Agriculture Reference
In-Depth Information
Psyllids (Psylloidea)
zebra chip in north-western USA in 2011, po-
tato psyllid has been documented as overwinter-
ing in potato producing parts of that region in
association with the perennial vine,
Solanum
dulcamara
L. (Murphy
et al
., 2013). Further,
Swisher
et al
. (2013) presented DNA-based evi-
dence that the psyllid occurring in the north-
western states was distinct from those in regions
such as California and Texas, and has been a
resident of the north-west since at least 1998.
Potato psyllid can have several generations
per year, developing from egg to adult in as little
as
3
weeks under ideal conditions. It performs
best at moderate temperatures, and fails to de-
velop and/or dies at high summer temperatures
in the
32-
35°C range.
Recognition
Psyllids are small (
2-
5 mm) sucking insects
similar to winged aphids in size and appearance
as adults
(Fig. 9.3c-d
)
. Unlike aphids, they re-
produce sexually in every generation, lay eggs,
are active jumpers, and the nymphs are usually
flattened and relatively sedentary. Nymphs are
also similar to whitefly nymphs, with the chief
distinguishing characteristics being distinct
wing pads and fully functional legs in psyllids, as
opposed to no wing pads and entirely immobile
nymphs (beyond the first instar) in whiteflies.
The predominant psyllid affecting potato
in the Americas and New Zealand,
Bactericera
cockerelli
(Šulc), is known as the potato psyllid.
Munyaneza and Henne (2013) mention other
species, including
Bactericera nigricornis
(Förster)
in Iran and
Russeliana solanicola
(Tuthill) in
South America. The potato psyllid has been stud-
ied thoroughly since early in the 20th century,
due to its ability to cause a plant syndrome known
as psyllid yellows and much more recently the
advent of a new potato disease known as “zebra
chip”, which is associated with the bacterium
Candidatus
Liberibacter solanacearum and is
vectored by
B. cockerelli
(Munyaneza, 2012).
Damage
Potato psyllid in a crop can lead to three main
types of damage: general plant weakening from
direct feeding, psyllid yellows, and zebra chip.
Direct feeding damage is generally slight, since
it would only be expected under low psyllid pressure.
Higher psyllid pressure results in psyllid yellows
disease, characterized by a suite of symptoms
including leaf yellowing, upward rolling, purp-
ling, short and thick terminal internodes, axil-
lary branches, and aerial tubers. These symptoms
are similar to other diseases that affect phloem
transport, such as purple top caused by phyto-
plasmas, zebra chip associated with
Candidatus
Liberibacter solanacearum, and even stem-
girdling caused by the fungus,
Rhizoctonia solani
.
An interesting feature of the psyllid yellows
disease is that the affected plants will recover if
psyllids are removed. The largest, most dam-
aging psyllid populations in potatoes have often
been associated with heavy, but inappropriate,
insecticide use aimed at psyllids or other insects.
For example, insecticides in the pyrethroid class
have very poor field efficacy against psyllids, and
also eliminate beneficial arthropods. Their use
when psyllids are present can lead to crop failure
from psyllid yellows.
Zebra chip disease was first detected in
Mexico in the mid-1990s and has since spread
throughout most of Mexico, Central America,
and the USA west of the Mississippi River. The
putative zebra chip pathogen,
Candidatus
Liberibacter solanacearum, is closely related to
the Liberibacter associated with citrus greening
Distribution and species
The potato psyllid is about
2-
3 mm long, the
body is mostly dark with prominent white mark-
ings on the abdomen, and the wings are clear
without dark markings. Nymphs are flat, light
green, and camouflaged on the leaf and stem
surfaces where they feed. Eggs are yellow to or-
ange and mounted on a short stalk.
Native to North America, especially along
the Rio Grande in the southern USA and nor-
thern Mexico, the psyllid now occurs through-
out much of Central America and western and
north-western USA. Host range for reproduction
and development is largely limited to species of
the Solanaceae and Convolulaceae, but adults
have been found on reserve hosts in many plant
families (Wallis, 1955).
In central USA, the potato psyllid is known
to overwinter in the south near the US/Mexico
border and to migrate north each year to neigh-
boring regions and states. Since an outbreak of
