Blue Mistflower, Hyperparasitoids, and the Toxic Queen

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Conoclinium coelestinum

Asteraceae

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Today John and I resumed work on our upcoming wildflower photo atlas shelved a year ago during Covid.   We’re starting over at the top of the alphabet, which brought up a curious member of the Asteraceae in full autumn bloom now, Blue Mistflower.    Saw a lot of it flowering today.

Now a small disclaimer: some of today’s blog is generalized from closely related species of Conoclinium.  When one species is not well studied, turn to the rest of the genus.  Mistflowers attract a broad array of pollinators, including Monarch and Queen butterflies.   To dig in on that, we’re going to learn a bit from Texas biologist Monika Maekle summarizing earlier research largely by the late insect-chemical ecologist Thomas Eisner.   If today’s story seems spotty, it is. It is cobbled together from different studies and has swiss cheese gaps. Call it food for thought.

Blue Mistflowers. Pollinator AND parasite magnet. All Mistflower photos by John Bradford.

Mistflower plants stink.   Not in a bad way, I kind of like it.  They have a strong sharp biting odor I associate with the alkaloid family of plant chemicals, including such familiar plant compounds as nicotine, caffeine, and ephedrine.    Mistflowers, among many interesting compounds produce an alkaloid called intermedine, which is known from additional plants, and which is involved in insect-to-insect signaling.   Its reported role among Queen Butterflies is remarkable.

Male Queen Butterflies draw nectar from Mistflowers, which no doubt protects the male Butterflies from predators, and more intricately, serves upon some chemical alteration as a sex attractant to draw the female and her eggs poisonous to pests.   It may be, but not proven(!), that the toxin makes the female less attractive to subsequently encountered males.

Queen Butterfly. Photo by my butterfly-loving wife Donna Rogers

It gets even more complicated.  Remember how Mistflower draws a lot of pollinators?  Remember how it reeks with chemicals known to function as insect signals?    The alkaloids attract Butterflies. Seems that parasitic wasps have “learned” to follow the scent to dinner. Around 2010 UF entomologist John Sivinski and colleagues conducted a survey of numerous plants in terms of their widely varied tendencies to attract parasitoid wasps.  Guess what species was #1 for Chalcid Wasps.  Yep, Blue Mistflower by a whole heck of a lot.  Chalcid Wasps parasitize butterfly larvae, among other vics.  Some Chalcids are hyperparasitoids, parasitizing other parasitoids.

Chalcid Wasp, photo by Jean and Fred. Much magnified—they are tiny

Let’s now wrap this up with some speculation:  Male Queen Butterfly takes in intermedine with nectar.  He uses its chemical derivative to attract a female. Upon mating, intermedine transfers to the female, with an advantage to the male of protecting the eggs the male fertilized.  And maybe repelling other males?  Intermedine or some other alkaloid(s) probably draw Chalcid wasps to the Mistflower which is rich in Butterflies to victimize.  Wasp attacks on Queen Butterflies may (speculatively!) be mitigated by the alkaloid in the male, female, and eggs, although the eggs are deposited for larval development ordinarily on plants of the Milkweed Family.