hard brown cases with a grub inside. found inside a hole in an apple tree trunk
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Oh well, I got excited about this! thanks for the info anyway.
These things are worth checking out, you may discover something new about the biology of a species, which can be valuable even if the species is common. For a picture of a chafer beetle pupa (actually rose chafer but should be similar to Gnorimus) see: www.amentsoc.org/insects/glossary/terms/pupa
Lat/Lng: 52.5572831, -1.7781504
OS grid ref: SP151955
Located in an orchard with apple pear & plum trees