Mites - Pests of Ornamental Trees, Shrubs and Flowers - page 418

Family TETRANYCHIDAE (spider mites)

DAMAGE
Infested foliage becomes pallid and silvery, and may
turn brown.

Spider-like mites with long, needle-like chelicerae and a
thumb-claw on each palp. They develop from egg to
adult through larval, protonymphal and deutonymphal
stages.

Bryobia cristata (Dugés)
Grass/pear bryobia mite
A polyphagous species, occurring throughout the year
on various grasses and herbaceous plants. Infestations
often occur on ornamentals such as bell flower
( Campanula ), Cyclamen , Dianthus , gentian ( Gentiana ),
Iris , Polyanthus and saxifrage ( Saxifraga ). The mites
feed mainly on the upper surface of the leaves, and
cause a mottling and general silvering of tissue. In
common with Bryobia kissophila , breeding is
continuous throughout the year, with many generations
annually. During May the mites often disperse from
their normal hosts to various trees and shrubs, including
fruit trees and ornamentals such as flowering cherry
( Prunus ), hawthorn ( Crataegus ) and rose ( Rosa ), where
two summer generations occur before a return migration
to herbaceous plants. The mites are distinguished from
Bryobia kissophila by the narrower dorsal setae and by
other microscopic features.

Bryobia kissophila van Eyndhoven ( 1128 )
Ivy bryobia mite
Common in the wild on European ivy ( Hedera helix )
and often a troublesome pest on ornamental cultivars.
Present throughout Europe.

DESCRIPTION
Adult female: 0.7 mm long; dark reddish brown or red;
body oval and rather flat, with spatulate dorsal setae;
first pair of legs very long. Egg: 0.2 mm across; dark
red and more or less spherical. Larva: bright reddish-
orange; 6-legged. Nymph: dark red, brown or dark
green; 8-legged.

LIFE HISTORY
Adult and juvenile mites are present on the upper
surface of ivy foliage throughout much of the year.
However, populations often decline during the summer.
The mites then occur on clover ( Trifolium ) and usually
return to ivy in August. Eggs tend to be deposited on
supporting stakes and walls rather than on host plants.
Breeding is continuous throughout the year, with about
5-8 overlapping generations, the duration of each
generation varying according to ambient temperatures.
Although development of the mites is greatly protracted
during cold winter weather, there is no diapause stage in
the lifecycle. Males are unknown and reproduction is
entirely parthenogenetic. Bryobia mites do not produce
webbing.

Bryobia praetiosa Koch
Clover bryobia mite
During the spring vast numbers of this mite occur on
sunny walls, particularly on those of new or recently
renovated buildings. Fully grown nymphs and adults of
this and the previous species also invade buildings
through doors and windows, to moult or to lay eggs in
cracks and crevices. Eggs deposited in the spring
produce a summer generation of mites which feed on
grasses and herbaceous plants (including certain
ornamentals) and mature by the autumn. Eggs laid in
late summer or autumn produce mites which develop
throughout the winter and reach maturity in the
following spring. The mites are structurally similar to
Bryobia kissophila .

1128

Bryobia rubioculus (Scheuten)
Apple & pear bryobia mite
This species overwinters in the egg stage and usually
completes no more than three generations annually. It
occurs mainly on rosaceous fruit trees, but also attacks
related ornamentals such as crab-apple ( Malus ) and
flowering cherry ( Prunus ). Although the mites feed on
the upper surface of leaves, they often congregate on the
trunks and branches. Such aggregations occur mainly in
late May and June, and in August and September. The
mites also cluster beneath the shoots and main branches
whilst moulting from one growth stage to the next, and
masses of greyish-white cast skins (which are a

1128 Ivy bryobia mite ( Bryobia kissophila ) damage to leaves
of Hedera .