Last updated on July 23rd, 2013
RECENTLY, while pruning a row of paste tomatoes, I noticed a strange-looking worm (above; click to enlarge) on one of the plants. What this worm is, why it has white projections on its body, and why — if you ever see such a thing in your own garden — you should leave it alone:
A quick Google search revealed the odd fellow is the Tomato Hornworm. This Manduca quinquemaculata feeds on the leaves and stems of tomato plants, as well as other plants in the Nightshade family, like eggplant and potatoes. It can devour an entire plant in a matter of days. Worms should be picked from plants, and dealt with as your conscience permits.
However, if the worm has white ovals on its body, you should take no action at all. The white projections are the larvae of the braconid wasp, Cotesia congregatus. Larvae that hatch from the wasp’s eggs, which are laid on the hornworm, feed on the inside of the hornworm until the wasp is ready to pupate. Such “host” hornworms should be left in the garden in order to conserve the beneficial parasites. The wasps will kill the hornworms when they emerge from their cocoons. They will also seek out other hornworms to feed upon and kill.
Want to attract this hornworm-destroying wasp to your garden? Then plant, and preferably near your tomatoes, such things as parsley, dill, yarrow, and mustard. Adult wasps feed on the nectar of these plants. Also, provide a source of water. A birdbath will suffice.
And finally, I hope you won’t scream if you notice a host-hornworm on your tomato vines. For it means your garden is ecologically balanced, thanks to your non-use of pesticides.
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