Wanna Know What Really Makes A Sunflower Lose its Head?

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?)

Weevil damage

I found this sad-looking stiff sunflower (Helianthus pauciflorus) during a prairie hike back in August.

Maximilian

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.

I have rarely seen the head-clipping weevil itself, and had never photographed it.  On the day I photographed the sunflowers shown above, though, I finally saw one fly off a stem and managed to get a documentary photo of it.  Look at all the sunflower pollen stuck to it!

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!

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About Chris Helzer

Chris Helzer is the Director of Science for The Nature Conservancy in Nebraska. His main role is to evaluate and capture lessons from the Conservancy’s land management and restoration work and then share those lessons with other landowners – both private and public. In addition, Chris works to raise awareness about the importance of prairies and their conservation through his writing, photography, and presentations to various groups. Chris is also the author of "The Ecology and Management of Prairies in the Central United States", published by the University of Iowa Press. He lives in Aurora, Nebraska with his wife Kim and their children.
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12 Responses to Wanna Know What Really Makes A Sunflower Lose its Head?

  1. Kim says:

    Go for it, Chris! For good or weevil, this was a most interesting blog!

  2. phrelanzer says:

    Thanks, Chris. I send my prairie restoration group a monthly update, and I’ll be sure to include a link to this blog post in my December one. It’s been a hot question this season — we had a lot of decapitations! I always appreciate your informative, well-written posts. Keep ’em coming!

  3. David Ellis says:

    Your sense of humor brightened my morning considerably!

  4. athada says:

    These weevils are alive and well in NE Indiana. Now I know what has been happening to my Silphiums… thanks!

  5. brvogt says:

    Every year in my prairie garden I lose many a young milkweed shoot to black stem weevils. The milkweed never recover and I end up losing the plant (I’m guessing because they expending energy to grow, and don’t have any new energy to regrow or come back next year). The weevils clip the tops of new shoots and they look just like your sunflower shots, sans blooms.

  6. Patrick says:

    I’d be curious to know what, if any, specialized natural predators exist to control these types of weevils. For example, are there parasitic wasps that target the fallen blossoms to prey on the eggs/larvae, or nematodes or other soil predators that go after the larvae when they overwinter? Certainly a potentially rich food source for some other little critter that can take advantage of it.

  7. Brett Budach says:

    This happens a lot to Silphium here in Ks/Mo. I usually don’t see it happen as much to Helianthus. I just noticed it this past summer, and it took a while for me to catch one in the act. It seemed so horrible at first, but most plants seemed able to resprout and flower just fine afterwards.

  8. steve says:

    It is common to see Helianthus mollis so decapitated here in Missouri and have thought it was caused either by insect or large herbivore. Does anyone know if pale prairie coneflowers and other Echaneous species are susceptible. Many have blamed cattle or deer but maybe the critter is much smaller. I’ll try to be vigilant for a weevil.

  9. Alison says:

    I’ve never seen Echinacea affected in this manner but Helianthus yes! I saw it a lot this year and Chris thank you so much for posting this. I’ve often wondered but not worried about it because it never causes too much loss even in our seed production plots. If I were more production oriented I wonder if mowing the plant high to delay flower development would reduce this pest?

  10. Your post reminds me of the one and only prairie joke that I know told to me years ago by Ray Schulenberg which I will share with you now: There are two destructive weevils in the prairie – One weevil (Haplorhynchites aeneus) decapitates the heads of Silphiums, effectively preventing any seed production. The other weevil (Trichapion rostrum) feeds on the seeds within Baptisia pods, destroying many but usually sparing a few. So, you could say that the Baptisia weevil is the lesser of two weevils.

  11. chrsfrncs says:

    Love dsollenberger2013’s joke.

    Thank you for the post. This was very helpful for me. New cut flower farmer in Northern Illinois. The weevils are really doing a number on my biggest, most valuable sunflowers. I have been just leaving the heads on the ground, but now I’ll do something different. Sanitation this year seems like it should help a lot next year, based on life cycle.

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