it practical to purchase and release beneficial insects
to help control pests in my yard and garden? I try to avoid
pesticides as much as possible, but when the bad bugs are causing
too much damage, I feel like I should do something.
There are numerous insects that can be considered “beneficial” in
that they are
predators or parasitoids of pest insects.
Predators feed on various life stages of insect pests, while
parasitoids live in or on them, eventually killing the pest. Unless
you regularly use broad-spectrum insecticides, they already are more
active in your garden than you realize. Everyone recognizes lady
beetles and praying mantises, but few are aware of the most
effective beneficial insects.
Photo: Robert Donnan
Gypsy Moth caterpillar
include parasitic wasps, some of which are smaller than the period
at the end of this sentence. Still others are parasitic flies that
resemble houseflies. You
may have even swatted a few of them, thinking that they were
nuisance pests. Ground beetles look fierce and may be mistaken for
bad guys, but they are important predators of many pests, including
gypsy moth larvae and many soil-dwelling insects. Adult flower flies
may be mistaken for yellow jackets, but they do not sting; their
larvae are voracious aphid predators.
species of beneficial insects are available commercially,
and are becoming increasingly popular to help control pests in
greenhouses. The U. S. Department of Agriculture, in conjunction
with agricultural research stations, has introduced predators and
parasites of foreign pests that were accidentally introduced into
this country. These include
that are parasites of gypsy moths, twice-stabbed lady beetles that
are predators of euonymus scale, and vedalia beetles that are
predators of cottony cushion scale on citrus.
While buying and releasing beneficials can help
control large populations of insect pests, a better approach in the
home garden is to attract and encourage existing populations of
beneficials. The most important thing you can do to protect and
encourage beneficial insects in your garden and landscape is to
choose insecticides with care.
beneficials are more sensitive to insecticides than the pests you
are trying to control.
While it is true that beneficials can reduce your pesticide use,
realistically you will still have to use pesticides to deal with
serious pest outbreaks from time to time. The key is to choose
products that have little or no residual activity. While the
beneficials present when you spray will be killed, new ones coming
into your garden will not be affected. These insecticides include
insecticidal soap, horticultural oil, and botanical insecticides
such as neem, pyrethrins, rotenone, and sabadilla. The botanicals do
have brief periods of residual activity, but they are much shorter
than most synthetic insecticides. Most break down rapidly when
exposed to the sun.
It is also important to have as much
diversity as possible in your plantings.
A mix of trees and shrubs, turfgrass (yes, low maintenance turf is
an important habitat for some beneficials!), and annual and
perennial flowers is best. Permanent plantings such as trees, shrubs
and turf provide a place for beneficial insects to overwinter. The
adults of many beneficials feed primarily on pollen and nectar, so
it is important to have something in bloom from early spring until
late fall. Some of the best flowers for attracting beneficials
include the following families:
- plants in the carrot family are especially attractive to small
parasitic wasps and flies. Interplant them in your vegetable garden
and flower beds. Plants in this family include: caraway (Carum carvi);
coriander/cilantro (Coriandrum sativum); dill (Anethum graveolens);
fennel (Foeniculum vulgare); Bishop's flower (Ammi majus); Queen
Anne's Lace (Daucus carota); and toothpick ammi (Ammi visnaga).
- attractive to larger predators such as lady beetles and soldier
beetles. Incorporate into the vegetable garden and flower beds.
Plants in this family include: blanketflower (Gaillardia spp.);
coneflower (Echinacea spp.); coreopsis (Coreopsis spp.); cosmos
(Cosmos spp.); golden marguerite (Anthemis tinctoria); goldenrod (Solidago
spp.); signet marigold (Tagetes tenuifolia); sunflower (Helianthus
spp.); tansy (Tanacetum vulgare); and yarrow (Achillea spp.).
- generally grown as cover crops and attractive to many beneficials.
Plants in this family include: alfalfa (Medicago sativa); fava bean
(Vicia fava); hairy vetch (Vicia villosa); and sweet clover (Melilotus
Mustard Family (Brassicaceae)
- attractive to beneficials that are parasites and predators of the
insect pests of the mustard family (broccoli, Brussels sprouts,
cabbage, cauliflower, kohlrabi, mustard greens). Be sure to plant
these away from the garden rather than in the garden since these
plants attract pests as well as beneficials. Some are common weeds,
such as yellow rocket and wild mustard. Plants in this family
include: basket-of-gold alyssum (Aurinia saxatilis); mustards (Brassica
spp.); sweet alyssum (Lobularia maritima); yellow rocket (Barbarea
vulgaris); and wild mustard (Brassica kaber).
Verbena Family (Verbenaceae)
- attractive to a variety of beneficial insects. Many plants in this
family are favorite garden flowers. They include: lantana (Lantana
camera); Buenos Aires verbena (Verbena bonariensis); hybrid verbena
(Verbena x hybrida); and lilac vervain (Verbena rigida).
Beneficial insects also need a
Shallow containers such as ceramic pot saucers with pebbles for the
beneficials to rest on are best.
The following books and websites have information on
a variety of beneficial insects as well as good pictures to help you
More About It
“Natural Enemies Handbook: The Illustrated Guide
to Biological Pest Control,” Mary Louise Flint and Steve
Dreistadt, University of California Press, 1999.
“Insects That Feed on Trees and Shrubs,”
Warren Johnson and Howard Lyon, Cornell University Press, 1991.
“Controlling Vegetable Pests,” Pamela Pierce,
Ortho Books, 1991. ISBN-10: 0897212304
Biological Control Information on the Web
Nematodes as Biological Control Agents of Insects
Pennsylvania IPM Program