Tomato Pests (Hornworms) – and THEIR Pests (Braconid wasps)

I don’t have a picture of a hawkmoth, aka sphinx moth or hummingbird moth (so named for its ability to hover and its very long tongue). But if you see one of these gray-brown creatures, almost big enough to pass for a small bird, you’re seeing disaster on the wing. The Hawkmoth’s very large green children are hornworms.

In our New York and Maine gardens, hornworms usually show up in late July or August. But I’m thinking about them early this year because a Facebook friend in Virginia is already beset.

“Hornworms are eating my tomato plants,” she wrote, “anyone have advice on how to get rid of them?”

But of course!

Try the tips on Hornworm eradication at the end of this post, I replied, and if you get the chance, employ these two major organic defenses:

1. Bt (Bacillus thuringiensis), kurstaki strain, a widely-sold bacterial insecticide that kills caterpillars but is otherwise more or less harmless. It must be eaten to do its work, so baby butterflies are safe as long as you spray it only on the  hornworms’ dinner.  Unfortunately, Bt is most effective on hornworms when they’re still small. By the time they’re big enough to notice – or do damage that’s noticeable – Bt is no match for them.

2. The Braconid wasp Cotesia congregatus. These tiny, deadly parasites have evolved to prey only on hornworms and are generally available anywhere hornworms are found. To get some, simply notice which hornworms have white bumps and leave those alone.

I used to think the white bumps were wasp eggs, which would on hatching enter the hormworms and eat ‘em up, but that was literally backwards. The bumps are cocoons, spun by the wasp pupa after they’ve eaten the hornworm and emerged, ready to transform themselves into adult wasps.

Same difference in the control department except you don’t have to worry about how much Mr. Bumpy might eat before the wasps get busy. By the time you see the cocoons, he’s on his last legs and no longer very hungry.

PS. Wondering what the Luna moth has to do with anything? Nothing, except that it’s prettier than a hornworm. To view the Luna moth’s children, check out this series of photos.