Hark Orchideen - Schädlinge

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

Woodlice

Hark Orchideen - Schädlinge: Asseln

Biology
Woodlice (Isopoda) are crustaceans and have a broad, oval to long shape. Their size varies from animals of 3 mm to animals of up to 20 mm large pillbugs (Armadillidium sp.), scabby slaters (Porcellio scaber Latr.) and dooryard sowbugs (Oniscus asellus L.). Most woodlice are plain grey, pillbugs can also be black to brown-black, all of their bodies have seven pairs of legs. They love dark, humid and warm habitats. During the day they hide in pots, under moss, in substrates or similar safe places. Their preferred food is dead plant material, occasionally and in cases of high population density, they also feed on young, fresh plant material.
Damage
The pattern of damage is similar to that of snails, but without the slimy traces. They mainly damage young, fresh plant parts, usually gnawing seedlings, aerial roots or root tips. But flower stalks can be damaged, too. Considerable damage may also be caused to the structure of the substrates.
Control
Using clean substrates with stable structure prevents infestation. The removal of hiding places in greenhouses can also be a good thing to do. Direct control with chemicals is not very successful, the most effective products are Methiocarb-containing baits which are used against snails as well.
Biological plant protection
Watering the plants with insect-pathogenic nematodes (Steinernema feltiae) can be effective against the grubs of the pests. Use them twice with a period of 4-6 weeks in between to reduce the pest.

Aphids

Hark Orchideen - Schädlinge: Blattläuse

Biology
Aphids are winged or wingless insects of 1.0-4.0 mm in size with long legs and antennae. Their development happens in different cycles, it is often complicated and should not be described in detail here. In greenhouses there is often virgin birth (parthenogenesis), the females regularly produce new insects without being fecundated. This results in high reproductivity, usually there are infestive nests with high population density. Mainly young sprouts and soft leaves are infested. The appearance of the aphids shows some significant features. The sucking beak is bent backwards in its resting position and is below the body. At the back laterally there are so- called siphuncles which discharge a secretion. Between these parts there is a little tail called the cauda. Cauda and siphuncles are very important to determine the different species. All aphids on orchids are phloem suckers, so there is considerable formation of honeydew. Aphid infestation might result in virus transmission, some species are probably vectors for the Short Orchid Rhabdovirus (KORV).
Major aphid species in greenhouses:
Green peach aphid (Myzus persicae Sulz.): Green to reddish colour with antennae as long as their body, marked frontal tubercle, length 1.2-2.6 mm. Resistant to various insecticides.

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.
Damage
Aphids usually infest blossoms; infestation on young sprouts and soft leaves is generally connected with marked honeydew formation. This results in settlements of dark mildew. Poisonous saliva causes malformation, deformation, crinkles or torsion of the leaves.
Control
When using chemical products for spraying, integrable agents should be preferred.
Biological plant protection
Due to their ability of mass propagation, infestation should be treated as quickly as possible. Curative use of beneficial animals is not effective enough on orchids, prophylactic release of Aphidius ervi, Aphidius colemani, Lysiphlebus testaceipes or Aphelinus abdominalis parasitic wasps is necessary. The parasitic wasps are released into the greenhouse from glass tubes and usually infest the aphids that are common on orchids. In cases of regular aphid infestation in a company, “open breeding” of aphid-parasitic wasps on cereal plants is recommended. In practical gardening, a combination of parasitic wasps and the midge Aphidoletes aphidimyza has proven to be successful. Spontaneous appearance of various other beneficial arthropods in greenhouses may result in a considerable reduction of aphids.

