Acalitus essigi Hassan Blackberry mite

This species is widely distributed and sometimes common on cultivated and wild blackberry. The mites do not damage the leaves (cf. raspberry leaf & bud mite, Phyllocoptesgracilis, p. 259) but cause a characteristic uneven ripening of infested fruits, the basal drupelets of which remain hard and greenish-red to red whilst the rest mature, a condition known as 'red-berry' disease. The incidence of 'red-berry' tends to increase as the season progresses, with late-maturing fruits the most severely affected. Physiological factors may cause uneven ripening of blackberries, but not necessarily of the basal drupelets, and affected areas often become softened (a clear indication that mites are not the cause).

BIOLOGY

Mites hibernate in various sheltered situations on host plants, and become active in the early spring. They then move to the new shoots to feed and breed amongst the hairs on the leaves and petioles. Later, the mites migrate to the opening blossoms and will eventually become established around the base of the developing fruits, sheltered by the remains of the calyxes; here, they feed on the basal drupelets. There are several overlapping generations annually. Populations diminish rapidly in the autumn, and survivors eventually overwinter.

DESCRIPTION

Adult mite 0.16-0.18 mm long, whitish and vermiform; prodorsal shield setae long and directed backwards.

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