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Moths (noctuids)

The roots, crown and lettuce leaves are susceptible to being devoured by the caterpillar stage  of several more or less polyphagous Lepidoptera. These insects belong to various families, especially noctuids. These include the defoliating moth Autographa gamma (L.), and the soil- moths dwelling Agrotis segetum (Denis & Schiffermüller) and Agrotis ipsilon (Hufnagel) . We find these moths (loopers), and many others, in many production areas around the world where they sometimes cause considerable damage in field crops, such as under cover of salads.
  • Nature of damage
It is the oldest larvae of moths, whether defoliators or soil-dwelling, which cause the most damaging damage on lettuce, especially on young plantations:
- leaves with holes, perforations, more or less devoured and cut (figure 1);
- presence of blackish or greenish droppings (figure 2);
- shearing of the apex (figure 3);
- perforation of the pivot at the level of the collar (Figures 4 and 5);
- collar more or less devoured ...
- wilting of plants at the damaged neck (figure 6).
  • Biology
Lepidoptera go through 4 stages of development: egg, larva or caterpillar, pupa or chrysalis, and butterfly (Figure 1).

- Forms of conservation and / or alternative hosts : most of these butterflies hibernate through pupae, or even larvae, although other stages of development may contribute to the winter conservation of these insects. They can be hosted by many cultivated and non-cultivated hosts.

- Stages of development : the eggs (figure 7-1), transparent, white, black-brown, mauve, etc., with a diameter less than a millimeter, are deposited singly or in groups on the surfaces of the leaves or various supports (figure 8 ). Subsequently, they hatch and give birth to caterpillars (figure 7-2) measuring 25 to 50 mm depending on the species, equipped with powerful mandibles that allow them to constantly consume plants, especially leaves (figures 3 and 5 to 7).

These caterpillars, of variable color (green, sometimes becoming brown to reddish as they age, gray-brown with longitudinal black dots, etc.) (figures 9 and 10), moult several times before pupation or chrysalization. The pupae (Figure 7-3), which measure from 2 to 2.8 cm and on which we can clearly see the sheaths of the legs and wings as well as the abdominal segmentation, are reddish-brown in color. The adults (figure 7-4) are butterflies with 2 pairs of wings and whose wingspan varies from 25 to 45 mm for the species of interest to us. The fore and hind wings present a variable coloring according to the species (reddish brown, brown, gray ), as well as more or less characteristic patterns (figure 1).

The duration of their cycle varies depending on the temperature, from ten days to several weeks. The caterpillars are mobile and move easily from one leaflet to another like the adults who do so more easily. We should add that the reduction in soil disinfection practices seems to be contributing to the resurgence of this pest, on vegetable crops among others.
  • Protection methods
Several protection methods are recommended to control the development of noctuids on lettuce in France:
- turn over the land in winter so that predators devour the larvae and the cold destroys them;
- weed and hoe regularly in order to eliminate certain weeds that may harbor these insects (long-leaf rumex, sheep sorrel rumex, plantain, hairy burdock, Canada thistle, dandelion);
- install canvases insect-proof  at shelter openings;
- install pheromone traps outside the shelter to monitor the presence of adults;
- use plants that repel female noctuids such as wormwood and tansy (scattered branches, infusion);
- Keep the soil moist and carry out regular hoeing to bring them to the surface and destroy them;
- Dig the soil one or two centimeters deep all around the attacked plants, and eliminate the caterpillars found there;
- maintain biodiversity in the garden because certain species of ground beetles are predators of lepidopteran larvae with nocturnal activity.
- promote the presence of Blackbirds, crows that eat caterpillars;
- use a biopesticide based on Bacillus thuringiensis which is rather active on young caterpillars;
- reasoning about chemical protection * ( e-phy-Noctuids defoliatrices ; e-phy-Noctuids soil ).


* 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.
Last change : 04/29/21
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