TOEFL統合ライティング

📖 読解文章

The decline of the honeybee population, known as colony collapse disorder (CCD), has been a major concern for ecologists and agriculturalists. Several theories have been proposed to explain this phenomenon. First, the widespread use of neonicotinoid pesticides is often cited as a primary cause. These chemicals, applied to crops, are absorbed by plants and contaminate nectar and pollen, which bees then consume. Studies show that even sublethal doses can impair bee foraging behavior and navigation, weakening colonies. Second, the parasitic Varroa mite is considered a key factor. These mites attach to adult bees and larvae, feeding on their bodily fluids, and they also transmit viruses that can devastate a hive. Third, habitat loss due to intensive agriculture and urbanization has reduced the availability of diverse floral resources, leading to nutritional stress among bee populations, which makes them more susceptible to diseases and environmental stressors.

🎧 リスニング講義

The professor challenges the three explanations presented in the reading. Regarding pesticides, she argues that while neonicotinoids are harmful, the correlation with CCD is not consistent. In many regions where CCD occurs, pesticide use is low, and conversely, high-use areas sometimes show healthy colonies. Moreover, laboratory studies often use doses far higher than what bees encounter in the field. More compelling evidence points to a combination of stressors, but pesticides alone cannot explain the phenomenon. As for the Varroa mite, the professor admits its impact but notes that CCD was first reported in 2006, whereas mites have been present in the U.S. since 1987. If mites were the primary cause, CCD would have emerged much earlier. Additionally, some CCD-affected hives show no significant mite infestation, suggesting other factors are at play. Finally, on habitat loss, the professor acknowledges that reduced floral diversity is a problem, but it does not account for the sudden and widespread nature of CCD. Bees have historically survived in fragmented habitats, and CCD affects even colonies in diverse, rural areas. She suggests that a more likely culprit is a novel pathogen, such as the Israeli acute paralysis virus, which has been detected in many collapsed colonies, though this is still under investigation.