Animal pests on Phalaenopsis and other orchids
In the professional production of Phalaenopsis, insects, spiders and other animal pests repeatedly infest the plant. In the following, the most important economic pests are listed, including their biology, damage pattern and control options. Recommended chemical control methods must be checked against the applicable approval regulations of your country. All plant protection recommendations are made with the exclusion of any liability
Green melon aphid, cotton aphid (Aphis gossypii Glover): Dark green marbled, light green to yellow with dark siphuncles, no frontal tubercles, marked honey formation, length 0.9-1.8 mm. Marked resistance tendency e.g. to Pirimicarb.
Foxglove aphid (Aulacorthum solani Kalt.): Light green with antennae longer than her body, siphuncles with dark spot, base of siphuncles with dark green spots, terete with pointed hind body, length 1.8-3.0 mm.
Potato aphid (Macrosiphum euphorbiae Thomas): yellowish-green with black siphuncles and antennae longer than its body, length 1.7-3.6 mm.
Other aphids that might occur on orchids are the Crescent-marked Lily Aphid or Mottled Arum Aphid (Myzus circumflexus Buckton) and the Violet Aphid (Myzus ornatus Laing.). In individual cases a differential diagnosis had to be carried out by experts.
Pyralidae (Duponchelia fovealis Zeller)
Cabbage Leafroller (Clepsis spectrana Treit.)
The problematic pest Duponchelia fovealis Zeller originates from Southern Europe. It is mainly found in cold greenhouse cultivation and in cooled Phalaenopses. The butterfly is about 19-21 mm long, brown to brown-black with lighter coloured rings on the hind body. A characteristic is the upwardly bowed hind body. The insects usually sit on the underside of the leaves and quickly fly away when they are disturbed. The caterpillars are 2-3 cm long, the basic colour is white with many small brown spots and the head is dark. The caterpillars eat hidden, usually on the substrate surface or in the upper soil layer. Their fine webs are visible there, under which the insects are safe and the caterpillars pupate there. The insect development in greenhouse conditions from egg to adult insect takes about 6-8 weeks with the active eating period of the larvae being 3-4 weeks and taking most of the development time.
Clepsis spectrana is a leafroller that often occurs in greenhouses in Central Europe. The butterfly is about 15-24 mm in size, ochre-coloured to yellowish with dark spots. The caterpillars are 20-25 mm long, brown to olive-green, the head is black.
Hypoaspis predatory mites can be used to control various pests living in the ground. The mites open the eggs by biting into them shortly before the larvae emerge. Insect-pathogenic nematodes (Steinernema sp.) can also be used for biological plant protection. Repeated application can markedly reduce the number of larvae within a very short time.
Bacteriae offer good results as insect pathogens. The Bacillus thuringiensis strain (the so- called B.t. products) are effective against harmful butterflies. The bacterium multiplies in infected insects and forms permanent spores there. During spore formation, protein crystals are produced (the so-called endotoxin crystals). If these bacterial products are eaten by sensitive insects, the crystals will destroy the cells of their intestines. They get into the body causing the insects to die within a short time. B.t. products are not contact products, but purely stomach insecticides. After having eaten the bacterium, the larvae will soon stop eating. The smaller and younger the larvae are, the quicker and more effective the used B.t. products will be.
Darkwinged Fungus Gnat
The 4-7 mm long larvae are transparent, whitish, slim with a black head capsule. They live in humid substrates and eat decomposing plant tissue, but big populations can also damage living plants. The darkwinged fungus gnats often occur in connection with fungus infestation in the thick roots of Phalaenopsis and Paphiopedilum. Weak plants or plants pre-damaged by harmful fungi are very attractive places to lay their eggs. The larvae are often imported into the stands in sphagnum. The eggs are small, oval, transparent whitish and lain in humid substrates. The development from egg to adult takes about 4 weeks. The main species found in greenhouses are Sciara and Bradysia.
The Orfelia larvae are significantly bigger and slimmer, 15-20 mm long animals have been found in roots. The adult animals (8-10 mm) are also much bigger than the darkwinged fungus gnats and also markedly differ in habitus. The back part of the body has horizontal stripes. Most animals of this gnat species all over the world live on funghi, fungus infested substrates, in moss or under the barks of trees. This may confirm the theory that the gnat was imported in orchid-breeding companies in substrate containing bark and sphagnum.
