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Beneficial Insects

Predators of bad garden insects

By: Sandy Feather ©2012
Penn State Extension

Q. Is 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.

A. 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.

gypsy moth caterpillar
Photo: Robert Donnan
Gypsy Moth caterpillar

These 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.


Beneficial insects

Many 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 tachinid flies 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.

 

Many 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.


Planting Diversity

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:

Carrot Family (Apiaceae) - 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).

Aster Family  (Asteraceae) - 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.).

Legumes (Fabaceae) - 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 spp.).

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).

verbena
Verbena

Beneficial insects also need a source of water. 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 identify them.


Read More About It

Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control,” Mary Louise Flint and Steve Dreistadt, University of California Press, 1999. ISBN-10: 0520218019

Insects That Feed on Trees and Shrubs,” Warren Johnson and Howard Lyon, Cornell University Press, 1991. ISBN-10: 0801426022

Controlling Vegetable Pests,” Pamela Pierce, Ortho Books, 1991. ISBN-10: 0897212304

Biological Control Information on the Web

Nematodes as Biological Control Agents of Insects

The Pennsylvania IPM Program

 

     


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