Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 137

Phratora laticollis (Suffrian) ( 296 )
syn. Phyllodecta laticollis Suffrian
Small poplar leaf beetle
Locally common on Populus , especially aspen
( P. tremula ) and Lombardy poplar ( P. nigra 'Italica');
also found on grey willow ( Salix cinerea ) and other
broad-leaved willows. Adults occur from early spring
onwards, at first attacking unopened buds but later
feeding on the expanded leaves. Eggs are laid in early
June. Larvae (up to 6 mm long) are mainly grey, with
numerous black plates and verrucae and a black head.
They feed during the summer, at first removing tissue
on the underside of the leaves, the upper surface turning
brown. Young larvae typically feed gregariously but
towards the end of their development individuals often
become solitary. Heavy infestations cause extensive
skeletonization of the foliage. Fully fed larvae drop to
the ground to pupate. Adults, which emerge in the
autumn, are 3.5-5.0 mm long and mainly metallic blue
with black legs; the head has a characteristic
longitudinal depression and the elytra are somewhat
elongate. In most areas this species is single brooded.
However, in especially favoured districts there may be
two generations annually.

Phyllotreta cruciferae (Goeze)
Turnip flea beetle
A generally common pest of brassicaceous plants,
including ornamentals such as stock ( Matthiola ) and
wallflower ( Cheiranthus cheiri ); also occurs on
nasturtium ( Tropaeolum ). Holarctic. Widepsread in
Europe.

DESCRIPTION
Adult: 1.8-2.4 mm long; metallic greenish-black and
somewhat rounded in outline, with black legs; antennae
11-segmented, mainly black, with the second and third
segments yellowish red. Egg: 0.3 mm long; yellowish
white and oval. Larva: up to 6 mm long; head black;
body white and narrow, with blackish plates and
pinacula on the thoracic and abdominal segments; legs
very short.

LIFE HISTORY
Adults are active from early spring onwards, feeding on
the leaves and cotyledons of various brassicacous
plants. Eggs are deposited in the soil close to host
plants, usually in batches of 20-30, and hatch about two
weeks later. The larvae attack the roots, feeding
externally for about two weeks. Individuals then pupate
and new adults emerge two weeks later, usually in July
or August. There is just one generation each year.

Phratora vulgatissima (Linnaeus)
syn. Phyllodecta vulgatissima (Linnaeus)
Blue willow leaf beetle
A locally common pest of Populus and Salix , especially
aspen ( P. tremula ), hybrid black poplar ( P. serotina ),
Lombardy poplar ( P. nigra 'Italica') and osier
( S. viminalis ). Often of importance in nursery beds,
where young plants may be destroyed, but apparently
more restricted in its range than formerly. Adults occur
from mid-April or May onwards, eggs being deposited
in double rows between two major veins on the
underside of the leaves. Eggs hatch in about 1-2 weeks,
the larvae then feeding on the leaves for about four
weeks before pupating in the soil. Young adults appear
in July and August, producing a second generation of
larvae which reach adulthood in the autumn. The adults
(4-5 mm long) are distinguished from those of
Phyllodecta laticollis by the slightly narrower body and
the blue or green colour; lateral punctation on the elytra
is irregular.

DAMAGE
Adults bite into the cotyledons and leaves, forming
small pit-like blemishes which enlarge as the tissue
grows. Attacks are usually most serious in May and
June, particularly on seedlings or recent transplants
whose growth is retarded by lack of moisture. Larvae
destroy the outer tissue of the roots, and heavy attacks
affect plant vigour.

296

296 Larva of small poplar leaf beetle ( Phratora laticollis ).