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Midge larvae Aphidoletes

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aphidimyza are highly effective predators of aphids.

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and burrow 3/4-1V2 inches into the soil to pupate. Optimal conditions for their development are 73°-77°F and a relative humidity of 80-90%.A.aphidimyza enters diapause under short day conditions.This insect is commercially available.

Chrysoperla (=Chrysopa) carnea— green lacewing. The larvae of these lacewings are known as aphidlions for a reason—they are voracious feeders that can consume up to 425 aphids or other prey per week.The light-green adult lacewings have slender antennae, golden eyes, and large, veined, gauzelike wings that are V2-3/4 inch (1.3-2 cm) long.They are slow-flying, nocturnal insects that feed on nectar and pollen, and emit a foul-smelling fluid from special glands when captured. Female green lacewings usually lay up to 300 eggs in groups on leaves, over a period of 3-4 weeks. Each egg sits on the end of a slender stalk, about V3 inch (8 mm) long, attached to the leaf's surface. Freshly laid eggs are green, but they change to whitish gray as they get close to hatching.

The aphidlions that emerge look like green-gray alligators with mouthparts like ice tongs. An aphidlion seizes its prey, punctures it with its long jaws, then injects a paralyzing venom and sucks out the body fluids. In addition to aphids, aphidlions will feed on a wide variety of soft-bodied insects including thrips, mealybugs, immature whiteflies, and small caterpillars, as well as insect eggs and spider mites.They will also consume each other if no alternative prey is available. After growing to 3/8 inch (1 cm) long during a 2-3 week period,the larva spins a spherical, white silken cocoon in which it pupates, emerging in 5 days as an adult.The adults require pollen in order to reproduce. Green lacewings are available from many commercial suppliers.

Chrysoperla comanche—Comanche lacewing. This commercially available species of green lacewing is closely related to C.rufilabris (below). It commonly occurs in orchards and vineyards at low elevations in the southern parts of Texas, New Mexico, Arizona, and California. Its biology and development is similar to C. carnea, but it is better adapted for development under dry conditions.

Chrysoperla rufilabris. This is another species of green lacewing sold for control of soft-bodied pests, including aphids. It is common in tree crops in the northeastern United States. Its biology and development is similar to C. carnea, but it is better adapted for development under humid conditions than C. carnea.

The distinctive stalked egg of the green lacewing, Chrysoperla carnea.The stalk is about !/3 inch long.

A green lacewing larva,also called an aphidlion,of Chrysoperla comanche.

The distinctive stalked egg of the green lacewing, Chrysoperla carnea.The stalk is about !/3 inch long.

Deraeocoris brevis. This mirid bug feeds primarily on aphids and whiteflies, although it will attack thrips and small caterpillars. Both nymphs and adults are predaceous.The 3/i6 inch (5 mm) long females lay up to 200 eggs in plant tissue. Nymphal development takes 25-30 days, and the adults live about 3 weeks. Optimum conditions are 64°-85°F with 30-60% relative humidity. D. brevis enters diapause when daylength is less than 10 hours and temperatures are below 73°F.This bug is commercially available.

Hippodamia convergens—convergent lady beetle. Adults are the common red lady beetles with black spots on each wing cover. Although they will attack various soft-bodied insects, convergent lady beetles are sold primarily for aphid control. Each will consume as many as 2,000 aphids during its life. Females lay up to 1,500 orange, bullet-shaped, 1/25 inch (1 mm) long eggs in clusters on leaves near the prey.These hatch into tiny, black, alligator-shaped larvae with conspicuous orange markings.They are somewhat slender, with the body tapering to a point at the rear and prominent legs that stick out from the sides.They feed for 3-4 weeks, consuming 500-1,000 aphids or similar prey during their growth.They generally pupate where they were feeding. Hippodamia convergens is one of the most widely available lady beetles in North America.

