Leafhoppers

Identification

Small (2-10 mm), elongated true bugs, usually greenish or yellowish, which when disturbed nimbly jump and scurry sideways across the leaf. They suck sap mainly from the underside of leaves, causing fine pale stippling, discolouration and mottling of the blade. Many species are vectors of phytoplasmas and viruses, so the damage can be more serious than the feeding itself. They feed on perennials, vegetables, grapevine and ornamentals. The body is wedge-shaped, tapering towards the rear, and the wings are held roof-like over the abdomen at rest; the characteristic oblique, sideways gait and the ability to make long leaps are what give the group its name. The larvae (nymphs) are wingless, paler and smaller than the adults, cling to the leaf underside and also move sideways; they pass through several moults, and the white, transparent cast skins they leave stuck to the underside of the blade are one of the more reliable signs that leafhoppers are present. The feeding symptoms result from the emptying of mesophyll cells: fine, pale flecking appears first, then merges into marbled pale patches, and in some species (e.g. leafhoppers of the genus Empoasca) the leaf margins yellow, brown and curl, a condition known as hopperburn. Unlike aphids, leafhoppers usually do not coat the plant with abundant honeydew, so sooty moulds rarely develop with them. The eggs are laid singly into slits cut in the tissue - into veins, leaf stalks or young shoots; many species overwinter as eggs, some as adults in leaf litter or on evergreen plants, and one to several generations develop over the season. Their role as vectors is, however, the most important: leafhoppers transmit, among others, phytoplasmas (aster-type yellows - carried by leafhoppers of the genus Macrosteles, and on grapevine the golden yellows, flavescence doree, carried by the leafhopper Scaphoideus titanus) and viruses, so that even a small population can be dangerous in crops susceptible to these diseases.

Treatment

Hanging yellow sticky traps to monitor and catch adults, systematically removing weeds that act as a reservoir for the pest and a source of infection, and spraying larvae with potassium soap or plant extracts. Encouraging predatory and parasitic natural enemies; insecticides only under heavy pressure and where there is a risk of disease transmission. Yellow traps serve a dual purpose - they signal the appearance and intensity of the adult flight, which is the basis for deciding on treatment, and they catch some of the insects; it is worth supplementing them by shaking the plants over a light-coloured surface. Because many species overwinter on weeds and develop on them in spring, careful weeding of the site and its surroundings limits both the population and the reservoir of transmitted phytoplasmas; plants showing yellows symptoms are best removed, since insecticide treatments will no longer reverse an infection that has already taken hold. Contact products - potassium (soft) soap and oil-based preparations - work by dehydrating and clogging the breathing apparatus, so they require thorough coverage of the leaf underside and repeat applications; they hit the sluggish nymphs more effectively than the nimble, jumping adults, which is why the treatment is best carried out early and in the evening. Natural enemies are supported by the presence of nectar plants: leafhopper eggs are parasitised by small wasps (including Anagrus), nymphs are attacked by the family Dryinidae, and the insects themselves are eaten by lacewings, ladybirds, predatory bugs and spiders - this is, however, a supporting method that will not stop a mass influx. In vegetable crops susceptible to vectored diseases, a cover of horticultural fleece put in place from emergence or after planting is an effective barrier. Reach for insecticides only once the damage threshold has been exceeded or where there is a real risk of disease transmission: contact pyrethroids kill adults and larvae (treat in the evening to protect pollinators, rotating chemical groups against resistance), and with systemic preparations it must be remembered that most neonicotinoids have been withdrawn or heavily restricted in the EU, so the choice of product should be checked each time against the current register. It is worth being aware that ecological methods reduce numbers, but when the leafhopper is a vector, prevention remains crucial: healthy planting material, removal of infection sources and covers.

How to tell it apart from look-alikes

Control — organic and chemical methods

We give active-ingredient groups and modes of action, not brand names — specific products and their approval vary by country and are sometimes withdrawn. Always check and follow the current label.