Leafhopper: the problem of lavender producers
Leafhoppers are small insects (a few millimetres to 1.3 cm long for the largest species), whitish in colour (they are covered with wax), brown, beige or green depending on the species, belonging to the order Homoptera. Their name, which means little cicada, gives a fairly accurate idea of their appearance. Like cicadas, leafhopper larvae have no wings and live underground, where they feed by stinging the roots of plants that the species usually feeds on.
Leafhoppers, like almost all Homoptera, feed on the sap of plants, which they obtain by driving in their rostrum (their mouthparts are transformed into a punch capable of puncturing even wood) and creating access to the vessels that carry the sap. Leafhoppers are too small for the amount of sap they absorb to be detrimental to the plant. But like many insects that bite animals or plants, leafhoppers can transmit diseases caused by viruses, bacteria or fungi.
Many farmers, especially lavender and grapevine growers, have been facing early mortality in their plantations for several years, the main cause of which is dieback due to Stolbur phytoplasma. This is a pathogenic microorganism: a filamentous, wall-less bacterium that needs a "host" to survive; plant or insect. It invades the vessels of lavender and lavandin but also other cultivated plants: vine (blackwood disease), sugar beet (low richness syndrome), tomato, pepper, tobacco... It can also be found on plants around the plots: thyme, bindweed etc. A leafhopper is responsible for the spread of stolbur, it is called Hyalesthes obsoletus. The bacterial filaments end up clogging the vessels that carry the elaborated sap (the one containing the nutrients the plant needs). This obstruction of the vessels leads to a progressive atrophy of the ends of the branches. First the leaves and green parts turn yellow, then they disappear and the branches become blackish-brown and dry out. Unfortunately, during the first phase of disease development, the disease is not detectable with the naked eye, so genetic analyses (PCR, infamous in these times of covid19 ) must be performed on lavender plants to confirm the presence of the bacterium.
IRSEA researchers first set out to develop a reliable method to detect the disease on different plants. Then, we studied the chemical information, emitted by the plant, that will guide the choice of the leafhopper to bite such or such plant.
This work has allowed us to identify a complex set of chemical signals that we are testing to determine the ideal message to divert adult leafhoppers in search of food or a plant on which to lay their eggs.
