Practice English Speaking&Listening with: Managing Garden Insects Begins with a Question: Friend or Foe?
[Background music]
>> Managing garden insects begins with a question.
"Friend or Foe?"
One of the most common questions that people ask
entomologists about insects in the garden is
“How do I kill it?”
However, many kinds of insects are actually helpful in the garden
and getting rid of them can lead to problems.
Before you decide whether an insect is friend or foe,
you must first answer the important question
“What is it?”
The answer will tell you if it is a useful partner,
a minor problem, or has the potential to become
a serious problem.
Once you know what it is, you can easily learn
where it lives, how it lives and if necessary,
the options for effective management.
The most sensible and intelligent option for
managing insect pests is IPM or
Integrated Pest Management.
IPM allows us to reduce reliance on one single method,
like the use of pesticides, which is not always the most
effective or environmentally friendly option.
IPM allows us to make intelligent and
thoughtful decisions about pest management.
The steps of IPM are:
• Monitor the garden
• Identify the problem pest
• Evaluate the situation and predict the impact of the damage
• Then make a decision about the best course of action and choose your control methods.
Insects are the most diverse creatures in the world and
they also play many roles in the environment.
At any given time, your home garden may have
over 1,000 different insects.
Some people consider insects as 'bugs' or pests that are
annoying and must be destroyed.
It is not possible or even desirable to get rid of all
the insects in the garden.
Many insects are garden friends, others are foes
and a wise gardener knows the difference.
Among the million or more insect species known on earth,
less than 3% cause problems to humankind
and can be called 'pests.'
The other 97% are either harmless or
actually beneficial.
Let’s start with some of the friends or
the helpful insects in your garden.
Most people are aware of beneficial insects that
pollinate our crops, and provide us with products
like honey, beeswax and silk.
Insects also serve as food for birds, fish and other animals,
so they are important links in the food chain
and for maintaining ecological balance.
Through biological control, harmful insect populations
can be reduced by using other live organisms,
including insects.
Sometimes natural enemies are mass-produced and released.
However, in a landscape or home garden situation,
it may be difficult to introduce, release, or retain
commercially-reared predator insects or parasitoids.
So the best thing to do is conserve the existing
natural enemies and avoid practices that harm them,
such as, unnecessary insecticide use.
Predatory insects and other natural enemies
can be attracted to your garden simply
by providing food, water, and shelter through a
diverse array of plant material.
Planting a variety of pollen and nectar bearing flowers
can help conserve and increase the number of
beneficial insects in your garden.
Predatory insects are especially beneficial
in the garden because they eat harmful insect pests.
Predators are generally larger than their prey and faster.
They have to capture and eat many individuals to
complete their life cycle.
Birds, amphibians, reptiles, fish, spiders, and insects
are examples of predators that eat insects.
Let’s focus on some common predators.
Spiders are some of the most common and important predators
that can be found in a landscape or garden.
Most are general predators that feed on a variety of prey.
Spiders can be easily identified by their
body shape and eight legs.
Although there are several mites that can cause
significant damage to plants,
there are also some predatory mites that prey on pest mites
as well as small insects like whiteflies and thrips.
Predatory mites are similar to pest mites,
with 8 legs and no antennae or wings,
but they are often larger, more colorful and move more
rapidly than pest mites.
Many of the true bugs - Heteroptera - are predators
and prey on other smaller, soft-bodied insects
like aphids, white flies and even caterpillars.
Assassin bugs are relatively large.
Some can be identified by the wheel-like structure on their
back and are often called ‘Wheel bugs’ because of this.
Damsel bugs are smaller and have large eyes.
Both of these hunters have
a strong proboscis - long flexible snout-
that can pierce the exoskeleton of other insects.
Other true bugs,
such as shield bugs, also known as stink bugs,
may be either hunters or plant eaters,
depending on the species.
Some insect eating stinkbugs,
unlike their plant- feeding counterparts,
have spine-like extensions on their shoulders;
for example, the two-spined soldier bug.
Plant bugs can also be pests.
Once again, check the proboscis.
The plant eating bugs will have a delicate proboscis.
Population size is another indicator of
the insect’s dining habits.
Often 10 to 100 individuals of a plant eating species
will be found on a plant whereas populations of a
predatory species will be relatively low,
with less than 10 individuals per plant.
Green and Brown Lacewings are very common predators found
in gardens and are fairly easy to identify
because of their distinctive lace-like wing pattern.
Adults feed on pollen and small, soft-bodied insects
like aphids, lace bugs, and mites.
Larvae are voracious predators with powerful sickle-shaped
mandibles - grasping appendages near the mouth.
Lacewing eggs are an easy to identify treat in the garden.
Each egg floats above the leaf surface,
supported by a thread-like strand.
This may serve to prevent cannibalism
among the young larvae as they hatch.
Praying Mantids are also large and powerful predators.
They use their strong front legs to capture
and devour their prey.
They are easily recognized and widely praised
for their hunting prowess.
However, they eat both friends and foes
including other praying mantids, so they may not be
the most dependable hunter in the garden.
Still who can resist their charms?
Several families of beetles are voracious predators
both as larvae and as adults.
Some of these may be common in your garden such as
Ground Beetles, Tiger Beetles and Rove Beetles.
These predators can be identified by their
sickle-shaped crossing mandibles.
Wasps, like paper wasps and yellow jackets should be
welcome in the garden because they do not attack plants
but instead protect them by feeding primarily
on caterpillars.
They have strong mandibles for chewing prey, as well as
a proboscis which they use to suck nectar from flowers.
Please do not attempt to check their mouthparts!
They are related to bees and may sometimes show
aggressive behavior by stinging when disturbed.
Give them plenty of space.
Flies, such as syrphid or flower flies and
robber flies can be very important predators.
