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Insecta, Coleoptera, Curculionidae .
Description, Biology, Life Cycle, Damage, Common Names, Images
[R]Biology
Most affected plants are hop and the Leguminosae, especially lucerne and clover. If such plants are not available, adults may attack vine, young beet, pea, cereals, bean, asparagus, etc.
- Eggs are laid singly or in small clusters.
- Number of eggs produced: about 400, 800 at the very most.
- Duration of egg development: 1.5-3 weeks.
- Duration of larval development: about 1 year; larvae overwinter 30-40 centimetres in the soil.
[R]Life Cycle
- This insect overwinters in the soil.
- Reproduction is mainly parthenogenetic, males being very rare. Adults leave their earthen shelter in April, migrating to alfalfa fields or, in their absence, to other plants. They cannot fly, elytra being fused together. Eggs are deposited on the roots of host plants.
- Emerged larvae feed until the autumn, enclosing themselves in a subterranean cell, which they will leave in the spring. Feeding continues until June, pupation occurring at that time. Adults emerge in the summer but stay in the soil, remaining in a state of diapause until the following spring. If climatic conditions are unfavourable, certain larvae pupate after again overwintering, that is during the 3rd year.
- Colonies develop more easily in dry weather and during mild winters.
[R]Damage
- Adults bite the margins of leaves and may cause complete defoliation.
- Damage is often caused to buds, shoots and flowers. Affected hop shoots can be easily broken. In case of heavy infestations, aerial parts of hop may be directly devoured.
Larvae dig groove-shaped galleries and holes in the roots of Leguminosae and hop: plants wither, stop developing and die.
On lucerne and clover, the economic injury threshold is 1 adult every 40 m2.
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