Orfelia gnaws in the thick roots of various orchid varieties and in some cases, the stem base is severely damaged, whereas the fine roots remain intact in the initial phase of infestation. Usually, only few larvae are found in the damaged plants, at times even only one single larva causes the damage. Obvious are also the markedly visible slime traces on the substrate surface. These insects mainly infest Phalaenopsis and Miltonia, but also other pot orchids such as Dendrobium, Oncidium or Cambria hybrids.
Depending on the degree of infestation, 250,000 to 500,000 nematodes per m² are applied on the plants in water. Applications on spliced young plants are recommended and meristems seem to be slightly more prone than seedlings. As Orfelia is a relatively big larva, Heterorhabditis are certainly better to use than Steinernema, they effectively control the gnat larvae that usually occurs in combinations. As it is difficult to find out which of the larvae really causes the respective damage, combined treatment with both nematode species would be best.
Insect-pathogenous bacteriae (Bacillus thuringiensis israelensis = B.t.i.): Products with the bacterium B.t.i. are brought onto the plant by watering. The bacterium forms permanent spores and at the same time protein crystals (the so-called endotoxin crystals). If these bacterial products are eaten by the sensitive insects, the crystals destroy the cells of the bowel walls. The bacterium gets into the body, the insects die within a very short time. B.t.i. is no contact product, but a pure feed poison. After intake of the bacterium, the larvae stop eating very quickly. The smaller and younger the larvae are the quicker and better the effect of the products applied. Bti. takes effect only against gnat larvae. Compared to nematodes, bacteriae have a very short life. Usually, the effect is over after a maximum of one week, so several applications are necessary in case of infestation. It also has to be considered that they take no effect against adult insects, maggots or eggs, but only against the larvae that take them in with their food. Due to the relatively high damage potential caused in orchids by Orfelia, accompanying measures using nematodes or B.t.i. should be carried out on Orchids, until no more larvae or adult insects are seen.
Predatory mites (Hypoaspis miles, H. aculeifer): Predatory mites are ideal for biological plant protection. These beneficial insects are very polyphagous, they feed on many different insect larvae and among them also the larvae of Bradysia. and Sciara. Hypoaspis can reduce the pest when applied regularly and as a prophylactic to slow down the population growth. They are effective later than nematodes and therefore are not suitable for direct, quick treatment, but rather as a medium to long-term strategy to control the pest. For this purpose, about 200-250 animals per m² are spread prophylacticly every 4-6 months in the greenhouse. The predatory mites are especially effective, when orchid substrates mixed with sphagnum are available. In these conditions the predatory mites multiply quickly in the greenhouse and even after some months there is still a sufficient number of them in the stands. As the predatory mites have a comprehensive prey spectrum and eat their prey in the upper ground layer, those animals can stay in greenhouses for a relatively long time and be active there up to 6 months in high population densities.
Robber flies (Coenosia attenuata Stein): Coenosia robber flies are predatory species of the Muscidae family. In many orchid stands these flies settled as spontaneous beneficial animals and have taken over an important task in the treatment of darkwinged fungus gnats. The robber flies which come from North Africa resemble our common flies, but they are a bit smaller. They have probably been accidentally imported into greenhouses in young plants. The adult animals sit still on leaves in the stand and wait for their prey and catch insects flying by. They open their soft-skinned body parts and suck their prey. Proof of their successful activity is empty skins of the pests on the upper leaves. In addition to darkwinged fungus gnats they also feed on white flies, peat flies and leaf-mining flies. The Coenosia larvae are predatory and live in the substrate and among other insects also feed on the larvae of darkwinged fungus gnats.
False spider mites
Tenuipalpidae are very small, 0.25-0.3 mm long, usually greenish to reddish coloured flat oval mites. They are relatively slow and appear to be almost immobile. The pest slowly spreads in the plant stand, some species can propagate very quickly in temperatures of 21°C and more. As soon as damage is visible, infestation has usually considerably already. The mites do not build any webs. Three species are particularly harmful to orchids: the bunch mite (Brevipalpus californicus Banks), the privet mite Brevipalpus obovatus Donn. and the phalaenopsis mite (Tenuipalpus pacificus Baker). The entire development cycle is 4-6 weeks for Brevipalpus and 2 to 3 months for Tenuipalpus depending on the temperature and humidity. Brevipalpus obovatus tend to mass propagation in temperatures above 21°C. The animals live on parts of the plant, but the main damage is done to the underside of the leaf. Large amounts of mites are usually found along the leaves veins. The mites are often introduced into greenhouses on plant material, especially from tropical and subtropical areas.
