Q What is raspberry beetle?
A An inconspicuous beetle (Byturus tomentosus) with a grub that feeds on raspberries and other cane fruit.
Caption: Using a raspberry-beetle trap is a good way to know when is the best time to spray
Q How do I recognise it?
A The adult beetle is pale brown, around 4mm long and covered in short hairs. The grubs reach 8mm long, have a creamy-white body with pale-brown marks on the back, a brown head and three pairs of legs.
Q Can you tell me more about raspberry beetles?
A The adult beetles emerge from the soil from April to June and are good fliers. They feed on the flowers of the rose family, starting with apple, pear and hawthorn, then move on to soft fruit to lay their eggs in the flowers. The grubs first feed on the outside of the fruit, then move into the central plug. Once fully grown, the grubs leave the ripe fruit, drop to the ground and pupate in the soil.
Q How serious is the damage?
A If present in large numbers, the adults can do significant damage to the flowers, with many fruits being malformed or not developing at all. However, this does not happen very often; the larvae are far more of a problem as the immature grubs spoil the fruit. They produce characteristic dried-out and blackened areas near the plug in the centre where they have eaten some of the developing drupelets – the tiny segments which make up this type of fruit.
Q How do I control it?
A If you see grubs on the surface of the berries they can be sprayed with a contact insecticide based on pyrethrum. Ready-to-use pyrethrum-based sprays are convenient to use. To help know the best time to spray, you can use a raspberry-beetle trap four to size weeks before first flower during April to July.
Q What if I don’t want to spray?
A Most grubs will have left the fruit by the time it is ready to pick, or will be removed with the plug. The others should be removed, along with any damaged areas, as the fruit is prepared.