Aphids On Plants: Appearance, Origin And Profile
Where do aphids come from? What do aphids look like and how do I recognize an infestation? In our fact sheet, you will learn everything about the different aphid species.
Mostly one speaks of “the aphids”, but we know about 3000 species of which 850 species are found in Central Europe alone. They differ not only in their coloration, but also prefer different host plants. Therefore almost every plant can be attacked by aphids. Everything worth knowing about the probably best-known plant pests can be found here.
Information About The Aphid
Aphids belong together with leaf fleas (Psylloidea), scale insects (Coccoidea), and the moth scale insects (Aleyrodoidea), better known as whitefly, to the plant lice (Sternorrhyncha).
The small insects grow to only a few millimeters in size and show themselves in different colors depending on the species. Most aphids are green, black, or reddish in color. The aphids are usually unwinged, but winged individuals also occur for distribution purposes.
Aphids (Aphidoidea) feed exclusively on plant sap and cannot infect animals or humans. To get at the plant sap, the aphids have a stinging trunk. Most of the plant-sucking aphids are so-called phloem suckers. The phloem is a leading tissue in plants, in which the particularly sugary sap is transported.
However, because aphids also need other nutrients such as protein, they have to absorb an extremely large amount of the plant juice, as there is hardly any protein in it. Most of the sugar is therefore excreted again as honeydew. Besides ants and mushrooms, beekeepers also enjoy honeydew – this is how the well-known forest honey is created.
Besides the food intake, the way of life of aphids is also very interesting. Many aphid species alternate between a winter and summer host. The winter host often only serves as a protection for the next generation of aphids. Usually, only the eggs of the aphids survive the winter. However, if the temperatures remain mild during the cold season, even adult aphids can survive.
After such a mild winter, true aphid infestations of beans, peas, and other herbaceous plants can already occur in early spring. The aphids then start looking for their summer host in spring. To cover longer distances, many aphid species still have wings at this time.
Once a host is found, the way of life often changes. There is a generation change and wingless females are formed, which are capable of producing young. This kind of reproduction enables a very fast reproduction.
This is usually also the time when aphids become a problem for the hobby gardener. Because of the high number of offspring, aphids can weaken and damage plants. If the food source is exhausted, winged females have formed again, which attack plants again.
In autumn, the females lay fertilized eggs that survive the winter and from which a new generation of aphids hatches the following spring.
Where Do Aphids Come From?
Aphids are not only annoying pests but are also often worn unconsciously as amber pendants. The animals trapped in amber show that the pests have been around for over 200 million years. Aphids are spread all over the world and have adapted to a wide variety of conditions.
In the Middle Ages, it was believed that aphid infestation was caused by special rain, the “nephew rain”. Today we know that there are winged individuals who can fly quickly from plant to plant. But from where do the aphids come into our garden?
Since aphids lay their eggs in autumn on specific winter hosts, depending on the species, the animals hatched from them start their search for a summer host in spring.
The black bean aphid (Aphis fabae), for example, likes to spend the winter on Pfaffenhütchen (Euonymus europaeus) or the common snowball (Viburnum opulus), whereas the green peach aphid (Mycus persicae) spends the winter on sloes (Prunus spinosa) or peach trees (Prunus persica).
For this reason, it may help not to plant such winter hosts in your own garden.
Among the hundreds of different species of aphids, there are a few species that are particularly common in our domestic gardens.
Pea Aphid (Acyrthosiphon Pisum)
The pea aphid is a rather large aphid species with a length of two to four millimeters, which, as the name suggests, particularly likes to infest legumes like peas. It usually forms only small colonies and prefers to infest young shoots and flowers as well as pods of peas and other papilionaceous plants (Fabaceae).
The affected shoots and legumes often wither, contain fewer seeds and the yield can drop significantly. This species shows no-host change and lays its eggs in autumn to hardy papilionaceous plants for overwintering.
By the way, research is very interested in this plant pest. The aphids appear in different colors, such as yellow, green, and red, but have the same genetic material. How these different colors come about is a current question in science.
Green Peach Aphid (Myzus persicae)
This is a smaller representative of aphids, with a maximum size of two millimeters. The flightless aphids are colored green, while the flightless generation is black-brown to black. They hibernate, as the name suggests, on a peach tree or sloes.
Potatoes and other herbaceous plants also belong to the summer hosts. The infestation by the green peach aphid is mainly visible through curled and yellowed leaves. When sucking on various plants, the aphids transmit viruses that can damage your plants, even after the aphids have disappeared again.
Black Bean Aphid (Aphis fabae)
This aphid species is a matte black, sometimes dark green aphid about two millimeters in size. They overwinter exclusively on the Pfaffenhütchen (Euonymus europaeus) or the Common Snowball (Viburnum opulus). From there, they attack herbaceous plants such as the field bean, potatoes, and even turnips from spring onwards.
Here, too, the leaves often curl up during an infestation, and viruses are transmitted. The colonies can become very large and therefore cause severe damage to infested plants.
An infestation of a few aphids is not noticeable at all, because they hide quite well under the leaves. Only when mass reproduction occurs, countless little pests can be seen. They are then partly also on the leaves and especially on the freshly formed flower buds and shoot tips.
The plant suckers, which are usually two to three millimeters in size, can lead to deformed and curled leaves in the event of a severe infestation. Due to their sucking activity, they draw a lot of water locally from the plant, and shoot tips hang down.
When aphids suck up the sugary plant sap, they always excrete a large part of the sugar in the form of honeydew. The honeydew attracts more ants, which can be an indication of aphid infestation. If the honeydew falls on lower-lying leaves, a sticky layer forms there, which is also typical for aphids.
Damage Pattern Of Aphids
Due to the sucking activity and thus the withdrawal of sugar, proteins, and minerals, as well as the aphid saliva, infested plants are weakened and fruits or leaves are deformed. This can reduce yield and quality, for example in tomatoes, peppers, lettuce, and cucumbers.
Further damage can be caused to plants by infection with viruses transmitted by aphids. If an aphid sucks on a virus-infected plant, the aphid will also absorb the virus. If the aphid changes the host plant and starts sucking on the new plant, the virus can be transmitted.
This can happen even if only a few animals are infected. Common symptoms of plant viruses are yellow-green, mosaic-like leaf discoloration. But don’t worry: plant viruses are not dangerous for us humans.
On the honeydew excreted, black and sooty dew fungi can form on the leaves. The plant gets less light and is additionally weakened. Harvest material, which is overgrown with these fungi, should not be consumed.
What does the damage of aphids look like?
- Deformed leaves or fruits.
- Possible transmission of plant-pathogenic viruses and therefore resulting in leaf discoloration.
- Black fungus on honey exchange layer on leaves.
With these types of damage, we recommend that you take biological measures as soon as possible to control the aphids. Biological pesticides based on neem oil are a natural and very effective way to get rid of aphids. The herbal agent ensures a quick stop of the aphids’ sucking activity and can be applied easily in the field as well as in the home. Before use, please read the instructions on the enclosed leaflet.
Aphids are particularly common on roses in early summer. Here they can damage the flower buds to such an extent that the flower splendor is in danger.