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The most obvious symptom of damage is to the raspberry fruit (See Pictures). Large, frass-filled tunnels are present in the receptacle of the flower and in many cases they contain a single larva (See Pictures). Larvae also browse on the proximal drupelets of the developing fruit causing characteristic feeding damage. The feeding sites may become infested by the grey mould fungus (Botrytis cinerea). Adult raspberry beetles browse on the young expanding leaves of the primocanes causing characteristic inter-veinal feeding holes. Non-migrating adult beetles feed on the developing raspberry flower buds. At open flower, all adults feed on the nectaries causing characteristic brown feeding lesions. They also feed on the anthers and stigmas.
Current control strategies rely on use of insecticides applied to kill the adults (pre-flowering), or in some countries, at green and pink fruit stages to kill the eggs and larvae. A wide range of insecticides have been approved in the past, but with the recent review of pesticide approval in the European Union and withdrawal of many products due to environmental or economic grounds, the range of available products is rapidly diminishing. At the time of writing (January 2003), chlorpyrifos is the only organophosphorus-based insecticide approved in the UK. Control can be achieved by use of synthetic pyrethroid-based products, but in many instances their use can lead to the build up of two-spotted spider mites (Tetranychus urticae). Organic raspberry growers use sprays of rotenone to manage raspberry beetles. Research in the 1970s showed that rotenone, although effective, was less so than the then currently available synthetic insecticides in controlling raspberry beetle larvae in the fruit (Taylor, 1971). There are several new compounds under development and they may be suitable for raspberry beetle control. Thiocloprid may be available shortly as an alternative to the organophosphate insecticides (Erdelen, 2001).
The framework for an IPM approach to the control of raspberry beetle is now in place. The use of non UV-reflective traps pioneered in Switzerland (Höhn et al., 1995) has been further tested in Switzerland, Finland and the UK (Woodford et al., 2000, 2003) (See Pictures). Provisional thresholds for chemical spaying have been established for use in Switzerland and the UK. The thresholds are based on the numbers of adult raspberry beetles trapped on the adhesive surfaces of the white traps placed within the raspberry crop from first adult beetle emergence to first open flowering. Two threshold limits have been set depending on the designated market for the crop. The fresh fruit and high quality IQF frozen fruit has a threshold of less than five adult beetles per trap, whereas the processed crop has a higher threshold of less than 20 adult beetles per trap over the same period. In addition, the identification of volatile flower derived chemicals (Birch et al., 1996; Griffiths et al., 2000) has led to the development of more effective traps which may lead to improved detection and control of raspberry beetle (Woodford et al., 2003). The role of these enhanced traps is currently being investigated in the UK.
B. tomentosus is a major pest in western and northern Europe, although it can be found in most raspberry-growing regions in Europe extending into Asia.. Most high quality producers (fresh fruit and quality processed fruit) have a zero tolerance to larval contamination and fruit injury. Raspberry beetle is primarily a pest of fruit quality, the adults directly damage the flower buds and flowers and the larvae damage the fruit (See Pictures). In addition, the feeding of raspberry beetle larvae directly damages drupelets on the fruit and this damage can lead to further infection by grey mould (Botrytis cinerea) (Woodford et al., 2002) which leads to considerably reduced shelf-life of fresh raspberry fruit.