Brevipalpus

Hark Orchideen - Schaedlinge: Brevipalpus

Biology
False spider mites, orchid mites (Tenuipalpidae)

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.
Damage
In general, older leaves are a dull green, on their undersides indented spots are visible, and the upper surfaces show bright silver spots. Infested leaves later get a bronze to yellow-orange colour. Infested areas may scar, leaves often dry up from the edge and finally fall off. There are no webs below the leaves. All orchid varieties are susceptible to infestation by Brevipalpus. However, the mites mainly occur on Phalaenopsis, Doritinopsis, Paphiopedilum and Masdevallia.
Control
In contrast to spider mites, Tenuipalpidae have only a very restricted action radius and spread very slowly in the stand. So the mites need a relatively long time to form a harmful population. When damage is clearly visible, the number of mites on the plants is relatively high already and the necessary treatment with acaricids will take more time. As Brevipalpus mainly stay on the undersides oft he leaves, chemical treatment is quite difficult. Treatment with insecticides must be done every 2-3 weeks until the new leaves are visibly free from infestation. When using wetting agents, the undersides of the leaves can at least be wetted partly. Spraying without wetting agents are insufficient for Phalaenopsis.
Biological plant protection
Brevipalpus may develop great dynamics particularly on Phalaenopsis and propagate quickly, if left undisturbed. However, as soon as an antagonist appears, the development is either reduced or, in the best case, stopped completely. The safest and most sustainable treatment is done with mesostigmata. Brevipalpus sp. can be treated excellently with Amblyseius swirskii. A number of 50 animals per square metre, every 14 days (medium dosage) is optimal. This quantity is sufficient to fight early infestation of Brevipalpus on the plants and to sustainable prevent the formation of a population. A dosage interval of 4 weeks (low dosage) is sufficient as prophylaxis for plants showing now symptoms. However, this will not be sufficient to avoid the development of a population. As soon as the first symptoms are visible, the quantity used must be increased. 100 animals per square metre (high dosage) makes sense in case of more serious infestation at the beginning, later on, the lower dosage may be applied. The use of Amblyseius swirskii is much more efficient than chemical treatments.

Weevils

Hark Orchideen - Schädlinge: Dickmaulrüssler

Biology
There are many different species of weevils (Curculionidae) all over the world, they count among the major plant pests. Special features are the head with a snout and mouthparts. On orchids, especially Phalaenopsis, one species of weevil is of major importance. Black vine weevil (Otiorhynchus sulcatus Fabr.): The beetle is about 9-12 mm long, black in colour with a brownish, metallic and hairy upper top. The snout is relatively short, thick and sulcate in the middle. The beetles are unable to fly, they lay their eggs in substrates. The white, footless maggots live in the ground or in substrates. They are about 12 mm long, characteristic is the reddish brown head capsule. The maggots are not often found in orchid substrates, however, accidental importation in humus or peaty products may occur. The beetles sometimes migrate into greenhouses and stay there all year.
Damage
Typical symptoms of damage done by black vine weevils are curved feeding traces on leaves or blossoms, the buds might be eaten. Maggots eat underground plant parts and as a consequence of this, the plant dies. However, maggots are rarely found in orchid substrates.
Control
Accidental importation of maggots in substrates must be avoided. When initial damage is visible, contact insecticides can be sprayed to kill the adult beetle.
Biological plant protection
Insect pathogenic nematodes (Steinernema carpocapsae, Heterorhabditis bacteriophora) in the water can be used to control the maggots. The plants are watered with the water containing the nematodes which are about 1 mm long and they penetrate the maggots in the ground. Once they are in the maggots, they release a bacterium that kills them. However, as the nematodes are only effective until they reach the 3rd larvae stage, repeated treatments have to be considered. To control this pest, biological pest control measures are far more effective than chemical methods.

Mice

Hark Orchideen - Schädlinge: Mäuse

Biologie
Mice, Voles and Shrews (Muridae, Arvicolidae and Soricidae) are rodents and invade glasshouses especially in autumn and in periods with longer precipitation. There they may cause considerable damage. Harmful mice in orchids include amongst others the field voles (Microtus agrestis L.) and the common voles (Microtus arvalis Pall.). Zoologically, both species are root voles (Arvicolidae) and live near small woods, forest edges, meadows or cultivated fields. Another species of mice (Muridia) is the wood mouse (Apodemus sylvaticus L.). The wood mouse is an excellent climber and can easily scale greenhouse tables. Shrews (Soricidae) may also get into greenhouses and they live mainly on insects, woodlice, snails, spiders and worms and are therefore not harmful - on the contrary, they can even help to considerably reduce the pest population.
Damage
Mice mainly feed on buds and young fresh leaves, but also blossoms and flower stalks of Phalaenopsis. As a consequence, leaves may be damaged so much that they fall off. Mice sometimes pull out newly picked young plants and feed on the freely accessible roots.
Control
For direct control in greenhouses, traps with baits like carrots, nuts, apples or nut-chocolate spreads are very helpful. Poisoned baits containing Zinc Phosphide or Chlorphacinon should only be placed safely in special bait areas.

