Nearly-decapitated sunflower heads, scattered across the prairie. Oh, the devastation! Who could be carrying out such an evil plan?
(Ok, more accurately, a weevil plan?)
I found this sad-looking stiff sunflower (Helianthus pauciflorus) during a prairie hike back in August.
Stiff sunflower was not the only species being targeted. Maximilian sunflowers (Helianthus maximiliani) were also dangling… This photo was taken just a few minutes after the first.
The head-clipping weevil, aka the Silphium weevil (Haplorhynchites aeneus) is a small dark-colored weevil, less than a centimeter in length. Females girdle the stems beneath sunflower heads – as well as other plants such as compass plant and rosinweed – so that the flower head falls over, but usually doesn’t drop completely off, at least not right away. Once a flower has been knocked over, other weevils usually show up – male and female – to feed on pollen, mate, and lay eggs in the blossom.
Doing some research for this post, it was hard for me to confirm what happens next, but it seems the eggs usually don’t hatch until the flower eventually falls to the ground. The larvae feed on the decomposing flower head and then burrow into the earth to overwinter. It is thought that clipping the flower before laying eggs on it might make the flower a less attractive place for other insects to lay eggs, saving more food for the weevil larvae.
Before that August hike, I hadrarely seen the head-clipping weevil itself, and had never photographed it. Not long after looking at the sunflowers shown above, I finally saw a weevil fly off and managed to get a documentary photo of it when it landed. Look at all the sunflower pollen stuck to it!
The clipping behavior by weevils can cause problems for those raising sunflowers commercially, but I’ve never seen it impact enough flowers to cause any serious issues in prairies. I’m guessing that some of you readers will know much more about the head-clipping weevil than I do, and I hope you’ll contribute additional information in the comments section below. Thanks in advance!
So, to summarize the weevil plan: The weevil female nearly decapitates a flower and then mates with weevil males and lays weevil eggs right on the mortally wounded blossom. The weevil babies eat the dying flower and then burrow into the ground until the next spring. Then they make a triumphant return and hatch their weevil plans once again. And who do we have to thank for finding out about all of this?
Weevil scientists, of course!
The Prairie Ecologist 