Description, Biology, Life Cycle, Damage, Common Names, Images
- The adult cockchafers feed on forest and fruit tree leaves, in particular oaks (Quercus), beech (Fagus), maple (Acer), sweet chestnut (Aesculus), walnut, plum.
The larvae are very polyphagous; they attack the roots of various crops cereals, red beet, potato, meadow grasses, fruit or forest trees.
- Adults: they appear in April-May, fly singly, particularly at dusk, then migrate towards a feeding site: forest or isolated tree (pre-feeding flight). After 10 to 15 days of feeding, the females have acquired their sexual maturity and make the egg-laying flight towards fields and meadows in the opposite direction to that of the pre-feeding flight.
Each female deposits about 20 eggs in soft soil, at a depth of between 10 to 15 cm (*) . Many egg-laying females die, but about a third return to feed and lay for a second time; some lay for a third time.
- Egg: embryonic development lasts 4 to 6 weeks.
- Larva: directly after its hatching, end of June-July, the young larva starts to gnaw the rootlets (*) . It moves about horizontally distances of up to 30 cm per day. When the first cold weather appears, it buries itself in the ground and hibernates.
The second year, it surfaces from mid-April and resumes its feeding; it is then extremely voracious. In October, the second period of deep hibernation begins. In the third year, the chafer grub resumes feeding near the surface until July; it then buries itself deeper in the ground and pupates. The adults are formed in August but remain inactive until the next spring.
- Pupa: in a small cell, at a depth of 30 to 40 cm (*) .
- In France, the developmental cycle lasts 36 months spread over 4 years. The "major flights" take place every 3 years but the year differs from one region to another.
- The adults, leaf consumers, are only occasionally harmful in cherry or plum orchards.
- On the other hand, the larvae destroy the underground parts of the plants and the damage is greatest during the year which follows the laying. The presence of larvae is revealed in meadows by the reddening of large zones where the grass pulls away in tufts. Potato tubers and turnip roots are gnawed in various places. In red beet, the attack begins on the rootlets and continues in the stem base (*) ; the injured tissue can favour the development of bacterial or fungal diseases. The roots of fruit or forest trees are peeled. Young vine plants can be totally destroyed.
Cockchafers, until recently important pests of crop in shrubland regions or of those close to deciduous forests, have become rare and today cause almost no damage at all in France. This is most probably due to the widespread use of mechanical cultivation which kills the very fragile larvae, as well as to the change in production systems.
DE: Maikäfer, Feldmaikäfer ES: Abejorro común FR: Hanneton commun IT: Maggiolino PT: Melolonta, Larva pão-de-galinha GB: Common cockchafer
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