It is the larvae of raspberry beetle that affects fruit. The larva feeds at the stalk end of the fruits. It is mainly a problem on summer-fruiting raspberries. Early fruits on autumn raspberries may be damaged, but those ripening after late August are less likely to be affected.

Raspberry beetle adults are small 4mm long pale brown beetles in the family Byturidae. There are only two species of beetle in this family found in Britain. The other species B. ochraceus looks similar to the raspberry beetle but is associated with Geum urbanum (wood avens) and does not affect garden plants. UK beetles information on Byturidae. 

• Damaged ripe berries have greyish-brown dried up patches at the stalk end
• A brownish-white grub, up to 8mm (about 1/4in)  long, may be found inside the fruits

If raspberry beetle has been a problem in previous seasons consider control actions before the crop develops. Check susceptible cane fruits frequently as fruit develops so action can be taken before a damaging population has developed. When choosing management options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section and avoiding pesticides. Within pesticides the shorter persistence products (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.

Non-pesticide control

• Where possible tolerate some beetle damage, often only a small proportion of the crop is affected. Later ripening berries tend to be less affected
• Encourage predators and other natural enemies in the garden such as birds, hedgehogs and ground beetles
• A host plant odour (karimone) water trap is available from Agralan, Ken Muir, Harrod Horticultural and some other suppliers. This will trap both male and female beetles which may help reduce infestation levels.  

Pesticide control

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

• Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer). These pesticides although broad spectrum have a very short persistence and so may require reapplication to keep beetle numbers in check
• More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)

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Pesticides for gardeners (pdf document)

• The 4mm (about 1/8in) long adult beetles are pale brown and they lay eggs on the flowers in May to mid-July
• The young larvae feed at the stalk end of the developing fruit, but later move inside to feed on the central plug
• In late summer, the fully-fed larvae move into the soil where they overwinter as pupae