Bruchid beetle – Bruchus rufimanus Images
Bruchid beetles belong to a group of insects originating in Africa and the Mediterranean area. They were probably bought to the U.K. in imported seed where they pupate. Adults appear in spring or summer, usually when temperatures exceed 20oC for a number of days and lay their eggs on the flowers, young pods or seed of bean crops, boring into the young pod and seed. Larvae pupate and hatch into adults which bore out of the seed leaving characteristic exit holes which ruin their appearance. Bruchid beetle damage can reduce seed germination, especially if establishment conditions are poor as solutes leak from the endosperm through the exit holes, encouraging soil fungi and damping off diseases. However, the main effect of bruchid beetle damage is to reduce the quality of beans grown for human consumption. These are mainly spring beans, especially the tannin free varieties.
Control is difficult since the adults are present over a long period of crop growth and insecticides are not persistent. Applications of pyrethroids during flowering are most effective, the first applied when adult presence is first detected (usually early May) followed by a second at late flower to early podding.