Natural Pest Control: Attracting Beneficial Insects

• By Jeanne Hepler
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• June 2020-Vol.6 No. 6
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• 1 Comment

If you’d like to keep destructive insects off of your garden plants, there is a way to do it without using toxic sprays, and, indeed, without spraying at all.  Simply attract beneficial insects to your garden and let them do all the work.  

I first learned about beneficial insects while studying Permaculture, which is a design system that mimics nature to turn your garden into a balanced ecosystem.  A successful Permaculture ecosystem does not need external additives such as chemical sprays and toxic powders, relying instead on natural systems for pest control. Not all bugs are bad for the garden.  The “bad bugs” are those that damage plants.  The “good bugs,” or beneficial insects, are those that prey on the bad bugs. If your garden is buzzing with beneficial insects, you will find that the bad bugs will be few and far between. This is using nature’s natural systems to your advantage, a key element of Integrated Pest Management.  To review those principles, look at the article in last month’s issue, “Integrated Pest Management” May 2020, The Garden Shed.  

The first thing to do to attract beneficial insects to your garden is to stop using chemical pesticides immediately.  These will kill both good and bad bugs.  To attract the beneficial insects, all you need to do is create the kind of ecosystems they like and wait for them to find you.  If you build it, they will come.  

Attracting beneficial insects to your garden is as easy as planting flowers, because that’s exactly what you’ll do.  Specifically, you’ll need to plant the types of flowers that beneficial insects seek out for nectar and pollen.  The goal is to interplant the flowers that attract beneficial insects near the plants you wish to protect from the bad bugs. Strive to have their favorite nectar sources blooming throughout the gardening season to keep the good bugs near your plants.  Select a variety of flowers that will provide a long bloom season. 

Beneficial insects have definite flower preferences. Most of them have short mouthparts and lack the specialized mouthparts needed to access nectar from deep or tubular flowers, so they need small flowers with shallow, exposed nectaries.  Flowers with shallow nectaries include those of the following families:

The Umbelliferae family, which have flowers born in umbels or flat-topped clusters, such as fennel, dill, cilantro, parsley and carrot.

The Asteraceae or Compositae family, which includes small and flat flowering varieties such as yarrow, chamomile, daisy, feverfew, and aster. 

The Brassicaceae family also offers many options for nectar sources, such as sweet alyssum (Lobularia maritima), basket-of-gold (Aurinia saxatilis), and candytuft (Iberis empervirens) as well as the flowers of garden vegetables like broccoli and mustard. 

The Mint family, which includes spearmint, peppermint, lemon balm, and natives such as mountain mint (Pycnanthemum), as well as hyssop, monardas, salvias, stachys, and others.

Photo: Va. Tech. Dept. of Horticulture, “Farmscaping Techniques for Managing Insect Pests”

Interplanting flowers to attract beneficial insects is also being used in commercial agriculture, where it is called farmscaping.  Virginia Tech has compiled a useful list of popular farmscaping plants. Improving Pest Management and Pollination with Farmscaping,   Another list of plants and the beneficial insects they attract has been compiled by the Natural Resources Council of Maine.  https://www.nrcm.org/wp-content/uploads/2016/05/Plants-that-attract-beneficial-insects.pdf.

THE SHORT LIST

For those of you who want to skip the research, I have compiled a brief list of plants that seem to attract the greatest variety of beneficial insects: 

Sweet alyssum (Lobularia maritima) should be at the top of your list, as it is long-blooming, easy to grow, and a favorite of beneficial insects.  This low-growing hardy annual will bloom all season, from spring until frost.  It is easily grown from seed and can be direct seeded in the garden in early spring.  It is also a lovely ornamental for the front of the border or for planters and is delightfully fragrant with a scent reminiscent of honey.  They will grow in full sun or part shade.  

Sweet alyssum, NC State Extension. Photo: Carl Lewis, CC BY 2.0

Sweet Alyssum
Photo: Jim Robbins, CC by NC-ND 4.0

Yarrow, both common yarrow (Achillea millefolium) and fern-leaf yarrow (Achillea filipendulina), attract a great variety of beneficial insects. These perennials are available in many colors, from the tall yellow common yarrow to the many newer varieties of fern-leaf yarrow in pastel and gem tones, to the wild native white fern leaf yarrow to be found on roadsides and fields everywhere. They are drought-tolerant sun lovers and easy to grow. 

Photo: “Peckover, July 2011” by Sunchild57 Photography. CC BY-NC-SA 2.0

Photo: “Achillea” by infoerbe, CC BY-NC-SA 2.0.

Dill, Coriander, and Fennel, in bloom, attract many beneficial species.  Dill and coriander grow and bolt quickly, but they can be seeded weekly or biweekly throughout the season to provide a procession of blooms as well as delicious leaves to flavor your dishes in the kitchen.  Let some of your dill and coriander go to seed.  The seeds are useful in cooking, and can also be saved and planted next season.  

