Broad bean seed beetle

What is broad bean seed beetle?

The adult insect is a small beetle that belongs to a family of seed-infesting beetles that are known as bruchid beetles.  It is the larval stage feeding inside the seeds that causes the damage.

Symptoms

• Circular holes, just over 1mm diameter, occur in the seed coat of dry broad bean seeds saved from a previous crop
• Four millimetre long beetles, mottled with black, brown and white scales, may be found with the seeds
• The species most frequently associated with broad bean seeds in Britain is Bruchus rufimanus
• Other Bruchus species are associated with the dried seeds of other legumes

Control

There is no control available to amateur gardeners. Fortunately, affected seeds will usually germinate as the grubs feed in the cotyledon part of the seed, most of which survives, and the seed embryo is undamaged.

Biology

• Adult broad bean seed beetles lay eggs on broad bean pods in early summer
• After hatching, the grubs bore into the developing seeds but are too small to be noticed in beans picked for eating. However, the grubs continue to feed in those beans allowed to develop as dry seeds
• In the warmth of a house, adult beetles emerge during winter, leaving tell-tale circular exit holes in the seed coats