The broad mite (Polyphagotarsonemus latus) occurs in the tropics and in greenhouses in temperate regions.
Mites belonging to the family of tarsonemids (Tarsonemidae) display a greater diversity of feeding habits than any other mite family. There are species that feed on fungi, algae, plants, as well as insect and mite predators and parasites. Those living on plants can cause considerable damage to their host.
Tarsonemids like the broad mite (Polyphagotarsonemus latus) can occur both on vegetable and ornamental crops.
The life cycle of tarsonemid mites has the following stages: egg, larva, and adult. The larvae have three pairs of legs, adults possess four pairs. The last pair of legs in both males and females is different to the others and not used for walking. The larvae stay in their larval cuticle for one or two days and then emerge. This stage is often considered a fourth stage called pupa, false pupa or quiescent nymph. The males use their fourth pair of legs to carry around young pharate females (quiescent nymphs) that are still in their larval cuticle. Mating occurs as soon as the adult female emerges from the larval cuticle. Tarsonemid mites have no eyes.
Female broad mites (Polyphagotarsonemus latus) lay their eggs mainly on the underside of the leaf or on the fruit surface. The elongated, oval eggs are firmly attached to the surface and are rather large (about 0.07 mm) compared with the subsequent, active stages. They are transparent and speckled with white dots.
The larva of the broad mite (Polyphagotarsonemus latus) resembles the adult, but is slightly smaller and has only three pairs of legs.
The emerging adult mite is roughly 0.2 mm long, oval and broad, and pale yellow or yellow-green, depending on the type and quantity of food consumed. Female mites have a white stripe on their backs.
The damage caused by the broad mite (Polyphagotarsonemus latus) can look similar to the damage caused by viruses. The typical pattern of damage consists of malformation and distortion of the above-ground growth of the plant. The mites show a preference for young, developing plant tissue, like the growing tips, young leaves and flower buds. The mechanism causing the deformation is not yet fully understood, possibly the mites, whilst sucking out the contents of plant cells, secrete substances that disturb local growth.
Leaf feeding is mainly concentrated on the underside near the leaf stalk, which tends to cause the leaf to turn brown and curl up. A typical indication of an attack of broad mite (Polyphagotarsonemus latus), is the appearance of dark brown edges at the base of young leaves. In case of a mild infestation, one can often see brown, frequently collapsed spots, or brown stripes forming a fine network on the leaves. In case of a more serious infestation, this network becomes so dense that there is no more green tissue visible. In most cases, the main veins are untouched, causing them to stand out as a green pattern against the brown leaf tissue. Brown, corky patches can appear on the leaf stalks and main stems.
The growing tips of affected plants acquire a misshapen appearance, with contorted leaves and sporadic brown discolouration caused by cork formation. When plants are severely attacked, the growing tip can be killed, plant growth stops and, in time, the whole plant dies off.
Flowers are often discoloured, and with a severe attack, deformed. Extensive damage can be caused by relatively low populations.
Frequently, the lower leaves of a plant remain unaffected while the younger leaves are badly damaged. Most broad mites (Polyphagotarsonemus latus) are found on the undersides of young, expanding leaves. Symptoms of an attack remain visible several weeks after the mites have been removed.