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 garden.
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. |