A small black weevil 1.4 to 2 mm, with heavily punctured elytra.  Short broad mines are formed by the larva, most often on sallows.  The larva is small, squat, and yellow or orange in colour, with a dark head, and mines sallow, poplar or ocasionally birch leaves, in a short, broad gallery becoming a blotch; often pear-shaped.

Several species of moths also mine leaves of sallows, birch and poplar

Adult Mine

Adult: Unless identified by a recognised expert, photographic evidence is required and the specimen should be examined with a microscope. In the comments box, state the key or ID method used. Note the beetle's size and describe the identifying characters. It is advisable to retain the specimen in case further checks are needed.  Mine: provide a good backlit photograph that shows the larva inside the mine, and state the host plant.

Where the larval foodplants - Birch, Willow, and Poplar - occur.

The larval mines can be seen from August to October.

The larva feed on Birch, Willow, and Poplar producing a mine in the leaves. 

Widespread, particularly in the southern half of Britain.

Only occasionally recorded in Leicestershire and Rutland.

http://www.leafmines.co.uk/html/Coleoptera/r.pulicarius.htm

https://bladmineerders.nl/parasites/animalia/arthropoda/insecta/coleoptera/polyphaga/cucujiformia/curculionoidea/curculionidae/curculioninae/rhamphinini/rhamphus/rhamphus-pulicarius/