Monday, August 3, 2009

Coneflower-cutting weevil

One of our showiest prairie plants is the Purple Coneflower, Echinacea purpurea. They aren't particularly common here in Ohio, at least in a wild state, and finding their rosy-purple blooms in prairie remnants is always a treat.

For years I've noticed that something attacks coneflowers in a most interesting way, and it wasn't until a recent field trip that I learned who the culprit was. We had seen some coneflower damage in a neat little patch of prairie in Clark County, and naturalist extraordinaire Jim Davidson knew, in a general way, who the attacker was.

Perhaps you've seen this sort of thing. It's as if a mad gardener with nicely sharpened clippers has come along and clipped the flower, leaving it to dangle. The cuts are perfectly straight and quite well done.

Well, it turns out the mad clipping is the work of a tiny weevil. These small beetles apparently saw through the coneflower stem, and lay their eggs in the gooey sap which forms at the wound. Once they mature, the blackish, long-beaked adults clamber down to the dangling flower and commence feeding.

The dark adult weevils can be seen here, frolicking amongst the disk flowers. If you see this sort of damage on your local Purple Coneflowers, inspect the wilting blossoms and you should find the adult weevils tucked within. They're devilishly hard to get good shots of, as if overly molested they drop out of there like cannon shot and disappear. When I did manage to get one in the hand it was in perpetual motion and I'd probably have had to conk one over the head to subdue it into stillness.

A bit closer in, and you can see the adult weevils glistening from within the flower. I wish I knew more about them, including the exact species. If anyone knows, send a shout out. The whole modus operandi of these weevils intrigues me. I can see cutting the stem - quite an operation in itself for such a small beast! That stimulates sap flow which hides and nourishes the larval weevils.

But it obviously does the flower in. Maybe that creates the perfect conditions for other predators to invade the dying flower, such as aphids or other wee creatures, and the adult weevils feed on those. Or perhaps it causes the developing seeds to atrophy and become easier to eat, better meals.

Whatever the case, the complexity of the insect world never ceases to amaze me.


Steve Willson said...

Jim, I see the weevils doing the same thing to Whorled Rosinweed, Ashy Sunflower and Prairie Dock. I've always wondered if it was a strategy to reduce sap flow to the part of the plant they were feeding on. Some insects that feed on milkweeds use this method to get a meal without a mouth full of sap. I've also witnessed these cut flowers rain weevils as the insects used gravity to power their escape.

Anonymous said...

OSU recommends taking the broken flower and tossing it into soapy water. This will kill the weevils and perhaps prevent the problem in the future. I'm getting more angry at this critter than at the ever present japanese beetles!!!

Kim Landsbergen said...