Leaf miners & climate change?

OK, I'm going to be a bit speculative here... In April this year, I found abut 20 leaf mines of the agromyzid fly Chromatomyia aprilina on honeysuckle (Lonicera periclymenum) in Stoke Park Woods near Eastleigh in Hampshire. Although probably under-recorded in the county (the local records centre had a single record, and I found one more on the excellent British Leafminers site), there is nothing inherently astonishing about finding this species, except for the date when I found it and the form its mine took.

Spring mine of C. aprilina (note pupa just above the midrib).

The usual more-or-less stellate start to C. aprilina mines in summer & autumn.

C. aprilina is usually considered to have two generations ('bivoltine') - one in early summer and one in the autumn. However, in February 2009 a new 'spring' form was found in Kent with further records in March that year from Gloucestershire. This appears to be an early generation and has a different mine structure with the initial stellate section much reduced and mining occurring away from the leaf midrib.

Again, this may not be astonishing in itself, but it does raise some interesting questions:

1. Why has this new form of mine appeared; is it an adaptive reponse to the earlier spring seasons associated with climate change allowing an extra generation to be squeezed in? This appears to be a well-known miner, so it seems unlikely that the spring form was simply overlooked until last year. I wonder if the spring generation will begin to appear further north as temperatures increase, and if so whether this spread could be separated from the distribution of the species as a whole.
2. Whatever the cause, why does it have a different form? Are conditions in the leaf different in spring in some way that affects mining?
3. Are other leaf miners exhibiting similar changes?

Any thoughts on this are most welcome - with only two years of records, maybe little can be inferred but it will be interesting to see if the above questions can be tackled.

Pupa (c. 3mm) of C. aprilina in the leaf. Note spiracles to the left. This pupa was raised to an adult.

References

D. Hubble (2010). Hampshire records of Chromatomyia aprilina Goureau 1851 (Diptera, Agromyzidae) - an under-recorded leaf miner? Dipterists Digest, 17 (1), 63-64

Spencer, K.A. (1972). Diptera, Agromyzidae. Handbooks for the Identification of British Insects 10(5g): 1-136.