This page summarizes several current and previous research projects on monarch butterfly parasites from people in the Altizer lab.

Contents: Click on the link below to jump to the section of interest.

1. OE transmission in eastern North American migratory monarchs
2. Disease risks in migratory animals

3. Wing morphology differences in monarch populations
4. Virulence-transmission trade-offs in OE
5. Effects of host plant species on parasite infection
6. Parasite replication and virulence
7. Parasites and monarch flight performance
8. Geographic variation in prevalence

Other citizen science programs

1. OE transmission in eastern North American migratory monarchs

Spring 2011 - A study from the lab shows how seasonal migration is likely to influence interactions between monarchs and their parasites. The study was by Becky Bartel, Karen Oberhauser, Jaap de Roode, and Sonia Altizer and was published in Ecology. Click here to view the pdf version of the paper.

Highlights from the study:

How does seasonal migration influence interactions between animals and their parasites?

To look at how host migration affects infectious disease processes, we focused on the monarch-OE system. We combined field-sampling efforts with data from Monarch Health to examine patterns of parasite prevalence.

We found that OE infection levels increased from early to late in the breeding season for all years (2006-2009, graph of 2009 values shown on left, below). Because breeding habitats are heavily infected, migration may allow monarchs to flee areas with high levels of parasites. Among adult monarchs captured at different points along the east coast fall migratory flyway, parasite prevalence declined as monarchs progressed southward, and was also lower among monarchs sampled at two overwintering sites in Mexico than among monarchs sampled during the summer breeding period (graph shown on right, below) . These long-distance movements might weed out infected animals.

2. Disease risks for migratory animals

Spring 2011 - A study from the lab shows how animal migrations can affect disease dynamics. The study was by Sonia Altizer, Becky Bartel, and Barbara Han and was published in the Science. Click here to view the pdf version of the paper.

Highlights from the study:

Animal migrations are expected to enhance the global spread of pathogens and facilitate cross-species transmission. This does happen, but new research has also shown that migration allows hosts to escape from infected habitats, reduces disease levels when infected animals do not migrate successfully, and may lead to the evolution of less virulent pathogens. Migratory demands can also reduce immune function, with consequences for host susceptibility and mortality. Studies of pathogen dynamics in migratory species and how these will respond to global change are urgently needed to predict future disease risks for wildlife and humans alike.

3. Wing morphology differences in monarch populations

Spring 2010 - A study from the Altizer lab shows how migratory distance may affect the form and structure of wings in monarchs. The study was by Sonia Altizer and Andy Davis and was published in the journal, Evolution. Click here to view the pdf version of the paper.

Highlights from the study:

Does seasonal migration affect the form and structure of monarch wings?

The demands of long-distance flight represent an important evolutionary force operating on the traits of migratory species. We examined divergence in wing morphology among migratory monarchs from eastern and western N. America, and non-migratory monarchs in S. Florida, Puerto Rico, Costa Rica and Hawaii. We used image analysis to measure multiple traits including forewing area and aspect ratio; for laboratory-reared monarchs we also quantified body area and wing loading.

Results showed wild monarchs from all non-migratory populations were smaller than those from migratory populations. Wild and captive-reared eastern monarchs had the largest and most elongated forewings, whereas monarchs from Puerto Rico and Costa Rica had the smallest and roundest forewings (graph shown on left, below). Eastern monarchs also had the largest bodies and high measures of wing loading, whereas western monarchs had less elongated forewings, smaller bodies and lower wing loading (graph shown on right, below).

4. Virulence-transmission trade-offs in OE

Fall 2007 - This research in the Altizer lab examined the trade-offs of parasite dependence on their hosts for survival and the possibility of their effects on host disease or death. The study was by Jaap de Roode, Andrew Yates, and Sonia Altizer was published in the Proceedings on the National Academy of Sciences. Click here to view the pdf version of the paper.

Highlights from the study:

Why do parasites harm their hosts? The study asked if parasites could evolve virulence by balancing the benefits of using their hosts to transmit disease and the costs of possible host death due to their effects.

Using the monarch-OE system, researchers compared the effects of # of parasites on a host to mating success, lifespan, lifetime reproductive success, and infection rates in monarch butterflies.

Among their results, they found that higher #s of parasites led to lower proportions of monarchs surviving to adulthood (graph shown on left, below). They also found females monarchs that were more infected passed along higher amounts of parasites to eggs and on milkweed plants. The greater the # of spores on the plants, the more likely the larvae were infected (graph shown on right, below).

5. Host plants affect parasite replication and virulence

Fall 2007 - A study from the lab shows how the infection severity of OE and effects on monarchs depends on what milkweed species the larvae eat! The study was by Jaap de Roode, Amy Pedersen, Mark Hunter, and Sonia Altizer and was published in the Journal of Animal Ecology. Click here to view the pdf version of the paper.

