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Pollen Beetle
Meligethes aeneus F
General Description
The adults are commonly seen on oilseed rape flowers.
They are approximately 2mm in length, black with a shiny green/blue metallic appearance.
They are unlikely to cause great damage to winter oilseed rape, but they are greater threat to backward winter crops and to spring oilseed rape crops.
Biology
In the spring, adult pollen beetles fly to winter oilseed rape crops. They initially colonise the field margins before venturing further into the crop. The beetles feed on pollen. This means they are of no threat to crops in flower, but at green and yellow bud growth stages, they can damage the flowers.
Spring oilseed rape crops tend to be at a greater risk of damage from pollen beetles, which is why thresholds are different for winter and spring sown crops.
Advice
Crops at risk are those still at green-yellow bud where the beetles have to chew their way through the bud to get at the pollen – this kills the bud leading to blind stalks as no flowers will consequently form.
Healthy well established winter oilseed rape crops would need 15 beetles per plant to warrant an insecticide. Stressed winter oilseed rape crops cannot cope with the added stress of pollen beetles, so these crops only need 5 beetles per plant at green-yellow bud to justify treatment.
The threshold for spring oilseed rape crops when treatment is required is one beetle per plant
If these thresholds are reached when the crop is in flower, forget about applying any insecticides for pollen beetle control as the beetles can now gain easy access to the pollen they hanker after.
Applying an unnecessary insecticide treatment to flowering oilseed rape compromises bee safety, and can ultimately lead to a lowering of yields, as bee pollination is essential for achieving good yields from oilseed rape.