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The polyphagous leafhopper Hyalesthes obsoletus (figure 1) is the main vector of the phytoplasma (Candidatus phytoplasma sp.) that causes stolbur in tobacco. This stinging insect feeds on leaf vessels sucking the sap of the plant..
Hyalesthes obsoletus will pick up the phytoplasma from  the phloem tissues when it feeds on infected plants. This phytoplasma will pass through the digestive system of the leafhopper, through its haemolymph and finally reach the salivary glands. Then the leafhopper becomes an infected insect host. These insects can sometimes fly long distances or stay in the same place when conditions are favourable to them.
The leafhopper prefers certain plants in which it lives its whole lifecycle (figure 2). The following plants on which the insect has been captured in larval or adult stage are susceptible host plants:

- Amaranthus retroflexus L. (pigweed, amaranthaceae)
- Cirsium arvense Scop. (thistle, Asteraceae)
- Taraxacum sp. (dandelion, Asteraceae)
- Cardaria dabra L. (passerage, Brassicaceae)
- Chenopodium album L. (lambsquarters, Chenopodiaceae)
- Convolvulus arvensis L. (bindweed, Convolvulaceae)
- Lavandula hybrida Rever (lavender, Labiaceae)
- Rumex crispus L. (curly dock, Polygonaceae)
- Rumex sp. (dock, Polygonaceae)
- Solanum tuberosum L. (potato, Solanaceae)
- Lycopersicum esculentum Mill. (tomato, Solanaceae)
- Urtica sp. (nettle, Urticaceae)
Tobacco is not a host plant of the leafhopper. Therefore the insect is using tobacco to  make only test bites. In fact tobacco seems to attract it for a while, or in a certain environment, perhaps because it is a plant that remains green (irrigated field)

Lifecycle of a leafhopper

Hyalesthes obsoletus lives almost all its lifecycle in the soil. There is only one cycle per year. The five larval stages take place in the soil. Sometimes the fifth larval stage may already be infected if the larva feeds on the roots of infected plants.  
It favours well exposed fields but also clay or sandy soils. An adult leafhopper emerges from the soil and lays the eggs on the collar of the host plants.
Adult leafhoppers are easy to recognize : 4 mm of size, vermilion red eyes, translucent wings.
Apparently the epidemics caused by leafhoppers follow cycles and the outbreaks are favoured by hot and dry summers (a stimulating factor for this  pest). Other factors may also influence the outbreaks, for instance pesticide treatments.

Last change : 04/22/13
Figure 1