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Mites are one of the most prolific groups of arthropods. They can be found both indoors and outdoors in crops, both as plant pests and also as natural enemies of other pests. Because of their small size, they are not often seen until damage symptoms have become severe, at which time the number of mites present is already very high.
Two spotted spider mite (TSM)— Tetranychus urticae
Two spotted spider mite, (also called red spider mite) is a major pest in vegetable, fruit, flower and ornamental crops both indoors and outdoors all over the world.
Life-cycle and appearance
TSM has five stages in its lifecycle - egg, larva, first nymphal stage (protonymph), second nymphal stage (deutonymph) and adult mite.
The eggs of the spider mite can mostly be found on the under- side of the leaf. They are round, have a diameter of about 0. 14 mm and are transparent in color just after being laid. Later they become opaque. By the time the larva emerges the egg is straw-colored. Larvae have three pairs of legs and at emer- gence are colorless with two dark red eyes. After feeding on plant tissue their color changes to light green, brownish yellow or dark green. At that stage two dark spots appear in the middle of the body.
Protonymphs have four pairs of legs and are slightly bigger than the larvae. Their color varies from light to deep green. Their two body spots are bigger and clearer than on the larvae. After a period of eating, the protonymph rests and then develops into a deutonymph. This nymph is bigger, but has a similar coloring to the protonymph. Once it has become a deutonymph, differences can be seen between males and females. An adult mite develops from the deutonymph once it has had a feeding and a resting stage.
The adult female two spotted mite is oval-shaped and rounded at the rear. The color can vary from orange, light yellow or light green to dark green, reddish brown or even black. The male is more active than the female. His body is small- er and more pointed at the rear. His coloring varies from light yellow or orange to dark yellow or brown. Often the color of adult mites depends on the crop on which they occur. For example, the mite may be yellowish brown on cucumber, but reddish brown on tomato. Both males and females usually have two large black spots on each side of the body, which can vary in size and shape. In summer the female can be a bright red colour, and there can also be an or- ange overwintering form.
A spider mite population consists of about 75% females and 25% males.
Males often hang around females in the last stage of development in order to ma- te with them as soon as they become sexually mature. One single mating is suffi- cient to fertilize all the eggs. Fertilized females produce females as well as males, whereas unfertilized females produce only males.
Depending on the temperature it takes 0. 5 to 3 days for the female to start de- positing eggs. The number of eggs she lays per day and the number of days she produces eggs depends on a number of factors:
the temperature,
the crop,
the humidity,
Mites
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Adults, juveniles and eggs of the two spotted mite
Normal colour form
Life cycle of two spotted spider mite
plant nutrition
and exposure to pesticides.
Under ideal conditions a female can lay more than 100 eggs.
All life stages of two spotted mites (except eggs) can cause damage to the plant. Mites mostly appear on the underside of the leaves where they pierce plant cells and suck out their contents. Those cells then turn yellow, and on many plants the damage caused by the mites can be seen on the upper surface of the leaf as small white yellow spots. With increasing damage the leaves turn completely yellow or brown. With the photosynthetic area gone the leaf dies and the whole plant can eventually die. Nymphs and adults also produce webs. If large numbers of mites are present, the plant can be covered completely with webs which are swarming with mites.
For plants this can have the following effects:
the chlorophyll is destroyed or disappears. Photosynthesis and therefore plant growth decreases. Crop losses occur on tomato and cucumber when about 30% of the leaf surface is damaged;
the spots on the leaves/flowers and the webs damage the appearance of the crops, This is especially important for ornamentals, and flower crops
Measures like fertilization and pruning to improve crop growth can also improve the quality of the food source, and thus promote faster reproduction of the pest.
Because of it’s fast development, high reproduction rate and pressure from chemicals, two spotted mites are able to quickly develop resistance to many miticides.
The regular use of pesticides can inhibit the use of natural enemies and the use of some insecticides (such as Imidacloprid) increases the egg laying capacity and reproduction rate of two spotted mites. Climate control (e.g. low humidity for the prevention of mildew in greenhouse roses/cucumbers) can inhibit the effectiveness of natural enemies, allowing pest numbers to spike.
