Insects of Southern Australian Broadacre Farming Systems - Grains ...

General aphid lifecycle and biology
In Australia, most pest aphid species only produce
females, which may be winged (alates) or wingless
(apterae), and these give birth to live young. In other
countries some aphid species have different (or altered)
lifecycle phases (e.g. sexual/asexual) that are initiated
by host-insect interactions and/or environmental
conditions. Many aphids are plant host (crop) specific.
Some aphids are vectors of crop diseases that can be
detrimental to growth and limit yield. These diseases
include barley yellow dwarf virus in cereals, cucumber
mosaic virus in lupin and pea seed borne mosaic virus
in field peas. These viruses have the largest yield impact
when they are introduced early in the life of the crop,
usually within the first ten weeks of growth. Aphids are
efficient in spreading diseases due to their sap-sucking
mouthparts. Transmission occurs via feeding on the
vascular tissue (phloem) of infected plants. Once the
virus is picked up, it can be carried in the salivary glands
or restricted to the stylet of the aphid. The virus can be
carried for a long (persistent transmission) or short (nonpersistent)
period of time after aphids feed on infected
plants. These different modes of transmission influence
the effectiveness of chemical sprays against virus spread.
Figure 4.1 An example of an aphid lifecycle (Aphis sp.)
Source: Modified from
Blackman and Eastop
(2000)
Primary host plant
eggs
Spring migrants
alate
males
apterous
autumn migrants
Summer/autumn
Aphids require specific host plants for their
survival. Aphid populations usually decline over
summer. The availability of suitable host plants (e.g.
specific weed families on roadsides and verges) allows
populations to survive and increase. Winged aphids
move into crops in autumn and aphid numbers
will usually start to build up along crop edges. The
formation of winged aphids and aphid movement
generally increases when host plants are dying or when
overcrowding occurs with high populations.
Winter
Low temperatures and heavy rainfall in winter often limit
aphid populations. Nymphs go through several growth
stages, moulting at each stage into a larger individual.
Sometimes the delicate pale aphid skins or casts (the
exoskeleton they have shed) can be seen. Nymphs do
not have wings.
Spring
Spring often triggers a rapid increase in aphid numbers
as increasing temperatures and flowering crops provide
favourable breeding conditions. Most aphids form
dense colonies before winged aphids are produced.
These move onto surrounding plants further into the
crop creating hot spots. In some seasons, aphids form
large colonies (especially at flowering) and heavy
infestations may produce large amounts of a sticky
secretion (honeydew).
Secondary host plant
alate
SECTION 4 COMMON Pest, Beneficial AND EXOTIC Species
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Insects of Southern Australian Broadacre Farming Systems Identification Manual and Education Resource © 2012