University of Minnesota

Monarch Lab Research Updates

Posted on Thursday, January 1, 2004 at 9:51 am in Monarch Lab Research Updates

2004 Monarch Lab research updates: Monarch Sperm, Mosquito Spray and Monarchs, and Monarchs and Global Climate Change.

Monarch Sperm

Eupyrene sperm bundles (3 large lines) and many smaller apyrene sperm (smaller lines). (Photo: M. Solensky)

We've been studying monarch reproduction in the U of M Monarch Lab for 20 years, learning about factors that influence the number of eggs females lay, the number of times monarchs mate, and over the past two summers, the number of sperm males transfer. During mating, male butterflies and moths transfer a mass called a spermatophore, that consists of accessory gland material (mostly protein) and two kinds of sperm. Eupyrene sperm are capable of fertilizing eggs. Apyrene sperm are smaller, lack a nucleus and are incapable of fertilizing eggs. However, apyrene sperm can comprise 3-99% of the total number of sperm a male transfers. Shortly after copulation ends, sperm move from the bursa copulatrix where the spermatophore is deposited, into an organ called the spermatheca, where they are stored before fertilizing eggs.

By carefully removing the spermatophore from the female immediately after pairs separated in the middle of the night, Michelle Solensky, Lynnette Batt and Julie Brophy were able to catch the sperm before they left the spermatophore. At this time, eupyrene sperm are in large bundles that result from eight cell divisions (producing 28 or 256 sperm) that can be easily counted  with a microscope. Apryene sperm are not in such handy bundles, and must be counted by diluting the sample, and then counting several small samples to estimate the total number of sperm.

On average, males transferred 70, 854 eupyrene sperm and 1,496, 342 apyrene sperm each time they mated. Larger males transferred more eupyreen sperm and males who had mated more recently transferred fewer. Interestingly, males transferred more eupyrene sperm to females who had mated previously, possibly because their sperm would have to compete with sperm from other males. If this is the case, we don't know how males sense whether their mate has already mated! 

Mosquito Spray and Monarchs

Sara Brinda weighs monarchs. (Photo: MITC)

By: Sara Brinda, Senior High School Student, and Karen Oberhauser

Humans use many methods to control mosquitoes, including insecticides targeted at mosquito larvae (larvicides) and adults (adulticides). Adulticides are general insecticides, and thus pose a threat to other insects. In the Monarch Lab last summer, we studied potential impacts of an adulticide called permethrin, which is sprayed on the edges of parks, playing fields, and other areas where people hope to enjoy mosquito-free activities.

To determine if normal field applications of permethrin killed monarch larvae, we exposed them to milkweed leaves collected from sprayed locations in the Minneapolis/St. Paul area or to control leaves from unsprayed areas In addition to determining the lethality of sprayed leaves, we measured how the time that had elapsed since spraying affected whether or not exposed larvae died.

We tested over 550 larvae. There were high rates of mortality in the groups fed permethrin sprayed leaves; depending on how long they were exposed, from 85 to 100% died This was much higher than the mortality rate among control larvae Interestingly, and contrary to our hypothesis, the time that had elapsed since the area was sprayed did not affect the likelihood of mortality; larvae were Just as likely to die on leaves sprayed almost three weeks prior to the study as those sprayed the day before. 

This study demonstrated that monarchs exposed to normal applications of permethrin are likely to be killed Clearly, mosquitoes are a bother to humans, and in rare cases, can carry diseases. However, our efforts to ensure our own comfort and safety affect other organisms, and we need to be aware of this. A more complete summary of this research will soon be on our website (Sara was selected as an alternate for the International Science and Engineering Fair in Portland, Oregon, and won the Intel Excellence in Environmental Health and Safety Award for this research.)

Monarchs and Global Climate Change

Monarchs may soon need to either change their fall destination, or adapt to very different winter conditions, according to a study published by Karen Oberhauser and A. Townsend Peterson. Over the next 50 years, the high altitude forests that support monarchs could become unsuitable wintering grounds. These oyamel fir forests in Mexico contain specific emlogical niches. The cool and relatively dry conditions provide a safe haven for monarchs that can surviveonly in a narrow climatic band Too much wet, cold weather will kill the butterflies.

Using ecological niche modeling, Oberhauser and Peterson found that climate changes predicted under global climate models are likely to result in conditions that are too wet for wintering monarch butterflies. WhiIe monarchs can survive cool, even sub-freezing conditions during their winter hibernation, they freeze to death under higher temperatures when they are wet (-4 oC) than when they are dry (-8 0C). Increased precipitation is liketyto result in more frequent combinations of cold a nd wet conditions, and thus more monarch mortality. This happened during Jan 2002 and Jan 2004 storms.

Oberhauser and Peterson used a computer analysis based on artificial intelligence. Using predicted climate data, they found that wh ile the temperatures are unlikely to get any cooler, increased moisture is likely to make all of the current sites unsuitable within fifty years. The model did not take into account other events, like logging, that couId aIso endanger the monarch's habitat.

For more detail, see Oberhauser, K.S. and A.T. Peterson. 2003. Modeling Current and Future Potential Wintering Distributions of Eastern North American Monarch Butterflies. Proc. Nat. Acad. Sci. 100:14063-14068

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