The adult males are found on Ash, and can be identifed to species by examination of external genitalia (terminalia) - see RES guide to Psylloidea.

The psyllid produces galls on ash leaves.  The leaf edges are loosely rolled, usually downwards, swollen and pale in colour with purplish markings.   Inside is white wax and pale green nymphs with darker markings when mature.   The galls cannot be assigned to a species, but should be recorded as Psyllopsis fraxini agg.  Sometimes nymphs of Psyllopsis fraxinicola are inside the galls; these are inquilines and are pale green all over. 

Psyllopsis distinguenda and Psyllopsis discrepans are also found on Ash.  The adults also have dark markings on wings, but the intensity of the markings may vary, and for safe ID the male terminalia should be examined.  P fraxinicola adults do not have dark wing markings. 

The barkfly Graphopsocus cruciatus is superficially similar. 

Photographs of adult insects and details of male terminalia.  We recommend you retain the specimen in case expert verification is needed.

Ash trees

Common

Status unknown. The galls caused by the species aggregate are very common in some years, but adults are rarely recorded to species.

British Bugs webpage