the hornworms

The tomato hornworms have arrived in our Edenic greenhouse, the green tunnel greenhouse. We hadn’t picked in there since Tuesday, and went in yesterday evening to get ready for market, and there they were, munch munching away. They are huge, juicy, beautifully strange bugs, the larvae of the hawk moth. When pulled away from their dinner, they are likely to gyrate wildly and poop all over your hand, a watery green goo dribbling down towards your wrist.

I’m not usually squirmy about bugs, but tomato hornworms kinda freak me out.

Fortunately, they are easily controlled with an organic spray, bt. Bt is actually a bacterium, and it kills tomato hornworns quite handily. When the hornworm eats tomato or foliage that’s been sprayed with bt, the bacterium eventually ends up in the worm’s gut. There the worm’s digestive juices break down the bacterium and a toxin is released. Because the gut of the tomato hornworm is only one cell layer thick, the toxin literally eats a hole in the gut, and the hornworn dies.

Fortunately, the action of bt is very specific, and it’s not toxic to most other critters. In many other insects, as well as all types of people, birds, and fish, bt has no deleterious effect at all.

So we’ll use that, but we’ve got some volunteer help as well.

This poor guy has been colonized by a parasitic wasp, most likely Cotesia congregatus. The wasps knew the hornworms were in the greenhouse before we did and are already hard at work. Larvae will hatch out of those white eggs and will feed on the insides of the dying hornworm until they are ready to pupate. Once they have emerged from their cocoons as adult wasps, they will seek other hornworms, to lay their own eggs upon. It’s one of the great advantages of growing organically, that when you have an excess of some pest (aphids, tomato hornworms), there is often some other natural predator (ladybugs, wasps) that is already on the case. You could just get some spray and kill everything, true. But those natural predators would be a real loss for any kind of grower.