The Occurrence and Effect of a Protozoan Parasite, Ophryocystis elektroscirrha (Neogregarinida: Ophryocystidae) on Overwintering Monarch Butterflies, Danaus Plexippus (Lepidoptera: Danaidae) from Two California Winter Sites

1. Monarch butterflies, Danaus plexippus, from two overwintering populations, were found to have Ophryocystis elektroscirrha spores on their scales at rates between 53% and 68%. The frequency of butterflies with O.elektroscirrhaspores remained about the same between sites and throughout the winter. 2. The spores, recovered from all parts of the body of the butterfly, were most numerous on the abdomen, particularly near the posterior third. 3. Butterflies with spores survived as long as those without detectable spores at 10.1°C ±0.4 SE and 78.3% r.h. ±0.6SE. Insects with spores held at 19.4°C ±0.4SE and 44.9% r.h. ±1.5SE showed a significantly higher rate of moisture loss and survived a shorter period than monarch butterflies without detectable spores