We often talk about plant lice but the correct name for these pesky creatures that create problems for our home vegetation, and it is not aphids. These are rather small insects that focus their destructive attention above all on ornamental plants without getting too many problems whether they are from inside or outside. This does not mean that plant lice are not affected by those used in agriculture.
Plant aphids: characteristics
When I talked about small insects, I wasn't kidding. These lice can be long from one to four millimeters, therefore it is almost difficult to see them with the naked eye. They can have different colors, from light yellow to green, from light gray to black, and are covered with a thin integument.
There are different types of plant aphids, some are wingless, called hateful, they are like this because they lose them and they are very fast in the reproduction process coming to give life to very numerous colonies. The forms with wings, and which preserve them over time, are instead feared because they can pass much, too much, easily, from one plant to another and not only a few meters but also hundreds of kilometers away.
For feed on plant sap to which they attach themselves, these animals are equipped with a piercing-sucking mouth apparatus. When they come into contact with plant tissues to eat them, at the same time they are also able to enter their saliva, indeed, even two types of saliva.
The first has the characteristics of a coagulating substance and isolates the mouth stylets from the vegetables. Type 2 saliva is very rich in enzymes, therefore also of the hormone that stimulates the growth of green tissues. This encourages the formation of hyperplasias that nourish the colonies and protect them.
When plant aphids feed on sap, they take in a significant amount of sugar, sometimes more than needed. In this case, the excess sugars are excreted in the form of honeydew, one sugary substance which forms real droplets on the leaves and stems of the plants under attack. Always for the same mechanism, gods can also develop saprophytic fungi with dark mycelium, called fumaggini, which damage the fruits, often making them unsaleable and which block or disturb the photosynthetic activity of the plant.
It's not over! When honeydew is formed on plants, it attracts many other insects that eat it, including for example some useful and harmless beings such as bees, hoverflies and chrysopids. Of note, however, is the mutualistic symbiosis that has formed between plant aphids and ants. How does it work? The former produce the honeydew with which the ants feed themselves and the ants, in turn, to deserve this delicacy, carry these lice around, from one shoot to another.
The ants often help aphids to defend themselves even if to tell the truth they know how to defend themselves through the siphon, an organ in their abdomen that is able to produce and emit waxy substances that trap the predator as they solidify as soon as they come into contact with the air. When an aphid spots a predator, in addition, it raises the alarm to alert the entire colony by emitting a pheromone that causes them to flee.
Plant aphids: symptoms
When an attack by these lice is in progress, the lymph is taken directly from the plants, but not only that.When the saliva is introduced into the plant tissues, some heavy physiological alterations which produce serious indirect damage. This is because precisely in the saliva of aphids there can be many viruses that they carry from one plant to another, infecting all those that have remained healthy.
Plant aphids and biological control
To counteract the attacks of these lice it is possible to use gods biological means, this means that one goes to ask for help from other creatures of the animal kingdom who eat it. In particular, I refer, for example, to predators and parasitoids such as entomophagous insects that often lay their eggs near aphid colonies.
In the category of predators we find the coccinellida beetles, diptera hoverflies and cecidomids; the chrysopid neuropterans; anthocorids and various birds such as tits, blackcaps, swallows and others. Among the parasitoids, on the other hand, we have the Hymenoptera aphidids and the aphelinids.
In practice, how is biological control carried out? Once a attack of aphids we can use organic pyrethrum-based products deriving from the Chrisanthemum cinerariaefolium plant, or rotenone-based products deriving from Derris elliptica and other tropical legumes.
Both pyrethrum and especially the rotenone, they are toxic substances so we must be very careful when handling these products which usually act by contact. To make them more effective it is better to make sure that the treated plants are wet at best.
If the situation is not dramatic, you can also act by spraying water added with Marseille soap in flakes on the plant that will detach and remove the aphids from leaves and stems.
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