The black vine weevil, Otiorhynchus sulcatus, is a pest in many ornamental crops (e.g. rhododendron, cyclamen and azalea), as well as in strawberries and other fruit crops in both temperate and sub-tropical regions. It belongs to the family Curculionidae.
Life cycle and appearance of Black vine weevil
The life cycle of the black vine weevil consists of an egg, 6 or 7 larval instars, a pupal instar and the adult beetle. In temperate climates in the Northern hemisphere, the first adult weevils appear around May. They are approximately 7 - 10 mm long, brownish black and have dull yellow spots on their back. The wing covers are grooved and fused with the body. Therefore, vine weevils cannot fly but can walk very well. They are strictly nocturnal; during the day they hide, and can often be found between the inside of a plant pot and its contents, under lumps of e, in vegetation and under planks etc.
In temperate climates, the small (0.7 mm diameter), spherical white eggs are laid from the beginning of July until around the end of October. The larvae that hatch have a white, translucent to pinkish body and a reddish brown head. These larvae live in the root zone in the soil where they feed on the roots. They are legless, roughly 1 mm long at hatching, but grow to approximately 12 mm. A larva is often curled into the typical C-shape which it assumes whenever it is disturbed. The body is covered with stiff white to light brown, bent hairs. Overwintering occurs in the larval stage, usually as medium sized instars. Once the temperature rises, the larvae become active again. The full-grown larvae pupate in spring in the soil. The depth where the pupae can be found varies between 2 and 20 cm. Pupae are white to cream coloured and 7 - 10 mm long. Outdoors there is a single generation each year. A population of black vine weevils consists entirely of females and reproduction is by parthenogenesis.
As vine weevils cannot fly their dispersal ability is limited compared to many other insects. Spread over longer distances usually occurs with infested plant material. Because Otiorhynchus sulcatus is parthenogenetic a single female is enough to start a new population.
The major damage is caused by the feeding of the larvae on the roots. After the roots have been destroyed the larvae move into corms, rhizomes and stem bases of plants. Larvae can also feed above ground within the stems of the plants. Both adult beetles and larvae are polyphagous and feed on a large number of plant species. High populations of larvae can destroy plants under field conditions. Established crops are more resistant to damage than young plants or just planted cuttings. The adult beetles are only active at night, taking round bites out of the leaves, starting from the edge. This damage is usually not a problem in vegetables and fruit crops but reduces the value of ornamental plants.