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Bruchid beetle – Bruchus rufimanus
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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 (Figure 1).
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Figure
1. Comparative efficacy of
insecticides to control bruchid beetle in spring beans
cv. Quattro. Mean of three years trials
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here for a larger image
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