Oribatids

Hark Orchideen - Schädlinge: Moosmilben

Biology
Usually dark coloured, shining globose mites. Skin markedly chitinised, hard or leathery. They live on the ground and eat moss, algae, fungal threads or dead plant parts, they are often found in bark substrates. In general, they do not count among the pests. They usually get into the glasshouses in bark substrates and in some cases their dense population may exceed the damage threshold.
Damage
Damage usually only on young leaves of Phalaenopsis plants. The infestation mainly xepends on the species. Deformation of younger leaves with slight leaf edge necroses are formed. When the plants grow, the damaged areas restrict the growth and the developing leaves are markedly curved. The young soft leaves of Phalaenopsis seem to be supplementary food for oribatids. Small spots of necroses and slight deformation is found on blossoms. Monitoring should normally be done in the morning and/or after watering because this is when most of the animals are on the plants.
Control
Accidental importation is done in substrates. Careful initial control prevents damage. Reduce high air humidity when mites occur. Spraying with chemical products has to be carried out repeatedly.
Biological plant protection
The use of predatory mites (Hypoaspis miles, H. aculeifer) is a good plant protective method. These beneficial mites are very polyphagous and live on other ground mites, Collembolen (springtails) and many different maggots. They also eat the maggots of the wood mites. When used regularly and prophylactically on orchids, Hypoaspis can help to reduce many potential pests and to stop them from building a population. However, Hypoaspis are only suitable for direct control to a certain extent, i.e. large amounts of them would have to be spread. Predatory mites are especially efficient when orchid substrates mixed with Sphagnum are available. The living conditions in such substrates seem to literally animate Hypoaspis to multiply. In these conditions, predatory mites will multiply quickly in the greenhouse and even after a few months, there will still be enough of them in the stands. As predatory mites have a considerable and varied bait spectrum in the upper ground layer, they can live in the greenhouses for a long time and be active up to six months with a high population density. The following strategy can be used when problems with oribatids occur on orchids: at first repeated chemical treatment with integratable insecticides. Subsequent use of Hypoaspis predatory mites 2-3 times a year (150-250 animals/m²) to prevent new populations to grow.

Scales

Hark Orchideen - Schädlinge: Schildläuse

Biology
Scales (Coccina), armoured scales (Diaspidae) and soft scales (Coccidae or Lecaniidae)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.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.
Damage
Extreme honeydew formation with subsequent dark mildew infestation is characteristic of soft scale infestation. Infested blossoms fade prematurely. While eating, the armoured scales secrete poisonous saliva, yellow to reddish brown spots form where the insects had sucked. Where there is noticeable infestation the growth of the plants will be disturbed, in rare cases there is deformation.
Control
Pesticide control has to be carried out consequently and repeatedly. In case of infestation, at least 2-3 treatments have to be carried out in intervals of 2 weeks are required. Mineral oil has a reliable effect, but is problematic when used frequently, as some orchids might not tolerate it. When using pesticides it has to be ensured that the groups of effective agents are changed regularly.
Biological plant protection
Prior to applying biological treatment against scales in orchid stands, an exact diagnosis of the respective species has to be carried out, because some beneficial animals are specialised in certain scales only. No differential diagnosis is needed in cases of armoured scale infestation. The commercially available beneficial insects do not make a difference between the species and exterminate all of them. Beneficial insects to be used to control armoured scales are parasitic wasps Aphytis melinus and several ladybird species (Chilocorus nigritus, Rhyzobius sp.). In cases of soft scale infestation, the respective species has to be determined. The parasitical wasps Microterys flavus, Metaphycus helvolus and Encyrtus lecaniorum can be successfully used to control Coccus hesperidum. If there are Saissetia species, the parasitic wasp Coccophagus lycimnia can also be used in addition to Metaphycus and Encyrtus.

