A number of species of aphis are to be met with under glass; on cyclamen, Myzus persicae (the Green Peach Aphis) and, in the last few years, Aphis gossypii (Cotton Aphis) are damaging pests.
They attack the young leaves, and can develop unnoticed at spectacular speed.
They are also liable to transmit any of over 40 viruses, including CMV and TMV.
This pest can be effectively controlled by means of specific insecticides.
Natural predators of aphides, such as some midges and ladybirds, give satisfactory results.
The aphides are a large insect group, forming a superfamily, Aphidoidea, in the suborder Homoptera of the order Hemiptera.
A number of species of aphis are encountered under cover (glasshouses, polytunnels, &c.), depending on the plants grown and the consequent physical circumstances. The best known cyclamen pests are Myzus persicae (the Green Peach Aphis), Macrosiphum Euphorbiae (Potato Aphis), Aphis gossypii (Cotton Aphis), Aulacorthum solani (Glasshouse Potato Aphis), Nasonovia ribis-nigri (Lettuce Aphis), Aulacorthum circumflexum (Greenhouse Aphis), all of which feed on more than one kind of plant.
Aphides feed mainly on sap from leaves and young shoots. The damage they can do to plants is enormous because of their enormous reproductive capacity. They are also a well-known vector for viruses.
Aphides have a comparatively complicated life cycle, with many cases of polymorphism. Depending on circumstances, the adults may be either winged or wingless. The essential point is that the aphis feeds at all stages of its cycle. A number of variables affect the time taken to develop, but, to cut a long story short, under optimal conditions a few days are enough. Immediately upon hatching the larvae feed on sap, like the adults. They shed their skin a number of times, leaving tiny white husks on the leaves. Whether the adults have wings, which is how they spread from plant to plant, or not is determined by population density on the plant. In glasshouse conditions, reproduction is essentially asexual: females produce only females. Individual aphides can produce 3 to 10 more aphides a day over many weeks. The females produce eggs which can over-winter, but the eggs can also hatch while still inside the mother, so that she gives birth to live aphides. This is what makes reproduction so rapid.
Adult and nymph stages of aphis are piercing and sucking insects which extract sap from growth areas of plants. They insert their mouth stylet into the plant’s sap vessels and absorb the contents.
The stylet is a twofold tube: one channel injects saliva while the other is for the sap. The aphis will sometimes make a number of trial pricks to taste the sap and assess its nutritive value: this extraction upsets the transmission of growth hormones and slows down plant growth and development. Leaves curl up; and to make up for the deficit in some areas, the plant distributes a greater quantity of minerals, which is good for the aphides.
The sap made by the plant is rich in sugars but has little protein, which is what the aphides like best: they will consume a great quantity of sap in order to get enough protein. The sugars are regurgitated and build up on the leaves and stems as a nectar, which reduces photosynthetic production and is unsightly on an ornamental plant such as cyclamen. Moreover it is an invitation to moulds, such as Cladosporium spp. Lastly, the aphis’ saliva contains toxins.
Aphides can also transmit viruses and harm plants by poisoning them.
Damage on leaves caused by aphides
Where cyclamen are grown aphides are generally wingless. When food runs short, winged versions appear spontaneously in the population and migrate to colonise new hosts.
This aphis feeds on many types of plant, so that it can remain on weeds, even in an empty glasshouse. Under cover it can exist in winged or wingless form.
The adult Green Peach Aphis is 1.2 to 2.5 mm long, normally grey-green or yellow-green, but also sometimes pinkish-reddish. The winged version has a green abdomen with a black spot on its back. The thorax is black and there is a pair of long, translucent wings. The wingless version is a bit smaller, light green with small siphunculi (‘horns’) and a shorter tail than the winged one.
Under glass a Green Peach Aphis population consists of a series of generations which overlap, of adults and 4 larval stages. The form which predominates here is the parthenogenetic. The biology of this aphis is affected by temperature: at around 25ºC (77ºF), the adult lives 10 days, and the larval stages 7. The reproduction rate is very high.
Among aphides, the Green Peach Aphis is the foremost carrier of viruses (for instance, CMV).
The Cotton Aphis is a world-wide pest, though it prefers hot climates. Only in the last few years has it begun to attack plants grown under glass in Europe.
In Europe there is no fixed annual life cycle for the Cotton Aphis, and it does not migrate from plant to plant. Its colour varies from yellow to green, tending to black, and it measures 1 to 2 mm, with red eyes, antennae shorter than its body, and a short tail. It has ‘horns’, which are always black. The adults live for 2 to 3 weeks, producing 3 to 10 aphides a day.
Damage may start to be seen from the beginning of March. The features of the attack are similar to those of other aphides: extraction of sap, secretion of nectar, secretion and injection of toxins into the plant. This aphis however may transmit any of 44 different viruses, including TMV.
The black aphis prefers the underside of leaves, young shoots, and young leaves.
The adult Potato Aphis is almost 4 mm long, and most often green, though it can be yellowish or pink. It has green ‘horns’, a tail, and red eyes. The antennae are considerably longer than the body.
This aphis is extremely mobile.
Both winged and wingless adults are 1.8 to 3 mm long. The winged version has a dark green head and thorax, antennae longer than its body, and a medium length tail: it has no sexual stage. It causes curling of the tips of the plant, and its saliva is poisonous.
The wingless version is pear-shaped, greenish yellow and shiny, with darker patches at the base of the ‘horns’, which are long and thin with a fringe. The antennae are almost as long as the body.