Highlights from the study:

The study involved rearing monarch larvae on either swamp milkweed (Asclepias incarnata) or tropical milkweed (Asclepias currasavica), which both differ in cardenolide (milkweed toxin) content (left graph).

Then the larvae were experimentally inoculated with OE and reared to adulthood. Their spore loads and survival were recorded.

The results showed that monarchs reared on tropical milkweed lived longer when infected and had lower spore loads during infections.

6. Parasites replicate rapidly and reduce monarch survival

Spring 2007 - A study from the Altizer lab shows how the severity of OE infection influences the biology of monarchs. The study was by Jaap de Roode, Laura Gold and Sonia Altizer and was published in the journal, Parasitology. Click here to view the pdf version of the paper.

Highlights from the study:

Since the study involved examining variation in infection levels, Jaap had to devise a method of experimentally infecting larvae with single spores! He ended up making super-tiny glass rods (left) with which he could pick up and transfer single spores and place them on monarch eggs (below)!
The chart above depicts the relationship we found between the number of OE spores ingested as larvae (X axis) and the number of spores that adults have on them when they emerge (y axis). The different lines represent different OE parasite types. Amazingly, monarch larvae infected with a single spore during the second instar had over 100,000 spores on them as adults!
We also found that the life-span of butterflies decline the more infected they are. The chart above shows that monarchs infected with one spore as larvae lived an average of about 11 days as adults, and about 4 days when infected with 100 spores.

7. Parasites hinder monarch flight performance

Spring 2005 - A study from the Altizer lab on the effects of OE on monarch butterfly flight is released, with lots of press (below)! The study was by Catherine Bradley and Sonia Altizer and was published in the journal, Ecology Letters. Click here to view a pdf version of this paper.

Highlights from the study:

The objective of the study was to determine if monarchs infected with OE were capable of flying equally as well as uninfected ones. To do this, the team solicited the help of the Emory University Physics dept, who designed a 'butterfly treadmill' (or flightmill, pictured right) to test the monarchs.

Infected and uninfected adult monarchs were tested using this apparatus, which measured their flight speed and endurance.

The results showed that infected monarchs were not able to fly as well as uninfected - their speed was lower (below) and their endurance was also lower. These results have large implications for monarch migration.

Flight mill designed by Horace Dale to test flight endurance of healthy and parasitized monarch butterflies

Horace Dale, Sonia Altizer and Catherine Bradley

Below are several articles in the popular press that were written about this study:

By Stéphan Reebs in the October 2005 issue of Natural History magazine:

In the American Society of Microbiologists' Newsletter, 2005:

This article was written by our very own Jaap de Roode:

Other articles...

Emory Press Release: Monarch Health Tied to Migration

Highlighted in Science Editor's Choice section [PDF]

Release on

Earthwatch Radio: Migratory Immunity

BBC Wildlife: Butterfly Purges Travel Bug

8. Prevalence of OE varies among global monarch populations

Research in our lab and others has revealed that the OE parasite infects populations of monarchs differently around the globe. Although much of our research is aimed at identifying the reasons for this variation, we do know what proportion of individuals is infected from North American populations. Below is the variation in prevalence (percent of individuals with HEAVY OE infections) in the three known North American monarch populations. The prevalence is lowest in the eastern monarch population (which migrates the longest distance - shown by arrows), and highest in the non-migratory South Forida population. Anecdotal evidence suggests that a high proportion of monarchs from Hawaii are heavily infected. Click here to view the original paper with this data.

These prevalence estimates have stayed the same through time as indicated by the chart above. In this chart, yellow points represent eastern monarchs, orange represents western, and green represents monarchs from South Florida.

Global population prevalence of OE varies according to the migration tendency of the population.

The monarch population in eastern N. America (that has the longest migration) has the lowest prevalence of OE.

The populations with no or little migration have the highest prevalence.

Other citizen science websites with monarchs

Monarch Larva Monitoring Project began in 1997 at the University of Minnesota. It involves citizens in collecting data that will help to explain the distribution and abundance patterns of monarch butterflies in North America.

Journey North helps students study wildlife migration and seasonal change. They track the coming of spring through the migration patterns of monarch butterflies, robins, hummingbirds, whooping cranes, gray whales, bald eagles— and other birds and mammals; the budding of plants; changing sunlight; and other natural events.

Monarch Migratory Association of America: A network of existing monarch migration projects that all focus on : counting the annual numbers of monarchs that migrate though specific sites in North America.

Monarchs Across Georgia: A collaboration of teachers, students, families, communities, businesses and others, all working together to study Monarch butterflies and restore butterfly habitat across Georgia.