Vine weevils
The fat white grubs of the vine weevil live in the soil, feeding on plant roots. A symptom of their presence is plant wilt.
Many types of plant may be affected, such as bedding plants. Plants under glass are also susceptible. They can be controlled applying a biological control which is watered into the soil or compost.
A chemical is also available with an active ingredient called thiacloprid. If the grubs are discovered in the roots of a pot plant, either destroy the plant or else remove the compost, wash the roots and repot. The adult weevils feed on the leaves or ornamental plants.
They are mainly nocturnal, hiding in the soil or in plant debris during the day. Clear away any rotting plant material that might serve as hiding places for them.