Other lady beetles. Scientists have examined several species of lady beetles as potential biological control agents of aphids in greenhouses. Introduced at a ratio of one adult lady beetle to 20 aphids, Cycloneda sanguinea larvae controlled cotton aphid on cucumber. In a series of experiments on cucumbers in small greenhouses, the second and third generations of the beetle eliminated the cotton aphid. However, the commercially available Coleomegilla maculata was ineffective against cotton aphid on cucumber because it would not remain on the leaves. Adalia bipunctata and Coccinella septempunctata have been used experimentally in Finland for aphid control on chrysanthemums and roses. Lemnia biplagiata, imported from Vietnam for use in Russian greenhouses, controlled cotton aphid on cucumber and green peach aphid on peppers. Many of these beetles are not suitable for commercial production and only C. maculata is currently available.

A convergent lady beetle, Hippodamia convergens. Lady beetles are voracious feeders, consuming as many as 2,000 aphids in their lifetime.

Lady beetle larva feeding on aphids. Note that some aphids have already been parasitized by braconid wasps.

Macrolophus costalis. This mirid bug was investigated in Poland for controlling aphids on greenhouse crops. It feeds on aphids and greenhouse whitefly larvae and was able to control aphids at predator-to-prey ratios of 1:2 and 1:3. It reduced aphid numbers best when the aphid populations were high. It is not commercially available, although a related species, M. caliginosus, is offered as a predator of whiteflies.

The minute pirate bug, Orius spp., is a generalist that feeds on aphids, thrips, spider mites, whiteflies, and caterpillar eggs,as well as pollen and plant juices

Micromus angulatus. This brown lacewing has recently been investigated as a beneficial insect for the biological control of small, soft-bodied insect pests in greenhouses. Its prey includes small aphids, immature whiteflies, and insect eggs. It has been successfully mass reared in Germany but is not yet commercially available in North America.

Orius spp. Several species of minute pirate bug, which are generalist predators, feed on aphids, thrips, spider mites, whiteflies, and caterpillar eggs, as well as pollen and plant juices.They are also cannibalistic under crowded conditions.The black, 1/i6-3/i6 inch (2-5 mm) long adults are ovoid and somewhat flattened, with distinctively patterned black and white wings.They lay their eggs in leaf tissues with one end of each egg sticking out.The tiny Orius nymphs are pinkish-yellow to light brown. Both nymphs and adults are very active and will feed on small aphids,although they will feed on other prey if available. Several species of Orius are available commercially.

An Orius nymph.

Syrphid or hover flies. The larvae of many species of syrphids can control aphid populations rapidly.They occasionally move into greenhouses from outside, where they are common and important natural enemies of aphids. The adult flies, which are often seen on or hovering near flowers, are small to medium in size (3/8-3/4 inch, or 8-20 mm), often with a striped yellow and black body resembling honey bees or wasps. Females lay eggs near aphid colonies.The slug-like, pale green to yellow maggots feed on aphids, scales, and other insects, growing to 3/8-5/8 inch (10-15 mm) in length. Larvae can consume as many as 400 aphids during their development. Some species pupate on the foliage near the feeding site, whereas others leave the plant to pupate in the soil.The pupa is enclosed within a puparium—the hardened skin of the last larval instar—which is often teardrop-shaped, smooth, and tan colored.The life cycle of most species lasts 2-4 weeks. Syrphid flies are not commercially available.

An Orius nymph.

Pathogens

Beauveria bassiana.This is a common soil-borne fungus that occurs worldwide. It attacks a wide range of both immature and adult insects, including some natural enemies. As with all insect-pathogenic fungi, Beauveria produces spores that are resistant to environmental extremes and are the infective stage of the fungal life cycle. The spores (conidia) infect directly through the outside of the insect's skin. Under favorable temperature and moisture conditions, a conidium (singular of "conidia") adhering to the host cuticle will germinate.The fungal hypha growing from the spore secretes enzymes which attack and dissolve the cuticle, allowing it to penetrate the skin and grow into the insect body. Once inside the insect it produces a toxin called beauvericin that weakens the host's immune system. After the insect dies, an antibiotic (oosporein) is produced that enables the fungus to out-compete intestinal bacteria.

Eventually the entire body cavity is filled with fungal mass.When conditions are favorable the fungus will grow through the softer parts of the insect's body, producing the characteristic "white bloom" appearance. Relative humidity must be 92% or more for B. bassiana to grow outside the insect.These external hyphae produce conidia that ripen and are released into the environment, completing the cycle.This fungus is commercially available.

