We are constantly analyzing the numbers of monarchs found by
MLMP volunteers every year, looking for changes and trends in population
numbers. We’ve also shared a lot of
data with the scientific community in several publications. Here are summaries of
a few of these publications; you can link to the full publication of most papers.
Pleasants, J.M. 2015. Monarch Butterflies and Agriculture. Monarchs in a Changing
World: Biology and Conservation of an Iconic Butterfly. 14: 169-178. The author
shows that herbicide kills monarch eggs and larvae by defoliating plants and examines
several reasons for the observed high density of monarch eggs on agricultural milkweeds
and estimate the potential milkweed resource in pre-settlement times.
Batalden, R.V., Oberhauser, K.S. 2015. Potential Changes in Eastern North American
Monarch Migration in Response to an Introduced Milkweed, Asclepias curassavica.
Monarchs in a Changing World: Biology and Conservation of an Iconic Butterfly. 19:
215-224. The authors investigated fall and winter breeding behavior by eastern North
American migratory monarchs. Using data from two citizen science projects (the Monarch
Larva Monitoring Project and Journey North), they documented monarch egg and larva
presence in Texas and other Gulf Coast states throughout the fall and winter.
Ries, L., Taron, D.J., Rendon-Salinas, E., Oberhauser, K.S. 2015. Connecting Eastern
Monarch Population Dynamics across Their Migratory Cycle. Monarchs in a Changing
World: Biology and Conservation of an Iconic Butterfly. 24: 268-281. Here, the authors
followed monarch population dynamics throughout the annual cycle, using data from
seven large-scale monitoring programs, most relying on citizen scientists to look
for evidence that dynamics at one step of the migratory cycle carry over to subsequent
steps using linear regression.
Oberhauser, K.S., Ries, L., Altizer, S., Batalden, R.V., Kudell-Ekstrum, J., Garland,
M., Howard, E., Jepsen, S., Lovett, J., Monroe, M., Morris, G., Rendon-Salinas,
E., RuBino, R.G., Ryan, A., Taylor, O.R., Trevino, R., Villablanca, F.X., Walton,
D. 2015. Contributions to Monarch Biology and Conservation through Citizen Science.
Monarchs in a Changing World: Biology and Conservation of an Iconic Butterfly. 2:
13-30. Here, authors review past and current programs, focusing on characteristics
of successful programs and their wide-reaching scientific, environmental, and educational
outcomes. We also present a data gap analysis to ask what locations and times of
year have limited data on monarch biology, to inform the targeted recruitment of
monarch citizen scientists into current and future programs.
Oberhauser, Karen. 2012.
Tachinid Flies and Monarch Butterflies: Citizen Scientists Document Parasitism Patterns
over Broad Spatial and Temporal Scales. Am. Entomol. 58(1): 19-22. Karen Oberhauser
used parasitism data collected by 130
volunteers throughout the country to determine patterns of tachinid fly parasitism
in monarchs. She reports that even though monarch larvae can be parasitized by a
tachinid fly in any instar, the daily risk is higher for second through fourth instars.
The data also show that in the Upper Midwest there is a correlation between the
rate of parasitism and the monarch population density the previous year.
Pleasants, J. and K. Oberhauser. 2012.
Milkweed loss in agricultural fields because of herbicide use: effect on the monarch
butterfly population. Insect Conservation and Diversity. doi: 10.1111/j.1752-4598.2012.00196.x.
This article reports that in the past decade there has been a large decline in milkweed
in agricultural fields that is coincident with the increase in the use of glyphosate
herbicide. They report an estimated 58% decline in milkweeds on the Midwest landscape
and an 81% decline in monarch production in the Midwest from 1999 to 2010.
Lindsey, E., M. Mudresh, V. Dhulipala, K. Oberhauser, S. Altizer. 2009.
Crowding and disease: effects of host density on response to infection in a butterfly-parasite
interaction. Ecological Entomology 34:551–561. This study shows how the changes
in the density of monarch affect their susceptibility to the parasite Ophryocystis
data were used to show the degree to which monarch butterfly larval densities vary
over time and space in eastern North America. The study showed that the probability
of infection increased with the increase in population density.
Oberhauser, K. S. and M. D. Prysby. 2008.
Citizen science: creating a research army for conservation. American Entomologist
54:97-99. There are many conservation outcomes of engagement in a citizen science
project like the
MLMP. Volunteers often work to preserve habitat, share their findings with
others, and collect information that allow us to assess overall population trends.
Kountoupes, D., and K. S. Oberhauser. 2008.
Citizen science and youth audiences: Educational outcomes of the Monarch Larva Monitoring
Project. Journal of Community Engagement and Scholarship. 1:10-20. Many adult
volunteers engage students in the project. This study summarizes the educational
and scientific value for these students, many of whom have gone on to do their own
independent research projects because of monitoring.
