Developing Methods to Detect Specialist Parasite Ophryocystis elektroscirrha in Coastal California Monarch Populations.

Background/Question/Methods

The dramatic decline of monarch butterflies in coastal California can be attributed to a combination of climate change, pesticide use, habitat loss, disease and parasitism (Inamine et al. 2016). As monarch populations reach unprecedented lows they become especially vulnerable to pathogens and parasites. The specialist protozoan parasite Ophryocystis elektroscirrha (OE) infects monarch butterflies throughout their global range and is especially prevalent in populations with little or no migration, including the western population. Monarch larvae feed exclusively on milkweed species within the genus Asclepias; native Californian milkweeds such as Asclepias fascicularis go dormant in winter but the exotic and commercially planted Asclepias curassavica can negatively affect monarchs by providing a year‐round source of food, reducing the propensity to migrate, and thereby increasing disease prevalence in non‐migratory populations (Satterfield et al. 2015). Despite the suspicion that A. curassavica is a prominent vector of OE transmission, research on this topic is severely limited and frequently planted by homeowners and even professional conservationists. In order to understand how OE is contributing to the decline of monarchs at coastal breeding and overwintering sites, we will develop methods to detect OE in the environment and on leaf surfaces.

Results/Conclusions

We have collected Ophryocystis elektroscirrha spores from university collections at the Cheadle Center for Ecological and Biological Restoration. We then developed OE-specific qPCR primers in order to temporally and spatially track OE abundance and are able to determine if certain plants, such as A. curassavica, indeed harbor more parasites than other host plants. We tested three DNA extraction methods and established an efficient protocol for eDNA sampling. Once genetic material was successfully extracted, universal eukaryotic primers were used to sequence a conserved region of the OE genome to design and develop OE-specific PCR primers, which can then be used to identify OE in the environment, including both caterpillar host plants and overwintering roost sites. This study contributes to the understanding of how OE is impacting western monarch butterflies by providing information on plant species and the time of year that OE is most prevalent. This technique will enable the initiation of numerous studies investigating OE resilience on different milkweed species, possible monarch defense mechanisms, and predict how anthropogenic change affects OE virulence. By answering these questions, scientists and land managers will be informed on how to best aid the recovery of the culturally valuable and critically vulnerable monarch butterfly.