Beneficial insects are those which are helpful to us in some way. These
include well-known flower pollinators such as bees and butterflies, and those
which are natural enemies of insects we consider pests. The purposeful use of an
insect to suppress other insects is one type of biological control and dates
back at least to the fourth century A.D. when ants were manipulated to control
citrus pests in China. Insect predators, in the immature and often adult stages,
feed directly on their prey, killing them immediately. Examples of predator
species are the praying mantis and the ladybug (lady beetles). Other insects
parasitize their hosts by depositing eggs on or in them. Larvae emerging from
the eggs typically develop within and emerge from the host. Parasitized insects
usually continue to feed for a time before they die. Examples of insect natural
enemies which parasitize pest species include many tiny wasps and flies.
Natural enemies are an important component of integrated pest management
programs. For example, in home flower and vegetable gardens adult and immature
lady beetles can quickly reduce a population of aphids thus eliminating the need
to apply a chemical spray. Suppression of pests by beneficial insects alone,
however, can be variable. When pest populations are large and there is enough
food and the proper habitat to support the growth and reproduction of natural
enemies, the impact of beneficials on pest populations can be greater. When pest
populations are low, beneficials will search elsewhere for a food source.
Beneficial insects tend not to recover as quickly from exposure to insecticides
as pest species do.
A number of beneficial insects occur naturally in your yard and garden. Learn
to identify them and consider their needs in planning and maintaining your
Attracting and Keeping Beneficial
Insects in the Yard and Garden
Alternative sources of food:
Many predaceous insects feed on pollen, nectar or plant juices to supplement or
replace their insect diet when host populations are low. Flower nectar also
provides nutrition for egg-laying parasitoid species. Favored plants include
daisies, Queen Anne's Lace (wild carrot), yarrow, alyssum, goldenrod, alfalfa,
soybeans, clovers, and vetches.
Shelter: Provide areas of
stable habitat in the yard and garden where beneficial insects can find
protection from mowing, tilling and other disturbances. Perennial flower beds
(especially those planted with pollen- and nectar-producing plants), hedgerows
near flower or vegetable gardens, or plots of cover crops like alfalfa or
soybean provide excel-lent shelter for beneficial insects. Predaceous ground
beetles and rove beetles will take cover in permanent grass pathways in the yard
and garden, in compost or mulch, and under rocks. Avoid excessive tilling by
growing vegetables and flowers in raised beds.
Sources of water: Bird baths, small shallow containers, and
temporary puddles provide water for insects. This is important especially during
periods of dry weather. Change the water in containers every 2-3 days to
discourage mosquitos from breeding in standing water. Sticks or rocks placed in
the water serve as perches for insects so they won't drown.
Incorporating natural enemies with other pest
management strategies: Beneficial insects usually won't solve
all your pest problems because it is to the benefit of the beneficials to allow
some of their prey to feed and reproduce. In natural systems, a balance is
maintained between predator and prey/host species so resources are not
completely destroyed. Other pest control practices can be used in combination
with natural enemies. Reduce pest pressure in the landscape by selecting plant
varieties bred for resistance to insect pests. Try not to disturb the shelter
areas described above. If it is necessary to apply pesticides, first choose
products that target specific pests. For example, different strains of the
bacterium, Bacillus thuringiensis (B.t.), attack caterpillars, beetle
larvae, or various flies. These products will not harm beneficial species. A
second choice would be materials that act as stomach poisons to foliage feeders.
These materials are less harmful to beneficials because these insects don't feed
directly on plants. Insecticidal soaps or horticultural oils are other
alternatives. These effective contact insecticides are less likely to devastate
populations of beneficials.