Practice Abstract 34 - Bruchid beetle - background

Short title (native language): 
Bruchid beetle - background

Short summary for practitioners (native language): 
Bruchus rufimanus (bruchid beetle) is widespread in field and broad beans in many parts of England. Damage to field beans is visible as circular holes in the seed where adult beetles have emerged. In broad beans, seeds may be blemished or infested with immature larvae. The most significant effect of damage is to reduce the value of the crop for human consumption or seed and at high levels, germination of seed may be significantly reduced. Bruchus rufimanus is endemic in the UK, has one generation each year and does not multiply in stored produce.
Adults are 3.5 - 4.5 mm long, oval, black or dark brown in colour with small, grey flecks along the wing cases. Larvae are white, segmented, fleshy grubs, 3 - 4 mm long when fully grown, and have a light brown head with small legs on the forward three segments.
Adults emerge from overwintering sites during April and May in the UK and eggs are laid singly on the surface of developing pods. Eggs are translucent, 0.5 mm long and are fixed to the pod surface. Egg laying is concentrated on lower pods and after a few days larvae hatch and bore through the pod wall into the developing seed. Development continues in seeds where the larva feeds and pupates, usually at the time that seed is mature and dry. After pupation the adult bites through the seed coat, leaving a circular hole in the bean. Many beetles emerge before harvest, but emergence may take place in store. Some smaller holes are made by the parasitic wasp Triaspis luteipes.