Causal agent(s) and transmission
The common cockchafer (Melolontha melolontha) is an insect of the order Coleoptera; the damage is caused by its larva, which can measure 20 to 50 mm depending on the stage and is commonly called “white grub” because of its whitish and shiny colour and its arc-shaped and curved body. White grubs have a large brown head, bearing strong mandibles; they have 3 pairs of legs situated just below the whitish thorax and a blackish extremity on the abdomen (photo 1).
The larvae of the common cockchafer can cause serious damage to many crops, in highly infestated areas, when feeding on roots. On potato, they can also feed on the tubers and dig galleries in them (photo 2).
The adult cockchafer hibernates deep down in the soil, in its pupal shell, between 20 and 100 cm; its life cycle lasts for 3 or 4 years.
High infestation of cockchafers is rare when soil cultivation is properly managed.