Three new mite species attacking strawberries
in Benguet was reported by Dr. Leonila Corpuz-Raros of the
Department of Entomology, College of Agriculture, University
of the Philippines at Los Baños (UPLB). These are:
cyclamen mite Steneotarsonemus pallidus (Banks), lewis spider
mite Eotetranychus lewisi (McGregor), and the two-spotted
spider mite Tetranychus urticae (Koch).
Spider mites are sap-sucking insects. Feeding
damage depends on the kind of spider mite and plant species.
Feeding by spider mites affect the health of the plants reducing
the quality and yield and may lead to stunting or death.
These minute insects can be found under leaves,
inside buds and flowers making them difficult to detect or
hit when spraying pesticides. They reproduce rapidly and also
attack many ornamental and greenhouse crops.
To effectively manage spider mites and avoid
unnecessary use of chemicals, Dr. Raros said that studying
the biology and life cycle of the mites is important.
- Cyclamen mite
The cyclamen mite is the smallest among the three spider mites,
its adult measuring only 0.001 inch. Mature cyclamen mites
are elliptical, semi-transparent, pinkish orange and shiny.
Their hind legs are thread-like in the female and pincer-like
in the male. At low populations, cyclamen mites are usually
found along the midvein of young leaves and under the calyx
or the green, outermost whorl of flower buds. However, when
the plant is highly infested, these mites can be found on
almost any plant part.
- Two-spotted spider mite
Two-spotted spider mites are light to dark green with two
distinctive black spots on the abdomen. Eggs are spherical
and clear when first laid. After hatching the larva has three
pairs of legs, but at later stages it will have four pairs.
Males are smaller with more pointed abdomen than females.
- Lewis spider mite
The lewis spider mite looks like the two-spotted spider mite
minus the black spots on the abdomen. They are half the size
of the spider mites at 0.01 inch.
Biology and damage
Adult female cyclamen mites may live for one month
and can reproduce without mating. Each female lays 2-3 eggs
per day for 2-3 weeks. The eggs are laid in moist, dark
places in crevices and at the base of the plant. Most eggs
develop into females. Nymphs hatch from eggs in 3-7 days,
and feed for 4-7 days. Adults emerge in 2-7 days. The two-spotted
and the Lewis spider mite thrive well in hot and dry conditions.
The typical life cycle (egg to adult) takes 7-14 days, but
varies considerably depending on temperature.
Plants that spider mites infest become chlorotic and sickly
looking. Clorotic plants have yellowish to white leaves
and stems because spider mites extract the green pigment
chlorophyll from them.
Large numbers of mites produce visible webbing, which
can completely cover leaves and flowers. Cobwebbing may
occur between the leaves. These are areas where the spider
mites have spun webs to connect a path for their feeding
efforts.
The two-spotted spider mite feeds on the undersurface
of strawberry foliage, especially young leaves in the crown.
Feeding causes discoloration, leaf crinkle, and browning
and curling of the leaves. When populations of two-spotted
spider mites are very high, the plants produce very small
fruits or none at all.
Testing for spider mites
To test for the presence of spider mites, place a sheet
of white paper beneath the strawberry plant you think is
infested. Tap the leaf and if spider mites are present,
they will fall onto the paper like pepper grains. Bronzing
may also occur on fruit if populations of either two-spotted
spider mite, or strawberry mite (cyclamen mite) are high.
Two-spotted spider mites can be detected by checking the
underside of leaves and the calyx of the fruit using a 10X
hand lens. They are normally found in the crown and unexpanded
leaves of the strawberry plant; however, they may also be
found under the calyx of the fruit.
Control of spider mites
To rid plants of spider mites, apply insecticidal soap
weekly. Be sure to include the undersides of leaves because
that is where these pests can be found feeding. Remove and
destroy infested plants. Apply insecticides. Pesticides
registered for use include diazinon, dicofol, and endosulfan
(Thiodan).
Hot-water dips have been used for years to treat plants
infested with cyclamen mites. Before planting, plants are
treated in hot water at 100 F for 30 minutes.
To monitor for mites, walk diagonally across the field
and randomly pick one mature leaf from every other row until
60 leaves are collected. If 25% of the leaves are infested,
a miticide spray is recommended.
Spray at seven-day intervals throughout the growing season
as long as spider mites, or spider mite damage is evident
on the strawberry plants. Make sure that you spray the undersides
of leaves where spider mites most commonly feed and cobweb.
At the end of harvest be sure to clear away all plant debris
and fallen fruits.
Spider
mites are "small but terrible". While these are
very minute insects measuring 1/50 to 1/100 of an inch , they
can cause serious damage to your strawberry fields. 
