Monarch butterflies in Northern California are adapting to a changing climate by breeding in the winter, a strategy that is key to their survival, according to a study published in the Journal of the Lepidopterists’ Society. Led by David James, an associate professor of entomology at Washington State University, the study found that monarch pupae developed during the winter of 2021/2022 had a survival rate of around 50%, building on a previous study that first documented winter breeding in the region during the winter of 2020/2021.
Over the past five years, overwintering populations of monarchs on the California coast have seen dramatic fluctuations, with a historic low of just 1,899 butterflies in 2020 before rebounding to 335,479 in 2022. Concurrently, there has been an increase in winter-breeding monarchs that feed on non-native milkweeds in the urban Bay Area. This study is the first to estimate the viability of monarch pupae during winter, with a success rate of 49.4% in pupal eclosion and the ability to survive and produce adults for up to seven weeks during winter.
The study also explored using shed-skin of pupae to detect the presence of the parasite Ophryocystis elektroscirrha, finding that around 70% of the winter breeding population was likely infected. This highlights the need for further research into the impact of this parasite and other stressors on western monarch populations under natural conditions. The rise of winter-breeding monarchs signals an adaptation to warmer winters, offering an alternative to traditional overwintering sites. Conservation practices may need adjustment to support this new behavior, such as shifting the timing of pruning milkweed to late summer.
To support healthier winter-breeding populations, conservation guidelines may need to be modified to ensure the availability of plants for monarchs. Currently, ornamental milkweeds that winter-breeding monarchs primarily use are cut down during winter to minimize parasite infection, which may be detrimental to the winter-breeding population. James suggests that guidelines should be adjusted to have milkweed cut back during late summer instead of late fall, still minimizing parasite infection while supporting winter-breeding monarchs.
Going forward, James and his team will continue to monitor winter breeding monarch populations in the south Bay Area to gather more data. They hope that these monarchs will play a crucial role in ensuring the sustainability of the nation’s western monarch population. This research highlights the importance of understanding how monarchs are adapting to a changing climate and how conservation efforts can be adjusted to support their survival. By learning from the strategies monarchs are using, conservationists can develop more effective strategies to ensure the future of these iconic insects.