Photo: “0707130539” by Mr_robin53, CC BY-NC-ND 2.0

Photo: “Cosmos Twins” by Dulup, CC BY-SA 2.0

Photo: “Marigolds in the Garden” by MattX27, CC BY-SA 2.0

Cosmos, Marigold, Zinnia.  These colorful, long-blooming, easy-to-grow annuals can be direct-seeded in the garden or bought individually as bedding plants and incorporated into the garden for easy care blooms until the first frosts of autumn. 

Photo: “Flowers” by mag3737, CC BY-NC-SA 2.0

GET TO KNOW YOUR ALLIES

It’s a good idea to be able to identify the beneficial insects when they arrive, so that you don’t inadvertently kill them.  While there are a lot of insects (and spiders) that can be beneficial to your garden, I’m going to focus on a short list of species that are most widely known to be useful in keeping pests at bay.  

Ladybugs or Lady Beetles (Coccinellidae) (Harmonia axyridis, Asian Lady Beetle)

These are probably the most identifiable beneficial insects around, the iconic little red beetle with black polka-dots.  Adult ladybugs will be attracted to your flowers for their pollen, and hopefully will plant her eggs in your garden.  While adult ladybugs are omnivorous beneficial predators, the larval stage of the ladybug is a voracious consumer of aphids and other harmful soft-bodied pests.  Ladybugs only live an average of 3 to 6 weeks, but will lay up to 1,000 eggs during that time, and the average ladybug may eat as many as 5,000 aphids during its lifetime.  So, plant flowers to attract them, but also learn to recognize their larval stage and leave them be.  

Photo Credit: University of California Integrated Pest Management Program

Lacewings (Chrysopidae and Hemerobiidae)

Just like the ladybugs, it is the larvae of the lacewings that prey on harmful pests, so you will want the adult lacewings to visit your nectary flower plants and lay their eggs in your garden.  The adult lacewing feeds only on flower nectar, but their larvae will eat aphids, caterpillars, mealybugs, leafhoppers, insect eggs, and whiteflies.  These are reportedly the most effective predators you can find.  Full-grown laceworm larvae can consume 100 or more insects a day.  

Green Lacewing.   Photo Credit: University of California Integrated Pest Management Program

Brown Lacewing. Photo Credit: University of California Integrated Pest Management Program

Hoverflies or Syrphid Fly or Flower Fly (Syrphidae)

You will want hoverflies to visit your flowers for pollen and nectar, because they will lay their eggs near aphids and other soft-bodied insects, and their larvae will eat up to 60 aphids per day.  The adults resemble little bees, but they do not sting.  They lay eggs (white, oval, laid singly or in groups on leaves) which hatch into green, yellow, brown, orange, or white half-inch maggots that look like caterpillars. They raise up on their hind legs to catch and feed on aphids, mealybugs and others.

Hoverfly.   Photo Credit: University of California Integrated Pest Management Program

Parasitic Mini-Wasps (Trichogramma spp; Ichneumidae; Braconidae)

These tiny wasps do not sting.  They lay their eggs inside the eggs of moths and butterflies, whose caterpillar stages inflict much damage on our crops.  Their prey include the alafala caterpillar, armyworms (but not beet armyworms), bagworms, bollworms, cabbage looper, cankerworm, codling moth, corn borers, corn earworm, cutworm, fruitworms, leafworms, peach borers, squash borers, tomato hornworm, wax moth, and webworms.  

The adult cycle lasts only 9 – 11 days, during which an adult female may lay eggs in up to 300 pest eggs on average.  It is believed that the adults feed on the nectar of tiny flowers such as those listed.  These wasps are so tiny (less than 1 millimeter or 1/50th of an inch) that you probably won’t be able to identify them.  

Parasitic wasps. Photo Credit: University of California Integrated Pest Management Program

Tachinid Flies (Tachinidae)

These flies are very beneficial parasites of many damaging caterpillars such as corn earworm, cabbage worm, cabbage looper, cutworms, armyworms, as well as some damaging bugs such as stink bugs, squash bug nymphs, beetles, and fly larvae.  The adults deposit white eggs on foliage or directly on the body of a host.  The larvae are internal parasites, feeding within the body of the host and killing it, then emerging to pupate.  Tachinid flies may complete one to several generations per year.  

Tachinid flies. Photo Credit: University of California Integrated Pest Management Program

Praying Mantis (Mantidae)

The praying mantis is a well-known insect eater, but keep in mind that it does not discriminate and will also eat your beneficial insects if it gets a chance.  It is generally believed, however, that their usefulness outweighs this drawback.  

