The raspberry beetle and its maggot - grub, is probably the most destructive annoying pest of raspberries, blackberries and loganberries. Many are not found until the ripe raspberries undergo the ritual 'drowning' in cold water before being prepared as puddings etc.
The adult beetles feed on the flowers, where they lay their eggs. The young maggots than bore into the young fruit where they feed until either picked or the fruit drops. The maggot then lives in the ground - overwinters and emerges as the adult beetle, ready to begin the life cycle again with either raspberries, blackberries or loganberries as hosts.
Derris is still being suggested as a control on some web sites and many books. We do not agree with this, as derris is now withdrawn, and in any case cannot be used after September 2009. As far as we are concerned, if it is bad enough to be withdrawn, then responsible gardeners should not use it.
Bifenthrin can be used - a contact insecticide - on Raspberries as the fruits first start to turn pink, on blackberries just prior to flowers opening and on other hybrids, loganberries etc, spray when the petals have fallen.
The image of the Raspberry beetle, its larvae maggot above is considerably larger than actual.