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8.4 Aphids
Level 2 Plant health problems
APHIDS
incomplete metamorphosis
Aphids often have two hosts eg Black Bean Aphid - beans and spindle
tree. In summer adult females produce live nymphs – VIVIPARY
without an egg stage and without fertilisation - PARTHENOGENISIS.
A new productive adult can be produced in7-28 days depending on the
temperature.
PEACH POTATO APHID Greenfly Myzus persicae
Very common on vegetables, flowers, bedding and glasshouse plants
where it often survives winters as a breeding population. The adult is a
six legged insect 3mm long, light green- pink- orange. A complex life
cycle alternates between a winter host - peaches /nectarines, and a
summer host. It is the most important VECTOR or carrier of virus
diseases between plants.
Life cycle
Summer: June-September
Females constantly produce live nymphs without an egg stage or
fertilisation. Both wingless and winged females are produced. There are
no males.
Autumn / Winter
In September both sexes are produced both of which have wings so they
can fly to their winter host - peaches/nectarines. Fertilised females lay
overwintering thick-walled eggs on twigs. In glasshouses aphids may
survive as nymphs and adult females on pot plants.
Spring: March-May
Eggs hatch to form nymphs which produce first wingless and then
winged parthenogenic females in May, these fly to their summer hosts,
including potatoes and lettuce, in May. This is when most virus diseases
are spread.
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8.4 Aphids
Level 2 Plant health problems
Damage caused by nymphs and adults
1. Sap sucking nymphs and adults cause severe distortion to young
shoots and leaves by injecting a digestive juice into the phloem.
2. Adults excrete Honeydew, a sticky substance which may block
stomata and reduce photosynthesis especially if a secondary
fungus, sooty mould, develops on the excretion eg lime trees.
3. Aphids may transmit virus diseases in the sap they suck eg Dahlia
mosaic, Lettuce mosaic, Cucumber mosaic.
Control
1] Biological
Outdoor crops: several natural organisms may reduce aphids in a good
season eg ladybirds, hoverflies, lacewing.
Glasshouses: a parasitic wasp, Aphidius matracariae, can be introduced
to control aphids. Also lacewings.
2] Chemical
 Contact insecticides which penetrate the thin cuticle eg Malathion.
Needs to be applied at seven day intervals. Systemic insecticides
which poison the stomach via the plant sap eg Dimethoate - non
specific so it may kill predators too.
 Fumigant which enters the spiracles eg Nicotine
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8.4 Aphids
Level 2 Plant health problems
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