Praying mantis. Photo Credit: University of California Integrated Pest Management Program

These are only a few of the beneficial predators.  For more information on beneficial allies, the University of California Agriculture & Natural Resources has compiled useful lists of beneficial insects, as well as a color poster of these allies. http://ipm.ucanr.edu/PMG/NE/index.html  Get to know your allies and be sure not to harm them.  You may refer to the Virginia Cooperative Extension’s slideshow of some of the bad bugs. https://www.pubs.ext.vt.edu/2909/2909-1414/2909-1414.html

MORE FLOWER CHOICES

While planting the flowers on the short list will attract beneficials to your yard, for more variety, there are many other choices to consider, including but not limited to the following:

Agastache:   Agastache scrophulariifolia and Agastache foeniculum (North American native)

Ajuga reptans (carpet bugleweed)

Antennaria neglecta (field pussytoes) (Native)

Anthemis tinctoria (chamomile)

Asclepias (butterfly weed) (Native)

Aster novae-angliae (Native)

Aurinia saxatilis (basket of gold alyssum)

Chrysanthemum parthenium (feverfew)

Coreopsis (Native)

Dianthus (pinks)

Echinacea (Native) (read all about the echinaceas in this issue, “In The Ornamental Garden”

Eutrochium  (Joe Pye) (three species) (Native)

Hedeoma pulegioides (American pennyroyal) (Native)

Helianthus annuus (sunflowers) (Native)

Helianthus maximilianii (prairie sunflower) (Native)

Lavendulan augustifolia (lavender)

Liatris (Native)

Liriope muscari (lilyturf)

Melissa officinalis (lemon balm) (Native)

Mentha Pulegium (pennyroyal)

Mints (Native)

Monarda (bee balm) (Native)

Perthenium integrifolium (wild quinine) (Native)

Phlox paniculata (Native)

Phlox subulate (creeping phlox) (Native)

Potentilla (cinquefoil) (Native)

Pycnanthemum (mountain mint) (Native)

Sedum (Native)

Solidago canadensis (goldenrod) (Native)

Tanacetum vulgare (tansy)

Thyme

Veronica Americana (Native)

Veronica spicata (spike speedwell)

GO NATIVE

Consider choosing native species.  Since the beneficial insects are often native species themselves, they will be naturally inclined to prefer the native flowers as food sources, so consider native species whenever possible.  

THINK BIG

Beneficial insects like blooming shrubs and trees, too, so consider extending your bloom season with trees and shrubs, especially natives such as redbud (Cercis canadensis), serviceberry (Amelanchier arborea, edible berries), elderberry (Sambucus canadensis, edible and medicinal), American holly (Ilex opaca), summersweet (Clethra alnifolia, fragrant blooms), Virginia sweetspire (Itea virginica), winterberry holly (Ilex verticillate) and deciduous holly (Ilex decidua, an important source of winter food for birds).  If you’re ambitious, you can get a jump start on the season by planting a winter crop of buckwheat, which beneficial insects find highly attractive, and which is useful for soil improvement and weed control.  https://www.canr.msu.edu/uploads/234/78912/buckwheat.pdf

STRATEGIC NEGLECT

If you grow vegetables, let some of them strategically go to flower.  The good bugs love carrot flowers as well as the blooms of the mustard family like turnips, broccoli and kale.  Beneficial insects love all blooming herbs, so let at least some of your herbs blossom.  

Reconsider the clover, violets, and dandelions in your grass.  Beneficials and pollinators love them, so let them bloom.  

Stop spraying the undersides of leaves to remove aphids manually, as you may also be removing the eggs that will hatch into aphid eaters.  

TO SUM IT ALL UP

Establishing this type of system takes patience and will initially require that you let some damage be done to your plants while you wait for the cavalry of beneficials to appear, but it pays off in the long run, and it is better for the environment.  So make your garden a magnet for beneficial insects, and they will happily battle your pests for you while you relax on your veranda enjoying your garden.  

SOURCES

“Attracting Beneficial Insects,” PennState Extension https://extension.psu.edu/attracting-beneficial-insects

“Attracting Beneficial Insects with Native Flowering Plants,” Anna Fiedler, Michigan State University MSU Extension https://www.canr.msu.edu/resources/attracting_beneficial_insects_with_native_flowering_plants_e2973

“The Virginia Gardener Guide to Pest Management for Water Quality,” Virginia Cooperative Extension https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/426/426-615/426-615_pdf.pdf

“Permaculture Design,” North Carolina Extension Gardener Handbook https://content.ces.ncsu.edu/extension-gardener-handbook/appendix-g-permaculture-design

“Beneficial Insects,” University of Florida IFAS Extension https://edis.ifas.ufl.edu/topic_beneficial_insects

“Encouraging Beneficial Insects in Your Garden,” Oregon State Extension Service https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/pnw550.pdf

Featured Photo of syrphid (hoverfly) on alyssum flower by Steven Ash, courtesy of the Univ. of Delaware Coop. Extension, “The ‘New’ Companion Planting: Adding Diversity to the Garden,” https://www.udel.edu/academics/colleges/canr/cooperative-extension/fact-sheets/adding-diversity-garden/