Causal agent(s) and transmission
Flea beetles (Epitrix, Psylliodes) are a common and widespread group of phytophagous insects (Coleoptera; Chrysomelidae). Their common name derives from the ability of the adults to jump when disturbed (see the enlarged femur of the hind legs, photos 1 to 3). Most of the Epitrix spp. adults are similar in appearance, being dark, tiny (1.5-2.0 mm long), oval, convex and having pubescent bodies. This common overall appearance renders their specific identification very difficult.
The young adults gnaw the leaves, only damaging part of the skin, and they cut many minute, circular holes on the leaves, producing a characteristic ‘shot-hole’ pattern in the leaflets (photo 5). The larvae (photo 4) usually feed on the roots and, when they are extremely abundant and depending on the species, they may feed on tubers, leaving feeding signs on the surface, i.e. superficial galleries, the walls of which suberise (photos 6 and 7). Prior to the pupal stage, the larvae leave the tubers to resume their development in the soil.
The flea beetle species, currently known in Europe (E. cucumeris and E. hirtipennis), only cause damage to the potato leaves but different Epitrix species, causing damage on potato tubers have been described in North America (E. tuberis), and recently, in Portugal and Spain (E. similaris). Until further biological information is available, E. tuberis, E. cucumeris, E. similaris and E. subcrinita are regulated pests within European countries.
As potato tubers or soil attached to the tubers can carry the pest (as over wintering adults) over long distances, the inspection of imported tubers from infested areas is an important preventive measure to avoid its dissemination, as eradication would be almost impossible because of the wide range of hosts of these insects. Indeed, these insects feed mainly on Solanaceae but the adults may subsist on the foliage of plants from other botanical families such as cabbage, cucumber, beet, lettuce, maize, bean and various weeds.