Agriculture Reference
In-Depth Information
Galerucella grisescens
(Joannis)
Although recorded mainly on
Hydrocharis
morsus-ranae
and
Lysimachia vulgaris
this
wetland species will also feed on other plants,
including cultivated rhubarb. Adults and larvae
graze on the leaves and can cause noticeable, but
economically insignificant, damage. Adults are
4-5 mm long and mainly brownish-yellow with
black antennae. The larvae (up to 7 mm long) are
mainly black and shiny, although paler-bodied
with distinct pinacula when young.
shiny black;
thoracic legs
well developed;
anal
pseudopod
prominent.
Gastrophysa polygoni
(L.)
Polygonum leaf beetle
This often abundant beetle is associated with
Polygonum aviculare
and is not normally a pest.
However, the adults sometimes move into adja-
cent crops, including bean and beet, to cause
slight but insignificant damage; in continental
Europe, the beetles are sometimes reported
as pests of buckwheat. The beetles frequently
rest on leaves of cereals, especially on weedy
headlands, and are then often mistaken for
cereal leaf beetles,
Oulema melanopa
(p. 145).
Adults are 3.5-4.5 mm long, with a bright,
metallic-blue head and thorax, purplish-black
elytra and mainly orange legs and antennae; they
are broader and more rounded in outline than
adults of
Oulema.
Gastrophysa viridula
(Degeer)
Dock beetle
This generally common species occurs mainly on
Rumex.
The adults and larvae graze the surface
and also bite out large holes in the leaves be-
tween the major veins. Infestations also occur on
crops of rhubarb, and on certain other cultivated
plants, the insects causing minor damage to the
leaves and petioles.
Leptinotarsa decemlineata
(Say)
Colorado beetle
BIOLOGY
Adults emerge from hibernation in late March or
April. They then invade host plants to feed on the
leaves. After mating, impregnated females (each
now with a greatly distended abdomen) deposit
groups of eggs on the underside of the leaves,
each egg being placed more or less flush with the
leaf surface. Eggs hatch 1-2 weeks later. The
larvae feed for about 3 weeks, passing through
three instars. When fully grown, they drop to the
ground and enter the soil to pupate a few centi-
metres below the surface. Adults of the next gen-
eration appear 1-2 weeks later. There are usually
three overlapping generations annually.
The Colorado beetle is a notorious pest of
potato. Infestations may also occur on related
plants, including aubergine, tomato and common
related weeds (Solanaceae) such as
Solanum
dulcamara
and
S. nigrum.
The pest is of North
American origin and was first noted in Europe
in 1877, where it is now widely distributed; al-
though often accidentally introduced, it is not
established in the British Isles. The adults attack
the leaves of host plants, but most damage is
caused by the larvae. They feed ravenously and
heavy infestations often lead to complete defo-
liation; infested plants are also contaminated
by masses of black, wet frass excreted by both
adults and larvae. Severe damage, often resulting
in 50% yield loss, is most likely to occur in hot,
dry summers. Direct feeding on potato tubers
may occur, but usually only in store.
DESCRIPTION
Adult
4-6 mm long, metallic green, but some-
times blue to purplish or coppery;
legs and anten-
nae
black;
thorax and elytra
distinctly punctured;
in impregnated female, the black and greatly
swollen abdomen protrudes beyond the tips of
the elytra.
Egg
1.5 x 1.0mm, elongate-oval,
pale yellow and shiny.
Larva
up to 8 mm long;
body
sausage-shaped and shiny black;
head
BIOLOGY
Adults hibernate deep in the soil, often up to half
a metre below the surface. They emerge in the
