Atomaria linearis Stephens Pygmy mangold beetle

This locally abundant pest is associated mainly with mangold and sugar beet; adults also occur on red beet and spinach but attacks on these crops are rarely serious. In the British Isles, infestations are most frequent in southeastern England. The adult beetles bite into the roots and hypocotyl of plants, producing characteristic pits that soon turn black (see also damage caused by blind springtails, Onychiurus spp., p. 87). Heavy attacks on seedlings may lead to significant loss of plants, whereas those on the roots of older plants may result in distortion. Adults also feed on furled leaves at the heart of young plants, to produce small holes and notches that become obvious as the foliage unfolds; damaged leaves may later tear and appear ragged, but such damage is unimportant. Larvae also feed on the roots but their depredations are of little significance.

BIOLOGY

Adults appear in the spring and make mass dispersal flights from 'old' beet fields when temperatures exceed 20°C. Eggs are laid in the soil from April or May onwards. Larvae feed on the roots of host plants for up to 6 weeks and then pupate. Adults emerge soon afterwards. There are two main generations annually, but egg laying is protracted so that breeding appears to be continuous throughout the summer months. Populations in infested fields are often considerable and may exceed several million per hectare by the end of the season. The winter is passed in the adult stage, with individuals hibernating in the ground.

DESCRIPTION

Adult 1.3-1.5mm long, brown and elongate, the body surface finely punctured; antennae prominent, 11-segmented and slightly clubbed (Fig. 210). Larva up to 3 mm long; body elongate and whitish, with several short setae and

Fig. 210 Pygmy mangold beetle, Atomaria linearis (x30).

longer bristles on each segment; anal segment terminating in a pair of short, curved projections.

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