Butterflies

Hark Orchideen - Schädlinge: Schmetterlinge

Biology
Butterflies (Lepidoptera)
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.
Damage
Young leaves and blossoms can be gnawed by Duponchelia. On the substrate surface, fine webs are visible and the caterpillars eat below them. In some cases the larvae enter into the leaf base. Clepsis spectrana occurs in greenhouses from June onwards. The caterpillars eat the softer plant parts under fine webs, e.g. the blossoms of Masdevallia.
Control
To determine the degree of infestation, UV light traps can be installed in the greenhouses. Their flight activity may also be monitored with pheromones or yellow boards. Chemical treatment can be carried out with contact insecticides. Due to their hidden way of life, insecticide treatment must be repeated regularly until all insects are exterminated.
Biological plant protection
Biological control is possible, e.g. using chalcid wasps (Trichogramma sp.). The small parasitic wasps are about 0.5-2.0 mm long and parasitize only the eggs of harmful butterflies. The parasitized eggs turn black and a short time after that the adult parasitic wasps emerge leaving a round hole in the empty eggshell. Most species are polyphagous, but prefer certain hosts. Some dealers of beneficial animals offer different mixes for commercial gardening purposes.

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.

Slugs & Snails

Hark Orchideen - Schädlinge: Schnecken

Biology
Slugs and Snails are molluscs (Mollusca). They have a chitinous-like friction plate with numerous teeth, the so-called radula helps them to literally graze their food from the surface. Snails are crepuscular or nocturne, during the day they live under barks, pots or between plants. All snails produce slime and are usually very polyphagous. They lay their eggs in substrate. The young snails that emerge from the eggs look very much like their parents.

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.
Damage
Snails and slugs cause superficial scraping damage with their scraping tongue on root ends, bulbs and pseudobulbs, leaves and flower buds. When there is more eating activity, small holes are created. On bigger and thicker leaves, they mainly gnaw the undersides. These feeding marks may scar later on and when the plants grow, large suberisation can be seen in some cases. The roots are often gnawed close to the root ends and wounds occur on the roots leading to secondary infestation by secondary parasites. As to Cattleya, Phalaenopsis and Phaius, the snails and slugs mainly gnaw their blossoms. Another symptom of snail or slug infestation is the often large slime traces and irregular looking black dung spots at their feeding sites.
Control
In horticulture, three substances in the form of slug pellets are available: Methiocarb, Metaldehyde and Iron-III-Phosphate.

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.

Spider mites

Hark Orchideen - Schädlinge: Spinnmilben

Biology
The common spider mite found on Phalaenopsis (Tetranychus urticae Koch) is about 0.5 mm long, of yellow, red or green colour with two dark spots on its back. It is also called red spider resulting from the red colour the winter females get in autumn due to climatic conditions. The development period from egg and larvae to the eight-legged adult animal depends largely on the temperature and humidity and takes between 10 and 20 days. Spider mites have optimal multiplication conditions in high temperatures around 27°C and low air humidity. During their life, which lasts about 4-5 weeks, the females lay their eggs mainly on the underside of the leaf. When there is marked infestation, the animals form webs. Buds and blossoms are infested by spider mites, too. Especially during the summer months, there may be a population explosion in spider mites.
Damage
Spider mites empty individual cells by sucking them and subsequently air gets into the cell. Therefore, in the beginning, the leaves show silvery or white spots. With increasing infestation the spots unite, the leaves become lurid and finally dry. On the underside of the leaves, fine bright webs can be seen and in them eggs and sloughs are visible with a magnifying glass. Spider mites mainly suck on orchids with softer leaves such as Cycnodes, Calanthe or Phaius, but also occur on Phalaenopsis and Paphiopedilum.
Control
To avoid infestation, relative humidity must not drop below 60 %. Chemical treatment is difficult, spider mites become resistant quite soon. It is absolutely necessary to change the active substances used for treatment. Spraying must be done repeatedly and to protect useful predatory mites, integratable substances should be used.
Biological plant protection
Biological plant protection is possible using predatory mites (Phytoseiulus persimilis, Amblyseius swirskii, Amblyseius californicus) and the predatory gall midge (Feltsiella acarisuga). However, the most important predator is Phytoseiulus..The adult animals suck the eggs and larvae of the spider mites. In temperatures between 17°C and 25°C and relatively high humidity of 75%, the predatory mites have ideal multiplication conditions and develop better than the spider mites. When the first spider mites occur, Phytoseiulus is distributed in the infested areas. When there is only slight infestation, 5 animals per m² should be placed every 14 days, in areas of marked infestation up to 30 animals per m² will be necessary.

