Agriculture Reference
In-Depth Information
various other vegetable crops. Adults and larvae
cause typical flea beetle damage (see Phyllotreta
cruciferae, p. 146); the adults are also vectors of
turnip yellow mosaic virus. The biology is essen-
tially similar to that of P. nemorum (p. 147).
Adults are 2.0-2.3 mm long and black with a pair
of centrally narrowed yellow bands on the elytra,
the black area between them narrowing notice-
ably both anteriorly and posteriorly; the tibiae
are mainly black, with just the basal third
yellow (cf. P. nemorum, p. 147). Larvae are up to
5 mm long, creamish-white and relatively nar-
row-bodied.
NOTE Differences between similarly coloured spe-
cies of Phyllotreta are often difficult to appreciate
without microscopic examination and reference to
specialist keys. The above-mentioned "descriptions'
are intended merely as general guides.
Psylliodes chrysocephala (L.)
Cabbage stem flea beetle
The cabbage stem flea beetle is a locally common
pest of winter oilseed rape; infestations may also
occur on overwintering vegetable brassicas. The
adults bite out irregular holes in the leaves but
such damage is usually unimportant unless plants
are small and growth is slow. Larval infestations
of stems, petioles and growing points are usually
more serious, and damaged tissue typically
rots and turns brown; larval-damaged plants
are also particularly liable to infection by canker
(Leptosphaeria maculans). Larval damage to
growing points causes discoloration and
distortion. Heavily infested plants are weakened,
stunted, malformed and, sometimes, multi-
stemmed (Plate 4f); if small, plants may wilt
and die. Light attacks, although not always sig-
nificant on older plants, can reduce the size of
heads of autumn cauliflowers. Adults may be
brought into store with harvested rape-seed;
however, they do not cause damage and do not
constitute a storage problem, as they soon
disperse.
Psylliodes affinis (Paykull)
Potato flea beetle
This species is a locally common but minor pest
of potato; it is also associated with weeds such as
Solarium dulcamara and S. nigrum. Larvae mine
within the roots, but most noticeable damage is
caused by newly emerged adults which graze on
the foliage during the late summer and early
autumn before hibernating.
BIOLOGY
Young adults are often abundant during July,
following their emergence from the pupal stage,
and may often be found in vast numbers amongst
harvested rape-seed being carried away from
fields in trailers. They remain active at or near
emergence sites for 2-3 weeks but then aestivate,
to reappear in September. They then migrate
to new host plants, where they feed and mature.
Eggs (up to 150 per female) are then laid in the
soil close to brassica plants, mainly from Sep-
tember to November but sometimes later. Most
eggs hatch from early October to December, but
cold weather can delay hatching until the late
winter or early spring. Young larvae invade the
petioles from above and also enter the stems,
boring into the tissue and feeding gregariously
within the pith; at intervals, they break through
the epidermis so their galleries remain partly
open; growing points may also be attacked.
Larvae feed throughout the winter and early
spring, passing through three instars. When fully
grown, they enter soil and pupate; adults appear
BIOLOGY
Adult beetles emerge from hibernation in May
but sometimes earlier. Eggs are laid in June,
either placed singly or in small groups just below
soil level, close to host plants. They hatch about
a week later. The larvae attack the softer parts of
roots and feed for about a month before pupat-
ing. New adults emerge about a month later; they
feed on the foliage of Solanaceae and then hiber-
nate. There is just one generation annually.
DESCRIPTION
Adult 2-3 mm long, reddish-brown to pale yel-
lowish-brown with the underside of the body,
femora and elytral suture black; antennae 10-
segmented (Fig. 220b). Egg 0.6-0.7mm long,
elongate-oval, yellowish-white. Larva up to
6 mm long; body whitish; head, prothoracic plate
and anal plate pale brown.
Search WWH ::




Custom Search