Isochnus sequensi

    Alt Name
    Isochnus populicola
    Description

    A tiny (2.0-2.5mm) black weevil with a white scutellum, pale tarsi and tibiae and yellow/red fore and mid femora. The antennal funiculus is six-segmented.

    Similar Species

    Mines are indistinguishable from the very similar but rarer Isochnus foliorum. Adults must be collected or reared to confirm identification. I. foliorum has pitchy fore and mid femora and seven segments in the antennal funiculus.

    To rear the adults a leaf or two containing mines should be collected and kept in a tupperware box with a little damp kitchen-towel wrapped around the stem to keep the leaf green. This should be kept in a cool dark place and checked every day for adults and wiped clean to avoid mold. The adults will usually emerge after several days.  To differentiate between species :-

    The front and mid femora of I. sequensi are red to yellow.

    The front and mid femora of I. foliorum  are black to pitchy. 

    Attached photo shows 6 segmented funiculus (funiculus = segments between scape and club) as opposed to 7 segments for I. foliorum.
    Identification difficulty
    Recording advice

    Not identifiable from the mine. Adults must be collected/reared.

    Habitat

    The larvae produce blotch mines in the leaves of Salix species, and sometimes Populus. The adults are usually found close by. The preferred species in Britain appears to be hybrid crack-willow, S. x fragilis.

    When to see it

    Mines can be found when the hosts are in leaf.

    Life History

    The larvae feed within a blotch mine and then pupate within the mine.

    UK Status

    The species had been considered local and scarce but is spreading and increasing from its strongholds in south-eastern England. It can be abundant where it occurs.

    VC55 Status

    First found in VC55 in August 2014 when it was discovered at two separate locations on the same day.

    Leicestershire & Rutland Map

    UK Map