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University of Minnesota Extension

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Findings

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 MLMP 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.

Publications

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 MLMP 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 elektroscirrha (O.E.). MLMP 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 MLMP 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 MLMP 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 projects.

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 MLMP 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 MLMP 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.