Two species are relevant on orchids.
Planococcus citri Risso: 3-5 mm long, oval, dark yellow to yellowish-brown, powdered with wax excrements, short and thick filaments on body edges. They live very polyphagous, and leave marked honeydew excrements. The yellow eggs are placed in mealy masses on the hind body, optimal temperatures around 24°C.
The longtailed mealybug (Pseudococcus longispinus Targ.-Tozz. [= Pseudococcus adonidum L.]): 3-5 mm long, reddish to orange, oval mealybug. Characteristic is the length of the tail threads (filaments) that are about as long as its body. Extremely marked honeydew excrements. These animals originate from tropical regions all over the world and have become the major pest in orchid cultivation over the last years. Massive populations are often found under the leaves, on blossom stalks and blossom leaves and other plant parts where they cannot really find food, e.g. pot rims, boxes, shelves, greenhouse parts, substrates, transport boxes etc.
They quickly spread in the stands. In contrast to other species, the females do not produce any egg packets. Multiplication is done by ovoviviparity, i.e. the larvae develop and emerge in their mothers’ body, living larvae are then released. The 1 st larvae stadium, the extremely small crawlers, soon leave their mothers’ body and spread all over the plant stand. Shortly after starting to eat, they cover their bodies with a white wax-like cover, which gives them a mealy appearance. That larvae stadium is by far the most mobile one and needs the longest development period. On temperatures of 25-27°C the development of L1-L3 takes about 30- 35 days. After the first moult, male and female animals can be distinguished. The females die after giving birth to the young animals. With a size of 1.5 mm, the male mealybug is smaller than the female. The body is divided into segments and in contrast to the female’s body, it shows an insect-like habitus. From the 2 nd larvae stadium on, the male animals form a longish cocoon-like shape made of wax excrements. In it, they develop to become a winged adult insect. They do not need any food, because they are inactive during the metamorphosis stage. The optimum temperature for Pseudococcus longispinus is at 25-27°C; in these temperatures, they produce the maximum of eggs and the larvae stadium progresses the fastest. The animals die in temperatures above 35°C. In general, more females than males are produced, only at 27°C the percentage of females -males is the same. In case of danger, the females can excrete a liquid which may stick to the mouth tools of smaller predatory insects and makes them unable to eat. Pseudococcus reacts less to pesticides than other species. When using biological plant protection, it is vital to determine exactly the respective species, because some commercially produced beneficial animals, especially parasitic wasps, only parasitise certain mealybug species.
The first step to prevent infestation is a careful check of the imported material. This has to be checked thoroughly, especially the leaf axils and the shoot tips. Pests entering the greenhouse without being noticed can hide for several months until visible damage is seen on the plants. As long as infestation is restricted to just a few individual plants, these should be destroyed. But if symptoms show on several plants or minor infestation becomes a problem, chemical control can no longer be avoided.
The most favourable time for chemical control is when the young animals leave the eggs. In this phase best results can be achieved with insecticides. Mealybugs can be controlled relatively well as long as there is no "waxwool" formation. As, however, all stadiums are found on the plants at the same time, i.e. there are constantly new young animals, repeated treatment has to be carried out in intervals of 10–14 days. The older the larvae get, the more difficult treatment becomes. As soon as the woolly wax cocoons are formed and the pest is protected, insecticides considerably lose effectiveness. Most systemic products, too, do not achieve good results in this phase. Oil-containing products have a better effect then, but they should not be applied too often, as with regular application of oils Phalaenopsis may develop phytotoxity.
Control of P. longispinus by spraying is most effective in high temperatures and relatively high humidity. Observations show that fewer mealybugs were found in the mornings when temperatures were relatively low, as the animals were hiding. As soon as the temperature started rising and the relative air humidity increased markedly, most mealybugs were found relatively unprotected on top of the leaves and put up their antennae, probably trying to get cool.
The male mealybugs increased their flight activity in assimilation lighting. Blueboards could be placed below lights to catch the males. Placing UV lamps is also recommended. Control of the male mealybug makes sense, because without them, this pest cannot reproduce.
Leptomastidea abnormis: yellow-brown, only about 2 mm long. They only parasitise Planococcus citri. Temperatures of 20-24 °C are ideal for the development of the parasitic wasp. As these animals do not require much light, they can also be applied in autumn and spring.
