Agriculture Reference
In-Depth Information
On a global basis, two species are by far the most
important,
Myzus persicae
(Sulzer) (green peach
aphid) and
Macrosiphum euphorbiae
(Thomas)
(potato aphid). For more detail on the identifica-
tion and basic biology of aphid species on potato
and other crops, see Blackman and Eastop (2000).
The green peach aphid has one of the wid-
est host ranges of any aphid, is probably origin-
ally from East Asia but is now found worldwide.
In colder climates, it is heteroecious, using spe-
cies of
Prunus
(Rosaceae) as overwintering hosts,
where eggs survive the winter, and migrating
to a wide variety of summer hosts in dozens of
plant families. In warmer climates, green peach
aphids are anholocyclic, and therefore repro-
duce parthenogenetically throughout the year.
The body length is 1.2-2.3 mm, color is extremely
variable, including white, yellow, green of various
shades, pale pink to darker red, with a tendency
toward darker colors in cooler conditions.
The potato aphid is of North American ori-
gin but has spread almost worldwide, and has a
host range almost as wide as green peach aphid.
Its life cycle in cooler parts of North America is
heteroecious, usually with eggs overwintering
on roses (
Rosa
: Rosaceae), and migrating to a
wide range of summer hosts, including many
crops. In most other parts of the world, and in all
warm/tropical regions, the potato aphid is en-
tirely anholocyclic. Larger than the green peach
aphid, the potato aphid is usually
2-
4 mm in
length, and can be a wide variety of colors simi-
lar to green peach aphid. In western North
America, the potato aphid is more common on
the potato crop in cooler regions and seasons
than the green peach aphid, which does well on
potato in midsummer.
Another cosmopolitan aphid that will com-
monly be found on potato is
Aulacorthum solani
(Kaltenbach) (glasshouse-potato aphid, or foxglove
aphid). It generally does not reach damaging
levels in field-grown potatoes. In eastern North
America,
Aphis nasturtii
(Kaltenbach) can be lo-
cally very important. Throughout the world,
various polyphagous aphids will appear on pota-
toes, but usually not in damaging numbers.
growth to aphid growth and reproduction.
Aphid populations can expand rapidly due to
their viviparous parthenogenetic reproduction.
In practice, population explosions of aphids in
potatoes are usually related to the application
of inappropriate or excessive insecticides for
the control of aphids or other pests. For example,
some potato entomologists intentionally foment
aphid populations in research plots by applying
pyrethroid insecticides. The presumed mechan-
ism behind such aphid population growth is
that broad-spectrum insecticides eliminate aphid
natural enemies and result in unchecked repro-
duction. On a related note, Lagnaoui and Rad-
cliffe (1998) showed that treatment of potatoes
with fungicides aimed at late blight resulted in
higher aphid numbers, and presented evidence
this was caused by inadvertent control of ento-
mopathogenic fungi.
By far the most important aphid-related
damage in potatoes is caused by the plant vir-
uses they transmit, including PVY and
Potato
leaf roll virus
. These and other viruses transmit-
ted by aphids are discussed in Chapter
12
of this
volume. In intensive production regions
such as western North America, the control of
aphid-transmitted viruses via aphid management
drives a large fraction of the cost of production.
Producers of seed potatoes often focus even more
diligently on aphid control because the value of a
seed crop is highly correlated to its virus content.
Sampling and monitoring
Aphids in the potato crop are most commonly
found on the middle to lower leaves, especially
in the case of green peach aphid. Methods for
monitoring aphids in potatoes include inspection
of leaves, beating sheet/tray techniques, yellow pan
traps, green tile traps, and suction traps. Each
method has its devoted adherents, with methods
such as pan and suction traps being employed
successfully in certain regions, while in other re-
gions those methods are unhelpful due to plant
and aphid phenology. A widely accepted and ef-
fective method for aphid detection and monitor-
ing is systematic sampling and visual inspection
of the middle and lower leaves. Beating sheet
sampling can be effective in cultivars with up-
right growth habits, if implemented consistently.
There are no broadly applicable treatment
thresholds for aphids in potatoes.
Damage
Aphids are phloem feeders, and in large num-
bers can cause substantial yield loss or even
plant death, due to energy diversion from plant
