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Whitehurst diaries: Garden Journal/Tomato Hornworms

Tiny creatures are Gradyville gardeners' best friends. They incapacitate tomato hornworms, make use of their bodies for nurseries, incubating more wasps to control the tomatoc enemy>
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By Sharon Whitehurst

Jim and I love to share photos of our garden. The garden triumphs, that is.

The first juicy sweet strawberries, ripe tomatoes, a bucket full of sleek green cucumbers - these all make good copy, with a subtle bit of [pardonable] pride involved.

What we less often share are the gardening failures - who wants to see a view of a zuchini plant which has just succumbed to an invasion of vine borers.

I've learned more about tomato wilts and blights in the past few days than is good for my spirits. [Who knew there exists "early blight," "late blight" and, oh joy, "Southern Blight!"]

Matt and Gina have been here today working on the strip of garden they planted while waiting to move into their recently purchased house down the Old Gradyville Road.

Matt presented me with the creature I recognize as a tomato hornworm. After insisting that he squash the thing, I deserted the green beans waiting in the kitchen sink and did some research.

The following is by Timothy J. Gibb, Insect Diagnostician, Department of Entomology, Purdue University:
Finding a large green tomato hornworm caterpillar on your tomato plant is never a good sign unless, that is, it has small white capsules attached all over its back.

The white capsules on its back, frequently mistaken for "hornworm eggs" are actually the pupal stage of a tiny wasp called a Braconid.

As Braconid larvae, these wasps fed on the insides of this hornworm and have now completed that feeding and are preparing to emerge as tiny wasps.

Under such circumstances, the hornworm caterpillar might be capable of slow sluggish movement but is incapable of further feeding and will die very shortly.

In the meantime it serves a very valuable function as a nursery for these wasps. When they emerge, the adult wasps will fly off to hunt for other hornworms to parasitize.

So, if you leave the parasitized hornworm in place and allow the parasites to emerge, you are in effect killing many other hornworms in the vicinity.

I call this good luck! Timothy J. Gibb
It appears that while the tomato worm is bad, the attached eggs might just serve a useful function. -Sharon Whitehurst

This story was posted on 2011-07-06 14:47:35
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When a tomato hornworm is welcome sight

2011-07-06 - Old Gradyville RD, Gradyville, KY - Photo by Sharon Whitehurst.
Sharon Whitehurst says a tomato hornworm in this condition is a welcome sight - when it's covered with the larval stage of tiny braconid wasps, which use the tomato hornworm for an incubator and make it too sluggish to continue its damaging feast on tomatoes.

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