Aculus schlechtendali Nalepa Apple rust mite

This mite is a widely distributed and generally common pest of apple; occasionally, the mites also occur on pear (cf. pear rust mite, Epitrimeruspiri, p. 258). Although implicated in causing leaf bronzing and fruit russeting in apple orchards, large numbers of mites can be toler ated before there is any adverse effect on cropping. Apple cultivars vary in their susceptibility to this pest. In integrated pest management systems, the presence of this mite can be useful for maintaining populations of predatory mites (e.g. Typhlodromus pyri Scheuten) at times when spider mites (the preferred hosts) are at low levels.


The mites are free-living and deuterogenous, with two adult female forms (protogynes and deutogynes) which differ both structurally and physiologically. Protogynes (= summer females) and males are the primary forms; these breed normally throughout the summer, and there are several (often four or five) overlapping generations each year. Development from egg to adult includes two nymphal stages and is completed in just over 2 weeks at temperatures of 16°C; the egg stage is relatively protracted. Deutogynes (= winter females), for which there is no equivalent male stage, appear in increasing numbers from July onwards. They hibernate under bud scales, and reappear early in the following spring. They then invade the opening buds and eventually lay eggs that give rise to the first generation of protogynes and males. Large numbers of mites of all stages of development may be found on expanded leaves throughout the summer months but populations decline rapidly following the production of deutogynes and their subsequent migration to overwintering sites.


Protogyne 0.14-0.18 mm long, yellowish-brown to dark orange-brown and fusiform; prodorsal shield slightly granular; prodorsal shield setae long and directed backwards. Deutogyne similar to protogyne but prodorsal shield not granular and prodorsal shield setae shorter. Adult male 0.14-0.15 mm long, orange-yellow to dark orange brown. Egg 0.05 x 0.03 mm, oval and translucent. Nymph whitish to pale orange-brown; prodorsal shield granular.

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