L’black bean aphid (Aphis fabae) is an insect of the order Rhyncotafamily Aphididaesubfamily Aphidinaetribe Aphidini. Despite its vulgar name, this species of aphid is among the most common and polyphagous, and its infestations affect numerous horticultural crops. It is a plant parasite that causes severe decay and smears the surface of the vegetation.
Its presence in the garden must therefore be monitored carefully and infestations prevented or treated with appropriate biological techniques. Let’s see how.
Description of the black bean aphid
L’Aphis fabae is a small black insect, also known as plant louse. It has several biological forms that often get confused on superficial observation. First there is the form alata virginopare, black or olive brown, 3.9 mm long (2.6 mm without wings). This form is characterized by the abdomen with segments affected by a large median and a lateral sclerification, which are flanked by some very small ones, and with the possible presence of segmental waxy efflorescences.
Then there is the form attera virginopara2,4-2,6 mm long, dull blackish color and abdomen with waxy spots in the dorsal-lateral position.
We therefore have the form sessupara gynoparavery similar to the previous one.
Shape male smaller in size. Finally, the shape amphigonic blackish-brown in color, 2.5 mm long, very short siphons, characterized by posterior tibias with subcircular placoid sensilli.
The eggs are shiny black and very small (0.5 x 0.25 mm).
Plants attacked and spread
The black bean aphid is widespread in all Italian regions.
As mentioned, it attacks many different plant species, both spontaneous and cultivated.
Among the spontaneous ones, often cultivated for ornamental purposes, the presence of Aphis fabae on the spindle (Euonymus europaeus), the snowball viburnum (Viburnum opulus) and philadelphus (Philadelphus coronarius).
As far as cultivated plants are concerned, the most affected by this insect are: the legumes (eg Fava beans, beans, green beansalfalfa), the chenopodiacee (as chard And spinach), the potatothe fennel. Infestations on pome fruit are rarer (Apple tree, However etc), citrus and on vine plant.
Damage to crops
Taking the broad bean as a reference, the colonies of the black aphid infest leaves, flower scapes, flowers and pods. These very dense infestations cause foliar curling, decay and, in the most serious cases, vegetative desiccation and even the splitting of the pods along the suture line.
Then there are the indirect damages typical of aphids, or the formation of honeydew and fumaggine. Even more frightening is the possibility that the bean aphid becomes a vector of persistent viruses, such as the yellow beet (beet yellow) and the curling of the potato (potato leaf roll).
The biological cycle of Aphis fabae
L’Aphis fabae it is a parasite with dioecious and holocyclic behavior. The wintering takes place with durable eggs laid on the primary hosts, namely the aforementioned viburnum, fusaggine and philadelphus. The new founders are born in April and from these originate a descendants of partogenic females (fondatrigenie) that do not need mating to reproduce. After some of these generations, the winged forms appear that migrate to all the other crops, on which more generations of virginogenies follow one another. In autumn the sessupare appear, then the amphigonic ones and, with the deposition of one or more durable eggs by the fertilized female, the annual cycle of the aphid ends.
The antagonists of the black bean aphid
In environments characterized by high biodiversity, aphid colonies are kept under control by natural predatorsin particular larvae and adults of ladybirdslarvae of diptera hoverflies, chrysopids and haemerobids.
How to prevent black bean aphid
To prevent large infestations of black bean aphid, it is necessary to act in time. Once the infestation is widespread, in fact, the measures that can be adopted will be less and less effective. What we recommend is, first of all, to use as a repellent on sensitive crops i natural maceratesfor example the macerated nettle or the garlic macerate, in order to avoid that the parasites establish the new colony on the plants. It is also good to inspect the crops often and carefully, paying attention to the presence of black dots along the stem, near the flowers or under the leaves in order to identify any outbreaks in time.
How to get rid of black bean aphids
We have already seen how eliminate aphids from plants. There are several Organic products usable, and their use is also effective in eliminating broad bean aphids. The most commonly used is the soft potassium soapthat easily found on the market. As the aphids are soft-bodied insects, contact with the soap dries the cuticle causing the parasite to die by asphyxiation. The potassium soap also has a cleaning effect, an important action for cleaning the vegetation from honeydew and fumaggine. As mentioned, the intervention with potassium soap is very effective at the first signs of infestation, but it is much less so on large colonies.
If the infestation is now extensive, therefore, the advice is to intervene with killing products, such as natural pyrethrum (that found here) or azadirachtin (that instead found here).
In carrying out the treatments, make use of a backpack sprayer and be careful to evenly wet the vegetation, especially the underside of the leaves, where the aphids most frequently nest. Finally, always do the treatments in the evening, in a cool place, in order to prolong the wetting time of the plants.
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