Syrphid flies can be voracious feeders on aphids
and will be attracted to pest populations
even when they are low in number.
They often mimic bees or wasps and appear to
hover in flight like hummingbirds.
Robber flies have heart-shaped heads
with an indentation between the eyes and a “bearded” face.
These flies may also mimic wasps and bees.
They are often seen capturing prey in flight.
You are probably familiar with parasites,
like ticks or fleas.
They are generally much smaller than their hosts
and live on or within the host for part or
all of their life cycle.
Generally they don’t kill their hosts.
Insect parasitoids are different.
They kill their hosts by eating them.
Adult parasitoids often lay their eggs
inside or on the host.
The immature parasitoids hatch and consume
their host during development.
Many insect parasitoids are found in the order
containing wasps, Hymenoptera.
Some are very specific in prey selection,
others prey on a wide variety of pests.
Parasitic wasps attack caterpillars and aphids.
They lay eggs in the host and when the larvae emerge,
they consume the host.
These wasps leave behind mummified hosts.
The mummies have darkened shells with exit holes,
from which the adult parasitoid emerged.
Sometimes the parasitoid will pupate on the host;
other species will pupate near the dead host.
Parasitic wasps are also very effective against
scale insects, and when large numbers of exit holes
can be seen on scale insects, avoid spraying insecticides
to conserve these natural enemies.
As every gardener knows,
not all garden insects are beneficial.
Insects are often the cause of the unsightly damage
seen on our plants.
In many cases, the insect damage may weaken the plant
and predispose it to diseases.
Destructive insects can be divided into
four basic categories based on the type of damage
they cause to plants:
chewing, discoloration, distortion, and die back.
Chewed, shredded, torn and skeletonized leaves,
flowers, buds, and fruits can be symptoms of insect
damage on plants.
This kind of damage is caused by insects with
cutting and chewing mouthparts.
These insects have powerful mandibles
that cut up plant parts.
Examples of such insects are
caterpillars of butterflies and moths
and larvae of sawflies,
larvae and adults of beetles, and grasshoppers.
Discoloration of leaves by stippling, flecking,
bleaching or bronzing, with no actual damage
to the shape or size of leaves is often caused
by insects with piercing and sucking mouthparts.
This damage is caused when the insects insert their slender,
needle-like mouthparts into the leaf tissue and
draw out plant sap.
In the process, they'll also damage the surrounding cells
which results in destruction of chlorophyll leading to
the leaf discoloration.
The discoloration begins as small white flecks or stipples
and gradually the entire leaf may become chlorotic
or bleached in appearance.
Some insects that cause this type of damage are lace bugs,
aphids, plant hoppers, white flies, and leaf hoppers.
Mites and thrips are very small and may not
be visible with the naked eye.
Sometimes webbing may be seen in plants
affected by mites.
Thrips - adults and juveniles -
can be identified under a microscope.
Distortion of plant parts into abnormal shapes or
structures can also be a sign of insect damage.
For example,
galls on leaves, flowers or stems,
leaf curling or cupping and
abnormally twisted leaves or stems.
This type of damage can be caused by different insects
like thrips, aphids, larvae of some wasps and moths,
and also gall mites.
It is important to note that some plant diseases
can also cause galls.
Sometimes twigs, stems, or branches or even
the entire plant appear to wilt and eventually die.
This symptom, called die back, can be caused by insects.
These dead twigs and branches are retained on the plant.
This damage is typical of scale insects because
they are not mobile and severely deplete
the branch or twig of plant sap.
Some moth larvae and beetles that bore
into stems can also cause this symptom.
In addition to damage or symptoms, insect products,
often called signs, such as fecal spots, honey dew, frass,
and cast skins are solid evidence of their presence
and/or activity on the plant.
These may not be directly harmful to the plant and
often remain on the plant for long periods of time
even after the insect has left.
Make sure there is an active infestation on the
plant before considering the application of an insecticide.
Sooty mold, a charcoal black fungus grows on honey dew
secreted by sap feeding insects such as aphids,
mealybugs, scales, and white flies.
It is another common sign of insect activity.
Though sooty mold appears to grow on the plants,
it is not a plant disease, and is a clear indication
of an insect infestation.
At times, sooty mold can also grow on other surfaces
like in this picture.
You can see how the honey dew dripping from the tree above
caused sooty mold on the wall and road along the tree line.
If the insect is controlled,
the sooty mold will go away on its own.
Chewing, distortion, discoloration and die back
symptoms can be caused by a wide variety of insects and
often a single pest may cause different types of symptoms.
Similar symptoms can be caused by plant disease or
even abiotic causes such as environmental stress,
extreme heat, drought, cold injury or chemicals.
Once potential insect damage has been identified,
the next step is to look for insects.
Symptoms and signs alone do not warrant action.
When you see any of these symptoms, look for insects.
Carefully check both sides of the leaves and
carefully study the stems.
Look in the branch forks and all around the flowers.
Insects can be very good at hiding.
After locating suspected pests,
the next step is to identify the host plant.
Once you know the name of the plant,
you can easily discover the common pests
associated with it.
At this stage in your diagnosis your
County Extension Agent will be a great resource.
Each state has a Pest Control Handbook
that will suggest control measures if needed.
Remember to consider the severity of the
infestation and damage, plant species involved,
and any evidence of predator or parasitoid activity
before applying pesticides.
We hope that this video will help you identify the insect
Friends and Foes that you will commonly encounter
in your gardens and landscapes.
You will be amazed at just how astounding and fascinating
the diverse world of garden insects can be.
In fact, if you take the time to get to know them,
you may find you enjoy your garden insects
as much as the plants!
© 2012 University of Georgia
College of Agricultural and Environmental Sciences
