|
Life without Beneficial Insects
|
People's lives would be very different without the benefits
provided by insects, and it is unlikely that we could survive
on earth without them. Our crops and homes would be overrun
by pest insects and weeds. We would not have fruits, vegetables,
and plants that depend on insect pollination. There would be
no honey, silk, and other useful products made by insects.
Dead trees and animals as well as animal droppings would cover
the ground. We would know much less about genetics and other
areas of biology. And we would not be inspired or fascinated
by the diversity and habits of beneficial insects
|
|
Predators and Parasites
|
Predators seek out and eat many prey insects during their
lifetime. Ground beetles, or carabids, include about 2,000
species of predators in North America. The larva of one
species, Calosoma sycophanta, has been reported to eat
more than 50 gypsy moth caterpillars during a two-week period.
Other beetle predators include rove beetles, checkered beetles,
lightning bugs, soldier beetles, and tiger beetles. Even
some crop pests, such as blister beetles, are beneficial as
larvae because they eat grasshopper eggs.
|
Ladybird beetles feed on scale insects and aphids. While it
is in the larval stage, one ladybird beetle species, Coccinella
californica, can eat nearly 500 aphids. During the late
1800's in California, the groves of orange and other citrus
fruits were almost completely destroyed by the cottony-cushion
scale. The vedalia ladybird beetle was found to be a natural
predator of this scale insect in Australia. About 500
individuals of this ladybird beetle were brought to California
from Australia, and it became established to control the scale
pest and save the citrus industry.
|
Most of the parasitic insects are wasps and flies, although
there are some parasitic moths and beetles. The parasitic
female lays an egg near or in the host insect. When this egg
hatches, the parasitic larva feeds on the host and kills it.
Ichneumon wasps often have long ovipositors for laying eggs on
beetle or moth larvae that are feeding inside some part of the
plant. Some chalcid wasps lay their eggs inside the eggs of
another insect. The parasitic larva is so small that it
obtains all its food inside just one egg of its host.
Tachinid flies also parasitize larvae of beetles and moths,
and some have been used to control corn borers and other pests.
|
|
Weed Control
|
Populations of weeds are often controlled or held in balance by
insects. Sometimes insects are introduced from another country
to control weed plants. A South American moth, Cactoblastis
cactorum, was introduced into Australia to control a cactus
that was ruining the range land of cattle. Many insects have
been introduced into the United States to help control alligator
weed, which clogs streams and lakes.
|
|
Decomposers and Recyclers
|
Insects aerate and nourish the soil by their burrowing and droppings.
Many insect species recycle organic materials, which in turn
promotes plant growth. Dead trees, leaves falling to the
ground, and dead animals are decomposed by insects. Many
different dung beetles have been introduced into the United
States to decompose cow droppings that would cover the ground
in pastures if beetles were not present. [Note: the
videotape Eyewitness: Insect has a time-lapse segment
of insects devouring a dead animal.]
|
|
Pollination
|
Each kind of plant has a different means of reproducing by
seeds. Some are self-pollinated, and others are pollinated by
the wind, birds, and even bats. Insects are the major
pollinators for many plants. The honey bee and many other
species of bees have special hairs for carrying loads of
pollen on their body. Other major pollinators include moths
and butterflies, beetles, and flies. Some flowers can be
pollinated by only one kind of insect. One such flower in the
tropics is pollinated by cockroaches. Yucca moths pollinate
their host's flowers to ensure that seeds will be produced to
serve as food for the moth larvae.
|
More than 200 species of cultivated crop plants in the United
States are pollinated chiefly by insects. Without insect
pollination, there would be no onions or pickles for the
hamburger, no carrots in the salad, no
watermelon or apple pie, and no vanilla or strawberry ice
cream. Many other fruits and vegetables would not be
present on the menu. Our gardens and houses would be bare
without the many flowers and ornamental shrubs that are insect
pollinated.
|
|
Useful Products
|
Insects have produced many products and substances used in
products that have been used by humans throughout history.
Humans' earliest sweetener was honey from the honey bee.