Cryptolaemus montrouzieri: The Australian Mealybug destroyer is 4 mm long, orange with black wing covers. The larvae are about 13 mm long and powdered with white waxy material. Cryptolaemus is a predatory insect feeding on all known mealybug species. It is especially helpful because it can also be used to control marked infestation. Usually this beetle does not fully complete its development in the greenhouse. It is not interested in Pseudococcus longispinus as it prefers other mealybug species. As the young larvae of the ladybug prefer to feed on eggs and the females are only viviparous, the reason for low control success is a lack of feed. However, it is able to sufficiently control Planococcus citri.
Anagyrus fusciventris: A small parasitic wasp that parasitises individual Pseudococcus longispinus that subsequently turn yellowish. It is difficult to determine its success, as parasitised stadiums are difficult to find in the stand. In high initial infestation, these animals are not very effective. Good results can be obtained in small populations, but the wasps are difficult to get from dealers and are relatively expensive.
Chrysoperla carnea: Lacewing flies are predatory insects with a broad prey spectrum. It is said that they are also able to control Planococcus citri. Lacewing fly larvae are applied to orchid stands in comb systems in 14-day intervals. They enter the small shafts where mealybugs sit in their early stadium of development. Chrysoperla also feeds on Pseudococcus and is able to keep populations low for some time. However, in case of massive infestation, their density and the intervals are insufficient. When the plants form flower stalks, the lacewing flies do not move up to them. Pseudococcus prefers those places on the buds and forms colonies on the developing blossoms.
Episyrphus balteatus: Syrphid larvae are also polyphagous. The larvae, in buckwheat glumes, are spread onto orchids. The larvae feed on mealybugs, but immediately hide in safe places. The relatively large amount of buckwheat glumes can be a nuisance. They do not remain on the leaves, but when the plants are watered, they can also get into the heart of the plants where they may cause secondary rot.
Millipedes are long and woodlouse-shaped animals whose outer skeleton is very hard due to chalk deposits. Their legs are all on the ventral side. The first and last body segments have no legs, the second to the fourth segments have one pair of legs and the other segments two pairs of legs each. The larvae have only six pairs of legs. Eggs are laid into the substrate, during the development cycle of several weeks the animals go through several phases. The animals often roll up, which is another characteristic. Centipedes need a high humidity, are nocturnal and hide under pots, in substrates and in similar places during daytime. They mainly live in the ground and are important humus producers. They usually feed on organic material and rarely on living plant parts, green plant parts are never eaten. A frequent visitor in greenhouses is the spotted millipede (Blaniulus guttulatus Bosc.). These animals are very slim, white to grey and about 10-18 mm long, live in the ground and roll up into spirals when disturbed. They live polyphagously on roots. Less frequent on orchids is the greenhouse millipede (Orthomorpha gracilis Koch), originating from tropical regions. It is about 16-23 mm long, dark brown to black and has 20 body segments.
Centipedes are small, whitish animals with only one pair of legs on each body segment. The posterior segment of a centipede has characteristic spinning glands and its head has a pair of multi-segment antennae. In contrast to the millipedes these very small animals have no chalk deposits. In greenhouses, the garden centipede (Scutigerella immaculata Newp. = Scolopendrella immaculata Newp.) might cause damage. These approximately 6 mm long animals need a lot of humidity and are very often found in humus substrates. Larger colonies tend to occur in peaty ground.
Root and Copra Mites
Armoured scales have a cover-shaped armour which is not connected with the body and can be removed easily. The insects suck the liquid from individual cells, so there are no phloem suckers.
There are many different species, the most common species on orchids is the Boisduval scale (Diaspis boisduvalii Sign.). The armour of the female is about 2 mm long, flat, oval, yellow to light brown and transparent covering the lemon-yellow insects and their eggs. The armour of the male is 0.8-1.0 mm long, oblong with white wax threads. In favourable conditions, large colonies are found especially on the underside of the leaves and on bulb-forming orchids. These insects are found regularly on Cattleya, Zygopetalum. The armour of Boisduval scales is tightly connected to their bodies, it is made of the bowed skin of the insects and cannot be removed. The armour is often shiny, like lacquer. Various species occur on orchids. The soft scale (Coccus hesperidum L.) is 3-4 mm long, flat, oval and of yellow-brown colour with a longitudinal rib in the middle. The females are viviparous and produce up to 1000 maggots in 2-3 months. Within only a few days, the emerging young maggots settle on other plants and are found along the middle rib. The development cycle from egg to adult takes about 2 months. This species excrements considerable amounts of honeydew. The wax scale (Saissetia coffea Walker) is up to 4 mm long, round-oval, 1-3 mm high, curved, dark brown to blackish and shiny. The females lay up to 2000 eggs under the armour. After the death of the mother, the armour opens and the young maggots migrate to new plant parts not yet infested.are small to medium insects with extreme sex dimorphism, i.e. males and females are very different as to their shape and size. Often male insects, which are nearly always wingless, cannot be found or they are at least very rare. In these cases there is virgin birth (parthenogenesis). The females never have wings, their body is compact and hardly segmented, they have no antennae and their legs are clearly visible. The bodies of the females are covered with a wax coating protecting them from unfavourable external conditions. During their development cycle the armour, which gives them their name, is formed by cast off maggot, faecal matter and other substances.
