Theme: Gardening
for a Sustainable Future
Pest Patrol
Insect
Predators and Parasites 
Insect
predators (such as ladybugs, praying mantids, and lacewings)
and parasites (such as certain species of tiny wasps) are the
garden dwellers typically referred to as beneficial insects,
since they take aim at garden pests.
Predators
consume other insects, whereas parasites lay eggs on or inside
other insects. When the larvae emerge, they feed in or on their
hosts, destroying them in the process.
Since insects
are the most successful living organisms on Earth, it makes
good sense to take advantage of these relationships by pitting
one against another, maintaining a reasonable balance. A healthy
garden will host a variety of insects that fall into both the
pest and beneficial categories. Some will even turn up in both,
depending on their life cycle stage and available food.
These
insect allies interact in different ways within your garden.
A predator might go straight to a pest, take care of it, and
then leave or die, for instance. At other times, a desirable
insect may have a limited effect on a large population of target
pests, but will settle in with a small population that reduces
the pest levels over time. Some "good" guys, such as praying
mantids, might eat just a few pests, and then fly away, or eat
a wide variety of pests, but fail to control any outbreaks of
a single pest type. Realize, though, that predators and parasites
certainly don't make our distinctions between "bad" and
"welcome" garden visitors, so they may also dine on your preferred
visitors, such as butterfly larvae.
The chart
below features the lowdown on a few of the most common beneficial
insects that target pests. You can order such organisms from
a science or beneficial insect supplier if you want to control
an outbreak or set up investigations. Better yet, try to create
a garden or habitat that will attract helpful creatures. In
addition to those listed, there are scads of other beneficial
insects that probably already inhabit your garden. These include
such seamy-sounding characters as assassin bugs, soldier beetles,
big-eyed bugs, spined soldier bugs, and hover flies. Challenge
your students to be keen garden sleuths who observe and identify
these characters that call your school garden home.
| Beneficial
Insect |
Target
Pests |
Comments |
Green
lacewings
|
leafhoppers,
mites, aphids, thrips, mealybugs, whiteflies |
The
larvae (sometimes called aphid lions) are voracious aphid
predators. The adults feed on flower nectar and honeydew
produced by aphids and other sucking insects. You can buy
eggs or larvae from suppliers and can attract adults in
most areas of the U.S. by planting flowers with abundant
nectar. |
Lady
beetles
|
aphids,
leafhoppers, scales, mites, mealybugs |
These
familiar creatures, in both larval and adult stages, feed
on soft-bodied insects, especially aphids. You can attract
them by planting nectar plants (nectar is an alternate food
source) and those that attract aphids. These include alyssum,
legumes, and flowers in the Umbelliferae family (dill, wild
carrot, fennel, yarrow, and so on). |
Parasitic
or predatory wasps |
caterpillars,
aphids, mealybugs, leafhoppers, greenhouse whiteflies |
Encarsia
formosa are small wasps that parasitize greenhouse whiteflies.
Trichogramma wasps parasitize eggs of leaf-eating
caterpillars such as cabbage loopers. |
Praying
mantids
|
most
pest insects and eggs |
They
can be wonderful allies for gardeners (and great fun to
watch), but they eat such a variety of insects that you
wouldn't want to use them for an outbreak of any one pest.
|
Insect
Appeal: Inviting in the Good Guys
Create
a garden that offers food, shelter, and nesting sites that beneficial
insects need, and they'll beat a path to your oasis. Here are
some tips on making your garden alluring.
Ensure
biodiversity. It
is key to a healthy garden ecosystem. Pests tend to flourish
in a simple environment (one featuring few plant types, for
instance). By increasing the diversity of plants and refraining
from using pesticides, you will attract a range of predators,
parasites, and pollinators, both generalists and specialists,
who will keep problem insects in check.
Avoid
using pesticides and herbicides.
Beneficial insects and their food sources can be harmed and
a healthy balance of pests and predators thrown askew when these
are broadly used.
Use
native plants, when possible. Not
only are they well adapted to local growing conditions, but
they have co-evolved with, and provide nectar and pollen for,
native insects. Many garden plants have been bred to make showy
blooms at the expense of producing accessible nectar or pollen.
lambsquarters
|
yarrow
|
Grow
a variety of plant types. This
includes pollen- and nectar-producing plants of different heights
and colors that flower at different times during the season.
(Many beneficial insects need pollen and nectar if their "target"
pests are in low supply.) Some plants nourish different insect
life cycle stages. Certain plants actually attract plant pests,
such as aphids, which, in turn, attract and keep beneficial
insects in the area! You might even leave a small corner of
the garden or schoolyard that contains weeds, such as lamb's
quarters or pigweed, that beneficial insects visit. Here are
a few good plants for enticing and sustaining pest control partners.
Flowers:
baby's breath, cosmos, goldenrod, nasturtium, tansy, Queen
Anne's lace, sunflower, yarrow
Herbs:
dill, caraway, fennel, lemon balm, lovage, thyme
Provide
water and nesting sites. Challenge your students
to figure out how to provide shallow pools of water both above
and on the ground. To encourage bees and other pollinators to
nest nearby, leave cut plant stems exposed, turn flowerpots
with bottom holes upside down, and leave twigs and brush in
small piles.
Ages
and Stages
All
insects go through different life cycle stages. Can studen
ts
find evidence of these stages in their outdoor laboratory? The
changes that occur as insects change form and mature are classified
as either complete or incomplete metamorphosis.
In the four stages of complete metamorphosis, an adult lays
eggs in a place where offspring will be able to find food (Consider
Monarchs and milkweed plants, for instance.) When the larvae
hatch, they eat voraciously, repeatedly shedding skin (molting)
as they grow. At a certain point, they stop eating and enter
the pupa stage, in which they might make cocoons or chrysalids.
While inside, the body changes form and an adult emerges that
looks very different from the creature of earlier stages. The
insects that go through this cycle include butterflies, beetles,
and wasps.
Incomplete
or gradual metamorphosis involves three stages. The insect also
begins life as an egg, which hatches into a nymph (a small-sized
version of the adult.) As they feed and grow, nymphs repeatedly
shed their skin (exoskeleton). This typically happens several
times until the insect reaches its adult size. Examples of insects
that go through these stages are true bugs, grasshoppers, and
praying mantids.
3.
Pupa makes a chrysalid attached to leaf |
4. Adult
emerges from chysalid and flies off to find food source |
2.
Once hatched, larva eats voraciously |
1. Egg laid on food source |
Author: Eve Pranis
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