This widely distributed gall mite is a generally common pest of pear. The mites induce the development of blister-like galls on the underside of leaves, especially along either side of the mid-vein. The often reddish-tinged galls are visible from above as pale green to yellowish blisters, each 2-5 mm in diameter; these may spread over much of the leaf surface. The galls eventually turn brown and, finally, black. Attacks can also occur on the developing fruitlets which, in common with badly affected leaves, may then become distorted and drop prematurely. Infestations also occur on other members of the family Rosaceae, including Crataegus, Malus and Sorbus; mites on such hosts are sometimes afforded separate subspecific or specific status.
Adult mites overwinter beneath the outer scales of buds and become active in the early spring as the buds begin to swell. The mites then penetrate deeper to feed and deposit eggs. Later, they feed on the underside of expanding or expanded leaves, forming distinctive blisters. The centre-most epithelial cells at the base of these blisters eventually die, so that pocket-like galls are formed, with an opening on their ventral surface (Fig. 338). Breeding in these galls continues throughout the summer, and newly reared mites regularly escape and migrate to younger tissue, where they initiate further galling. Galls are abandoned as they age and become uninhabitable, and breeding eventually ceases in the
autumn as young adults depart to take up their winter quarters.
Adult 0.22 mm long, whitish to pale brownish, and cigar-shaped; prodorsal shield setae directed forwards (cf. pear rust mite, Epitrimerus piri, p.
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