approach based on the Precautionary Principle could be exercised to avoid unforeseen negative effects; （ 3 ） more emphasis on assessment of ecological effects should be laid on the risk assessment of biological control agents.