Mites - Pests of Ornamental Trees, Shrubs and Flowers - page 424

Family TENUIPALPIDAE (false spider
mites)

Brevipalpus russulus (Boisduval)
A Central American species, introduced into Europe
many years ago; sometimes reported as a pest of cacti
(e.g. Mammillaria ) and succulents, most frequently in
Belgium, France, Germany and the Netherlands.
Infested plants often develop a reddish-grey
discoloration, and growth is checked. The mites are
similar in appearance to Brevipalpus obovatus but
possess an additional pair of dorsolateral setae on the
hysterosoma.

Distinguished by the absence of a thumb-claw on the
palps. Also, the mites do not produce webbing.

Brevipalpus obovatus Donnadieu
syn. Tenuipalpus inornatus Banks
A tropical or subtropical species, accidentally
introduced into Europe where it is a minor pest of
greenhouse ornamentals such as azalea
( Rhododendron ), bell flower ( Campanula ), Cissus ,
Gardenia and ivy ( Hedera ). In Europe found in various
countries, including Austria, England, Germany and the
Netherlands.

DESCRIPTION
Adult female: 0.25-0.30 mm long; red; body flat
and egg-shaped, with a reticulate pattern on the
idiosoma; five pairs of short dorsolateral setae on the
hysterosoma; palps 4-segmented; legs relatively short.
Egg: 0.1

× 0.07 mm; bright red and elliptical.

LIFE HISTORY
Mites occur on both sides of young leaves but are most
numerous on the underside of older foliage where they
often congregate around the margins. Eggs are
deposited close to the midrib, often in clusters of several
hundred. They hatch in 2-3 weeks. The juvenile stages
feed for 3-4 weeks before attaining maturity. Breeding
continues so long as conditions remain favourable, and
reproduction is typically parthenogenetic.

Family SITEROPTIDAE

Siteroptes avenae Müller
syn. S. graminum (Reuter)
Grass & cereal mite
This mite is reported occasionally in England and
mainland Europe on carnation ( Dianthus caryophyllus ).
The mites occur in association with the fungus
Fusarium poae , causing a brown necrosis of petals and,
sometimes, death of opening buds. This symptom is
commonly known as 'bud rot'. Bud rot on carnation is
less frequent than the condition described as 'silver top',
which occurs following the same mite/fungus
association on cereals and grasses. The mites breed
parthenogenetically on cereals and grasses throughout
the summer, passing through egg, larval and nymphal
stages, all of which develop within the much swollen,
sac-like body of gravid maternal females. Such females
measure up to 2 mm across, and are glistening, hyaline-
whitish in appearance. Infestations tend to spread onto
greenhouse-grown carnations in autumns that follow a
spell of hot, dry weather.

DAMAGE
The mites cause brown, necrotic areas to develop on
host plants, the discoloration commonly occurring
along either side of the midrib or appearing as a fine
rusty or bronze-like speckling over the entire leaf.
Heavy infestations check the growth of plants and may
result in premature senescence and defoliation. On ivy,
damaged leaves are often 'cupped' and reduced in size,
and growth from infested buds is typically weak and
pallid.

Brevipalpus phoenicis (Geijskes)
This mite is very similar to Brevipalpus obovatus .
Although of most importance as a pest of Citrus and tea
plant ( Camellia sinensis ), it also damages a wide range
of other plants. It is reported from various parts of the
world, including the Netherlands.