Crops
Pemphigus bursarius (L)
Poplar-lettuce gall aphid
Several species of aphids attack the roots of lettuce: Pemphygus bursarius (L.) (woolly lettuce root aphid), but also Protrama flavescens (Koch, 1857) (large lettuce root aphid), and other species of the genus Trama .
These polyphagous insects belong to the order Hemiptera, the suborder Sternorrhyncha and the superfamily Aphidoidea. They grow quite frequently on salads as colonies (Figure 1).
- Nature of damage
Bites and nutritional samples of aphids on the roots lead to wilting and death of the roots. As a result, the development of salads can be more or less reduced: salads not very vigorous, chlorotic, soft apple, sometimes complete wilting. This may affect returns over time.
Usually, the attacks of this aphid go unnoticed; It is especially during the uprooting of the crop that the root damage is observed: development of very many yellowish-white insects along the roots, these bearing a fairly conspicuous tuft of white wax. Their presence gives the impression that a white or ashy hair mixes with the roots (Figures 1 to 4). The attacked roots turn brown at first and die.
Remember that this aphid is also capable of transmitting Lettuce Mosaic Virus (LMV).
- Biology
This insect has a rather complicated biological cycle. It performs this on two different botanically unrelated hosts (dioecious): a primary host poplar ( Populus nigra var. Italica ...), and a secondary host which may be a plant belonging to the Asteraceae family (salads, chicory, endive, artichoke ...).
- Forms of conservation : it is its eggs that allow it to spend the winter on the poplar, in the crevices of the bark. They are small in size, greenish white and covered with wax, measuring 0.35 mm x 0.2 mm.
- Developmental stages : when poplar buds, the eggs hatch and give rise to wingless founding females which parasitize the leaf petioles (measuring 2.4 to 3.0 mm, with a greyish green body slightly covered with wax, antennae with 4 segments, a brown head and legs); these swell as a result of the numerous bites carried out and galls (cecidia) form, reconvigorating the aphids and their offspring. When the galls open, 100 to 250 adults fly to their secondary hosts, including young lettuce plants. The aphids initially feed on the leaves (virginiparous wingless measuring 1.5 to 2.7 mm, yellowish white with wax tufts on the posterior part of the abdomen), but quickly the newly winged aphids trained will be able to feed on the roots of lettuce and thrive there until the fall (Figures 3 and 4).
- Dispersion towards the primary host : At the same time, at the end of summer and the beginning of autumn, sexual and winged individuals reach the poplars where the winter eggs will be laid (winged sexupare measures 1.6 to 2 , 7 mm, orange brown, with wax glands on thorax and abdomen but no rostrum and 6 antennae sections).
- Favorable development conditions : The attacks of this aphid are especially observed in the open field near poplar hedges. It is more rarely found under shelters.
- Protection methods
The fight against this aphid is quite delicate given its location on the roots, organs that are difficult to access and therefore protectable.
Some protective measures can be recommended to control the development of this aphid on salads in France:
- produce the plants in an shelter insect- proof ;
- install canvases insect-proof at shelter openings;
- install canvases insect-proof at shelter openings;
- avoid setting up a salad crop near plantations or hedges of poplars, or other sensitive crops;
- work the soil in depth and let it dry before planting;
- avoid excessive nitrogen fertilization;
- provide plants with sufficient water supply;
- provide plants with sufficient water supply;
- monitor crops and detect the first pests thanks to the yellow sticky panels placed above the crop as soon as the plants are introduced;
- cultivate varieties resistant to Pemphigus bursarius.
Figure 1
Figure 2
Figure 3
Figure 4