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Biological Control of the Pollen Beetle, Meligethes aeneus

Updated on May 17, 2016
Meligethes aeneus
Meligethes aeneus | Source

How to control the pollen beetle without insecticides

The pollen beetle, Meligethes aeneus (Order: Coleoptera; Family: Nitidulidae) is also called blossom beetle and is a serious pest on oil seed rape. These black beetles are between 1.5 and 2.7 mm long. The wing cases are metallic blue or green with fine hairs; the legs are brown. They have clubbed antennae.

The larvae are about 4 mm long and yellowish white, with 2 or 3 small, dorsal spots on each body segment. The head and short legs are black.

A pollen beetle on a flower
A pollen beetle on a flower | Source

Biology of Meligethes aeneus

M. aeneus overwinters as adult beetle in the ground. In spring, when temperature rises to 15 °C or above, the beetles fly to rape fields, sometimes covering distances of up to 3 km. With the flowers still closed, they bite into the oldest flowers to reach the pollen inside. Apart from pollen, they also eat nectar.

The females lay eggs on the pistil or stamens, after having bitten a hole in the flower bud. Each female can produce some 200 eggs.

The larvae hatch after 4 to 7 days and eat from the pollen for about 3 to 4 weeks after which they pupate in the ground.

In June the young beetles emerge and one can find them on buds and flowers of many crucifers.

In August and September, the beetles fly to their overwintering sites, often at the edges of woods, where they dig themselves 2 to 5 cm deep into the soil.

Damage by the pollen beetle

In years when the weather in late spring is cool and wet, thus delaying flowering, M. aeneus can be an important pest of rape, as the adult beetles and larvae destroy large numbers of flowers and flower buds. It can also be harmful to brassica seed crops and to beans, which may fail to form seeds.

In warm and sunny springs, the flowers will already be open when the beetles arrive, and damage will be minimal or absent.

Remember

In warm and sunny springs, the flowers will already be open when the beetles arrive, and damage will be minimal or absent.

Tersilochus ningxiator
Tersilochus ningxiator | Source

Natural enemies of Meligethes aeneus

Pollen beetles have many enemies

Larvae will be attacked by various parasitoids, of which Phradis spp and Tersilochus spp (Order: Hymenoptera; Family: Ichneumonidae) are the most important, but Isurgus heterocerus (Ichneumonidae) and Diospilus capito (Order: Hymenoptera; Family: Braconidae) also attack pollen-beetle larvae.

The main predators of pollen beetles are ground beetles and rove beetles (Order: Coleoptera; Family: Staphylinidae) and wolf spiders, as well as the larvae and adults of ladybirds, such as Coccinella septempunctata (Order: Coleoptera; Family: Coccinellidae), larvae of the lacewing Hemerobius spp (Order: Neuroptera; Family: Hemerobiidae) and larvae of syrphid flies (Order: Diptera; Family: Syrphidae).

Predators of the pollen beetle

Click thumbnail to view full-size
A ground beetle.A wolf spider.A lacewing.A ladybird.A few rove beetles.A syrphid fly.
A ground beetle.
A ground beetle.
A wolf spider.
A wolf spider.
A lacewing.
A lacewing.
A ladybird.
A ladybird.
A few rove beetles.
A few rove beetles.
A syrphid fly.
A syrphid fly.

Treatment without insecticides

  1. Do not plough the field after you harvested oil seed rape. Ploughing brings overwintering parasitoids to the surface, which will make them an easy prey for birds and can kill them when there is a frost.
  2. Do not spray insecticides, as this will also kill off the parasitoids and predators of the pollen beetle.
  3. Plant clover between or around the oil seed rape. This will attract predators.
  4. When you design crop rotation, keep parasitoids of the previous field in mind: place the next field close to that of last year!

Two important books on the biological control of oil seed rape pests

Guestbook Comments

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    • profile image

      antoniow 5 years ago

      Fantastic lens, well done!

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      JoshK47 5 years ago

      Awesome info here! Thanks for sharing!