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Aphids - Who they are, how they live and how to fight them

Aphids - Who they are, how they live and how to fight them


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PESTS AND DISEASES OF PLANTS

Aphids

SCIENTIFIC CLASSIFICATION (1)

Kingdom

:

Animalia

Subphylum

:

Arthropoda

Phylum

:

Entome

Subphylum

:

Chelicerata

Superclass

:

Hexapoda

Class

:

Insecta

Order

:

Rhynchota

or

Acarina

Suborder

:

Homoptera

or

Acarina

Section

:

Sternorrhyncha

Superfamily

:

Aphidoidea

Common name

: plant lice aphid

GENERAL CHARACTERISTICS

Aphids are insects known as plant lice which infest almost all ornamental plants, both indoor and outdoor, as well as crops of agricultural interest.

The adults, from one to four millimeters long, are covered with a thin integument of light yellow or green, or gray, or black color. Some forms are winged so they can migrate from one plant to another, reaching new plant hosts up to hundreds of kilometers away. The non-winged (atherous) forms, on the other hand, after having lost their wings, concentrate all their resources in reproduction, thus giving life in a short time to very crowded colonies.

They have a mouthparts perforating-sucker with which they feed on the sap of plants; at the same time they introduce two types of saliva into the plant tissues: one that contains coagulating substances that isolate the buccal stylets from the plants and the other, rich in enzymes, among which there is a hormone that stimulates the growth of green tissues, thus inducing the formation of hyperplasia (galls and pseudogalle) which serve to protect colonies and provide nourishment.

The sap that the mites feed on is very rich in sugars, the surplus is expelled in the form of honeydew, thus staining the vegetables with sugary drops. Thus, dark mycelium funghisaprofytes develop, the so-called fumaggini (photo below) which can hinder the photosynthetic activity of the plant and commercially depreciate the fruit.

Honeydew (aphid droppings) is a food source for many insects (photo below), also useful, such as bees, hoverflies and chrysopids. In the course of evolution, a real mutualistic symbiosis was established between aphids and ants, which in many respects is similar to the breeding of domestic animals by humans. In fact the aphids provide the honeydew of which the ants are very greedy and these in exchange "cure the livestock" by transporting the various individuals on tender shoots and defending them from predators, even if many species of aphids are able to defend themselves.

Aphids are therefore able to defend themselves from predators through a particular organ called siphon placed in the abdomen, waxy substances are emitted which in contact with the air solidify thus trapping the predator. In case of danger they are also able to emit an alarm pheromone that causes the members of the colony to flee.

HOW THEY REPRODUCE

Aphids have a great evolutionary success thanks to the formidable reproductive capacity and a whole series of cunning strategies, such as viviparity and parthenogenesis that allow the so-called "boxing of generations" for which a female has already formed daughters inside. before they are born, they in turn contain other developing embryos. The newborn nymphs can be fed immediately; they grow rapidly and within a week, after four mild weeks, they reach the adult stage. In addition, females can give birth to three to six nymphs per day for several weeks.


Aphid giving birth


Aphid giving birth

In temperate climates, cycles with parthenogenetic reproduction only prevail (the eggs are fertile even if mating has not occurred between individuals of different sexes), while in the cold ones before the unfavorable season mating takes place and durable, capable eggs are laid. to withstand adverse weather conditions.

CONDITIONS FOR DEVELOPMENT

The climatic factors that can contain aphid populations are rain, strong wind and low temperatures. They are in fact favored by the heat and a dry environment.

Aphids have great adaptability, especially in temperate climates. Plants can be attacked by different species, more or less frequent and dangerous, oliphagous or polyphagous (which feed on a few or many species), often able to become resistant to insecticides. Fortunately, these pests have numerous natural enemies and it is on these antagonists that they rely on to contain infestations below the economic damage threshold in biological control programs.

PLANT SYMPTOMS

Aphids in addition to causing direct damage with the subtraction of the lymph and with the emission of saliva that causes physiological alterations, produce serious indirect damage as they are capable of transmitting many viruses by feeding on infected plants first and then moving on to healthy ones.

BIOLOGICAL AND CHEMICAL CONTROL

In nature, aphids are controlled by numerous predators and parasitoids.Among the predators there are entomophagous insects that often lay their eggs near aphid colonies such asladybird beetles, both adults and larvae; larvae of diptera hoverflies and caecidomids; adults e chrysopid duckweed larvae; youth and adult stages of antocoridi and various birds such as thetit, the blackcap, the swallows and others. Among the parasitoids we have the Hymenopterafidids, aphelinids etc. whose larvae develop inside the parasitized aphid (recognizable by the dark color of the body).

If you detect an attack in your house plants, you can intervene with aficidi allowed in the context of organic production such as products based on pyrethrum and rotenone. The first comes from the plant Chrisanthemum cinerariaefolium, the second from Derris elliptica and other tropical legumes. In any case, both products must still be used with maximum caution and attention as, especially rotenone is toxic. In reality, however, both products are not always effective as they act by contact and therefore in order to act they must reach insects, which is not always possible. In fact, in these treatments it is always recommended to ensure excellent wetting of the vegetation.

If the infestation is not particularly high, you can spray the plants with water added with Marseille soap in flakes. In this way the aphids detach and move away from the plant.

Note

(1) The views on the evolution of insects are often in contrast with each other and subject to continuous revisions. The same classification of the Arthropods is unstable and the subject of often fruitless controversy. The last relevant classification (Scudder et al. 1979) is reported here mainly for the purpose of scientific curiosity, at least from our "applied" point of view. (E. Tremblay - Applied Entomology, Vol. II, part 1, 1983)

Video: Green lacewing larvae vs. bird cherry-oat aphid