Metarhizium anisopliae. This insect pathogenic fungus infects over 200 species of insects. It occurs naturally in soils throughout the world. Green, cylindrical spores are produced in chains from infected insects. Because this fungus has a wide host range and infects some beneficial insects, including lady beetles, it may not be compatible with all aphid predators and parasites. However, it is not toxic to plants, honey bees, earthworms, fish, or humans. A formulation of this fungus can be applied like a conventional insecticide, but this is not yet registered for use in the United States on any greenhouse crops.

Paecilomyces fumosoroseus. This insect pathogenic fungus has a wide host range, with several strains infecting insects in over 25 different families, including aphids, whiteflies, thrips, and some natural enemies. Fungal spores bore through the insect's skin. As the spores grow, they consume the insides of the insect, eventually killing the host. External mycelium on infected insects is white at first, then changes to shades of pink.The infected insect eventually becomes light gray when spores are produced on the outside of its body.The infection cycle is very rapid, with sporulation occurring within 72 hours of infection and peaking at 5-7 days.This fungus requires humidity over 90% for infection and germination is poor when humidity is below 98%, which limits its utility.Virulence varies among strains; the most virulent strains are being com-mercialized.This fungus is commercially available in Europe, but is not registered for use in the United States.

Verticillium lecanii.This insect pathogenic fungus infects both aphids and whiteflies.The fungal strain with large spores infects aphids; the strain with smaller spores is specific to whiteflies. Relative humidity over 95% must be maintained for infection to occur. The fungal spores kill aphids by growing through the aphid's skin.The spores continue growing inside the insect, eventually consuming the internal contents. Aphids killed by this fungus remain on the plant, covered in spores. Under the right conditions spores stick to healthy aphids that touch them and initiate a new infection cycle.Vertalec and Mycotal are commercial formulations of the fungus specific to aphids that are available in Europe.They are not currently registered for use in North America.

The fungus Metarhizium anisopliae infecting a green peach aphid.

Possibilities for effective biological control

Aphids can be effectively controlled by several commercially available natural enemies, released singly or in combination. Aphid populations can increase very quickly, so it is best to release natural enemies while populations are low. If more than 10% of the plants are heavily infested,you should reduce aphid populations before you release parasites or slower-acting predators. Use either nonresidual chemicals (insect growth regulators, soaps, oils, etc.), or predators, such as green lacewing larvae, that will quickly eat large numbers of aphids.

Aphidoletes aphidimyza has been used successfully for biological control of aphids on cucumber, green pepper, tomato, chrysanthemum, rose, and many other ornamentals on a commercial scale. Unlike other predators, this midge reproduces during the growing season, so only a single release may be necessary, although two to four introductions are often required.A.aphidimyza may be more useful in a biological control program for aphids on greenhouse crops than lady beetles or green lacewings. However, many aphids killed by midge larvae remain attached to the leaves, which may detract from the value of ornamental plants.

Aphid midges are shipped as pupae (inside their cocoons) in moist vermicu-lite. Sprinkle the vermiculite with the cocoons on moist soil or root medium within the plant canopy. Adults will not emerge from cocoons that fall on dry areas in direct sunlight.The bright orange midge larvae should be visible among the aphids about a week after the adults have emerged.The adults hide beneath the leaves during the day and are active at night. Optimal conditions are 68°-81°F and 50-90% relative humidity. Recommended release rates vary depending on the plant type, growth stage, aphid species, and infestation level. Lower release rates may be used before aphids are observed for preventative control.Weekly or biweekly releases of one or two pupae per plant, or up to three pupae per 10 ft2,or 2,000-6,000 pupae per acre are successful for controlling aphids on most plants. Two to four applications are often necessary to achieve control. Additional introductions of the midge will not be necessary if successive generations are produced during the growing season. If aphids can be tolerated on the lower leaves of the plants, the midge populations will build up quickly on the supply of aphids.

Biological control of aphids with A. aphidimyza is most successful in greenhouses with soil beds or gravel floors, probably because the midge larvae easily find suitable sites for pupation. Sprinkle a thin layer of sawdust or peat moss between the rows on concrete or plastic-covered floors to provide suitable pupation sites in these green-houses.Without proper pupation sites on the floor, fewer midge offspring survive, and weekly releases may be necessary throughout the season to provide adequate control.

