Dear Monarch Watchers,
Through the Monarch Larva Monitoring Project, we are tracking tachinid fly parasitism rates throughout the US and some sites in Canada. These data allow us to measure changes in parasitism rates over broad spatial and temporal scales - we have well over 8000 records. If you rear monarchs from the wild, it is very easy to record and enter the data; you just need to record where and when you collected the monarch, the stage it was in at collection, and the outcome (monarch adult, tachinid fly or other parasitoid, died of another cause). It's important to record all monarchs, not just those that are parasitized. You don't have to have a regular MLMP monitoring site to do this. If you collect many monarchs from one site, you can sign it up as an MLMP site and enter the data through the site page, and if you collect them from other sites, you sign up and enter the data from a link called "Data on Monarchs You Rear from other Locations". For more information, please feel free to contact me, or check out the data sheet at http://www.mlmp.org/Monitoring/datasheets/activity3.pdf. If you don't want to enter the data online, you can send us the data sheets. We are also collecting the adult flies to determine if they are all the same species, or if different fly species attack monarchs in different parts of their range. You can see summaries of parasitism rates in each state or individual sites in the results section at www.mlmp.org.
One interesting finding is that parasitism rates are correlated with monarch densities in the previous year, at least in the Upper Midwestern US where we have the most data. This is published in the paper referenced below, which is posted on my website (http://fwcb.cfans.umn.edu/oberhauser/). We haven't detected a climate signal in the parasitism rate data, but it is possible that this would show up with more data.
Oberhauser, KS. 2012. Tachinid flies and monarch butterflies: Citizen Scientists document parasitism patterns over broad spatial and temporal scales. American Entomologist 58:19-22.
Associate Professor and Director of Graduate Studies, Conservation Biology
Department of Fisheries, Wildlife, and Conservation Biology
University of Minnesota