Garden Q&A: Parasitic wasps play crucial role
Q uestion: I've been gardening for many years and have never seen tomato hornworms with white eggs on their backs. What are they?
Answer: The white rice-like sacs hanging off the back of your tomato hornworms are not eggs. They are the cocoons of a very important parasitic wasp known as the Cotesia wasp, one of the more commonly encountered groups of parasitic wasp.
Different Cotesia species also parasitize cabbageworms, cutworms, corn earworms, gypsy moths, tobacco budworms and many other caterpillars. Female wasps lay eggs inside the hornworm, and the resulting larvae consume the caterpillar from the inside out. In 15 to 30 days, the larvae mature inside their host and then chew small holes through the skin of the caterpillar and spin external cocoons in which they pupate into adults. Once mature, the adult wasps “pop the top” off the cocoon and fly off.
They go on to parasitize and kill more hornworms and other caterpillar species.
There are literally thousands of species of parasitic wasps here in North America, and they are very important as they help control the populations of many common garden pests. Parasitic wasps are a very complex group of insects with a tremendous amount of diversity in their individual appearances and lifecycles.
Parasitic wasps can be smaller than a gnat or as long as your pinky finger (adult Cotesia wasps measure less than an eighth of an inch). Nearly all of them use other insects as hosts for their young, with many of them being host-specific and utilizing only one or two species of insects for this task.
Most often the females lay eggs singly or in groups on, or inside of, the host. The larvae then hatch and develop inside of the host, consuming the non-vital tissues first to ensure the host survives until the larvae are ready to pupate into adults. Though you will probably never encounter the larvae themselves, they are often cream-colored, legless, maggot-like creatures. Parasitic wasps attack almost every group of insects, including aphids, beetles, flies, scales, true bugs, and caterpillars of every sort.
Unlike yellow jackets, hornets, and paper wasps, nearly all species of parasitic wasps are incapable of stinging people, and what may look like a nasty stinger protruding from the abdomen of the females of some species is actually the ovipositor she uses to lay her eggs.
These valuable pest-controlling insects should be encouraged and valued. Do not destroy any hornworms you find with the cocoons already present, because at this point the caterpillars have stopped feeding and will die soon enough.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Grow Organic” and “Good Bug, Bad Bug.” Her website is www.jessicawalliser.com.
Send your gardening or landscaping questions to firstname.lastname@example.org or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.
Show commenting policy
TribLive commenting policy
You are solely responsible for your comments and by using TribLive.com you agree to our Terms of Service.
We moderate comments. Our goal is to provide substantive commentary for a general readership. By screening submissions, we provide a space where readers can share intelligent and informed commentary that enhances the quality of our news and information.
While most comments will be posted if they are on-topic and not abusive, moderating decisions are subjective. We will make them as carefully and consistently as we can. Because of the volume of reader comments, we cannot review individual moderation decisions with readers.
We value thoughtful comments representing a range of views that make their point quickly and politely. We make an effort to protect discussions from repeated comments either by the same reader or different readers.
We follow the same standards for taste as the daily newspaper. A few things we won't tolerate: personal attacks, obscenity, vulgarity, profanity (including expletives and letters followed by dashes), commercial promotion, impersonations, incoherence, proselytizing and SHOUTING. Don't include URLs to Web sites.
We do not edit comments. They are either approved or deleted. We reserve the right to edit a comment that is quoted or excerpted in an article. In this case, we may fix spelling and punctuation.
We welcome strong opinions and criticism of our work, but we don't want comments to become bogged down with discussions of our policies and we will moderate accordingly.
We appreciate it when readers and people quoted in articles or blog posts point out errors of fact or emphasis and will investigate all assertions. But these suggestions should be sent via e-mail. To avoid distracting other readers, we won't publish comments that suggest a correction. Instead, corrections will be made in a blog post or in an article.
- FDA rule to require chain restaurants to post calorie counts
- No. 15 San Diego State hammers Pitt, 74-57
- DUI checkpoints take on dangerous drivers
- Mon Valley preparing for Small Business Saturday
- Steelers’ lookahead: New Orleans Saints
- Steelers cornerback Taylor ready to swap earpiece for helmet
- Ehrhoff finding his way with Penguins
- Roundup: Mazda recalls cars to fix tire pressure monitors; Wal-Mart’s top merchant out as key holiday nears; more
- Rostraver business site ordered to close
- Retailers that won’t open on Thanksgiving hope move pays off
- Firefighters douse blaze at abandoned house