Aphids

Enemies

Parasitoids

Aphidoletes

Green lacewings

Deraeocoris

Lady beetles

Macrolophus

Minute pirate bugs

Syrphid flies

Beauveria

Metarhizium

adult

Natural enemy attacks the host

Effectiveness depends on species of enemy adult egg egg

Paecilomyces

The midge can also be introduced from open rearing units or banker plants placed in the greenhouse. Aphid species that do not infest commercial greenhouse crops—such as the grain aphids Sitobion avenae, Metopolophium dirhodum, and Rhopalosiphum padi—are used as prey for A. aphidimyza.Place these aphids on wheat or barley plants (the banker plants) in open trays or boxes.The predators develop on these aphids, and the adult predators disperse to lay eggs on infested crop plants.The rearing units must be established early in the growing season and maintained for several weeks so that a large midge population has developed by the time pest aphids appear.This is not a practical method in large commercial greenhouses, but boxes containing growing barley with grain aphids can be purchased from some suppliers for this use.

One drawback of A.aphidimyza is that it enters into diapause under cool, short-day conditions. Diapause can be prevented by leaving on a few incandescent walkway lights all night during winter months (through late February). Larvae are very sensitive to light, so a single, 100-watt bulb will prevent over half of the midges within a circle with a diameter of 24 yards from diapausing. This will not be effective when plants are so large that light does not penetrate between the rows. If supplementary lighting to prevent the midges from diapausing is not feasible, and aphids are a problem in the fall or winter, other natural enemies, such as the parasitic wasp Aphidius matricariae,can be used for aphid control.

Because Aphidius matricariae does not diapause under winter greenhouse conditions as readily as A.aphidimyza, it can be an important part of a biological control program from fall through early spring. On chrysanthemum, green peach aphid has been controlled within 2 months of planting when the wasp was introduced in parasitized aphids, packaged in boxes of rooted cuttings (50 aphids per box of 500 cuttings). It is not as effective against cotton aphid as it is against green peach aphid.

A.matricariae performs best when it is established in the greenhouse early in the growing season. Native A. matricariae entering the greenhouse from outside sometimes become established and provide effective control. However, in the spring and summer these wasps are frequently attacked by their own native hyperparasites, which reduce the natural or introduced A.matricariae population. Adult A. matricariae are attracted to the color yellow, so yellow sticky cards should be removed before releases are made. A release rate of two per 20-800 ft2 is recommended. It is effective when aphid populations are low, but should be used in combination with other natural enemies when populations are high.This wasp is not compatible with insect pathogenic fungi such as V.lecanii which kill the parasite larvae inside the aphid.

Diaeretiella rapae can be as effective as A.matricariae.It has eradicated green peach aphid on chrysanthemum in 6 weeks when released at a rate of one parasite per 500 aphids. Release rates vary by aphid species and stage of infestation and should be determined on an individual basis.

Aphidius colemani is a very promising candidate for biological control in greenhouses because of its high reproductive potential, short development time, and ability to parasitize several species of aphids, including cotton aphid, melon aphid, and green peach aphid. It is more efficient at parasitizing cotton aphid on cucumber than A.matri-cariae is.

Aphidius ervi and Aphelinus abdominalis are two other commercially available wasps that can be utilized against certain aphid species.A. ervi is most effective against potato and foxglove aphids when released before aphid populations build up. It should be released at a rate of about 0.15 adults per 10 ft2 every week. If aphids are already present, suggested release rates are 0.5 per 10 ft2 and introductions should be made every 3 days if aphid populations are high.A. abdominalis, another good parasite of potato and foxglove aphids, should be released in infested areas only since this wasp is not very mobile. Make weekly introductions of two to four adult wasps per 10 ft2 depending on aphid population density until 80-90% of the aphids have become black mummies. After that time small quantities can be released.

Many general predators, such as lady beetles, lacewings and hover flies, also provide effective and rapid control of large aphid populations. Adults lay eggs only near large numbers of aphids. However, most species will not reproduce in the greenhouse. In order to obtain control you must release them every 2-3 weeks.