Two spotted mites can infest or travel to the crop in several ways.
when a plant is heavily infested, mites will congregate at the top of the plant. Mites sometimes fall to the ground, after which they spread or they move along crop wires to other plants.
they can also spin silk threads which they use to release themselves from the plant surface, and then can be moved to new sites by air currents and wind.
they can be dispersed by infected plant seedlings, on machinery, workers hands or clothing, birds etc.
Control with Phytoseiulus persimilis (Persimilis), Neoseiulus californicus (Californicus) or Typhlodromus occidentalis (T.o’s)
Bean Spider Mite— Tetranychus ludeni
Commonly known as the dark-red spider mite, red-legged spider mite or bean mite, this species is found on over 300 plant species world wide including bean, eggplant, hibiscus, pumpkin and other cucurbits in warm areas. It is a common pest on green- house crops in temperate areas.
Eggs are usually laid on the underside of leaves, are spherical in shape and pale yel- low in colour. Adults are dark crimson red but lack the two dark spots that two spotted mites have. Legs are often dark red as well. This species is very similar in general appearance to Tetranychus cinnabarinus.
The life cycle of the bean spider mite is very similar to that of the two spotted mite.
Control with Phytoseiulus persimilis (Persimilis), Neoseiulus californicus (Californicus)
Tomato russet mite— Aculops lycopersici
The tomato russet mite (or tomato rust mite) can be a major pest of greenhouse tomatoes, eggplants and outside on potatoes and solanaceous weeds such as black- berry nightshade. The mite is easily spread on workers clothing, wind and leaves blown into a crop from outside. These mites are tiny <180μm and are difficult to see even with a 20 x hand lens. By the time the first symptoms are seen on plants, mite numbers are already very high. Most infestations start on the lower parts of the plant. Lower leaves start to yellow from the base of the leaf moving out towards the edge of the leaf. Leaves may turn silvery on the lower surfaces and curl before final-
Two spotted mite damage on strawberries
Bean spider mites and eggs
Webbing on a developing cucumber plant
Tomato russet mites—more than 20x magnification
roots may also be “mined” internally. Corms or bulbs grown in bulb mite infested soils will have distorted leaves and growing points. High numbers of bulb mites can quickly transform an entire bulb to a rotten pulp.
Bulb mites can be effectively controlled by Hypoaspis aculeifer.
Snake mites— Ophionyssus natricis
Snake mites are parasitic mites commonly found on snakes, but also occurring on captive lizards, turtles, crocodiles and other reptiles. Feeding causes the bodies of the mites to be engorged with blood from the reptile.
Clinical signs include anorexia, depression, frequent rubbing against cage furniture, increased sloughing, and prolonged soaking in the water bowl. Mites may be seen crawling on the skin of the snake. With heavy infections anaemia can occur.
The mites feed by puncturing through the snake skin which can provide a point of entry where diseases such as Aeromonas spp. and Inclusion Body Disease (IBD) can be transmitted. Snake mites have been shown to act as vectors for IBD.
There are five life stages for the snake mite: egg, larva, protonymph, deutonymph and adult. The intermediate stages (larva, protonymph and deutonymph) must moult at least once to de- velop into the next stage. The ideal conditions for the mite to fully develop into an adult are at temperatures between 24-29° C and a relative humidity of 70-90%. The life stages can usually be completed in 13-19 days. Unfavourable environmental conditions will slow or halt develop- ment and decrease survivorship of all stages of the mites. All mite stages are killed when ex- posed to temperatures above 41° C or below 2° C for several days. In terms of humidity, the mites will desiccate at levels below 20%. The mites will also drown if they are kept immersed in water.
After hatching, the young mites go through a larval stage, which takes one or two days. The larvae do not tend to move very far away from the eggs, despite having the ability to walk. They do not feed in the larval stage.
The larvae develop into the protonymph stage, which can last three days to two weeks. At this stage the protonymphs become attracted to the smell of snakes and require a blood meal to go into the next stage. The pro- tonymphs tend to walk around the scale surfaces and head plates of the snake.
The deutonymph stage takes place after a blood meal, usually away from the snake. Again, no feeding occurs while in this stage. Deutonymphs can survive for up to 31 days without feeding. Final moulting takes about a day to complete before the deutonymph becomes an adult mite. Adult mites continue to feed on the host and usually live for up to 40 days.
