Flat green corridors in the leaves. The only character to separate
this species from Hydrellia griseola is that adult flies
of griseola are dusted greyish-white, those of thoracica
not dusted, greyish brown (Hering,
1957) - see also Bladmineerders van Europa.
Larva: The larvae of flies are leg-less maggots without a head capsule (see examples). They never have thoracic or abdominal legs. They do not have chewing mouthparts, although they do have a characteristic cephalo-pharyngeal skeleton (see examples), usually visible internally through the body wall.
Puparium: The puparia of flies are formed within the hardened last larval skin or puparium and as a result sheaths enclosing head appendages, wings and legs are not visible externally (see examples).
Irwin and Chandler in Chandler
(1978) did not indicate whether their host record was British or Foreign
and is therefore included under 'Hosts in Britain' and 'Hosts elsewhere',
as is the record by Pitkin & Plant, which was previously assumed to be British.
Hosts in Great Britain & Ireland:
of year - mines:
April (Hering, 1957).
of year - adults: Currently unknown.
in Great Britain & Ireland: Widespread in Britain including Cambridgeshire (VC29), Dorset (VC9),
East Kent (VC15), Glamorganshire (VC41), Middlesex (VC21), Monmouthshire (VC35), North Somerset (VC6),
South Wiltshire (VC8), Surrey (VC17), West Lancashire (VC60), West Suffolk (VC26) and Westmorland
recorded in the Republic of Ireland (Zatwarnicki, 2004 in Fauna Europaea).
NBN Grid Map:
elsewhere: North and Central Europe including The Netherlands
(Bladmineerders van Europa), Belgium (Gosseries,
1991d), Austria, Bulgaria, Czech Republic, Finland, French mainland,
Germany, Hungary, Italian mainland, Poland, Romania, Slovakia, Sweden,
Switzerland and The Netherlands (Zatwarnicki, 2004 in Fauna Europaea).
NBN Interactive Grid Maps of known host species:
British and Irish Parasitoids in Britain and elsewhere: Currently unknown.