Space for life
There is not a strain "anti-parasitic” milkweed per se, but monarch caterpillars that fed on milkweeds with higher levels of cardenolides experienced lower parasite burdens. Also, infected monarch prefers to lay eggs on high-level cardenolide milkweed species when given the choice.
In other words, we can say that "anti-parasitic” milkweeds are milkweed species that have a higher level of cardenolides compared to the other species. In the papers cited in this blog, the "anti-parasitic” milkweed was the Tropical Milkweed or Bloodflower (A. curassavica).