Agriculture Reference
In-Depth Information
Fig. 213
A tortoise beetle,
Cassida nebulosa
(x8).
Fig. 214
Mangold flea beetle,
Chaetocnema concinna
(x25).
nobilis
(p. 138) by the more pointed hind angles
of the pronotum
(Fig. 212c).
upon which to feed. The overwintered beetles
are active in warm, calm, sunny weather and of-
ten occur in beet fields from mid-April to June.
Eggs are laid in the soil at the base of host plants
(Polygonaceae); they hatch 2-4 weeks later. The
larvae feed on the roots for up to 6 weeks. They
then pupate and new adults appear after a fur-
ther 2 weeks, usually from July onwards. These
young adults feed throughout the summer before
seeking overwintering sites.
Chaetocnema concinna
(Marsham)
Mangold flea beetle
Adults of this widespread and often abundant
flea beetle feed on various weeds (Polygo-
naceae), including
Polygonum aviculare
and
Rumex;
they also attack beet and mangold, and
are sometimes noticed on unrelated crops such
as rhubarb and strawberry. The adults bite out
small, circular pits in the cotyledons and leaves;
these feeding punctures often coalesce and, later,
develop into holes as the plant tissue grows.
Extensive feeding leads to defoliation and to the
death of growing points. Infestations are particu-
larly damaging on slow-growing beet seedlings
(e.g. in cold, dry conditions); attacks on older
plants are of little or no significance. Larvae,
although attacking plant roots, are of no
significance.
DESCRIPTION
Adult
1.5-2.0 mm long, black to bronzy-black
and shiny, with deeply punctured elytra and a
pointed projection on each middle and hind tibia
(Fig. 214). Larva
up to 6 mm long;
body
mainly
white;
head
small, brown;
thoracic legs
small;
prothoracic plate and anal plate
light brown.
Chrysolina menthastri
(Suffrian)
Mint leaf beetle
BIOLOGY
The adult beetles overwinter in herbage along
ditches and dykes, in hedgerows and woods, and
in other situations. They begin to emerge in the
following spring, from March or early April on-
wards. They then immediately seek host plants
This beetle feeds on wild
Mentha
and is some-
times a pest of cultivated mint. Individual adults
or larvae cause little damage but, when the pest
is numerous, attacks can lead to considerable
defoliation.
