Description, Biology, Life Cycle, Damage, Common Names, Images
- This beetle feeds on wild and cultivated brassicas, particularly rape, cabbage, cauliflower and mustard (Sinapis arvenis).
- Adult: depending on the time of year, it feeds on shoots, flower buds or flowers of the host plant. To lay eggs, the female digs a cavity in the plant's collar and inserts an egg, which she covers with an air-hardening anal secretion.
Fecundity: about 140 eggs. During autumnal egg laying, 20 to 30 eggs can be deposited on a plant.
- Egg: embryonic development lasts 23 days.
- Larva: it lives in a gall level with the collar (*) . When fully grown it perforates the plant tissue and enters the ground where it excavates a small silk-lined cell and pupates.
Larval development lasts between 28 days at 15°C and 190 days at 3.5°C.
- Pupation lasts 31 days at 20°C and 58 days at 15°C.
- 1 generation per year but 2 races occur: one is characterised by a summer diapause and reproduces in autumn; the other has a winter diapause and reproduces in spring.
- In the first case, the adults appear in spring after hibernation; they mate and lay eggs in May. The new adults resulting from this generation live for the whole summer on the brassicas then, when the first cold days arrive, take shelter in the ground to overwinter.
- In the second case, egg laying occurs in August and September. The larval development continues throughout the winter. The larvae pupate during the following spring and the adults emerge in June. They remain in diapause during the summer.
The substances introduced through oviposition and the larval secretions cause a hypertrophisation (a gall) of the collar, which can reach 2 to 3 cm in diameter in cabbage (*) .
Following multiple autumnal oviposition, the various neighbouring tumours meet and the composite galls can reach 8 to 10 cm in diameter. They should never be confused with the deformations of the collar due to the cabbage hernia which never contain a larval cell.
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