Scales lay eggs. The development of the insects may be completed after a few weeks depending on the species, as a result of this many generations develop quickly. The young maggots - the so-called crawlers – are able to move, whereas the adult insects sit on the plant nearly immobile.
Armoured scales on Orchids live on nearly all parts of the plant with the exception of the roots in the substrate. In the beginning they live hidden and are difficult to see. So there is a high risk of passive dispersal. As most species are adapted to high temperatures, considerable potentials have to be expected in imports from tropical and subtropical countries. The major pests on orchids are armoured scales and soft scales.
Armoured scales have a cover-shaped armour which is not connected with the body and can be removed easily. The insects suck the liquid from individual cells, so there are no phloem suckers.
There are many different species, the most common species on orchids is the Boisduval scale (Diaspis boisduvalii Sign.). The armour of the female is about 2 mm long, flat, oval, yellow to light brown and transparent covering the lemon-yellow insects and their eggs. The armour of the male is 0.8-1.0 mm long, oblong with white wax threads. In favourable conditions, large colonies are found especially on the underside of the leaves and on bulb-forming orchids. These insects are found regularly on Cattleya, Zygopetalum. The armour of Boisduval scales is tightly connected to their bodies, it is made of the bowed skin of the insects and cannot be removed. The armour is often shiny, like lacquer. Various species occur on orchids.
The soft scale (Coccus hesperidum L.) is 3-4 mm long, flat, oval and of yellow-brown colour with a longitudinal rib in the middle. The females are viviparous and produce up to 1000 maggots in 2-3 months. Within only a few days, the emerging young maggots settle on other plants and are found along the middle rib. The development cycle from egg to adult takes about 2 months. This species excrements considerable amounts of honeydew. The wax scale (Saissetia coffea Walker) is up to 4 mm long, round-oval, 1-3 mm high, curved, dark brown to blackish and shiny. The females lay up to 2000 eggs under the armour. After the death of the mother, the armour opens and the young maggots migrate to new plant parts not yet infested.
Slugs & Snails
On Orchids, slugs without shells and snails with more or less big shells occur causing more or less damage. Some snails or slugs can play an important role as carrier of viruses. The most common species of slugs is the field slug (Deroceras reticulatum Müller). This species can be 50-60 mm long in favourable conditions, the body is grey to reddish-brown with dark net-like lines and spots. The eggs with diameters of up to 2.0 mm are usually laid in groups of 4-10 eggs under pots, wood or bark. This species multiplies very quickly, in favourable climatic conditions in greenhouses, adult field slugs are able to lay eggs every 2 nd or 3 rd day. They mainly eat plant parts above the ground. They prefer young, soft plant tissue and are therefore often found on young plants and blossoms.
One species of snails is the orchid snail (Zonitoides arboreus Say). It is a North American species. The shell is about 2.0-2.5 mm high and 3.5-4.0 mm wide, brown-yellow to red- brown. They live on rotten and living plant material preferring the latter. This species loves bark substrates and finds ideal living conditions in it. The entire development takes about 3 months.
Snails usually occur on roots and root necks, they only cause slight direct damage, but create wounds. These wounds are then used as an entrance for harmful fungi. Snails are usually imported into the greenhouses in plant substrate, mainly in bark or coconut fibres.
Other snails and slugs in greenhouses that sometimes also eat on orchids are Opeas pumilum Pfeiffer, Oxychilus draparnaudi Beck, Discus rotundatus Müller and Lehmannia marginata Müller. Many snails are imported from tropical countries in plant material and especially in substrates accompanying that plant material.
Metaldehyde-containing products are effective in temperatures above 20°C and are effective for a longer time. However, when treated with those products, snails and slugs may recover again after non-lethal intake and in high humidity, so several repeated treatments are necessary. Snails and slugs that absorb the substance produce large amounts of slime.
