Marin IJ Articles
March 10, 2008
Pirates, assassins and soldiers, oh my! If you’ve got these adorning your flowers, vegetables and trees, how fortunate you are—if they’re bugs that is. You’ve got good bugs—ones that you want to protect and encourage to take out bad bugs that may be lurking around. While the media announces that the “only good bug is a dead bug,” don’t believe it. For every bad bug out there, there are plenty of good ones—many working 24/7 to help control the pests that assault your garden and lawn. Before you whip out some type of spray to wipe them out, know who you’re dealing with. You really want to preserve the garden good guys.
The world is filled with insects—there are more than a million named species of them. Yet it is estimated that only about one percent are truly harmful. Most insects go about their daily business pollinating plants, helping to decompose dead material, being meals for birds, fish and other creatures. One big service they provide that is hidden from most of us is keeping pest populations down—the good bugs battling the bad ones.
Also known as beneficial insects, bio-control agents, natural enemies, biological pest control and beneficials, good bugs are predators, parasites or disease producing organisms that help control pests by killing them, decreasing their ability to reproduce or reducing their numbers. While the majority of beneficials are insects, there are also spiders and mites (arachnids), nematodes and a wide range of microbes. The most effective natural enemies are relatively host specific—ones that go after a single pest species or a group of similar pests. Lady bugs (Coccinellidae) are generally associated with feeding on aphids, however other species within the group prefer to dine on scale, mealybugs, whiteflies or mites. Some less familiar but equally voracious beneficials are assassin bugs (Reduviidae), minute pirate bugs (Anthocoridae), soldier beetles (and Cantharidae) and syrphid flies (Syrphidae).
Encouraging beneficials in your garden is about the greenest method of pest control you can use. “Bug-on-bug” warfare is the way things exist in nature, and while it may not provide you with a pest free environment, if you give them time to do their magic, you can reach a level of tolerable damage without the use of any type of chemical control. It’s easy to do. Like any living creature, these good guys need food, water and shelter, all generally available in the garden. Diversity in plants encourages a range of beneficials; sequentially flowering species provide natural enemies with nectar, pollen, and shelter throughout the growing season. Some favorites include members of the carrot family (Apiaceae), dill, fennel and parsley; the daisy family (Asteraceae), coneflowers, daisies and yarrow; and herbs like rosemary and thyme. Tolerating low populations of plant-feeding insects and mites ensures that food is available to the hungry garden helpers. Reduce dust—it can interfere with natural enemies and result in outbreaks of pests such as spider mites. And go light on fertilization and irrigation; lots of lush new growth on plants actually encourages sucking pests like aphids to reproduce more rapidly than natural enemies can control.
Most importantly, don’t be too quick to whip out the insect spray. Broad-spectrum pesticides often kill a higher proportion of garden good guys than the pest species they are attempting to control; many are killed right away (contact toxicity) and any pesticide residue can also kill natural enemies that migrate in after spraying (residual toxicity). If they do survive, the pesticide residues can interfere with the beneficial insects’ reproduction and their ability to locate and kill pests. And be careful when using combined products—ones that both feed the plant and control pests. Most of these function as systemic insecticides, circulating toxic chemicals throughout the plant, so anything that feeds directly (an aphid feeding on a rose), or indirectly (the ladybug eating the aphid) on it can be affected.
How do you tell which bug is good and which isn’t? Steven Swain, UCCE Environmental Horticulture Advisor suggests, “Telling the good bugs from the bad ones can be difficult, especially at first. Syrphid fly larvae (beneficials) look a lot like green caterpillars (not beneficials), and spined soldier bugs (good guys) look pretty similar to some lygus bugs (generally bad guys). Since it doesn’t do a lot of good to learn about beneficial insects that you never see, perhaps one of the best ways to get familiar with them is to start with what is in your garden. Get a small, sealable glass jar, find one or two, catch them (gently), and identify them—there are a lot of resources out there to help you.
“Once you’ve identified what is in your garden, you can learn about their life cycle, what they like to eat, and the environments that best suit them, and keep these conditions in mind as you consider your next garden projects. The nice thing about this approach is that the more you learn to identify, the more things you start seeing in your garden, and it often makes the next identification even easier.”
For identification help, you might try the UC Davis Integrated Pest Management (IPM) website as a start. It has a plethora of information and wonderful photos of a wide range of natural enemies at http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74140.html. Other resources include your local library, the Sunset Western Garden Book, and the UC Marin Master Gardeners Desk, at 1682 Novato Blvd., Suite 150B, in Novato (415-499-4204 or HelpDesk@MarinMG.org).