Beeswax was the earliest form of wax and is still has special
uses by artists and others. In recent years more than 200
million pounds of honey and three million pounds of beeswax
have been produced every year in the United States.
|
Silk comes from the cocoons of the silkworm, Bombyx mori,
in Asia. Each cocoon has a single thread that is unraveled
until it is more than a half mile long. About 3,000 cocoons
are required to make one pound of silk. About 70 million
pounds of silk are produced every year.
|
Other useful products include tannic acid from insect galls,
which has been used for tanning hides to make leather. Some
insect galls have been used to make inks. Scale
insects have been the source of red dyes, used for food
coloring and cosmetics. About $9 million worth of shellac,
which is made from a scale insect, is used annually in the
United States.
|
Substances from some insects have been used in medicines for
arthritis and urinary tract infections. Blow fly larvae have
been used to treat battle wounds for centuries, and more
recently they have been used to treat bone infections. These
larvae feed on dead tissue and secrete a substance known as
allantoin, which helps the tissue to heal.
|
|
Scientific Tools
|
Insects are valuable tools for scientific research because of
their rapid reproduction rate and their ease of keeping them in
laboratories. The Drosophila fruit fly and other
insects have been major experimental animals in research on
genetics. Grasshoppers and cockroaches have been used as test
animals to study the effects of chemicals on nerves. Because
the nerves of an insect are similar to those of humans, new
drugs can be tested in laboratories without using humans.
Insects have been the primary tools for studying evolution,
ecology, growth of populations, and many other areas of biology.
In recent years insects have become tools for studying
pollution of the environment.
|
Forensic entomology is a new tool for investigating legal
issues, including murders and other crimes. There is a
natural succession of different insects that come to dead
bodies after death. Some come within the first few hours, and
others do not come until days later. By studying the insects
present on a dead body, entomologists can determine how long
the body has been dead and, in some cases, whether the body
has been moved. More information on how insects are used as
a tool to solve crimes can be obtained at the forensic
entomology homepage
Index of . . .Case Histories.
|
|
Food for Animals
|
Insects are an essential part of the food web that connects all
animals and plants. Skunks, bats, and raccoons subsist
largely on insect food. Many freshwater fish feed on aquatic
insects, such as mayflies, stoneflies, caddisflies, and midge
larvae. These insect-eating fish are a basic part of the diet
of larger game fish. Many birds feed entirely upon insects,
and some baby birds eat their weight in insects every day.
Toads, frogs, and lizards feed mostly on insects. Some
frogs specialize on small insects; one such frog was found in
Arkansas that had more than 800 ants in its stomach.
|
Many people in the United States eat lobsters, shrimps, and
crabs, which are close relatives of insects, but few people in
the U. S. eat insects purposefully. However, people in many
other countries eat insects. Insects have high nutritional
value, and many are considered tasty delicacies similar to
shrimp. Locusts, beetle grubs, ants, termites, and caterpillars
are eaten in parts of Africa. Giant water bugs and grasshoppers
are eaten in many areas of Asia. Insects also have been used
for seasoning food. In Venezuela, a hot sauce is made from
leaf-cutter ants. For more information on insects as food,
see Bugs on the Menu.
|
|
Aesthetic Value
|
Collecting and photographing insects has provided enjoyment
as hobbies for many people. Some people collect stamps,
coffee cups, and other items that illustrate insects. Many
butterflies, beetles, dragonflies, and other insects have been
used as models in art and jewelry. In some countries, the
actual insect or parts of the insect are used to make jewelry
and other items. The red and black abdomens of some weevils
are used to make beads in Africa. The bright blue wings of
Morpho butterflies are used to make pictures, dining
trays, and jewelry.
|
In recent years insect zoos and butterfly gardens have become
popular attractions. More than 45 public zoos and gardens
with live insects are present in the United States. Many
people are making their own butterfly gardens by planting
flowers and providing habitats for butterflies. The
Department of Entomology at the University of Kentucky has
provided information on How to make Butterfly Gardens.
|
|
