Autumn raspberries ripening after late August are generally unaffected.
The signs are damaged ripe berries drying up and turning greyish-brown.
On investigation an off-white grub approx. 8mm (3/8”) long, may be found inside the berry.
Adult Raspberry beetles overwinter up to 300mm (12") under the soil.
In southern parts of the UK they emerge from the soil in late April to mid May and upto a few weeks later in the north.
Newly emerged adults are about 4mm (1/8”) in length, golden brown, turning grey-green as they mature.
Adult beetles are very active during warm dry weather but less so in cool or wet weather.
The females lay small, white, shiny eggs into raspberry and blackberry flowers as the flowers open.
Eggs usually hatch around 10 – 12 days after being laid.
The larvae are yellow in colour with dark markings on the body and a brown head.
The young larvae feed at the stalk end of the developing fruits, and later move into the central plug.
Mature larvae grow to around 8mm (3/8") in length, then when fully fed, they fall from the fruit and burrow into the soil.
They remain there for about 4 weeks before pupating.
Approximately four or five weeks later the adults pupate and remain in the soil until they emerge in the following spring.
Spray or dust raspberries with a suitable insecticide when the fruit starts to change colour, and apply a second application two weeks later.
Treat Loganberry and Tayberry when 80% of the flower petals have dropped and Blackberries when the first flowers open.
Apply pesticides in the evening when bees are not active.