The introduction of invasive species is widely recognized as a major threat to biodiversity, but the use of biological control agents—natural predators or parasites introduced to control these invaders—has sparked considerable debate. While some ecologists advocate for biological control as an environmentally friendly alternative to chemical pesticides, others argue that it can lead to unintended consequences. This reading outlines three key arguments in favor of biological control. First, biological control is target-specific, meaning that the introduced predator or parasite typically feeds only on the invasive species, thereby minimizing harm to native organisms. For example, the introduction of the cactus moth (Cactoblastis cactorum) to control prickly pear cactus in Australia successfully reduced the cactus population without affecting native plants. Second, biological control is self-sustaining and cost-effective over the long term. Unlike chemical pesticides, which require repeated applications, a successfully established biological control agent can reproduce and spread on its own, providing ongoing suppression of the pest without ongoing human intervention. Third, biological control avoids the environmental pollution associated with chemical pesticides, such as soil and water contamination, and it does not harm non-target organisms through toxic residues. This approach thus aligns with principles of sustainable agriculture and conservation, making it an attractive option for managing invasive species.
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Professor: While the reading presents a rosy picture of biological control, I must emphasize that these arguments are often oversimplified and can be misleading. Let’s examine each point. First, the claim of target-specificity is not always true. Many biological control agents are not as specialized as assumed. For instance, the cane toad, introduced in Australia to control beetles, turned out to be a generalist predator that has devastated native amphibian and reptile populations. Even supposedly specific agents can shift their diet when the target prey becomes scarce, causing collateral damage to native species. Second, the idea that biological control is self-sustaining and cost-effective ignores the fact that once released, these agents cannot be easily controlled or recalled. If they fail to establish or if they spread to unintended areas, the economic and ecological costs can be enormous. Moreover, the initial research, testing, and monitoring required to ensure safety are extremely expensive, often surpassing the costs of chemical control. Third, while biological control avoids chemical pollution, it introduces a different kind of environmental risk: the potential for the agent itself to become invasive. This has happened with the mongoose introduced to control rats in Hawaii, which now preys on native birds. Furthermore, the effects of biological control are often irreversible, whereas chemical pesticides can be discontinued or reduced. In many cases, the cure may be worse than the disease.
📝 写作提示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