Once adults, the mites suck blood to engorgement (which takes four to eight days) and then lay approximately 20 eggs. Adult females feed two to three times at one to two week intervals and can lay up to 60-80 eggs in a lifetime. The eggs (off white to tan colour) are rarely laid on the snake, but are usually laid in dark and humid areas. Eggs laid at 25° C will hatch in 2-3 days, provided there is at least 85% humidity.
Snake mites are controlled by Hypoaspis miles.
Chicken mites— Dermanyssus gallinae
The chicken mite (also known as poultry red mite, red fowl mite, red poultry mite, roost mite) is a parasite that occurs world wide and can infest both domestic and wild bird species. It has also been known to attack humans and recent evidence shows it can complete it’s life cycle on humans as well. Chicken mites mainly affect laying hens. Adult female mites lay their eggs in hiding places such as cracks and crevasses in hen houses and enclosures. Four to eight eggs are laid at a time, up to a total of 25 during the mites life time, and usually hatch2-3 days after being laid. The hatched larvae do not feed, but molt into nymphs 1-2 days later. Nymphs need to have a blood feed and after several molts, they become adults (approx. 4-5 days). The mites favour hot humid conditions and in these situations, mites can complete their life cycle in as few as 7 days. Adult mites live for up to 8 weeks but are able to survive for up to 5 months without feeding. In cooler temperatures, development of the mites slows down and is almost stopped at 9°C. Because of this, mite problems are usually more prevalent in the summer months on birds kept outdoors, but can be all year round on birds kept indoors. Adult mites can grow to 1mm long and are a white/grey colour if they have not yet had a blood feed, or are dark red after a blood feed. Mites generally feed at night time, and after a blood feed, mites will leave their host and hide in cracks, hollow places on roosts, feed troughs close to the birds. Mites will often be found clustered in these areas, and may number in the thou- sands. When population numbers get very high, the mites may feed on birds during the day as well as the night. Mites are generally found around the beak, ears, back, legs and breasts of
Snake mites
Snake mites on a snakes head
Blood engorged adult chicken mite
Cluster of chicken mites in a hen house
birds. The mite bites cause itching and inflammation of the skin and when infested, skin on the birds legs may become, crusty and scaly. When infested, birds will often scratch and bite at themselves, causing injury and feather loss. Severe blood loss can cause anaemia and even death. Decreased egg laying in poultry houses can occur and infected birds become more suscep- tible to other diseases. Red poultry mites are controlled by Hypoaspis aculeifer
Tropical fowl mites— Ornithonyssus bursa
"Tropical fowl mites" or "Starling Mites" are common names for the bird mite Ornithonyssus bur- sa. These mites are often incorrectly referred to as 'bird lice', particularly within the pest control industry. Bird mites are most active during Spring and early Summer. Ornithonyssus bursa is a small but extremely mobile mite, barely visible to the eye, with eight legs (except the larva that has 6), oval in shape and with a sparse covering of short hairs. It is a para- site, which feeds on the blood of common birds including poultry, pigeons, starlings, sparrows, Indian mynahs, and some wild birds. Bird mites are semi-transparent in colour, which makes them difficult to detect on skin until blood is ingested and then digested; when they may appear reddish to blackish.
Contact with humans usually occurs after birds gain entry to roof cavities via broken tiles or through unprotected eaves, of homes, factories, barns and other dwellings to construct their nests in early spring or summer. However, some infestations also occur from birds roosting on the outside of dwellings such as window ledges or awnings. The mites feed on the unfeathered nestlings, as well as the adult birds, and the large amount of nesting material used by the birds provide the mites with an ideal environment in which to thrive. The mites have a short life cycle (approximately 7 days) and can rapidly generate large populations.
When the young birds leave the nest, or die, many mites (often many tens of thousands) are left behind in the absence of a suitable host, and these will disperse from the nest into and throughout the dwelling searching for new hosts. Most mites will die within 3 weeks without a blood meal from a bird host. They will bite humans they encounter but cannot survive on hu- mans.
There are no known biological controls for tropical fowl mites
Tropical fowl mite adult
