Black vine weevil | Biobest
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Black vine weevil

The black vine weevil (Otiorhynchus sulcatus) is a common pest in many garden and nursery plants. Feeding damage by adults and their grubs have been observed in many berry crops as well.

Damage

Adult weevils feed at night producing telltale notches around the edges of leaves and flowers. The damage is most severe when caused by their voracious grubs. As soon as they hatch, they start feeding on little roots. As they grow, they gradually attack bigger roots, tubers, rootstocks and even strip bark from woody stems. Damaged plants wilt and die off. Sometimes, it takes a long time before damage is discovered. At that moment, the plant is often already severely weakened and beginning to die off. Slow growing plants, which are unable to compensate for loss of root tissue are most susceptible to damage.

Description and life cycle

Adult black vine weevils are 8-12 mm long, have a grooved, dull black shell with patches of tiny yellow bristles. As they are well camouflaged and only active at night, they are seldom seen. If they are discovered, they play dead very convincingly. Adults emerge from the soil from spring onwards. They are wingless but walk and climb exceedingly well. Females hatch from unfertilized eggs though no males have not been found. Freshly emerged females feed for about ten days, and then start laying unfertilized eggs. Each female lays about 500 eggs, which are very small (0.8 mm) and round. Initially, these eggs are white, but they turn brown as they mature. Adults are relatively long-lived and egg-laying can extend well until autumn. Eggs hatch in 8-20 days, and the tiny emerging larvae burrow deep down into the compost. The larvae are C-shaped and legless. They have a creamy white colour with a shiny brown head. When fully grown, they are 10-14 mm long. Black vine weevils overwinter as larvae which pupate in spring as temperatures rise. These pupae are cream-coloured and soft bodied. They are found in cavities several centimeters down in the soil. Adult weevils emerge some 3-4 weeks later. In glasshouses, the life-cycle is completed more rapidly and several different stages of black vine weevil may be found at any time of the year.

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