Parthenolecanium corni Bouche Brown scale

The brown scale is a generally common, polyphagous pest of trees and shrubs; hosts include fruit trees, currant, gooseberry, raspberry and various ornamentals. Heavily infested plants are weakened and leaves may fall off prematurely.

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 commence feeding. Individuals moult to the motile second instar in August and these continue feeding 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 hardened. Several hundred eggs are laid under each

Fig. 196 Brown scale, Parthenolecanium corni: (a) dorsal view - with eggs; (b) lateral view (x7).

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.

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).

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