Oberhauser, K. S., I. Gebhard, C. Cameron, S. Oberhauser. 2007.
Parasitism of monarch butterflies (Danaus plexippus) by Lespesia archippivora
(Diptera: Tachinidae). Amer. Midl. Nat. 157:312-328. This study analyzes the
parasitism rates of wild monarch by the tachinid fly, using data collected over
7 years by 77 volunteers in the Monarch Larva Monitoring Project. In a sample of
2903 larvae from 1999–2005, 80.4% resulted in healthy adult monarchs, 7.4% died
of other causes, and 13% contained tachinid flies. Monarchs that were collected
in later stages of life were more likely to be parasitized, and there were no consistent
patterns in the parasitism rates from year to year.
Batalden, R., K.S. Oberhauser, A.T. Peterson. 2007.
Ecological niches in breeding generations of Eastern North American monarch butterflies.
Ecol. Entomol. 36:1365-1373. This study uses eastern North American MLMP data to
show a series of shifts in monarchs’ breeding season habitat. We used ecological
niche modeling to identify the ecological conditions that monarchs use for breeding
in successive summer months, and then see how climate might affect the habitats
in which monarch breed. In the early months of the breeding season (March-June),
monarchs will actually be able to use more habitat than they can now, but in June-August
the ideal conditions move farther north. Whether monarchs will be able to adapt
to these changes isn’t known.
Prysby, M. and K. Oberhauser. 2004.
Temporal and geographic variation in monarch densities: Citizen scientists document
monarch population patterns. Pp. 9-20 in: Oberhauser, K.S. and M.J. Solensky,
eds. The Monarch Butterfly: Biology and Conservation. Cornell University Press.
This paper, part of a collection of 27 studies on monarchs, used
data to look at immature monarch survival rates, and patterns within and between
years. Only about 10-20% of monarchs survive from the egg to 5th instar, and there
is a great deal of variation in monarch densities from one year to the next. Densities
tend to be higher in the central part of the US than the Northeastern. Prysby and
Oberhauser also compared findings from this project to other monarch monitoring
Prysby, M. 2004. Natural enemies and survival
of monarch eggs and larvae. Pp. 27-38 in: Oberhauser, K.S. and M.J. Solensky,
eds. The Monarch Butterfly: Biology and Conservation. Cornell University Press.
Michelle Prysby investigated the effects of natural enemies on the survival of monarch
eggs and larvae in three field studies. In an exclosure experiment, monarch survival
was significantly higher with terrestrial predators excluded. In a second study,
she investigated effects of an aphid-tending ant species on monarch survival. Survival
was seven times higher for monarchs on milkweed from which ants had been excluded.
Finally, she used both her own data and
to demonstrate that tachinid flies represent an important source of mortality; of
the fourth and fifth instars collected, 15% were parasitized by tachinids in 1999
and 23% in 2000.
Rea, B., K. Oberhauser, M. Quinn. 2002. A field guide to invertebrates on milkweed.
(96 pp.) Bas Relief Publishing Group, Pennsylvania. Milkweed, Monarchs, and More is a book that shows the
diverse natural community you may experience while monitoring. It helps show the
exciting world of monarchs and milkweed with tons of pictures and information.
Oberhauser, K.S., Prysby, M.D., Mattila, H.R., Stanley-Horn, D.E., Sears, M.K.,
Dively, G., Olson, E., Pleasants, J.M., Lam. W.F. & Hellmich, R. 2001.
Temporal and spatial overlap between monarch larvae and corn pollen. Proc.
Nat. Acad. Sci. 98 (21): 11913-11918. This study observed the milkweed and monarch
densities in cornfields to determine the likelihood that the monarchs would be exposed
to Bacillus thuringiensis (Bt) pollen. In order to collect their data, they
used MLMP monitoring protocols. The findings showed that many monarchs used milkweed
in cornfields, indicating that changes in the agricultural practices of these areas
could have large impacts on both milkweed and monarchs.
Prysby, M. and K. Oberhauser. 1999. Large scale monitoring of monarch populations.
Proceedings of the 1997 North American conference on the Monarch
Butterfly, pp. 379-384. Hoth, J, I. Pisanty, K. Oberhauser, L. Merino and
S. Price, editors. Commission for Environmental Cooperation: Montreal, QC. Our first
paper on the
provided an overall summary of the distribution and abundance of larval monarch
populations during the breeding season in North America. Among other things, we
showed that the abundance of monarchs did not increase uniformly throughout the
season, but showed two or more peaks in abundance. Mortality appeared to be high
in the egg and early instar stages at all sites, based on the densities and proportions
of individuals in each stage in consecutive week.