About 96 percent of all bugs you see are beneficial insects. These insects provide plants with protection, help with pollination and keep the bad bug population in check. They’re not only beneficial to plants but they’re also beneficial to gardeners.
You’ve heard it, read it, or seen it in just about every gardening publication out there: “Beneficial insects are [insert particular importance here].” Just what is a beneficial insect? And what makes it so? When I first started lecturing about bugs (I use “bug” and “insect” interchangeably), I made the assumption that everyone would know the difference between good and bad insects. I figured most gardeners would be able to distinguish good from bad by what the bug was doing when they spotted it. Was it munching on a leaf or stem or was it munching on another insect? If the answer to the first part of that question is “yes,” then it’s probably not a beneficial insect, or is it? And what if you answered “yes” to the second part of the question? When you see an insect eating another insect how are you supposed to know who the good guy is? Answers to questions like these vary, and knowing the specifics about insects when there are more than one million different species is practical only for entomologists.
Could you name five beneficial bugs if asked? Ladybugs, praying mantis, green lacewings, butterflies and parasitic wasps are probably common enough in your garden. But what makes them beneficial? Insects such as these provide plants with protection, help with pollination and help keep the bad bug population in check. They’re not only beneficial to plants but they’re also beneficial to gardeners. Ladybugs dine on aphids, spider mites, whiteflies and the larvae of many other insects. A praying mantis will eat Colorado potato beetles, earwigs, four-lined plant bugs and squash bugs. Green lacewings munch on aphids, cabbage worms and the larvae of the Colorado potato beetle and asparagus beetle. Parasitic wasps are one of the most beneficial of all insects to have in the garden and target over 200 different species of bad bugs.
Butterflies, moths, bees and other pollinators are important beneficial insects that are recognized instantly, but “it’s the ‘less famous’ beneficial insects that we need to begin to appreciate, understand and encourage,” Jessica Walliser writes in her book Good Bug, Bad Bug (St. Lynn’s Press, 2008). To better understand and appreciate the good bugs in your garden and landscape, you’ll have to do a little lab work. Start by purchasing a magnifying glass and a good insect ID book. Jessica Walliser’s book is a good choice, or you can search many other titles available. Garden Insects of North America by Whitney Cranshaw (Princeton University Press, 2004) has more than 600 pages of insect info with photographs. Speaking of photographs, you should be taking pictures of all the bugs you see in your garden and landscape, especially ones you don’t immediately recognize.
In the grand scheme of things, 96 percent of all bugs you see are beneficial insects. Considering how likely it is to harm them while using pesticides on something eating your beans or bell flowers, you need to be extremely cautious when spraying for bad bugs, especially when pollinators are active. Senior Extension Associate and Ornamental Entomologist Greg Hoover, with Penn State’s College of Agricultural Sciences, raised my awareness recently when I spoke with him on the phone. “Stink bugs are important beneficials but get a bad rap because of the brown marmorated variety.” Spined soldier bugs are in the same family, and they scour our gardens for pesky caterpillars, larvae, mites, aphids and many other damaging insects. Stink bugs (Pentatomoidea) are number three on Hoover’s list of favorite beneficials, ground beetles (Carabidae) are second and Hoover’s number one beneficial — ladybugs (Coccinellidae). “Ladybugs are the icon for biological control,” he said. “They prey on a wide range of pests including mealy bugs, scale insects and enstar nymphs.” When I mentioned praying mantis as beneficial, Hoover reminded me that mantids are generalist predators and will eat anything within reach, even other beneficials. He stressed the importance of ladybugs, ground beetles and stink bugs over other varieties and I got the impression that he considered them to be the work horses of the beneficial insect kingdom.
I contacted David Shetlar, associate professor at The Ohio State University Department of Entomology via email and he said, “The two most common predators in the home landscape are the syrphid (hover) fly and lady beetles.” Shetlar also pointed out the large number of parasitic wasps that are constantly patrolling the home garden. The most common one most gardeners would recognize is the one that parasitizes the tomato and tobacco hornworms. He added, “The best way to conserve these beneficials is to avoid cover sprays and plant a variety of annuals and perennials.”
Plants to Attract Beneficials
• For Lacewings: fern-leaf yarrow (Achillea filipendulina), dill (Anethum graveolens) and tansy (Tanacetum vulgare).
• For Ladybugs: Queen Anne’s lace (Daucus carota), common yarrow (Achillea millefolium) and butterfly weed (Asclepias tuberosa).
• For Sryphid Flies: feverfew (Chrysanthemum parthenium), ‘Liliput’ zinnia (Zinnia elegans ‘Liliput’) and white sweet alyssum (Lobularia maritima).
• Other Plants to Consider: sage, anise, bee balm, daisies, aster and nasturtiums.
A male ladybug grasps a female’s elytra (hard wings) during mating. The plant pictured here is a tansy.
Inset: Ladybugs are reported to have more of an appetite during the larval stage than when they’re adults.
(From State-by-State Gardening July/August 2011.)