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University
of Rhode Island GreenShare Factsheets
Beneficial
Insects on Lawns
Many
insects which occur in lawns are beneficial insects. They provide
a form of natural control of pest insects or assist in the breakdown
of organic matter so nutrients can be returned to the soil. Predatory
insects are relatively mobile insects that search out prey. Some
predatory insects (like the assassin bug) have sucking mouthparts
which penetrate the soft body of the victim and suck out the internal
fluids, leaving only the outer shell behind. Other predatory insects
(like ladybird beetles and ground beetles) have chewing mouthparts
and feed on the entire body of the victim. Predators will feed on
several victims during their lifetimes. Some of the more familiar
predators which occur naturally in New England lawns include: Ground
beetles: These may be the most common predators on lawns in
New England. The most common species are slightly smaller than
Japanese
beetles and are generally a shiny bronze or tan or green color.
Both adults and larvae feed on soft-bodied insects and various
caterpillars.
Ground beetles usually are very quick moving and can "seek and destroy" their
prey. Rove
beetles: Rove beetles may not be familiar to many people, but
they do occur commonly in turfgrass areas. They are somewhat more
elongated than other beetles, and the hindwings are not fully expanded.
They feed on a variety of soft-bodied insects. Spiders:
Spiders are surprisingly common and active in turf areas and
are very efficient predators. While they are not insects, many species
of spiders are definitely beneficial in the garden or lawn, feeding
on a wide range of immature insects and mites. Ants:
Some species of ants are carnivorous, and seek out insects and
other soft bodied organisms with which to provision the nest. In
addition, ant activity often can help in the general breakdown of
organic matter and the formation of soil. However, if ant activity
becomes excessive, the ants may become a nuisance or the soil may
dry out and turf damage will result. Another
general group of beneficial insects is the parasites. These are
small insects (generally smaller than the host) which develop inside
or on the body of a single individual. The adult female finds a
suitable host and lays her eggs on the outside of the body or inserts
the eggs through the skin into the internal tissue of the host.
The immature parasites feed on the organs and fluids inside the
victim and gradually weaken and kill the host. There
are many parasitic wasps which occur naturally in New England and
are active in lawn settings. Wasps such as Scoliid (family:
Scoliidae) and Tiphiid (family: Tiphiidae) wasps are
adapted to lay eggs in softbodied insects and do not bite or sting
people. Scoliid wasps are about 16 mm (5/8 inch) long and blue-black,
with blackish-purple wings. They have a yellow stripe on each side
of the abdomen. Their bodies are fairly hairy and the back part
of the abdomen is covered with reddish hairs. Tiphiid wasps are
black and somewhat hairy with short, spiny legs. Both wasps are
generally seen flying over the lawn during the day, leaving in early
evening. Scoliids and Tiphiids are beneficial wasps in that they
parasitize grub populations. They are not aggressive and generally
do not attack humans. Adults are often seen on golden rod flowers
in the late summer. Beneficial
insects are very sensitive to insecticides, so whenever a general
insecticide is applied to control a pest species (such as Japanese
beetle grubs or chinch bugs), the
material will usually have a detrimental effect on the beneficial
organisms, often for at least a few weeks. Consider using alternate
methods of pest management, biological control agents (if available
and suitable) or providing optimum cultural conditions so that the
lawn can tolerate higher levels of pest activity without visible
loss of vigor. If an insecticide application is deemed necessary,
make spot treatments rather than broad scale applications if at
all possible. Remember that
the statement, "The only good bug is a dead bug," could not be further
from the truth. Be sure you have an accurate identification of the
insects in question and only attempt to control those which really
warrant attention. There are in fact many "good bugs" out there!
Let them help! Adapted
from the University of Massachusetts Extension, 1999
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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