In humid biotopes, Methiocarb is more effective than Metaldehyde. Methiocarb has an ovicide effect, too, it is effective in low temperatures already but has a shorter period of effectiveness. After absorbing the substance, the snails and slugs remain active for some time. To improve the effectiveness, water must be available, in dry conditions the snails or slugs might recover again. There is no slime production as after absorption of Metaldehyde.
After absorbing Iron-III-Phosphate the animals are supposed to stop eating right away. There is no environmental damage, because the substance is degraded in iron and phosphor. The effectiveness is not based on dehydration, so there is no reduced effectiveness in humid conditions and no slime production.
Most products have only a relatively short period of effectiveness in very humid air conditions which are usually found in plant stands in greenhouses. So treatments have to be repeated at regular intervals of at least 3-4 weeks, better would be intervals of about 10 days until no new feeding sites are seen. To improve effectiveness, spreading combinations of different substances has proved effective in gardening practice.
Different varieties of orchids can be affected.
- Western Flower Thrips (Frankliniella occidentalis Pergande): most frequent species in greenhouses, very polyphagous. The adults are about 2 mm long, light yellow to brown- yellow, the larvae are usually golden-yellow. The development cycles includes two larvae and two nymph stadiums and takes about 2-3 weeks in temperatures between 20°C and 30°C. This species usually lives in blossoms, but can also multiply rapidly on leaves and then severely damage all plant parts above the ground. This thrips species is a carrier of the tomato spotted wilt virus which occasionally infests Phalaenopsis plants. Thrips become resistant to insecticides relatively quick.
- Orchid thrips (Dichromothrips corbetti Priesner): the female is dark brown, larvae are reddish. The species originates from East Asia, mainly appears on Vanda and Cattleya. Phalaenopsis may also be infested, mainly at the blossoms. Viruses are not transmitted.
- Tobacco Thrips (Thrips tabaci Lind.): very polyphagous, frequently found species, greenhouses are often infested by animals coming from outside. The adults are 1-1.3 mm long, grey-yellow to brown, sometimes nearly black, the larvae are white to yellow.
- American Thrips (Echinothrips americanus Morg.): a new species of thrips on orchids which occurred in the Netherlands in the mid-nineties for the first time. Up to now, these animals have only been found in the Spathoglottis species Caractea as well as in young Miltonia plants in orchid horticulture. They were also seen on willow and birch seedlings which were found as weeds in the substrate, but they have not moved onto other orchid cultures yet. Echinothrips cause bright silvery spots due to sucking the plants and marked dung formation.
- Greenhouse Thrips (Heliothrips haemorrhoidales Bouché): occasionally found in orchid greenhouses, mainly damaging leaves, sometimes blossoms, too. Adults are 1-1.5 mm long, dark brown with a bright hind body, antennae, legs and wings. Usually found on the underside of leaves and are able to settle down in greenhouses with constant temperatures. They prefer shady and humid places and develop slowly in high temperatures. Infested leaves turn bleak, paperlike and wilt, large amounts of honeydew pollute the leaf surface. Plant protective measures can markedly reduce the number of animals.
- Palm Thrips (Parthenothrips dracaenae Heeg.): Adult animals are about 1.3 mm long, with black and white stripes, the larvae are white. They are very slow and usually sit on the leaves forming large colonies and leave very typical silvery shiny bright spots with black dung drops after sucking. Particularly numerous populations are found, if the host plants are kept in the dark and in moderate temperatures during the autumn and winter seasons. Thrips do not occur in greenhouses with a high humidity. Chemical treatment is unproblematic, biological treatment is more complicated. Predatory mites do not attack these animals, only lacewing flies can be successful.
Those bags contain bran as a carrier material and also storage mites (Tyrophagus sp.) as food for the predatory mites. So these bags are breeding stations containing a sufficient amount of food which is the basis for continuous multiplication of the predatory mites. This bag system proved to be especially successful when Frankliniella build populations already in the vegetative phase of the plants. The reason to do this is the phenomenon of reproductivity of Amblyseius cucumeris Oud, if Frankliniella is the only food they can get. As there is no pollen or other food in green plants, the storage mites in the bags are a good food supplement making up for that negative effect.
In order to prevent marked fluctuations in thrips populations, integratable insecticides can be used. Amblyseius is not effective against Echinothrips oder Parthenothrips, which makes biological treatment of them considerably more difficult.