Trialeurodes Vaporariorum – Bemisia Tabaci
The white fly (T. Vaporariorum) and more recently the Bemisia Tabaci have become amongst the most dangerous phytophagous in greenhouses both for the great polyphagia and for their high reproductive capacity, finding in the warm-moderate areas and in greenhouse environments, optimal conditions for their development.
The insect improperly defined together with the B. Tabaci is considered to be of Central American origin. The adult measures about 1 mm. It has a wax-like body similar to white powder, which gives the insect its characteristic white-yellow appearance. The female is bigger than the male, and it lays the eggs in short stalks, on the undersides of leaves in groups from 20 to 40.
Initially the eggs have a clear yellow colour, but after a couple of days purplish.
The whole biological cycle occurs on the underside of the leaf, and is divided into 7 stages; the cycle includes 4 nymphs stages, an intermediate stage called pupa, during which ocular red spots are visible, and finaly the adult.
The stage 1 nymph is of a clear-green colour and initially mobile, subsequently it is able to insert it’s piercing sucking mouth parts into the leaf and it becomes sessile.
They are flat, appressed closely to the leaf, oval in shape, resembling pale green scales and have white, waxy threads, radiating from their bodies.
All other stages, excluding the adult, live attached to the leaf.
By making an opening on the back of the pupa the adult white fly is able to emerge, and immediately begins to feed. The virgin females lay only haploid eggs from which give birth to males only. With the mating process. On the other hand, both males and females are produced, with the females dominating in numbers.
Mating occurs 10-12 hours after leaving the pupa, and it continues for the whole duration of the adult life, for an average of 60 days. During their reproductive cycle the females can lay from 150 to 500 eggs. The number of generations is directly related to the temperature, below 10 C the white fly does not reproduce, it has its optimum temperature of around 29 C to 30 C, and above 34 C the cycle is unlikely to be completed.
These Aleyrodidae, live together in high numbers in a very sociable way on the under-sides of leaves. They are damaged by the sucking of plant sap, the production of abundant honeydew with the formation of sooty-mould, and as virus carriers.
In cases of serous infestation, the plant loses vigor and a general yellowing of leaves is noticed, due to the dry cell content.
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