1a small blotch mine, with an excision, not much smaller then the blotch itself: Incurvaria pectinea

1b primary blotch, without an excision => 2

1c tentiform mine => 8

1d corridor, abruptly widening into a blotch: Stigmella sorbi

1e corridor from start to end, only weakly widening; there may be a secondary blotch => 15

1f fleck mine => 21

1g galls, etc => Tables for all parasites per species

2a blotch full depth => 3

2b blotch upper- or lower-surface => 4

3a mine in spring: Incurvaria pectinea (young mine)

3b mine in autumn: Paraswammerdamia nebulella

4a oviposition spot (generally the tip of a leaflet) covered by a shining black drop of hardened secretion: Trachys minutus

4b no such drop => 5

5a blotch lower-surface, grey-brown: Parornix scoticella (young mine)

5b blotch upper-surface => 6

6a mine silvery, positioned over the midrib: Phyllonorycter corylifoliella or Ph. leucographella (young mines)

6b mine not silvery, not positioned over the midrib => 7

7a mine small, pear-shaped, often in number; much frass in a compact plug: Ramphus oxyacanthae

7b mine larger, circular; frass in concentric circles: Leucoptera malifoliella

8a mine upper-surface => 9

8b mine lower-surface => 10

9a full-grown mines silvery-white, without black speckles: Phyllonorycter leucographella

9b full-grown mines dirty grey because of numerous black speckles: Phyllonorycter corylifoliella

10a fresh mine grey-brown, larvae later live free => 11

10b fresh mine yellow green to whitish; pupation in the mine => 12

11a older larvae live in a leaf segment, rolled into a cone: Parornix anglicella

11b older larvae under a down-folded leaf margin or in a silk-covered leaf fold: Parornix scoticella

12a mine with some sharp folds; common species: Phyllonorycter sorbi

12b mine with either 1 strong or many feeble folds; rare species, in any case on this host plant => 13

13a pupa free in the mine, without a cocoon; cremaster with 1 pair of very slender spines: Phyllonorycter lantanella

13b pupa in a cocoon; cremaster with 2 pairs of short spines => 14

14a mine with numerous weak folds; frass in a line behind the cocoon: Phyllonorycter mespilella

14b mine with 1 sharp fold; frass in a clump in a corner of the mine: Phyllonorycter cydoniella

15a small branched mine without frass (rare on this host plant): Recurvaria nanella

15b mine does contain frass, not branched => 16

16a mine < 1 cm; first part stuffed with frass: Bucculatrix bechsteinella

16b mine much longer, not so full of frass => 17

17a no egg shell at the beginning of the corridor; corridor not infrequently crossing itself or the midrib; larval chamber at least 3 times as long as wide: Lyonetia clerkella

17b corridor begins at an egg shell, rarely crossing itself or the midrib; larval chamber less than 2 times as long as wide => 18

18a narrow corridor, crammed in a small space; frass in a narrow central line: Stigmella magdalenae

18b corridor winds freely through the leaf; frass coiled => 19

19a larva in June-July: Stigmella nylandriella

19b larva in September-November => 20

20a larva: meso- and metanotum with 10 setae: Stigmella nylandriella

20b meso- and metanotum with 9 setae (rare on Sorbus): Stigmella oxyacanthella

21a pistol case: Coleophora anatipenella

21b lobe case: Coleophora violacea

21c tubular silken case: Coleophora trigeminella

21d composite leaf case => 22

21e tubular leaf case => 23

22a rear end of the case crooked like the handle of a walking stick: Coleophora hemerobiella

21b rear end at most at right angle with the case: Coleophora spinella

23a case with large flaps attached to it: Coleophora siccifolia

23b case without such appendages => 24

24a case 8-11 mm, mouth angle 90°: Coleophora hemerobiella

24b case 6-7 mm, mouth angle 60°: Coleophora spinella