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Biological control of the lettuce root aphid

Updated on May 12, 2016

Controlling the lettuce root aphid in an environmentally friendly way

The lettuce root aphid, Pemphigus bursarius (Order: Homoptera; Family: Pemphigidae) is a host-alternating species that spends autumn, winter and spring on poplars, and summer on various Compositae, in particular lettuce and chicory.

A healthy lettuce head
Rasbak

Biology of the lettuce root aphid

The aphids (all females) that hatch from the overwintering eggs are greyish green and lightly covered with wax. These aphids suck sap from leaf stalks of poplar leaves, which results in the formation of hollow galls that enclose the aphid. The female aphids produce 100-250 offspring inside the gall, which are winged.

Wingless lettuce root aphids near the roots of lettuce
Rasbak

The winged aphids leave the galls and migrate to lettuce and other Compositae. They infest the foliage and produce wingless daughters which are yellowish white with waxy patches on hind part of the body, and which colonise the roots.

In late summer, the wingless aphids produce winged, sexual females and males, which fly back to poplar, where they mate. The females lay the overwintering eggs in crevices in the bark.

Some, however, do not get wings and these ar able to overwinter in the soil.

Damage by lettuce root aphid

Roots of lettuce and chicory become covered in a white, waxy secretion. Because of the aphids feeding from the roots, lettuces have difficulty forming heads. Leaves may turn yellow and plants may wilt and die.

Natural enemies of Pemphigus bursarius

The lettuce root aphid has different natural enemies during its different life stages.

The parasitic wasp: Pachyneuron spp (Pteromalidae)
James K Lindsey

When the galls open for the aphids to migrate to the lettuce plants, Syrphid flies and flower bugs (Anthacoridae) are able to enter the galls and kill all of the aphids. At this stage the main predators are the flower bugs Anthacoris nemorum and A. nemoralis.

During the underground stage, the aphids are attacked by rove beetle (Staphylinidae) and ground beetles (Carabidae). Also larvae ofThaumatomyia glabra and T. notata (Order: Diptera: Family: Chroropidae) are common predators at this stage.

When the sexual aphids leave the lettuce plants to fly back to poplar, they are attacked by ladybirds.

The Chloropid fly, Thaumatomyia notata

Photographer James K. Lindsey

Treatment

  • As the most damaging stage of this aphid lives on roots in the ground, use of chemical pesticides is unreliable and can sometimes even be damaging to the plants. Unfortunately, there is not much one can do against this pest, apart from pulling up lettuce plants that show symptoms of infestation and burning the aphid-infested roots (the heads are still edible if you act early enough!) to prevent further spread.
  • To attract Chloropids, one should grow flat topped flowers around the lettuce. For ground beetles, leave a heap of dead leaves in a corner to provide them with shelter, or place overturned flower pots nearby with uneven rims in which they can shelter.
  • Alternatively, one could grow lettuce plants that are resistant to Pemphigus bursarius

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      anonymous 5 years ago

      I had never heard of the lettuce root aphid but can see how they could devastate a crop. I've only grown leaf lettuce and that seems to do well, grows fast and is harvested often.