Springtails

HARK Orchideen - Springschwänze

Biology
Springtails belong to the oldest group of insects and are always wingless. The 1-4 mm small animals are white, sometimes silvery-black. A characteristic feature is the so-called furcula at the hind body which enables them to jump. Springtails live in humid biotopes only, they prefer Sphagnum-containing substrates or peat. Their main feed is dead organic material, however, when there are large populations, especially in humid or wet compost, they also feed on young living plant parts. They lay their eggs in the ground, the larvae are not much different from the adult animals. Springtails do not have special temperature requirements, they also multiply in cold greenhouses with temperatures between 10°C and 16°C.
Damage
Root tops or very young soft plants can be gnawed, leaving small holes and scratches in them. In humid conditions, masses of these small whitish animals can be seen on the substrate surface. However, the damage potential on orchids caused by springtails is regarded as being very low.
Control
Normally springtails infestation does not have to be treated as they only multiply in masses in wet substrates.
Biological plant protection
The larvae can be treated by insect-pathogenous nematodes (Steinernema feltiae) in the water, which markedly reduces the populations. A good possibility is the use of predatory mites (Hypoaspis miles Berl., H. aculeifer Can.). These beneficial animals that live on the ground are polyphagous and eat harmful ground pests and can settle well in greenhouses. Springtails are among their favourite prey. As the life cycles of Hypoaspis aculeifer and springtails are very similar, predatory mites are an ideal treatment against this pest.

Millipedes

Hark Orchideen - Schädlinge: Tausenfüßler

Biology
There are two different sub-groups of Myriapoda, i.e. millipedes (Diplopoda) and centipedes (Symphyla).

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.
Damage
Young plant parts on the substrate surface and root tops may be gnawed in exceptional cases. The spotted millipede sometimes feeds on root necks of young plants and makes holes into the roots. In connection with wet substrates there might be considerable damage due to pathogenous ground fungi. Large populations of Scutigerella immaculata might cause severe damage to young roots and sprouts. Large populations of millipedes and centipedes may also destroy the structure of the substrates and the consequence would be compression in the deeper part of the pot ground.
Control
Using clean and structure-stable substrates prevents infestation. There is a risk of accidental importation in substrates or young plants, sedation of substrates could be recommended.. Methiocarb-containing baits might be used to control snails and slugs.
Biological plant protection
Watering with insect-pathogenous nematodes (Steinernema feltiae) proved to be successful against the larvae. This method may reduce the pest by 50-70% after the first 2-3 weeks. Treatment must be repeated after 4-6 weeks. Good results may also be obtained by using predatory mites (Hypoaspis miles, H. aculeifer). These soil dwelling beneficial animals are polyphagous, feed on many different soil pests and can easily be kept in greenhouses. 50-100 animals per m² should be released to control centipedes.

Thrips

Hark Orchideen - Schädlinge: Thrips

Biology
Thrips are small, only 1-2 mm long slim insects with two pairs of fimbriated wings. The respective species are determined by the shape of the body and the bristles. At the end of their legs there are tarsal segments with small claws and adhesive bulbs. These insects have stinging and sucking mouthparts, they pierce into the cells and remove their contents. The cells fill with air and look silvery and shiny. Thrips are usually plant suckers, but there are also some predatory species. The plant damaging thrips lay their eggs on leaves and other plant parts with the help of a ovipositor. Development stages are two wingless larvae stadiums and then two to three nymph stadiums with the nymphs having so-called stumpy wings. The first larvae stadium and the adults are very mobile whereas the nymphs have phases of immobility. The development depends mainly on temperature and light. In constantly favourable greenhouse conditions there will be about 10-12 generations per year, depending on the respective species.

