Tuesday, September 7, 2010

Tomato Hornworm

The tomato hornworm is the caterpillar that transforms into the five-spotted hawk moth. Its vibrant green hue allows it to remain well camouflaged on one's tomato plants, even at a fat 3 or more inches long, unless . . . it has fallen victim to the Braconid wasp.Do you see the bumpy patch of white in the above photo? Those are the wasp cocoons covering a tomato hornworm!Here's the story: the female Braconid wasp lays her eggs IN a tomato hornworm (see the brown "horn" on the rear end of the above caterpillar?). The eggs hatch and the larvae develop. When they are ready to pupate, they come out of the caterpillar and spin cocoons. Eventually (I haven't yet found out how long this stage takes), the adult wasps emerge to mate and lay eggs in another garden pest.

So the wasp didn't stop this caterpillar from eating and growing, but she has very effectively prevented it from maturing and producing another generation of hornworms.

In this close-up you can see how cottony/fluffy the cocoons are. Also note (top, right) the larva getting ready to spin. We couldn't resist. One of our big jars now holds a dying hornworm and its many cocoons. We are waiting to watch the wasps emerge.Interesting things we've noticed so far:
  1. The seemingly dead caterpillar revived enough to climb back on the branch.
  2. A tiny (millimeters!), newly emerged tomato hornworm was found crawling quickly around the jar--doubtful that it's going to find much food in there.
  3. We watched larvae on the caterpillar and on the glass spinning their cocoons!
  4. Rebecca is fascinated rather than squeamish. She touched the caterpillar and the cocoons.
I found most of this interesting information (including pictures of emerging wasps) at garden grapevine.

2 comments:

Compass Points Road Trip said...

OK, now I wish I would've done the nature observation with my kids like you are doing. I saw a bunch of these (6-10 or so) on my tomato plants in the past few weeks and remembered (generally) the story, so I collected them all, bagged them up and threw them away to avoid having a bunch of wasps around. Now I'm going to check again to see if there are any more specimens. Thanks for the inspiration! Love, your sis

Barbara said...

The braconid wasps are quite small (tiny cocoons) and apparently don't sting humans. They're bad for the caterpillars but good for the garden!

Some of the cocoons are getting darker now. Maybe we'll have adults emerging soon . . .