This aphis usually disappears in summer.
This species is an important virus vector. Winged and wingless versions are both from 1.2 to 2.6 mm long, whitish to greenish yellow and shiny. The abdomen has black, horseshoe-shaped markings.
The antennae and legs are clear and elongated.
They have ‘horns’ and a tail, also clear and elongated.
The larvae look the same as the adults, without the black abdominal markings.
Reproduction is entirely parthenogenetic and can continue throughout the year.
They attack flowers and leaves.
Since aphis development is so swift, any control measures used must be deployed as quickly as possible.
Keeping the glasshouse free of weeds means no alternative hosts are available. Fine nets may also be set up at ventilation level to keep down the number of winged adult pests that get in.
Depending on the situation, biological control methods may be used as prevention or cure.
Midges are in the Cecidomyiidae family of the order Diptera. Although there are some species that themselves attack plants, there are also 5 that feed on aphides, of which the best known is Aphidoletes aphidimiza, currently used against over sixty aphis species.
The female midge mates and then lays her 100-150 eggs, oval in shape, 0.3 mm long and a shiny orange-red. She lays during the night or at dawn, choosing the underside of leaves with a large aphis population; sometimes she lays on the aphides themselves. The larvae when they hatch are a transparent orange, 0.3 mm long, and it is these which feed. When fully grown they measure 2.5 mm and can be clearly seen among the aphides.
The aphis has no defence: the larva injects a poison into its body, which paralyses it and its body contents dissolve in a few minutes. The larva then consumes this solution: the dead aphis hangs from the leaf by its beak and turns brown before decomposing. One larva can eat from 10 to 100 aphides.
The larvae then turn into nymphs, in the ground when possible. The emerging adults are 2.5 mm long, with long thin legs and a wingspan of 2.5 to 3.5 mm. From egg to egg, the cycle takes about three and a half weeks (at 21ºC (70ºF)). They are only active at night or at dawn or dusk: during the day they hide in sheltered parts of the plant. They live for around ten days.
The preparations sold are:
They should be introduced in small numbers as a preventive measure, and then in massive quantities if and when the first aphides are observed.
The midges are supplied as cocoons, in bottles. Recourse to this predator is recommended once the aphides have already formed a number of colonies and there is visible damage.
These are insects with membranous wings (order Hymenoptera) of the sub-family Aphidiidae in the Braconidae family.
As the females go hunting for aphides, and as the male midges hunt for females, the aphides go mad, emitting an alarm pheromone which causes panic throughout the colony. As a result, the aphides fall to the ground, where they finally die.
The female midge pierces the aphis with her drill in order to lay her eggs. The four larval stages develop inside the aphis, up to the nymph stage, at which point the larva spins a cocoon. The adult Aphidius develop there, inside the aphis, until the aphis is immobilised and swells up, turning chestnut-coloured. The adult parasite leaves this mummified aphis by cutting a kind of removable lid.
Adult male Aphidius have a rounded black abdomen with red-brown legs and long antennae.
The females are long and thin with the same coloration as the males.
Aphidius colemani colonises various aphis species including Myzus persicae and Aphis gossypii. It does not go for Aulacorthum solani.
The commercial preparations are:
These products may be used on ornamental plants under cover.
Aphidius colemani is recommended as a preventive treatment when there are few aphides about. Introduce them as soon as aphis is seen.
Aphidius erviis a parasite of Aulacorthum, Myzus persicae and Macrosiphum euphorbiae on vegetables and ornamental plants. These parasites are sold commercially as:
They should be introduced as soon as the first aphides appear.
The target aphides do not die immediately. When the parasites have been introduced, the aphides have a tendency to eat more; and they are still liable to transmit viruses.
Affected aphides are also still able to have offspring.
Verticillium lecanii is a common mould which attacks arthropods. There are some strains which are particularly effective against aphides, and highly selective. There is a commercial product, Vertalec, which contains spores of these.
This is another parasite of Macrosiphum euphorbiae, but does not go for Aulacorthum solani. The female lays her eggs inside the aphis. Larval development and nymphosis produce mummification and death of the host insect: the mummy turns blackish, and out of it emerges a new adult Aphelinus.
This parasite is sold as:
Preventive introduction is necessary so as to have a good number of predators once the aphides are present in swarms.
Convergent ladybirds (Hippodamia convergens) are carnivorous predators, and may be introduced where aphides have made a home. Both larvae and adults eat them. The commercial preparation is known as Aphidiama (not listed in the ACTA Index 1997).
Larvae of the Common Green Lacewing Chrysoperla carnea have a diet that includes aphides. There are commercial preparations under the names:
Preventive introduction is necessary, followed by release of larger numbers when aphides are present.
Hoverflies may also be used as a biological control. The maggots of certain hoverflies catch aphides with their small chitinous mouthparts and eat them whole.
A number of insecticides are currently recommended against glasshouse aphides.
The constant development of the regulations and homologations of phytosanitary treatment products, and the differences in regulations according to each country make it impossible for us to include updated information on homologations. Each producer will have to contact his local plant protection bureau to obtain the latest updates concerning the regulations and use of phytosanitary products. We strongly advise testing beforehand on a plant sample in order to measure the chemical’s activity (establishing the dose) and any effect on the plant (plant poisoning).
2565, rue de Montourey
83600 Fréjus - France
International telephone : +33 (0)4 94 19 73 04
Switchboard : + 33 (0)4 94 19 73 00
Fax : +33 (0)4 94 19 73 19