Monarch fall migration, overwintering mortality and the effects of defence compounds released by decomposing butterflies on the soil ecosystem.

黑脉金斑蝶是一种以往返于墨西哥越冬地而闻名的标志性昆虫，由于栖息地丧失和现代农业实践等一系列因素，北美的黑脉金斑蝶数量已经下降。由于非法砍伐造成的习性丧失已经减少，保护计划导致马利筋的可用性增加，马利筋是黑脉金斑蝶使用的唯一寄主植物。然而，其他可能有助于保护工作的方面受到的关注较少。迁徙到墨西哥的成年帝王蝶性成熟，在迁徙过程中需要花蜜来维持自己，并积累足够的脂肪储备以度过冬季，但在这一重要时期，我们没有详细的脂肪获取和使用信息。我们的假设是，在秋季，迁徙的成虫通过每天摄取当地的花蜜来源来维持足够的飞行和维持，只有当它们非常接近越冬地点时才显著增加脂肪储备。为了验证这一点，我们将在加拿大、美国和墨西哥沿迁徙走廊的不同地点监测帝王蝶的脂肪含量，以及到达越冬地点的帝王蝶。我们还将监测冬季死亡率的时间模式，以确定与出生来源和寄生虫负荷等因素相比，脂肪储备对生存的相对重要性。这项研究将持续5年，因为花蜜资源的年际可用性将随着气候条件的变化而变化。例如，由于2019年的温暖夏季，8月底，安大略省的早期成虫开始繁殖，而不是移民。如果后代成功地完成发育，当花蜜来源很少时，成虫就会出现，因此没有必要的资源来成功地迁徙。同样，由于干旱，今年墨西哥的花朵数量要少得多，因此移民将没有多少机会建立过冬所需的储备，这是至关重要的，因为越冬地点的花蜜资源很少。由于迁徙通道上任何一点的恶劣天气条件都可能对资源的可用性产生负面影响，我们的研究结果将有助于制定管理策略，确保在迁徙路线上获得花蜜来源，确保在迁徙和冬季都能更好地生存。目前，一个悬而未决的基本问题是“尽管以前从未去过那里，但帝王蝶是如何年复一年地找到相同的越冬地点的？”许多帝王蝶在冬天死亡，所以我们正在进行研究，以确定从腐烂的个体释放的化学物质是否会影响土壤生态系统，这些化学物质是活着的帝王蝶用来防御捕食者的，这些变化会导致化学信号的产生，这些化学信号是迁徙的蝴蝶用来定位越冬地点的。

North American populations of the monarch, an iconic insect known for its migration to and from overwintering sites in Mexico, have declined due to a number of factors including habitat loss and modern agricultural practices. Habit loss due to illegal logging has declined and conservation programmes have resulted in increased availability of milkweed, the only host plant used by the monarch. However, other aspects that could help conservation efforts have received less attention. Adult monarchs migrating to Mexico are sexually immature and need nectar sources to sustain themselves during migration, and to accumulate sufficient fat reserves to survive winter, yet we do not detailed information of fat acquisition and use during this important period. Our hypothesis is that in fall the migrating adults sustain just enough reserves for flight and maintenance by feeding daily on local nectar sources and only markedly increase fat reserves once they are very close to the overwintering site. To test this, we will monitor the fat content of monarchs at different sites along the migratory corridor in Canada, USA and Mexico with those arriving at overwintering sites. We will also monitor temporal patterns of mortality during the winter to determine the relative importance of fat reserves on survival, compared with factors such as natal origin and parasite load. This study will be run over five years as the inter-year availability of nectar resources will vary with climatic conditions. For example, due to the warm summer in 2019, at the end of August early emerging adults in Ontario started reproducing rather than emigrating. If the offspring successfully complete development, adults will emerge when very few nectar sources are available, and thus would not have the necessary resources to successfully migrate. Similarly, there are far fewer flowers available this year in Mexico due to drought, so immigrants will have less opportunity to build up the reserves required to survive the winter, which is critical as few nectar resources exist at the overwintering sites. As adverse weather conditions at any point along the migratory corridor could negatively affect resource availability the results of our research will help develop management strategies that ensure nectar sources are available along the migratory route, ensuring greater survival both while migrating and during the winter. Currently, one unanswered basic question is "how do monarchs, even though they have never been there before, locate the same overwintering sites year after year?" Many monarchs die during the winter and so we are undertaking studies to determine if the release of chemicals from decomposing individuals, which live monarchs use in defend against predators, impacts the soil ecosystem and that these changes result in the production of chemical signals that the immigrating butterflies use to locate overwintering sites.