Tarsonemus pallidus is the mite most often found on cyclamen.
Its reproductive cycle is extremely fast, especially in summer, when glasshouse infestations do most damage.
Because of its physiological requirements it stays hidden in the most damp parts of the plant. There is no real symptom to be seen on the outside at first, and the pest develops quickly right from when the plants are young.
Chemical treatment must be given regularly and as a precaution.
There are prospects for biological control.
Cyclamen mites are tiny mites, less than 0.5 mm long, of the family Tarsonemidae: a number of species are generally referred to as ‘cyclamen mites’. They are some of the cyclamen’s worst pests.
The parasites most often met with on cyclamen, and the ones that do most harm, are Tarsonemus pallidus Banks (Steneotarsonemus pallidus Banks), also known as Phytonemus pallidus, and Polypha Tarsonemus latus, larger and more mobile.
Cyclamen mites are extremely small, scarcely visible to the naked eye. The adults are oval in shape, from 0.2 mm long to about 0.25 mm. They look like small spiders. The females are a little larger than the males, and their colour varies with the stage of development, from yellow to brown at maturity. They have 4 pairs of legs.
The males are squat, with characteristic hind legs ending in a kind of hook. The sexes are very different in appearance.
Cyclamen mites hibernate in conditions which do not suit the adult female, in plant matter and never in the soil.
These females produce small eggs of a glassy white, about 100µ across, from April onwards.
A female can lay some thirty eggs in her lifetime; each hatches into a young larva from 4 to 8 days after laying.
The young larvae are milky white, translucent, and segmented. They moult once.
The larvae move towards the young buds and young leaves, before going into the nymph state after 4 to 10 days.
Here, sheltered from wind and weather, generations may succeed each other unnoticed on the outside.
The nymphs are around 0.25 mm long, white, motionless, generally heaped together with eggs.
In 8 to 10 days, the nymphs turn into adults. Males only appear in the summer months, but the females can lay either fertilised or non-fertilised eggs. To a great extent, reproduction is parthenogenetic.
In summer the development cycle is extremely fast. A generation may go from larva to adult in as little as 10 days: the result is a high number of generations in a year (8 to 10). In a glasshouse many generations will overlap. It is in summer also that cyclamen mite infestations cause most damage in the glasshouse.
An adult may live 10 to 30 days.
Cyclamen mites require a relative humidity of around 80% to 100% and a temperature of about 15ºC (59ºF) to 22ºC (72ºF). At all development stages they shun the light; they are not found on the parts of the plant exposed to sunlight or warmth, but shut themselves up inside flower buds, flowers and young leaves, to stop their bodies drying out. They have a soft outside, since their exoskeleton contains little chitin. Infestation can occur, therefore, with no outwardly visible sign.
When relative humidity is below 70% they die.
In glasshouses this pest is active all year round. Both larvae and adults feed and cause damage.
Choosing the underside of leaves, the mites pierce the plant tissue; they empty the surface layers of their content, and also secrete certain substances which throw the plant cells’ growth regulation out of order. The result is chestnut-brown, corky growth on the underside of the leaves.
The most typical features of cyclamen mite attack are the curling up of the young leaf edges, which become crisper and harden; flowers become crisper, develop asymmetrically and have difficulty opening; they barely rise out of the foliage.
Essentially it is the plant’s young parts, and the younger plants, which are susceptible, since the mites can only insert their piercing and sucking mouth parts into soft tissue. It is at the larval stage that they do the greatest damage.
Damage on leave caused by Polyphagotarsonemus latus
Flower buds attacked by Polyphagotarsonemus latus
Flower petals deformed by Polyphagotarsonemus latus
The adult mite moves around on its legs, but only to a limited extent. Attacks are therefore localised. Adults are happy to stay on the flower bud, flower, or leaf where they emerged, and only migrate in cases of massive overpopulation.
Transfer from one plant to another is done by contact and as a result of the various human operations on the cyclamen in the course of tending them. Cyclamen mites may also be spread by wind and draughts.
Tarsonemus latus (Polyphagotarsonemus latus)
Originating in the tropics and subtropics, this species is now well established in Europe, and infests cyclamen. It is yellowish or greenish and the females are between 0.14 mm and 0.24 mm, the males 0.11 mm and 0.17 mm. They make their home on the underside of leaves and invade the buds while they are still closed. Infested new growth of the plant is wizened and discoloured, shiny, crumbly and misshapen. The flowers are deformed and buds may fall off. Bad attacks may kill the plant.
Cyclamen mites may appear at any stage of the plant cycle, from seedlings all the way to flowering plants. Regular inspection of the plants will let the grower be quick in getting rid of any that are thought to be under attack.
As precautionary measures, one can:
Biological control of mite infestation can be done with the help of predator mites. These predators are often smaller than their prey. They do no harm to the plant.
There are a number of predator mites which feed on these pests, including Phytoseiulus persimilis (Phytoseiulus System, Phytoseiulus T. system, Phyto-line p, Spidex, Spidex Plus) and Amblyseius californicus (Californicus system, Ambly-line cal, Spical). However, they mainly prey on other mites, such as Tetranychus sp, and not on Tarsonemus pallidus or Polyphagotarsonemus latus.
Under glass there is no avoiding the preventive use of specific anti-mite chemicals: infestations are seldom all of one kind.
The constant development of the regulations and homologations of phytosanitary treatment products, and the differences in regulations according to each country make it impossible for us to include updated information on homologations. Each producer will have to contact his local plant protection bureau to obtain the latest updates concerning the regulations and use of phytosanitary products. We strongly advise testing beforehand on a plant sample in order to measure the chemical’s activity (establishing the dose) and any effect on the plant (plant poisoning).
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