Gardening

Plant aphids

Plant aphids


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Aphids: what they are


Aphids are the common "plant lice", well known by amateur and professional growers for their predilection for plant sap. This substance is their source of sustenance, but it is also a vital compound for plants, which, after repeated
banquets from these insects can become sick, weaken and die.
Their sizes vary from one to up to four millimeters and can be yellow, green, gray to black.
They go through two phases in life, a winged and an attera (without wings). When they are in the first form, they can easily move from one plant to another and migrate even for enormous distances. In the attera form, they devote themselves almost exclusively to reproduction, which gives rise, through rapid cycles, to an extremely numerous offspring. This is why we find our cultures literally covered with numerous colonies.

Damage to plants



Their mouthparts are of a piercing-sucker type, typical of the commonly called lice, which they use to access the veins of the leaves from which to suck the precious food. While sucking the sap, aphids introduce saliva. Saliva contains some substances, some of which contain a growth hormone. This hormone, by stimulating an abnormal growth of tissues, causes the formation of hyperplasias called "galle" or "pseudogalle". These new formations are used by aphids both as protection and as a source of nutrition.
The sap is a substance very rich in sugars, produced by the green parts of the leaf thanks to the chlorophyll synthesis. Aphids feed on them to excess and the surplus is expelled by the aphids themselves and remains on the surface of the plants, leaving the typical sticky and sugary spots, which are called "honeydew". These substances are also the favorite food of fungi and bacteria, in particular of particular saprophytic mushrooms called "dark mycelium" or "fumaggini".
In addition to the damage caused by vegetable-derived nourishment, a new problem arises, as these fungi filter the solar radiation, decreasing the photosynthetic activity of the plant and further lowering the concentration of nutrients within it.
For the professional grower, this damage synergy has significant economic repercussions, since the plant's products are of much lower quality and must be sold at a lower price.
In addition to fungi and bacteria there are other delicious sugar animals, such as ants. These have a symbiotic relationship with aphids, or they collaborate with each other helping one another. The ants, to guarantee the abundance of sugar on the leaves, help the aphids protecting them from predators and transporting them on the shoots. In this way they use aphids as a real breeding.
Aphids, in addition to ants, have other means of defense, such as the "siphon", an organ located in the abdomen that secretes particular waxy substances that, initially liquid, solidify in contact with air. In this way they trap the unfortunate predator that was attacking the insect. When the aphids are attacked, they produce a particular pheromone that is recognized by the companions as a signal of danger, thanks to which they move away from the dangerous zone.
Plants also suffer from the action of certain viruses and bacteria. Aphids passing from one plant to another can easily become carriers of pathogenic organisms, infecting healthy plants after feeding on a sick plant.
Furthermore, their complex action, in particular the drilling and introduction of saliva, cause physiological alterations that remain over time. The ducts that carry the sap to supply the various apparatus of the nourishment with nutrients may be compromised or otherwise deficient in their function. Consequently the whole plant will suffer in the future, following an intense aggression by aphids and pests.

How they reproduce



Aphids belong to those species of insects that reproduce by viviparity and parthenogenesis. This can be considered a type of asexual reproduction as fertilization is not necessary to originate the embryo. Furthermore, the aphids implement the so-called "boxing of the generations" for which the embryo becomes already formed in the body of the parent and is already able to host a new embryo.
The new unborn babies are called "neanids" and are already able to feed themselves. They face a week-long mute cycle, after which they can already be considered adult individuals.
Females can give birth to three to six nymphs every day, for a cycle that can last several weeks.

Plant aphids: the fight against aphids


Aphids do not tolerate cold climates very much, instead they prefer warm and dry ones. The strong winds and rain are also not tolerated, which disturb the attack on the plant, endangering their survival.
However, they manage to adapt easily to different types of temperate climates, and must above all beware of their predators.
Many pests, including several species of aphids, have developed effective insecticide resistance over time. These have always been the main weapon available to farmers to eradicate aphids. But it was precisely the abuse of these to induce such resistances, thus making them less and less useful. Furthermore insecticides contribute, together with other destructive practices, to the impoverishment of the land with the consequent, enormous, ecological damage.
The last frontier of the fight against phytophagous insects, including aphids, is represented by biological control. It consists of using the predators of such insects to get rid of them harmlessly. But it is not enough to obtain a large quantity of these aphid antagonists, since it would cause a new imbalance. Instead it is necessary to alternate, at different times or in alternate spaces at the same time, crops of plants that naturally attract this fauna.
This does not lead to a total destruction of the insects, but to their reduction in respect of an ecological chain of which they are part.
Among the numerous predators that feed on aphids we find the coccinellids, the dipterans, the anthocorids and the chrysopid neurotters, both adults and larvae. There are also numerous greedy birds of these insects, including swallows, warblers and tits.
The insecticides used are generally based on pyrethrin, but, as already mentioned, it is advisable to use them only in extreme cases.