Thursday, June 19, 2008

Tomato Hornworms and Braconid Wasp

When you've got hornworms (big fat green caterpillars with a red horn on one end) on your tomato plants you don't want the damage, however there are times when they are part of the process that makes them beneficial. Before you spray consider the hornworm's relationship to a beneficial wasp in the natural world.

Braconid wasps are considered beneficial bugs to your garden. They parasitize and kill aphids, flies, coddling moths, elm bark beetles, cabbageworms, hornworms, corn borers, armyworms, and other pest insects. Getting a garden in balance with nature working to protect your plants is a great way to garden in the rhythm of things. Avoiding all those chemicals makes you more healthy also.

These tiny wasps are not brightly colored like some other wasps, but generally come in black or brown with thin waists and long antennae. Their larvae are pale-colored grubs. They are rarely over inch long. The external cocoons they weave resemble insect eggs, but are actually made of silk.

Some attack the host internally, others feed from the outside of a host insect. Different species of braconids attack insect eggs, larvae, pupae, and adults.

With the tomato hornworm, the female wasps inject eggs into the caterpillar’s body. The larvae that hatch from the eggs feed inside the caterpillar until they mature and eat their way out through the caterpillar’s skin. They then spin the characteristic cocoons from which adult wasps later emerge.

Leave parasitized caterpillars with cocoons alone so the wasps can emerge to attack more hornworms.

Attract the adult braconid with nectar and/or water. It is particularly attracted to plants with small flowers, such as dill, fennel, parsley, Queen Anne's lace, clover, and yarrow. If you see caterpillars with attached cocoons, leave them so that the wasps can continue to develop.

Here's a great photo of a hornworm with the cocoons.

The die-off of bees and bats from the use of pesticides presents a challenge for our food supply being pollinated, so using natural methods to garden makes a big difference for the planet considering the dangers of pesticides.


Debbie Caldwell said...

This fascinating commentary has been here for two and one half YEARS and no one has yet commented? Well I, for one, loved it, and was told about it by someone else. So do not fear, we are here, enjoying you, dear. I am in Maine and have seen many a tomato hornworm, but never one with slug-like attachments that are really cocoons.

sharingsunshine said...

Glad you dropped by, Debbie. There are so many interesting things out there to see and know about! Never an end to that.

Anonymous said...

Cool,this is a little gross too though,.....

Anonymous said...

Great tips! I've been growing tomatoes for 4 years and just caught 2 hornworms in the last couple of weeks. I did this by looking as closely as possible at the tomato leaves and branches, which as we know, is very painstaking. I will definitely plant some of the suggested plants next year to attract these helpful wasps.

I heard someone say that marigolds are a deterrent for hornworms. Do you know if this is true? I have a bunch of them in my garden.

I also hear that you can hunt the hornworms at night with a UV light.

Thanks again,

sharingsunshine said...

We can't grow tomatoes since the deer and squirrels get to them before they ripen. But I did find this info on a forum along with other positive and negative comments of the same issues.

"Marigolds help deter harmful nematodes from attacking tomatoes. The pungent odor can also help confuse other insect pests. To deter nematodes, the best practice is to grow the marigolds, then chop and till them into the soil at the end of the season."

"The marigold is probably the most well known plant for repelling insects. French marigolds repel whiteflies and kill bad nematodes. Mexican marigolds are said to offend a host of destructive insects and wild rabbits as well. If you choose marigolds for your garden they must be scented to work as a repellant. And while this plant drives away many bad bugs, it also attracts spider mites and snails."

Anonymous said...

I found a hornworm yesterday morning. I got rid of it because I didn't know what it was. I assumed the worm was carrying eggs on her back. If I see any more, I will leave them alone. Interestingly, my next door neighbor has a hummingbird feeder with sugar water. I suppose that is what initally attacted the wasps. Also, I have marigolds planted in between my tomatoes. My parents always planted marigolds with the tomatoes to keep the bad bugs away. Thank you for the info!

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