If no control measures are used, populations of Raspberry beetle — Byturus tomentosus — can multiply so quickly that the damage caused makes any fruit harvested totally unmarketable. The larvae attack raspberries and blackberries and their presence in harvested fruit makes them unsuitable for fresh fruit outlets or for processing.
Early in the season adults cause considerable damage by direct feeding on nectar and stamens. Although adult feeding can leave black scars on tissue at the base of the stamen, the most serious damage is as a result of larvae feeding on developing fruit.
Adult Raspberry beetles overwinter in the soil, at depths ranging from 2cm to 30cm. They emerge from the soil in late April and during May in England and generally two to three weeks later in Scotland. In Scotland, small numbers can also emerge during July and August. Newly emerged adults are golden brown, turning grey-green as they mature, and grow to about 4mm in length. In warm conditions adult beetles are very active, but become sluggish whenever the conditions are cool or wet.
Females lay small, white, shiny eggs in the blossoms of raspberry plants during June and July. Egg laying in blackberries occurs later in the season. Eggs normally hatch around 10 – 12 days after being laid.
Larvae are yellow in colour with dark markings on the body and a brown head. Newly emerged larvae feed on the surface of young fruit, moving and feeding inside the fruit as it ripens. Larvae sometimes attack a second fruit. Mature larvae can grow to 8mm before they fall from the fruit and burrow into the soil. Larvae remain in the soil for about 4 weeks before pupating. By early autumn, normally four or five weeks after pupation, adults appear which remain in the soil until they emerge in the following spring.