Crops
Aphids
Several species of aphids * ( aphids ) can form colonies on the young leaves of lettuce (figures 1 to 5), this from the nursery: Myzus persicae (Sulzer 1776) (figure 6), Nasonovia ribisnigri (Mosley) (aphid of the lettuce), Aphis gossypii (Glover 1877) (in glasshouses in particular) (figure 7), Macrosiphum euphorbiae (Thomas 1878) (figure 8), Hyporomyzus lactucae (L.) ...
Other aphids attack the roots of lettuce: Pemphygus bursarius (L.) (woolly lettuce root aphid), Protrama flavescens (Koch, 1857) (large lettuce root aphid). To these 2 species, it is advisable to add others belonging to the genus Trama and also living on the roots of lettuce.
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).
To help you recognize aphid species, consult the INRAE site Encyclop'Aphid .
- Nature of damage
Nutritional bites of aphids have very little direct impact on salad leaves. The strong outbreaks of these insects contribute to soiling the final product which will thus be difficult to sell (Figures 2 to 5). Besides aphid colonies, one often observes white molts (Figures 4 and 5) and the presence of honeydew on the surface of above salads, which develops the Sooty mold (sooty mold).
On salads, they are especially formidable by their ability to transmit several Viroses . In addition, the chemical control of populations of these pests is often problematic because of their possible resistance to several insecticides.
- Biology
These insects have a rather complicated life cycle, with the possibility for adults of some species to change host in winter. We find eggs, founders of populations, adults, among them, winged viviparous females or not, and winged males. The length of the cycle varies depending on the species, the nature of the host plant and its condition, and climatic conditions.
- Forms of conservation and / or alternative hosts : it is often the eggs, laid in particular on many weeds at the approach of winter, which allow these insects to spend the winter. They can, of course, survive under heated shelters on existing crops, in the form of viviparous females in particular.
- Developmental stages : the eggs laid on various hosts, herbaceous or woody, hatch and give rise to founders. Subsequently, over a long period of time, viviparous females are found in the colonies.
Young larvae form, which immediately feed on the sap and molt 4 times before giving birth to the adult. White moults (exuviae) on vegetation indicate the presence of aphids in the crop. The adults are winged (1) or not; in the latter case, we speak of “wingless” individuals (2) (figures 9 to 11). Each individual can give birth to 40-100 offspring depending on the host and climatic conditions in particular.
Larvae and adults, often present on the underside of the leaf blade, feed through their rostrum. The excess sugar contained in the sap is rejected in the form of honeydew.
- Dispersion in the crop : a few plants scattered throughout the crop on which aphid colonies quickly gain importance constitute the first outbreaks. First wingless, aphids start by visiting neighboring plants. As soon as the adults appear (during outbreaks), they disperse in the crop or in nearby plots. Plants and workers can contribute to their spread.
- Favorable development conditions : these insects appreciate mild temperatures and summer conditions in shelters.
- Forms of conservation and / or alternative hosts : it is often the eggs, laid in particular on many weeds at the approach of winter, which allow these insects to spend the winter. They can, of course, survive under heated shelters on existing crops, in the form of viviparous females in particular.
- Developmental stages : the eggs laid on various hosts, herbaceous or woody, hatch and give rise to founders. Subsequently, over a long period of time, viviparous females are found in the colonies.
Young larvae form, which immediately feed on the sap and molt 4 times before giving birth to the adult. White moults (exuviae) on vegetation indicate the presence of aphids in the crop. The adults are winged (1) or not; in the latter case, we speak of “wingless” individuals (2) (figures 9 to 11). Each individual can give birth to 40-100 offspring depending on the host and climatic conditions in particular.
Larvae and adults, often present on the underside of the leaf blade, feed through their rostrum. The excess sugar contained in the sap is rejected in the form of honeydew.
- Dispersion in the crop : a few plants scattered throughout the crop on which aphid colonies quickly gain importance constitute the first outbreaks. First wingless, aphids start by visiting neighboring plants. As soon as the adults appear (during outbreaks), they disperse in the crop or in nearby plots. Plants and workers can contribute to their spread.
- Favorable development conditions : these insects appreciate mild temperatures and summer conditions in shelters.
- Protection methods
Several protection methods are recommended to control the development of aphids on lettuce in France:
- check the sanitary quality of the plants before and during their introduction into the shelter;
- produce the plants in an shelter insect- proof ;
- install canvases insect-proof at shelter openings;
- check the sanitary quality of the plants before and during their introduction into the shelter;
- produce the plants in an shelter insect- proof ;
- install canvases insect-proof at shelter openings;
- avoid excessive nitrogen fertilization;
- weeding the plots in the open field, the greenhouse and its surroundings;
- monitor crops and detect the first pests thanks to the yellow sticky panels placed above the crop as soon as the plants are introduced;
- weeding the plots in the open field, the greenhouse and its surroundings;
- 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 the aphid Nasonovia ribisnigri biotype Nr: 0;
- use auxiliaries such as the insects Aphelinus abdominalis, Aphidius colemani, Aphidius ervi, Aphidoletes aphidimyza and Macrolophus caliginosus (the latter is of secondary efficacy) and the fungus Verticillium lecanii (note that its efficacy may vary from strain to strain. other);
- use auxiliaries such as the insects Aphelinus abdominalis, Aphidius colemani, Aphidius ervi, Aphidoletes aphidimyza and Macrolophus caliginosus (the latter is of secondary efficacy) and the fungus Verticillium lecanii (note that its efficacy may vary from strain to strain. other);
- put in place practices in the open field which make it possible to maintain an active population of natural predators of aphids that pest salad: hoverflies, lacewings and ladybird larvae. The installation of hedges and flower borders, or an unharvested and untreated row left at the edge of the plot, allow useful fauna to take refuge and feed there.
- consider chemical protection (r) ( e-phy-Laitue ; e-phy-Scarole-frisée ) *, in particular if you use auxiliaries.
(r): resistance to insecticides or acaricides is known in these pests.
- consider chemical protection (r) ( e-phy-Laitue ; e-phy-Scarole-frisée ) *, in particular if you use auxiliaries.
(r): resistance to insecticides or acaricides is known in these pests.
* Chemical control : The number of pesticides available for a given use is constantly changing, we advise you to always confirm your choice by consulting the e-phy site of the Ministry of Agriculture and Fisheries which is a catalog in line of plant protection products and their uses, fertilizers and growing media approved in France. This also applies to all biological products based on microorganisms or natural substances.
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