The convergent lady beetle can suppress high aphid populations quickly, but establishing a population in the greenhouse is difficult.Thus, convergent lady beetles are used most effectively to reduce high aphid populations that can then be kept under control by other predators, parasites, or pathogens. Most commercially available convergent lady beetles are not insectary-reared, but are collected from winter hibernation sites. Only when their stored winter fat reserves have been depleted will they become predaceous. Even then, after consuming many aphids, lady beetles often fly to the vents and leave to lay eggs outside.These beetles may also be parasitized. Repeated releases of convergent lady beetles are often necessary. Determine release rates on a case-by-case basis. Make releases in the evening, because bright sunlight encourages their flight. Keep the vents closed or screened to prevent the beetles from leaving the greenhouse.

Green lacewing larvae have controlled aphids effectively on green pepper, parsley, chrysanthemum, snapdragon, and many other kinds of ornamentals. In an experiment on snapdragon, the flower quality of plants with aphids controlled by green lacewings equalled the quality of flowers produced with chemical applications. Lacewings are most effective at high aphid densities, eliminating large aphid populations or reducing them to such low levels that additional control is often not necessary. The effect of a release will be apparent in 1-2 weeks. If additional control is necessary, the next release should be delayed until the larvae from the previous release have finished their development so

Lady beetles can be good predators of aphids

these aphidlions do not eat the new lacewing eggs or larvae.Where aphid densities are low (four or fewer per plant) lacewing larvae are not effective, and the parasite Aphidius matricariae, which is more effective at low aphid densities, should be used. However, if this wasp is released while lacewing larvae are still feeding, the lacewings may consume parasitized aphids, thereby reducing the wasp population.

The number of lacewings needed for effective control depends on the crop, the growth stage, the aphid species, and the degree of infestation. Releases should be initiated early, when aphids are discovered on a few plants.You can achieve control at higher aphid densities, but the number of lacewing eggs needed is very high.Suppliers usually make recommendations based on specific situations. For control of moderate aphid infestations, 5-10 lacewing eggs per plant or 1,000 eggs per 200 ft2 are recommended. Release recommendations for larger areas start at 5,000 per acre for each application.These insects are extremely effective, but cannot multiply in greenhouses and must be released at regular intervals—about every 2 weeks.

Green lacewings are usually sold as eggs but also may be sent as larvae or adults. Eggs are sent in a packing material to cushion and separate the emerging larvae during shipment.The material—rice hulls, wheat bran, or corn grits, along with moth eggs for food so the larvae will be less likely to eat each other— also makes it easier to distribute the very tiny eggs evenly. Lacewing eggs can also be mixed with Biocarrier,a material that helps to glue eggs to plants or containers.This is especially helpful in making applications in hanging baskets.

The lacewings should be released as soon as they begin to hatch. Releases are made by sprinkling the contents of the container onto infested plants.The newly hatched larvae will be very tiny (about the same size as the eggs) so you may have difficulty seeing them.The released aphidlions will travel a considerable distance, up to 100 feet, in search of prey. Making releases early in the morning or late in the day when it is cooler, or on a cloudy day, increases the chances the lacewings will survive. Larger larvae, which consume aphids at a faster rate than newly hatched larvae, are available from some suppliers. Because they are cannibalistic, lacewings purchased as large larvae must be shipped in individual containers which increases the cost of the product. Lacewings released as pre-fed adults that are ready to lay eggs can fly away upon opening the shipping container, so greater care must be taken when releasing lacewings at this stage to ensure their establishment in the infested area.

The commercially available mirid bug Deraeocoris brevis can also be used to control aphids. Since this insect can survive on pollen if prey are scarce, including some pollen-producing plants, such as pepper, may help retain the insect in the greenhouse.The bugs are shipped as adults with some nymphs present. Release rates should be provided by the supplier.

Several natural enemies of aphids that are not commercially available in the United States have been investigated in Europe.The parasites Aphelinus flavipes, Ephedrus cerasicola, and Lysiphlebus tes-taceipes, and the fungus Verticillium lecanii show promise as effective biological control agents against aphids in greenhouses. Aphelinus flavipes is most effective at cooler temperatures, so the parasite can overtake a slow aphid population increase. A high parasite-to-host ratio and early introduction are necessary for reliable control. A.flavipes was only able to control cotton aphid on cucumber when the parasites were introduced before or at the time of aphid infestation.

