Curculio glandium Marsham, 1802

Acorn Weevil

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POLYPHAGA Emery, 1886

CURCULIONOIDEA Latreille, 1802

CURCULIONIDAE Latreille, 1802

CURCULIONINAE Latreille, 1802

CURCULIONINI Latreille, 1802

CURCULIO Linnaeus, 1758

One of several oak-feeding members of the genus, this species is locally common throughout Europe, extending north to the UK and Denmark but absent from Fennoscandia, it also occurs in Morocco and extends through the Middle East and Asia Minor to Siberia. Here it is widespread and generally common throughout England north to the Humber though very local and scarce in the West Country and Wales, it is typically a species of deciduous and mixed woodland with plenty of host material, often on trees exposed to the sun, but may also occur on individual trees in hedgerows, parkland or gardens etc, the usual host is pedunculate oak, Quercus robur L. but sessile oak. Q. petraea (Matt) is also commonly utilized. Adults appear in the spring, usually from late April, and are present until late in the autumn, they mate after a period of feeding on host foliage and flowers although they also occur on hawthorn blossom, but oviposition does not begin until late summer. The female searches for developing acorns in which to oviposit and when a suitable specimen is found she will insert her long rostrum into the base above the cup and repeatedly drill deep into the acorn at slightly different angles thereby fragmenting and softening the developing tissue on which the young larva will feed, she will then insert her ovipositor and lay one or two eggs, sometimes more eggs are laid but each acorn will accommodate only two larvae and any more will die off, she will then go on to find more suitable host material and it is thought that about fifty eggs in total will be laid. Larvae emerge after a week or so and feed initially on tissue prepared by the female but as they grow they will consume the developing cotyledons, they pass through three instars and development is rapid, they will consume the leaves completely and be fully-grown within three to four weeks. After the acorn has fallen the larva will chew a small circular hole through the wall of the acorn and emerge to bury itself in the ground, usually to a depth of about 5cm but much deeper larvae have been found, and here it will prepare an earthen cell in which it will remain through the winter and into the following autumn when it will pupate although a proportion of larvae will remain and spend another year in the ground, adults eclose in the autumn but remain in the cell until the following spring. The life-cycle, from oviposition to adults emerging from the ground therefore takes a minimum of two and a half years. Adults may be sampled by beating or sweeping foliage and even saplings may host them, we have also seen them in abundance attracted to UV lights placed in mixed woodland.

Adults are medium sized, 4.0-6.7mm and readily recognized as belonging to the genus on overall appearance, they may be distinguished from our other species by the quadrate scutellum (C. venosus (Gravenhorst, 1807) also an oak feeder), finely toothed front femora (C.betulae (Stephens, 1831), and C. rubidus (Gyllenhal, 1836), neither on oak), and the form of the antennal club which is more elongate (about 3:1) than in C. nucum L, 1758 (a hazel feeder) and C. villosus (Fabricius, 1781) (also on oak). Females may be distinguished by the much longer rostrum (almost as long as the body) on which the antennae are placed around the basal quarter, in the male the rostrum is shorter and the antennae are placed near the middle.

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