Before you mash, repel, or spray those insects in your
garden, make sure that they are not “beneficial,” that is, one of the “good
guys.”
There are a great many insects that fight on our side
against destructive insect pests. These allies and partners of the insect wars
are called “beneficial insects.” Many
times it is only through their assistance that the tide of battle turns our
way.
Consider aphids, for example. In the spring and early summer, and sometimes
again in the fall, populations of soft-bodied, sucking mouthpart aphids can
explode quickly when conditions are right for their growth. Caught in time,
most aphid problems can be averted by washing the plants with a strong stream
of water, applying insecticidal soap, and letting the beneficial insects clean
up any escapees. Sometimes the
beneficial insects will get there even before you do.
Beneficial insects work in two different ways. Predators feed on the insect itself, and
parasites generally lay their eggs on the host so that their young can feed.
Since predators feed outright on the bodies of insects, they
generally are generally as large or
larger than their prey so that they can compete in the battle royal that
usually occurs between them. Mobile bad
guys, insects that can easily move about, usually do not go down without a
fight. Lady beetles, lacewing larvae,
and assassin bugs are examples of predator insects.
The ladybeetle is one of the best known of the predator
insects. These rounded beetles come in
many sizes and colors. The most common
species found in Arizona is the convergent ladybeetle, named for the two
converging white stripes behind the head.
The beetles are brightly colored with red front wings speckled with
black markings. The adults lay orange
egg clusters on plants near groups of aphids.
The eggs hatch into tiny black and orange larvae which feed on aphids in
great numbers. As the larvae grow, they
resemble tiny beaded dragons. Once they
reach maturity, they form a rounded black and orange-marked pupa attached to
the plant. Pupae are often mistaken for
bird droppings.
The lacewing is another outstanding predator insect. Adult lacewings are delicate, pale green or
light brown insects about one-half to three-fourths of an inch long. Their wings have many veins, which gives them
the netlike or “lace” appearance. They
are attracted to lights at night and may be mistaken for moths except they have
a characteristic fluttering flight when disturbed. The adult stage feeds on flower nectar only
and is itself not predatory.
All lacewings lay pale green eggs on the tips of threadlike
stalks on the underside of leaves. The
immature lacewings hatch within a few days.
They are no longer than one-eighth inch and are light brown in
color. Their shape resembles that of
an alligator and have large,
sickle-shaped mandibles with which they suck the juices from insect eggs and
small prey. They are ferocious feeders,
and consume large numbers of aphids, other insect pests, and insect eggs of all
kinds. When the larvae mature they form
a yellow silken cocoon in which to pupate.
The praying mantis is also a well known predator
insect. It sits and waits on plants
until another insect crosses its path, and then it captures its victim with its
spiny front legs. Praying mantis females
lay their eggs in 1 to 2 inch long “cases” made of a dark brownish-gray papery
material with numerous compartments. The
egg cases are glued to twigs or branches, and are commonly found attached to
the underside of boards. Praying mantis
young emerge from the cases in the spring.
They look like miniature adults.
Other predators include assassin bugs and ambush bugs whose
names pretty much describe their predatory activities. There are also damsel bugs, big-eyed bugs,
minute pirate bugs, syrphid flies, wasps, and dragonflies. Altogether, they form a formidable line of
defense for garden and landscape plants and work in our favor to help maintain
the balance of nature.
Parasitic insects lay their eggs on or within the bodies of
their prey, and because of this, they do not need to be, and generally are not,
as large as the host insect. Once the
egg of the parasite hatches, it is the larva, or young of the beneficial insect
that uses the host insect for food.
Because adult parasite insects are often much smaller and weaker than
their prey, they must rely on their agility to provide the edge needed for
success. Parasitic wasps and flies are
included in this group of beneficial insects.
The adult stage of parasitic insects generally lives outside
of the host insect but lays the eggs on or within a living host. After the eggs hatch, it is the young which
feed on host tissues until the host is killed.
Immature parasites complete their development in only one host. Because they are extremely specialized, they
often only attack one or a few closely related species of insect. Parasites of insects do not in any way harm
humans or their pets.
A fascinating example of a parasite is the eucharitid wasp
which attacks ants. This particular wasp
lays her eggs on the leaves of trees.
The eggs hatch into mobile immature larvae that are able to crawl about
on the leaf surface. In the spring,
worker ants climb into the trees in search of aphids and other insects for
food. The parasite larva attaches itself to any worker ant that comes close and
hitches a ride back to the nest when the worker ant goes home. Once in the nest, the parasite drops off and
attaches itself to a larval ant. The
wasp larva feeds on the ant larva, eventually killing the ant. After emergence from the pupa, the adult wasp
flies out of the ant nest to lay her eggs on leaves once more.
Other types of parasitic insects control aphids, whiteflies,
grasshoppers, beetles, moths, bees and insects.
Even though they are often not seen by the average person, they are
definitely there and doing their job.
In the fight for control of the garden, the predator and
parasitic beneficial insects are the little known heros of the garden. Both types destroy many insects every day
that would otherwise damage or kill our tender garden plants. Some work quickly and produce dramatic
results; others work so slow that their efforts are rarely recognized in the
garden. Both, however, are critical to
maintaining the balance of nature in the plant’s favor. They deserve our respect, our appreciation,
and our protection.