Ephedrus cerasicola was considered better than A. aphidimyza in Norway, although control by both species was similar, because (1) it does not diapause and therefore provides control throughout the season, (2) it can be introduced at lower aphid densities, and (3) fewer individuals need to be released.When E. cerasicola was released early in the season, it kept green peach aphid populations on peppers below damage thresholds and eliminated the aphids within 2 months.

These wasps are released as pupae inside aphid mummies.Mummies can be placed among the plants or introduced on banker plants in a cage in the center of the greenhouse. Parasite-to-host ratios of between 1:5 and 1:10 are probably sufficient.Two introductions at 10-day intervals of four mummies per plant should be effective when there is less than one aphid per plant. At higher aphid populations, a single introduction of one mummy per 10 aphids should suffice. New introductions may not be necessary because this wasp will multiply in the greenhouse. However, if the aphids begin to increase or the parasite dies out, additional releases should be made at the same ratio.

The aphidiid Lysiphlebus testaceipes has been released outdoors in Mediterranean areas for control of several aphid species and is being investigated for control of cotton aphid in greenhouses. It has considerable potential for biological control, but because it does not parasitize green peach aphid well, an additional parasite might be needed to assist in control.

Several brands and formulations of the fungus Beauveria bassiana are available for use in greenhouses. Because it takes 3-7 days to kill an insect with B. bassiana, it will take some time to suppress the pest population when using these products.Thorough spray coverage is essential because fungal spores must contact the insect for infection to occur. This fungus is more tolerant of lower humidity than many other insect pathogenic fungi, so high relative humidity is not necessary for infection to occur.This fungus is susceptible to some fungicides, so chemical fungicide applications should not be made within 48 hours of B. bassiana applications.Three to five applications may be necessary to achieve control.

Although Verticillium lecanii is not available for use in the United States yet, this fungus may eventually be registered and provide effective control of some species of aphids here. Under the appropriate conditions, it has the potential to eliminate the need for insecticide applications for aphid control. V. lecanii effectively controls most aphids, including green peach aphid, but does not control chrysanthemum aphid. A single spray of V. lecanii was sufficient to control green peach aphid on chrysanthemum, but the fungus did not control chrysanthemum aphid on the same plants.The cotton aphid often escapes contact with the spores because it does not move around much. Only 80-90% control of cotton aphid can be expected. Plants should be treated when small to keep the aphid population under control. Otherwise, the fluffy white aphid bodies stuck to the mature foliage will make the plants commercially unacceptable. The fungus also kills A.matricariae and whitefly parasites inside the pest body, but it seems to be compatible with parasites of other pests, such as the eulophid wasp, Diglyphus begini,that attacks leafminers.

V.lecanii is applied as spores suspended in water for spraying. High humidity is necessary for spore production and infection.When humidity is low, the performance of the fungus is unpredictable. Humidity can be increased by dampening the plants with water sprays. Late afternoon applications reduce spore injury by ultraviolet light and desiccation, since the greenhouse is more humid at night. Alternating two nights of fogging—to produce the elevated humidity necessary for infection—with two nights of ambient conditions may provide an adequate environment for control. However, this fungus may be practical for use only in humid areas with moderate temperatures, such as rooting benches and shade-cloth covered areas used to induce inflorescence in chrysanthemums. Repeated applications of V. lecanii will be necessary if humidity is not high enough to allow continuous infection.This fungus may be susceptible to some fungicides.

If aphids are numerous, other means of reducing their numbers (such as releasing lacewing larvae or chemical control) must be used before treatment with V.lecanii.Two to 3 weeks are required to control an aphid population. If after 3 weeks of treatment less than 90% of the aphids are infected by the fungus, you should employ other means of control.

Other fungi, such as Metarhizium aniso-pliae and Paecilomyces fumosoroseus, may also provide effective control of aphids if these products become available in the United States. In lab experiments, Russian wheat aphid was more susceptible to P. fumosoroseus than to B. bassiana.

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