Museum collections reveal a global range of Ophryocystis parasites in Danaus butterflies

Understanding the host range, patterns, and consequences of parasite
infection is essential for detecting and responding to parasite-mediated
insect declines. The debilitating protozoan Ophryocystis elektroscirrha
(OE; Neogregarinorida: Ophryocystidae) was identified as a parasite of
monarch (Danaus plexippus) and queen (D. gilippus) butterflies in the late
1960s in Florida, USA. Recently, similar parasites were identified in
other Danaus species, but their occurrence among the diverse clade of
milkweed butterflies (Nymphalidae: Danainae) remains unexplored. This
study used museum collections to systematically investigate the host range
and global occurrence of OE and similar Ophryocystis parasites in milkweed
butterflies. We examined 2,727 museum specimens from 86 countries/areas,
spanning 61 milkweed butterfly species across 10 genera, to document
parasitism. Our findings revealed that, among milkweed
butterflies, Ophryocystis parasites were confined to hosts in the
genus Danaus and were widespread across five continents. Positive
specimens dated back to 1909. Lesser wanderers (D. petilia) exhibited the
highest percentage of positive specimens (16%), followed by monarchs
(12%), plain tigers (D. chrysippus, 11%), and queens (4%). We also present
the first documented infections in Jamaican monarchs (D. cleophile, 4%).
The patterns of parasite variation in size reflected the relatedness of
their host species but not their size. Overall, this research underscores
the value of museum collections for investigating geographic and temporal
host-parasite associations and provides foundational ecological data on
the relationships between Ophryocystis parasites and their milkweed
butterfly hosts.