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.
Damage
Plants damaged by thrips look brighter, later on they turn brown and are covered with small black dung drops. Buds do not grow properly and fall off very early. Sprouts can be deformed. Sucking by Frankliniella and Thrips tabaci does not result in deformation and growth inhibition right away, as it is the case in many other ornamental plants. However, bright spots can be seen, white spots on leaves and blossoms with dung deposits and growth may be inhibited when there is more severe infestation. This species of thrips is a carrier of the tomato spotted wilt virus which occasionally infests orchids. Particularly threatened are the blossoms of many orchid varieties, in particular those of Phalaenopsis, Miltonia, Cymbidium, Epidendrum, Vanda, Masdevallia, Cattleya and Epicattleya. The leaf thrips Echinothrips, Parthenothrips and Heliothrips leave typical silvery shiny bright spots with black dung drops. When there is marked infestation, the borders of the leaves might roll in and the leaves might turn brown.
Control
The most important measure to control thrips is comprehensive and adapted monitoring, i.e. all purchased plants must be checked for larvae, adult and infestation checks have to be carried out in the stands using blue boards. No weeds should be placed under the tables. Chemical treatment of Frankliniella occidentalis and Thrips tabaci can be done by spraying insecticides which have to be repeated after 3-7 days. Echinothrips, Parthenothrips and Heliothrips are very slow thrips, they stay on the leaves during their entire development. Chemical treatment with contact insecticides is unproblematic.
Biological plant protection
Predatory mites Amblyseius cucumeris, A. swirskii, A. limonicus can be used to control Frankliniella. As thrips are generally found on orchids, obligatory releases of predatory mites have to be done. It is difficult to make predatory mites settle on orchids, so it cannot be recommended to spread them in the greenhouse. More successful is to distribute them in little paperbags.

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.

Darkwinged Fungus Gnat

Hark Orchideen - Schädlinge: Trauermücken

Biology
Darkwinged Fungus Gnat (Sciaridae or Lycoriidae) : Sciara sp., Bradysia sp. Keroplatidae: Orfelia sp. (syn.: Lyprauta sp.) are small, 4-6 mm long, black fragile insects. The adult insects fly zigzag over the substrate surface.

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.
Damage
In humid substrates the larvae eat soft roots and as a consequence of that, parasitic root fungi can infest the plants. If infestation is more severe, the structure of the substrate is destroyed relatively quickly by fine crumb-like substances. This can be regarded as the real damage on orchids.

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.
Control
Greenhouses must be clean and free from wet places with algae and peat. Yellow catchboards can be used to determine the degree of infestation of Orfelia und Sciara, in addition light traps can be hung up. To check if any larvae are present, the substrates should be checked for slime traces and the roots of weakly growing plants should be checked, too. It might also be good to hang up yellow catchboards not only in the plant stand, but also in the workshop close to artificial lighting and in the substrate storage room.
Biological plant protection
Parasitic nematodes (Steinernema sp., Heterorhabditis sp.): When infestation with Bradysia or Orfelia has been detected, insect pathogenous nematodes of the Steinernema species and Heterorhabditis can be applied. The long-time larvae of the nematodes are able to locate harmful larvae and penetrate them through body openings. By secreting a bacterium, the cell structures in the gnat larvae dissolve. A few days later the larvae die. This can be seen when parasitised gnat larvae come to the substrate surface and look milky-white.

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.

