TROPICAL MILKWEED in Southern California can pose a risk to Monarch Butterflies if not properly managed because this species harbors Ophryocystis elektroscirria, a parasitic protozoan (a single celled organism). Scientists think OE co-evolved with tropical milkweed, but can interfere with migration and growth. So Native Milkweeds are recommended because they go through a winter die out (above the ground surface) where the protozoans reside.
Talking about monarch migration and natural history, expect to hear more about OE, since they also infect queen and lesser wanderer butterflies.
If your Monarch chrysalids are OE infected, they exhibit black blotches (as seen in the photo below) and should be completely isolated if they survive.
FIGURE 1: SIGNS OF OE INFECTION:
SPORES SEEN AS DARK PATCHES INSIDE THE CHRYSALIS
Photo credit: University of Georgia, Athens
The good news is that OE can be blocked before causing damage to butterfly populations.
Since the OE protozoan population increases on milkweed plants over the growing season, it's greatest threat is when, in warm climates like Southern California, tropical milkweed tops survive the winter and OE numbers become a threat the following year.
FIGURE 2 TROPICAL MILKWEED
Photo credit: Toby Manzanares
If you have tropical milkweed, as in Figure 2, the XERCES SOCIETY suggests:
With tropical milkweed so readily available... Some advice has suggested plants can be cut back to the ground twice during the growing season to limit the spread of disease, and that plants should be removed late in summer so as not to interfere with migration. In practice however, we’ve found it’s been a hard-sell to get anyone to cut back plants that are actively supporting monarch eggs or caterpillars, or remove lush plants in full flower.
The Xerces Society, with 16 scientific advisors on staff, is an international nonprofit working to protect the natural world through conservation of invertebrates and their habitats.
The staff of Monarch Joint Venture recommends cutting the milkweed stalks down to 6 inched in height. Thanksgiving is an easy date to remember. This eliminates OE spores present on the plants from contaminating spring sprouts. Source: https://monarchjointventure.org/faq/when-to-cut-back-tropical-milkweed
RECOMMENDATIONS:
1: Grow Native milkweed
2: Don't grow tropical milkweed unless your are willing to:
A. Inspect chrysalids for OE and
B. Cut back tropical milkweed stocks to six inches at Thanksgiving.
3. Compost tropical milkweed seed pods that are not eaten by monarch caterpillars so that seeds won't propagate in the wild.
If you have additional recommendations, leave them with your research sources in the comments section below.
In monarchs OE damage takes place during the chrysalid stage. While the infected adults do not survive to migrate, they do spread the protozoan parasite. If you see the sign of infection above, keep this butterfly isolated when it emerges. Place milkweed florets with blossoms to feed the isolated adult.
FIGURE 3: LIFE CYCLE OF Ophryocystis, elektroscirrha.
Resource credit: Project Monarch Health at https://www.monarchparasites.org/oe
Sunday, July 17, 2022 The good news is that none of our 9 Laguna Beach chrysalids showed signs of OE infection.
Figure 4: OE Spores
Photo credit: Chip Taylor
Monarch butterflies live in an ecological community that includes a multitude of flora and fauna. Of this collection of living things, 12 are diseases, parasites, and caterpillar killers.
Figure 5: Deadly Tachinid Parasitoid Flies
This explains why 90% of monarch caterpillars do not survive to reproduce.
