Instar Susceptibility of the Monarch Butterfly (Danaus plexippus) to the Neogregarine Parasite,Ophryocystis elektroscirrha

Abstract

The susceptibility of the monarch butterfly (Danaus plexippus) larvae to the neogregarine parasite, Ophryocystis elektroscirrha, was tested in the laboratory. Spore loads recovered from infected monarch butterflies were directly related to the inoculum level, larval stage of the host, and spore age. There was a linear relationship between spores ingested by first instar larvae and spore concentration. Larvae feeding on leaves treated with 0, 50, 500, 5000, or 50,000 spores averaged 0, 0, 193, 457, or 1,255 spores, respectively, on the abdomens of the adult butterflies. When first, third, and fifth instar larvae were given 14.5 spores/mg of body weight, there was no significant difference in the spore load of the adults resulting from the first and third instars. However, there were significant differences in the spore load from adults resulting from the first and third instars versus the fifth instar. In addition, 1-year-old spores were not as infectious as fresh spores. Our findings indicate that under field conditions, the first instar is most likely to become infected because one spore appears sufficient to produce a detectable spore load in the adult. Older instars are less susceptible and have fewer opportunities to encounter sufficient viable spores for infection to occur. Thus, vertical transmission appears to be the primary mode of parasite maintenance in natural populations of monarch butterflies.

Effects of phenological synchronization on caterpillar early-instar survival under a changing climate

“…Phenology can drive these relationships in similar ways as with multicellular natural enemies, as insect immunity can vary with host plant synchrony (Martemyanov et al 2015). The study of mycorrhizae (e.g., Tao et al 2016), phylloplane flora (e.g., Leong et al 1997), midgut biota (e.g., Mason and Raffa 2014;Martemyanov et al 2016), and pathogens (e.g., Hajek et al 1990;Leong et al 1997;van Frankenhuyzen et al 2007;Gowler et al 2015) in plant-herbivore systems is suggesting potentially important roles for multitrophic interactions with these poorly understood organisms. These relationships are only beginning to be identified and their phenologies or responses to climate have yet to be examined.…”

“…For instance, leaf surface microflora can affect herbivores and the scant evidence that exists suggests that pathogens from the phylloplane are more harmful for young than for older caterpillars (Leong et al 1997). However, the population-level consequences of these interactions remain unresolved.…”

“…Ingestion of latex can also cause larvae to become cataleptic and increase their chances of being mired, falling off the plant, or being killed by invertebrate predators (Zalucki et al 2001a). It is also at this early stage that caterpillars can acquire Ophryocystis elektroscirrha from the phylloplane: this neogregarine parasite causes developmental abnormalities during metamorphosis when ingested during the early instars (Leong et al 1997).…”

Genetic variation in resistance, but not tolerance, to a protozoan parasite in the monarch butterfly

“…Monarchs are commonly infected with the apicomplexan protozoan parasite O. elektroscirrha [41,42]. Infection with this parasite occurs when caterpillars ingest parasite spores scattered onto eggs or host plant leaves by infected female monarchs during oviposition.…”

Monarch butterfly migration and parasite transmission in eastern North America

“…Parasites can be transferred vertically, from infected adults to their progeny, and horizontally, when butterflies scatter spores that are ingested by unrelated larvae (Altizer et al 2004, De Roode et al 2009). Larva-to-larva transmission does not occur (Leong et al 1997b). Parasites occur in all monarch populations examined to date (Leong et al 1997a, Altizer et al 2000.…”