Many factors can affect the success and failure of classical biological control. However, these factors have mainly been studied independently of each other, which leaves their relative importance within the complexity of classical biological control (CBC) programmes unknown. Therefore, we set out to take a more holistic view on the factors that may impact the outcome of CBC of insect pests by insect predators and parasitoids. To this end, we filtered the BIOCAT catalogue to extract entries for the Greater Western Palearctic ecozone and added 15 new explanatory variables. These mainly concerned traits of released biological control agents, target pests, and host plants of the target, but also included the number of introductions for specific agent-target combinations as a management aspect. We then analysed the data regarding three levels of success: agent establishment, impact on the target population, and complete control of the target. Between 1890 and 2010 a total of 780 introductions of insects for biological control were undertaken in the analysed area, constituting 416 agent-target combinations. Overall success of agent establishment was 32%, successful impact of single agents on their target was 18%, and success of complete control was 11%. The number of factors significantly influencing the outcome of CBC decreased with increasing level of success. Remarkably few agent-related factors influenced the success: insect predators as agents decreased the probability of establishment and using oligophagous parasitoids significantly decreased the chances of complete control. Other significant factors were related to traits of target pests or their host plants. For example, sap feeders and target pests attacking reproductive plant parts were more likely to be successfully controlled. The rate of success increased with the number of introductions of CBC agents, in particular against univoltine target pests. These findings suggest that a focus on agent-related traits to increase the chances of successful CBC is not fully justified and should be complemented with the consideration of lower trophic levels and other aspects of CBC, such as abiotic factors and management.

中文翻译：

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欧洲、北非和中东对害虫的经典生物防治：是什么影响了它的成功？

许多因素会影响经典生物防治的成败。然而，这些因素主要是相互独立研究的，这使得它们在经典生物控制 (CBC) 程序的复杂性中的相对重要性未知。因此，我们着手更全面地了解可能影响昆虫捕食者和寄生物对害虫 CBC 结果的影响因素。为此，我们过滤了 BIOCAT 目录以提取大西部古北生态区的条目，并添加了 15 个新的解释变量。这些主要涉及释放的生物防治剂的性状、目标害虫和目标的寄主植物，但也包括作为管理方面的特定药剂-目标组合的引入数量。然后我们分析了关于三个成功水平的数据：代理建立、对目标人群的影响以及对目标的完全控制。1890 年至 2010 年间，在分析区域共引入了 780 种昆虫进行生物防治，构成了 416 种药剂-靶标组合。代理建立的总体成功率为 32%，单个代理对其目标的成功影响为 18%，完全控制的成功率为 11%。随着成功水平的提高，显着影响 CBC 结果的因素数量减少。显着地，很少有与代理相关的因素影响成功：昆虫捕食者作为代理降低了建立的可能性，并且使用寡食性寄生蜂显着降低了完全控制的机会。其他重要因素与目标害虫或其寄主植物的性状有关。例如，树液饲养者和攻击植物生殖部分的目标害虫更有可能被成功控制。成功率随着引入 CBC 试剂的数量而增加，特别是针对单价目标害虫。这些研究结果表明，关注与代理相关的特征以增加 CBC 成功的机会并不完全合理，应该辅以考虑较低的营养水平和 CBC 的其他方面，例如非生物因素和管理。尤其是针对单性目标害虫。这些研究结果表明，关注与代理相关的特征以增加 CBC 成功的机会并不完全合理，应该辅以考虑较低的营养水平和 CBC 的其他方面，例如非生物因素和管理。尤其是针对单性目标害虫。这些研究结果表明，关注与代理相关的特征以增加 CBC 成功的机会并不完全合理，应该辅以考虑较低的营养水平和 CBC 的其他方面，例如非生物因素和管理。