Mites - Agricultural Entomology - page 261

plants, including various ornamentals (e.g. be-
gonia, chrysanthemum, cyclamen and gerbera)
and vegetable crops (e.g. aubergine, cucumber,
sweet pepper and tomato). Affected plants are
stunted and discoloured, and the new growth
often becomes brittle, distorted and shiny. Fruits
of infested vegetable crops are small, deformed
and discoloured, and often develop a corky, re-
ticulated pattern (Plate 16e). Broad mite is a
persistent pest and heavily infested plants may
be killed.

ish and translucent. Larva whitish, 6-legged; tip
of body triangular.

Phytonemus pallidus ssp. fragariae
(Zimmermann)
Strawberry mite

This subspecies is a serious pest of outdoor
strawberries. The mites cause discoloration and
distortion of foliage and severe stunting of
plants; fruits are also affected, those on badly
infested plants remaining small and becoming
leathery and dull in colour. Damage is most evi-
dent from July onwards and tends to be most
significant on older plants, especially those
grown in perennial matted rows. Heavy infesta-
tions in 1 year will also lead to a significant reduc-
tion in cropping in the following season.

BIOLOGY
Broad mites breed continuously under favour-
able conditions, development including an egg, a
larval and a quiescent nymphal stage, the latter
being passed within the cast-off larval skin. At
normal glasshouse temperatures, eggs hatch in
2-3 days and larvae feed for about 4 days before
moulting into 'resting nymphs'. The adult stage is
reached a day or so later. Female nymphs are
often carried around by adult males which, un-
like other motile stages (e.g. larvae and adult
females), frequently wander over host plants.
Colonies of mites occur on the underside of
young, expanded leaves and amongst still furled
tender growth; leaves, however, become unsuit-
able as they mature and are then abandoned. All
stages may be found together on infested plants,
and adult females usually greatly outnumber
males.

BIOLOGY
Strawberry mites overwinter as adult females,
deep within the crowns of plants. They become
active in the following spring, and small colonies
then develop in sheltered sites on the furled and
unfurling leaves. The mites also occur under
rolled edges on expanded leaves. Populations
increase gradually to reach a peak in the late
summer and early autumn. There are several
overlapping generations each year, develop-
ment from egg to adult taking 2-3 weeks during
the summer months. Most females breed
parthenogenetically and males usually form only
a small proportion of the population. Unlike
Tetranychus urticae (p. 267), the strawberry mite
occurs mainly on young foliage; maturing leaves
are unsuitable feeding sites and are abandoned
as they harden.

DESCRIPTION
Adult female 0.2 mm long, broad-bodied, whitish
and translucent to greenish or yellowish;
hindlegs each with a long whip-like seta (see Fig.
170). Adult male 0.14mm long, long-legged;
body tapered posteriorly and with a genital
sucker; hindlegs stout but unflanged (Fig.
339) (cf. cyclamen mite, Phytonemus pallidus, p.
260). Egg 0.11 x 0.07 mm, oval and translucent,
with several rows of white, mushroom-like
tubercles on the exposed surface (Fig.
340). Larva similar in appearance to adult but
smaller and 6-legged; tip of body triangular (Fig.
341).

DESCRIPTION
Morphological differences between this subspe-
cies and Phytonemus pallidus (see p. 260) are
uncertain.

i

Polyphagotarsonemus latus (Banks)
Broad mite

In temperate regions, this tropical or subtropical
mite infests a wide range of glasshouse-grown