Chaetocnema concinna Marsham Mangold flea beetle

Adults of this widespread and often abundant flea beetle feed on various weeds (Polygo-naceae), including Polygonum aviculare and Rumex; they also attack beet and mangold, and are sometimes noticed on unrelated crops such as rhubarb and strawberry. The adults bite out small, circular pits in the cotyledons and leaves; these feeding punctures often coalesce and, later, develop into holes as the plant tissue grows. Extensive feeding leads to defoliation and to the death of growing points. Infestations are particularly damaging on slow-growing beet seedlings (e.g. in cold, dry conditions); attacks on older plants are of little or no significance. Larvae, although attacking plant roots, are of no significance.

BIOLOGY

The adult beetles overwinter in herbage along ditches and dykes, in hedgerows and woods, and in other situations. They begin to emerge in the following spring, from March or early April onwards. They then immediately seek host plants

Fig. 214 Mangold flea beetle, Chaetocnema concinna (x25).

upon which to feed. The overwintered beetles are active in warm, calm, sunny weather and often occur in beet fields from mid-April to June. Eggs are laid in the soil at the base of host plants (Polygonaceae); they hatch 2-4 weeks later. The larvae feed on the roots for up to 6 weeks. They then pupate and new adults appear after a further 2 weeks, usually from July onwards. These young adults feed throughout the summer before seeking overwintering sites.

DESCRIPTION

Adult 1.5-2.0 mm long, black to bronzy-black and shiny, with deeply punctured elytra and a pointed projection on each middle and hind tibia (Fig. 214). Larva up to 6 mm long; body mainly white; head small, brown; thoracic legs small; prothoracic plate and anal plate light brown.

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