Monday, August 8, 2016

Monitoring Milkweed with Dr. Karen Oberhauser in Canelo, Arizona



Dr. Karen Oberhauser at Canelo, AZ
The best way to monitor changes in the monarch population each year is to visit breeding areas around the state. For the last ten years that is exactly what we’ve done, visiting milkweed rich habitats in Canelo, Show Low, Springerville, Flagstaff and other representative locations where monarchs thrive. Just as other insect populations vary from year to year, so do monarchs. But this year I was fortunate to have Dr. Karen Oberhauser, Monarch Joint Venture (MJV) Chair and Monarch Larva Monitoring Project (MLMP) founder, join me last week monitoring the Forest Service area in Canelo along Turkey Creek. 

Monarch larva on A. subverticillata
I’m very fortunate to have known Karen a long time and she was very influential in growing my own interest in monarch biology. For years we have talked about the rich milkweed thickets in southeast Arizona in the Sky Island region, home of the most dense monarch population almost every summer. She was presenting at a workshop in Tucson, so the timing was ripe for our long hoped adventure. We left Tucson surrounded by pockets of monsoon rains but when we arrived in the higher elevation Canelo, conditions were perfect with temperatures in the mid-70’s and mostly sunny skies. Recent abundant rains created a lush blanket of milkweed with monarch and queens feasting at the rich nectar banquet. It didn’t take long to find the first monarch larva in tall fields of Horsetail Milkweed, Asclepias subverticillata.
 
5th instar frass
As we explored the abundant swales we found a diversity of butterflies nectaring on Butterflyweed, A. tuberosa, as well. That’s when Karen first spotted the frass, “That’s a fifth instar’s frass,” and of course she was right. We found several larvae on the tuberosa, fourth and fifth instars. As we continued our walk through the tall milkweed we found more and more larvae. But we kept hoping to find a female oviposting as well. We were surprised that even though there were more queens than monarchs during this visit (during the previous week the populations were reversed) we didn’t find any queen larvae at all. We found more fifth instar frass but no larvae nearby and surmised they may have been wandering for a place form a chrysalis. In the past we’ve documented monarch pupa in the grasses.

5th instar monarch larva A. tuberosa

Very worn female in A. subverticillata
In the midst of emerald fields of green, we spotted a quick flash of muted orange - a very worn female nestled deep in the grasses. Her scales were worn and her abdomen thin. Karen pointed out the spermatophore at the tip and said there were likely several of them from multiple matings. But we still hadn't seen any females ovipositing.
Karen Oberhauser pointing out spermatophore

Finally in the less dense areas of milkweed, in the midst of a composite patch with small wisps of fresh Horsetail Milkweed just emerging, Karen found what she was looking for, a female laying eggs. Here is a rather poor and bumpy video of our conversation, and our amazement at the gravid female’s choice of locations for oviposition. 


 Time flew by quickly as golden moments in the field often do. We explored other nearby locations and found patches of Zizotes Milkweed, A. oenotheroides with eggs, Antelope Horns, A. asperula, and Engelmann’s Milkweed, A. engelmanniana. We also stopped by Babocomari Ranch in Elgin to compare the density of milkweed there. It was a great day with a great scientist in the field!

Dr. Karen Oberhauser


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