Raspberry Beetle – Identification, Occurrence, and Control

The raspberry beetle (Byturus tomentosus) is a significant pest affecting raspberries and other cane fruits like blackberries, loganberries, and tayberries. This article provides guidance on identifying the raspberry beetle, understanding its life cycle, where it’s found in the UK, and practical steps to manage and control this pest without compromising garden biodiversity.

What Does the Raspberry Beetle Look Like?

The raspberry beetle is a small, golden-brown beetle, approximately 4 mm (about 1/8 inch) long. Adult beetles have a slightly oval shape with a pale brown to yellowish-brown body. Newly emerged beetles appear golden, while mature beetles may shift to a grey-green colour.

The larvae are pale brown with dark patches on each body segment and a brown head, reaching about 8 mm (around 3/8 inch) in length. They can often be found burrowing into raspberry fruits, particularly at the stalk end, where they cause visible damage that shrivels the berry and leaves dry, greyish-brown patches.

Where is the Raspberry Beetle Commonly Found in the UK?

The raspberry beetle is widespread throughout the UK, particularly in southern regions, where adults begin emerging from the soil as early as April. In northern parts, they may emerge a few weeks later, typically around mid-May. The beetles prefer gardens, allotments, and orchards where cane fruits are cultivated. They are attracted to the flowers of raspberries and blackberries, using both visual and olfactory cues to locate them.

How Can You Prevent the Raspberry Beetle?

Preventing raspberry beetles is essential to protect cane fruit crops. Since the beetles have a predictable emergence and breeding pattern, timely preventive actions can significantly reduce infestations:

  1. Soil Cultivation: Since adult beetles overwinter in the soil up to 30 cm (12 inches) deep, turning the soil in late autumn and early spring can disrupt their lifecycle and reduce populations.

  2. Trapping Methods: Non-pesticide traps can help catch adult beetles. Use traps with odour attractants to lure beetles as they emerge from the soil in April and May. These traps are effective in capturing beetles before they lay eggs on raspberry flowers.

  3. Encourage Natural Predators: Supporting ground beetles, birds, and hedgehogs in the garden can naturally reduce the raspberry beetle population. These predators feed on beetle larvae and adults, aiding in biological control.

  4. Selective Planting: Raspberry beetle populations tend to be lower on late-ripening varieties of raspberries, especially those maturing after late August. Opting for these varieties can help minimise early-season beetle infestations.

How Can You Control the Raspberry Beetle?

Effective control of the raspberry beetle requires a combination of monitoring, physical trapping, and selective use of insecticides when necessary.

1. Non-Pesticide Control Methods

  • Use of Traps: Raspberry beetle traps are a practical solution for monitoring and reducing beetle numbers. Place traps in the raspberry patch from late April to June before flowers bloom. Each lure typically lasts six weeks and can trap both male and female beetles.
  • Garden Hygiene: Remove fallen leaves, spent flowers, and any infested fruits to reduce places where beetles and larvae might hide or feed.

Non-pesticide control is highly encouraged in the UK to protect pollinators and other beneficial insects, as the beetles are primarily active in warm, dry weather, making physical controls effective under these conditions.

2. Pesticide Control Options

  • Approved Pesticides: For those considering chemical control, only use approved insecticides in compliance with UK pesticide regulations. Organic insecticides containing natural pyrethrum (such as Bug Clear Ultra 2) are available. These short-persistence options have a physical mode of action and are generally less harmful to larger beneficial insects.
  • Timing of Application: To protect pollinating insects, apply insecticides in the evening when bees are not active. Spray when berries begin changing colour and repeat the application two weeks later if beetles persist.
  • Avoiding Flowering Stages: Avoid pesticide application during flowering, as this can harm pollinators. Instead, use traps during the beetles' pre-flowering emergence to reduce adult populations before eggs are laid.

It’s essential to carefully read and follow pesticide labels, ensuring the product is approved for raspberries and observing recommended application rates and harvest intervals.

3. Considerations for Organic and Natural Growers

  • Rotenone Alternatives: While rotenone was historically used, it is no longer recommended due to its environmental impact. Today, organic growers may use natural pyrethrum or physical traps as safer alternatives.
  • Integrated Pest Management (IPM): Combining physical traps with soil management and encouraging natural predators provides an effective IPM approach, reducing the need for chemicals.

What is the Life Cycle of the Raspberry Beetle?

The life cycle of the raspberry beetle is an essential factor in controlling this pest:

  1. Adult Beetles Emerge: Adults emerge from the soil between April and June, depending on regional temperatures. They feed on young leaves and flower buds, causing early-season damage.

  2. Egg Laying: Female beetles lay small, shiny white eggs in raspberry flowers from May through mid-July. Each female can lay over 100 eggs, which hatch in about 10-12 days.

  3. Larval Feeding: The larvae feed on the fruit, burrowing into the stalk end and sometimes deeper into the fruit. Damaged fruits are often unmarketable, with dry and shriveled sections that become visible as the fruit ripens.

  4. Pupation: In late summer, fully grown larvae drop to the soil, where they burrow and pupate. They remain dormant throughout winter and emerge as adults in spring, completing the cycle.

What Damage Does the Raspberry Beetle Cause?

The raspberry beetle inflicts significant damage to both foliage and fruit, impacting the quality of raspberry and other cane fruit crops:

  1. Fruit Damage: The most apparent sign of infestation is the shriveled, greyish-brown patches on ripe fruits. Larvae burrow into the fruit, often at the stalk end, causing the berries to appear smaller and less marketable. Infested fruits are also more vulnerable to fungal infections such as grey mould (Botrytis cinerea), which can reduce shelf life.

  2. Foliage Damage: Adult beetles feed on young leaves, creating holes that give foliage a tattered appearance. In severe infestations, the leaf damage can affect plant vigour and fruit yield.

  3. Economic Loss: For commercial raspberry growers, raspberry beetle infestations can lead to significant economic loss due to reduced fruit quality. The presence of larvae within fruits may lead to crop rejection, especially for high-quality and fresh-market raspberries.

What Are the Signs of a Raspberry Beetle Infestation?

Raspberry beetle presence can be identified through several key symptoms:

  • Damaged Berries: Ripe fruits with dry, greyish-brown patches at the stalk end are an indicator of larval feeding. Inspect fruits for the brownish-white larvae, particularly if they appear shriveled.
  • Leaf Holes: Young leaves with small, elliptical holes may be the result of adult beetle feeding, giving foliage a “skeletonised” appearance.
  • Presence of Beetles: Adult beetles can be seen on the plants during their active period, from late April to mid-June. They are most active during warm, dry weather and often gather on flowers and buds.

Are There Natural Predators of the Raspberry Beetle?

The raspberry beetle has a few natural predators that can aid in its control:

  • Ground Beetles: These beetles are beneficial as they feed on raspberry beetle larvae and pupae in the soil. Encouraging ground beetles by maintaining garden diversity and using mulch can enhance natural control.
  • Birds and Hedgehogs: These animals can consume adult beetles or disturb larvae in the soil, providing another layer of pest management.

In the UK, raspberry beetles remain a common but manageable pest of raspberries and related cane fruits. By understanding their life cycle, using preventive trapping methods, and carefully selecting pesticide controls only when necessary, growers can effectively protect their crops from this persistent pest.