Agriculture Reference
In-Depth Information
about 3 months. The scales most often settle
along the major veins of leaves. Individuals fre-
quently overlap one another to form dense, typi-
cally ant-attended colonies. At normal summer
glasshouse temperatures, nymphs reach maturity
in about 2 months.
DESCRIPTION
Female scale
3.5-5.0mm long, translucent-
yellow to brown, with an often blackish median
longitudinal ridge and rib-like markings; oval in
outline and usually very flat but the exact shape
varies according to the substratum.
First-instar
nymph (crawler)
0.5 mm long, pale brown, flat
and elongate-oval with a posterior cleft;
eyes
dark purplish.
(b)
Fig. 196
Brown scale,
Parthenolecanium corni:
(a)
dorsal view - with eggs; (b) lateral view (x7).
Parthenolecanium corni
(Bouche)
Brown scale
protective scale in May or June, the female then
dying. Dead scales often remain attached to the
bark of host plants for several years. Under glass,
there may be two or more generations annually.
The brown scale is a generally common,
polyphagous pest of trees and shrubs; hosts in-
clude fruit trees, currant, gooseberry, raspberry
and various ornamentals. Heavily infested plants
are weakened and leaves may fall off
prematurely.
DESCRIPTION
Adult female scale
4-6 mm long, chestnut-
brown, more or less shiny, tortoise-shaped and
strongly convex
(Fig. 196). Egg
minute, white,
oval
(Fig. 196a). Nymph
oval, flattened, pale
translucent-greenish to brown, with prominent
antennae, legs and anal cerci
(Fig. 197).
BIOLOGY
Eggs of this usually parthenogenetic species
hatch from mid-June onwards. First-instar
nymphs (the so-called 'crawlers') then invade the
leaves and young shoots, upon which they com-
mence feeding. Individuals moult to the motile
second instar in August and these continue feed-
ing into the autumn. On evergreen hosts, the
nymphs overwinter on the underside of the
leaves; prior to overwintering on deciduous
hosts, however, the nymphs move to the twigs
and branches. Overwintering nymphs are small
(c. 0.5 mm long) and gradually darken to orange
or brownish. Activity is resumed in March. The
nymphs feed and eventually moult into adults
about a month later, each having then settled
permanently, usually on a branch or twig. The
sedentary adult female scales increase rapidly in
size and also become distinctly convex and hard-
ened. Several hundred eggs are laid under each
Pulvinaria ribesiae
Signoret
Woolly currant scale
This insect is a locally important pest of currant
and gooseberry. Heavily infested bushes are
weakened and often become festooned by
masses of white, flocculent 'wool'; the insects
also excrete considerable quantities of honey-
dew, upon which sooty moulds develop.
BIOLOGY
This species overwinters as mated adult females.
These eventually mature in May, each then pro-
ducing a large, white ovisac that pushes the scale
away (posteriorly) from the host twig. The
