Aphids

Aphids, commonly called plant lice, these insects, whose adults have varying dimensions of about 1,5-4.0 mm in length, possess an almost transparent thin external integument, in colours that range from clear yellow to black.

They have a strong polymorphism between the winged forms, whose task is to reach the new plant hosts up to distance of hundreds of kilometers away, and those apteral -wingless- that, with the loss of wings and wing-muscles, assemble all of their resources in the reproductive function, producing in a short time numerous colonies.

They possess piercing-sucking mouth-parts through which they pierce the most tender tissues from which plant sap is withdrawn.

This is rich in sugar but poor in amino-acids, for which reason they seek to retain the necessary nutritional elements and to expel the surplus water and sugars in form of sticky honeydew, through a posterior appendix of the abdomen.

In nature, these Homopteran have a very complex biological cycle, on the other hand in greenhouses they have a simpler cycle because the insect has at it's continental disposal a vegetable host - the Gerbera - and a mild climate. 

All of this allows it to have only parthenogenetic generations, with a phenomenal ability to multiply.

On average a female during her life cycle produces from 50 to 100 progeny, most of which other females that, within 8-10 days of their birth, are sufficiently mature to begin reproduction. The damage caused by aphids can be direct and indirect. 

The direct damage consists in the suction of plant sap, lesions and necrosis of the tissue subject to puncture by the insect. 

They also produce gall and hyperplasia, because of the effect of different substances which are injected into the plant, including Indoleacetic acid.

The indirect damages however, consists of excretion of honeydew that accumulates on the foliage of the plant. 

The honeydew supports the growth of block sooty-mould fungi, which often renders the effected plant unsightly and their flowers unsalably, because the photo synthetic activity of the plant is hindered. 

Further indirect damage is caused by Aphids' capacity to transmit viruses from healthy to sick plants.