The Good, The Bad and The Ugly! Insect Enemy Number One: Tomato Hornworm Wanted Dead or Alive!

August 4th, 2010 § 8 comments § permalink

The Hornworm (Manduca sexta) – Image ⓒ Tim Geiss at Poltergeiss

Wanted Dead or Alive: Manduca quinquemaculata (and also Manduca sexta) aka The Hornworm. Although he looks almost clownish in Tim Geiss’ photo (above), this garden pest is no laughing matter. The hornworm feeds on tomato plants and their relatives (other nightshades of the Solanaceae family; including peppers, tomatillos, eggplants, tobacco and the like) and a gang of these caterpillars can easily defoliate entire plants in a matter of days. Give these garden-thugs a week unchecked, and you can kiss your tomatoes, peppers, eggplants and tomatillos goodbye all together.

As you can see from the photo, Mr. Hornworm is a master of disguise. It’s nearly impossible to spot him as he crawls down the backside of leaves and stems, munching as he goes. In fact, most of the time, it’s easier to detect the tomato hornworm’s presence by the dark green droppings rapidly accumulating at the base of host plants. With this in mind, carefully inspect the soil/mulch in your garden as you weed and water. The best method of control is to handpick these caterpillars from garden plants manually (don’t worry about that menacing-looking horn – this bug looks tough but it’s all coward in the end). Step on ’em and squash ’em, or drop ’em in a bucket of soapy water and it’s bye-bye Joker!

The Hornworm (Manduca sexta) Tail Detail – Image ⓒ Tim Geiss at Poltergeiss

Gardener’s Supply Company Organic Thurcide: Btk Solution

Organic controls for tomato hornworm include Btk (Bacillus thuringiensis kurstaki) and spinosad (saccharopolyspora spinosa). Btk is a naturally occurring bacterium found in soil. When correctly handled and applied only to targeted foliage where caterpillars are feeding, Btk is both a safe and effective  organic solution for controlling tomato hornworm and other destructive caterpillars. However, it is important to note that Btk kills all worms and caterpillars —including butterfly larvae— when ingested. With this in mind, gardeners should never blanket-spray with Btk. Remember that the bacterium only works if the tomato worm actually eats it (and then it will take a few days). Target-spray the undersides of leaves and plant stems where the worms have been observed feeding. Spinosad is another biological insecticide product manufactured from a naturally occurring organism. When ingested (by caterpillars and other pests) spinosad will kill the host within a day or two. This is a low-toxicity product, but as with all organic pesticides, it should be used in a targeted manner and only when absolutely necessary. Try hand-picking first.

Gardener’s Supply Company Organic : Spinosad Pest Control Spray

Of course, as is often the case with villains, the hornworm has natural enemies. Birds will eat hornworms, so keeping bird houses and bird baths in your garden is definitely to your advantage if you’d like to encourage an aerial assault on the enemy. And, the appropriately named Assassin Bug (there are hundreds of individual species on the North American continent) should be welcomed to the garden as a member of your posse. In addition to the tomato hornworm, the assassin bug hunts down and kills many other ‘bad bugs’; including Colorado potato beetles, cut worms, aphids, Japanese beetles and many others. But in spite of his name, the Assassin bug isn’t the number one killer of hornworm. If you really want to see a hornworm taken down, you need to see the Braconid wasp in action…

No one stands between me and my golden tomatoes. Bring in the mercenaries: The Good, The Bad and The Ugly!

**   Click Here To Cue The Theme Song! **

The parasitic wasp (including the hornworm destroying Braconid) is a natural, female mercenary extraordinaire. Non-stinging and pollen-eating, parasitic wasps are attracted to flowering plants in your garden, where they will happily co-exist with other beneficial insects and animals. Draw braconid wasps to your garden with creative companion planting. Adult braconids are attracted to the pollen and nectar of flowers such as Queen Anne’s Lace and tansy, and herb blossoms; including dill, fennel, mint and parsley. So plant lots of flowering herbs, edible blossoms and posies for picking in your potager.

The braconid wasp is a clever killer. As you can see below, it’s not the delicate wasp herself who actually does the dirty deed to the hornworm. Oh no… She tasks her voracious off-spring with the job; depositing her eggs on the backs of her unsuspecting caterpillar victims! Gothic garden? Yes, indeed. This Kafkaesque process is true inspiration for a stomach-churning horror-flick. After the adult wasp lays her eggs on a wormy, slow-moving host, the tiny larvae hatch and burrow into the skin of the victim, devouring the caterpillar from within and pupating on its back. Warning: this process (captured below by photographer Tim Geiss) may be upsetting to some viewers. Sorry folks, Mother Nature isn’t always pretty! But, you really ought to take a close look to become familiar with your mercenary friends. You want to leave the parasite-infested caterpillars near your garden, protecting the living ‘nursery’ beneath nearby leaves and grass. The Braconid’s parasitic children may be the stuff of true hornworm nightmares, but they are a tomato lover’s best friend….

Braconid Wasp Larvae Eating a Hornworm – ALIVE ! – Image ⓒ Tim Geiss at Poltergeiss

It’s important for a gardener to know the difference between the good and the bad, and to learn to tolerate the ugly. Not sure of whom to trust? For some great resources, check out my post, “Good Bug, Bad Bug? Let’s See Some ID Please…” over at Barnes & Noble’s Garden Variety blog, and round up your posse. When it comes to protecting my veggies, I’ve learned to work with Mother Nature’s big gun mercenaries, and to show no mercy… Just like Clint…

Whom Do You Trust? YouTube Clip from The Good, The Bad and The Ugly Finale…

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Tomato Hornworm photographs are ⓒ Tim Geiss – many thanks to the artist for his patient stalking of the dread caterpillars!

The Good, The Bad and The Ugly images are ⓒ Untied Artist Pictures

Article ⓒ Michaela at TGE. All product images are courtesy of linked retailers.

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