Biological Control
Biological control options are
available for aphids and are more
environmentally friendly than
pesticides. The first, and arguably the
most common in outdoor gardens, is
the use of lacewings (or golden-eyed
flies). Green or brown lacewings,
which are widely available through
mail order, are voracious predators
when they are in larvae form.
There is also an aphid parasitoid
(Aphidius colemani) that is highly
effective at finding low populations
of aphids. These minute wasps lay
their eggs inside of aphids, where the
immature wasps eat the aphids from
the inside out, eventually emerging
from the hollowed-out aphids as adults.
Lastly, there are midges, which are
small flies whose larvae eat aphids. As
maggots, midges, which are blind, will
cruise around the plants, searching for
a group of aphids. They will then use a
sticky substance from their mouths to
grab hold of an aphid and consume it.
The maggot grows to several times the
size of an adult aphid before it matures
into an adult, providing significant
control of aphids.
Ladybugs (or ladybird beetles),
which are known to eat aphids, are
not actually good at reducing aphid
populations. This is partly due to
where a female ladybug lays her
eggs. She will only lay her eggs near
large infestations of aphids. If you
only have a few aphids on your crop,
ladybugs are likely to keep looking
for a better spot, which allows small
aphid populations time to grow to
levels not curable by ladybugs alone.
Another issue with ladybugs is they
tend to want to fly and won’t stay
where you release them long enough
to control your aphid problem.
No matter what biological options
you choose for dealing with an
aphid infestation, you will have to be
mindful of ants, since ants actually
farm aphids for their honeydew
and will protect the aphids from
predators and parasitoids. For this
reason, it is important to have your
ants under control at all times,
otherwise natural predators and
parasitoids will be unable to control
your aphid population. In addition,
any predators or parasitoids you
introduce into your crop will also be
ineffective if ants are present.
Aphids are a common problem in the
garden and controlling of them can be
frustrating. However, with the proper
plan and some knowledge about their
biology and natural enemies, aphids
can be managed effectively.
Danny Klittich, M.S., is a doctoral
candidate in entomology at the
University of California, Davis, and a
research consultant with CleanGrow.
His research focuses on increasing
plant resistance and tolerance to
arthropod pests. Other interests
include biological control, integrated
pest management and woodworking.
Maximum Yield USA | November 2015
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