Tarsonemids

Hark Orchideen - Schädlinge: Weichhautmilben

Biology
Tarsonemids (Tarsonemidae) are very small, about 0.2-0.3 mm long, elliptic, transparent mites that live hidden directly at the vegetation point of orchids, i.e. in the heart of the plants. Their fourth pair of legs is always different from the third one, in Tarsonemus pallidus Banks it is markedly stronger. The mites multiply in high temperatures and high relative humidity. Development from egg to adult takes about 14 days in temperatures between 20 and 25° C. The mites are sensitive to light and prefer young soft plant tissue.
Damage
The leaves are bowed, blossom stalks are shorter, sometimes with lateral necroses, and the blossoms are deformed. The stem base sometimes shows smaller rotten spots. Not often found on Phalaenopsis. More frequently on Aerangis, Paphiopedilum or Dendrobium.
Control
Reduce humidity, if possible. Spraying with acaricides has to be carried out repeatedly.
Biological plant protection
Biological plant protection is possible using Amblyseius predatory mites. As the predatory mites are difficult to settle in Orchids, we recommend distribution in small paper bags. The predatory mites can slowly leave the bags and settle in the stands.

Mealybugs

Hark Orchideen - Schädlinge: Wollläuse

Biology
Mealybugs belong to the scales family (Coccina). However, they have no armours like other scales, the adult animals are powdered with a white waxy secrete. The edges of the body are covered with thorns and wax threads, occasionally very long, especially at the hind body. They usually lay eggs, but in favourable conditions some species are mainly viviparous.

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.
Damage
Severe damage caused by honeydew and subsequent settling of black rot. In cases of massive mealybug infestation, the leaves are deformed, growth of the plants is severely inhibited and the places where the insects suck are surrounded by yellow to red spots. Masses of mealybugs are often found under the leaves, on blossom stalks and blossoms. They hide very well, on Phalaenopsis and Paphiopedilum the animals often sit deep in the leaf sheath. It was observed that often, especially during blossom induction in orchids, which is caused by a drop in temperature, masses of mealybugs occur. This propagation is probably due to the fact that the plants are stressed and are therefore more susceptible to pests and diseases. One reason why the mealybugs are often found at the blossom stalk or on the blossoms is probably the increased concentration of amino acids in these plant parts.
Control
Long-term plant protection has to be considered for chemical control of mealybugs. There is no knockdown effect as for example in aphid control.

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.
Biological plant protection
Leptomastix dactylopii: A small 3 mm long parasitic wasp, very effective to control Planococcus citri. The animals are of yellow-brown colour and are able to jump. High temperatures of at least 24-27 °C are needed for them to develop quickly. In these temperatures a sufficient number of eggs are laid into the third nymph stadium and in adult mealybugs. Much light is required, application in the summer would be ideal. Pseudococcus is not parasitised by the parasitic wasp.

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.

Root and Copra Mites

Hark Orchideen - Schädlinge: Wurzelmilben

Biology
The relatively big root mite Rhizoglyphus echinopus Fum. et Rob. is about 0.7-1.5 mm long, the body is oval and compact, pear-shaped, white and shiny. Legs are brown with strong thorns. Eggs are white, big and are placed on plant parts. High humidity helps the mite to develop more quickly. It lives as secondary pest on roots of already weak or ill plants. It "opens doors" for pathogenic fungi by destroying the roots and also spreads fungus spores. Rhizoglyphus can damage the base of low leaves lying on the substrate. Copra mites of the Tyrophagus family have a compact body, are whitish and very hairy. They often live between the leaf sheaths where mass populations are found frequently.
Damage
Rhizoglyphus feed on root tissue, epidermis and steles remain intact. In damaged plant parts the ducts with the mites in them are visible. Leaves lying on the substrate may turn brown and be destroyed. Tyrophagus can become harmful when mass populations occur and may then also damage healthy plant tissue. Damage on flower stalks, especially of Paphiopedilum looks similar to that caused by tarsonemids, with necrotic stripes. Infested leaves become soft and rot.
Control
Direct control of root mites is only possible to a certain extent; dipping the root ball in acaricide solution makes sense only for valuable individual plants because it is expensive. Multiplication can be avoided by optimal cultivation and strengthening of the roots. Rhizoglyphus can be controlled sufficiently by common acaricides. Natural enemies of root mites and rhizoglyphus that are often found in orchid stands are predatory mites (Hypoaspis sp.) and the larvae of gall midges.
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