Country diary: A gleaming beetle that could be bad news for my garden favourites | Susie White

Allendale, Northumberland: On a hot autumn day, I see rosemary beetles here for the first time. This could be a problem for many thriving plants

This year there have been several firsts in my garden: old lady, vestal and blood-vein moths attracted to the light trap; hummingbird hawk-moths, normally occasional, feeding summer-long from verbena and buddleia; and it’s a painted lady year – a once-a-decade event, these high-flying insects migrating from Africa through successive generations. Southerly winds and heatwaves have added to the species visiting my North Pennine garden.

Now, in a herb bed, I spot something less welcome. Among the resinous leaves of rosemary is a gleaming beetle, its elytra striped in purple and green, scintillating like lustreware. It’s not something I’ve seen before, but I immediately know what it means. Rosemary beetle, Chrysolina americana, is a Mediterranean species with no natural predators in the UK. It is shimmering and beautiful – but can reduce plants of the Lamiaceae family to bare sticks and cause them to die back. This includes my favourites: lavender, sage, thyme – and rosemary.