Piercing
& Sucking Insects >
Aphids, General
Pest: Aphids, general
Order: Homoptera
Family: Aphididae
Host Plants:
Many and varied
Description:
There are many species of aphids and all are a bit different
in appearance, biology and the host plants attacked. Therefore,
they will be discussed here in the general sense. Aphids are soft
and plump bodied, have long spindly legs, are often wingless and
posses cornicles, which immediately distinguish them from other
insects. Aphids have a piercing-sucking mouth-type that is adapted
to feeding on plant sap. Their guts are long, coiled tubes and as
the plant sap passes through this digestive tract, plant sugars
(among other compounds) are concentrated out into their blood. The
remainder of the sap in the gut is finally expelled as a clear liquid
that still contains many plant sugars; this waste is known as honeydew.
Honeydew appears as clear drops of liquid on foliage, as well as
whatever is under a plant housing aphids, and acts as a food source
for a group of fungi known as sooty molds. These molds colonize
the honeydew and become very black, hence the name. Heavy populations
of sooty mold can make a plant quite unattractive and even interfere
with the process of photosynthesis. Primarily, however, sooty mold
is an aesthetic problem. Occasionally, ants can be seen on foliage
tending to the aphids and collecting their honeydew for its sugar
content. These ants may also help defend the aphids against such
natural predators such as ladybug immatures and syrphid fly larvae.
Some aphids are categorized as woolly aphids and these produce waxy
strands over their bodies. One common member of this group is the
woolly beech aphid which is primarily found on European varieties
of beech (Fagus ). These are active in the spring only and
produce large amounts of honeydew that may create aesthetic problems.
Aphid feeding does not cause the typical yellow stippling injury
to the host plant that is so common for most other piercing-sucking
insects. Although, they may cause leaf distortion if new, emerging
foliage is fed upon.
General Life cycle:
Many aphid species have a primary host plant that usually involves
a deciduous tree species (at the beginning and end of the season)
and very many secondary host species during the summer. A generalized
life cycle for an aphid species with both a primary and secondary
hosts is as follows: Winged females lay eggs on the primary woody
host in the fall and then die. In the spring, these eggs all hatch
to be wingless females. Upon maturity, these wingless females give
birth to another generation of wingless females via parthenogenesis
(asexual reproduction). After several generations of wingless
females, crowding occurs and this most likely triggers a chemical
cue that leads to a hormonal response within the population and
a generation of winged females is produced. These winged individuals
then disperse from the primary host plant and venture far and wide
in search of a suitable secondary host plant. These can include
numerous different types of plants such as weeds, annuals, vegetables,
perennials and others. Once a quality host is found, the winged
female will then produce a generation of wingless females on this
plant. Several more generations of wingless females will follow
until late summer / early fall when a generation of winged males
and females are produced that will seek out the primary host plant
species for that specific aphid species. They will then find a mate,
the female will produce eggs, and the adults will then die. The
eggs will over-winter and hatch in the spring.
Management Strategies:
Aphids can cause curling of the foliage, as with the Snowball
Aphid on certain viburnums, and much honeydew that can lead to unacceptable
levels of sooty mold. To deal with sooty mold, one must manage the
aphids. Several common groups of predators occur naturally and visual
monitoring should be performed to determine their presence and numbers
prior to administering any chemical controls that may be extremely
detrimental to their population numbers. These natural controls
include: ladybugs, lacewing larvae, wasp parasites, and syrphid
fly larvae, among others.
Images:
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A typical aphid displaying the plump body, long spindly legs
and the characteristic pair of cornicles (R. Childs)
The woolly alder aphid. At certain times of the year, certain
aphid species, such as this one, will cluster together on
a specific host plant and produce large amounts of waxy strands
thus giving the name of "woolly aphids". (R. Childs)
Distorted and curled foliage on a viburnum that was caused
by the feeding activity of the Snowball aphid early in the
spring. (R. Childs
Aphids are often found feeding together in large clusters,
especially on the undersides of host plant foliage. (R. Childs)
Linden leaves displaying large amounts
of sooty mold on the upper leaf surfaces.
The primary cause was from the honeydew
produced byu aphids that colonized the
tree throughout the growing season. (R. Childs)
An alder leaf displaying much honeydew
from a large aphid population. These
leaves later became very blackened by
sooty mold. (R. Childs)
Distorted foliage of a viburnum that
was caused by Snowball aphid feeding
activity as the foliage emerged from
the bud in the spring. (R. Childs)
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Piercing-sucking
index:
Adelgids, General
Andromeda Lacebug
Aphids, General
Balsam Twig Aphid
Beech Blight Aphid 
Boxwood Psyllid
Hemlock Woolly Adelgid
Hemlock Woolly Adelgid Frequently Asked Questions
Honeylocust Plantbug
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