Crops
Noctuids
General
- Rather polyphagous insects widely distributed in the world, rather damaging in tropical areas. They belong to the order Lepidoptera, to various families, in particular the Noctuidae.
- Numerous species parasitizing vegetable crops in tropical areas:
- Agrotis segetum (harvest moth,
- Agrotis ipsilon (noctuelle ypsilon)
- Autographa gamma (noctuelle gamma),
- Chrysodeixis chalcites
- Chrysodeix
- Euxoa nigricans (blackish moth),
- Gortyna xanthenes (artichoke moth),
- Helicoverpa armigera (tomato moth)
- Lacanobia oleracea
- Mamestra brassicae (Cabbage moth),
- Mamestra oleracea (Vegetable moth),
- Mythimna unipunctata (Spotted noctuid),
- Spodoptera eridania
- Spodoptera
- Spodoptera frugiperda
- Spodoptera littoralis (Mediterranean moth)
- Moths whose coloring and designs on their fore wings allow them to blend in with the substrate.
- Almost all phytophagous caterpillars; some are soil-dwelling ("cutworms"). They are more or less polyphagous and damaging to the aerial and telluric organs of vegetables.
- The decrease in soil disinfection practices seems to be contributing to the resurgence of these pests.
- Insects observed in the open field and in crops under cover.
* Species of the genera Spodoptera , Argyrogramma and Chrysodeixis are observed on cabbages in Guyana.
- Sensitive botanical family (s)
| Many botanical families |
- Affected production areas :
| Mayotte | Reunion island | Guyana |
| Guadeloupe | Martinique | New Caledonia |
| French Polynesia |
- Organs attacked
| Leaves | Flowers | Fruits |
| Stems | Snares |
Symptoms, damage
- Symptoms :
- Consumption of tips and leaves and leaflets by the larvae, especially the older ones. They form large holes located on the leaf blade or at its periphery, sometimes leaving behind only the main veins and thus greatly reducing photosynthesis.
- Perforation of stems and fruits which they subsequently invade. In addition to the perforations, galleries and cavities are observed. Many droppings are visible inside and also outside. Parasitized fruits, for example tomato, stop growing, ripen prematurely and fall off. Note that these perforations facilitate the penetration of many rotting agents, such as Choanephora cucurbitacearum , etc.
- The flowers are also attacked and the seed envelopes are punctured.
- Signs : Presence of larvae, sometimes butterflies on plants and in the culture (figures).
- Possible confusion :
Biology
- Development cycle : includes 4 development phases: egg, larva or caterpillar, pupa or chrysalis, and butterfly (figures). Most of these insects overwinter through pupae or even larvae, although other stages of development may contribute to winter conservation of these insects. They can be hosted by many cultivated and non-cultivated hosts.
- Transparent eggs, white, black-brown, mauve, etc., with a diameter of less than a millimeter, are deposited singly or in groups on the surfaces of leaves or various supports.
- Subsequently, they hatch and give birth to caterpillars (figure) measuring 25 to 50 mm depending on the species, provided with powerful mandibles that allow them to permanently consume plants, especially leaves. The caterpillars, of variable color (green, sometimes becoming brown to reddish as they age), moult several times, before pupation or pupae.
- The pupae, which measure from 2 to 2.8 cm and on which we can clearly distinguish the sheaths of the legs and wings as well as the abdominal segmentation, are reddish brown in color.
- The adults are butterflies with 2 pairs of wings and whose wingspan varies from 25 to 45 mm for the species that interest us. The fore and hind wings present a variable coloring according to the species (reddish brown, brown, gray, etc.), as well as more or less characteristic patterns.
- The duration of their cycle varies depending on the temperature, from ten days to several weeks.
- Dispersal : Caterpillars are mobile and move easily from leaf to leaf like adults, who do so more easily.
Protection
- Weed the crop and its surroundings.
- Produce the seedlings in an nursery insect-proof .
- Check the sanitary quality of the plants before and during their introduction into the crop or shelter.
- Install canvases insect-proof in nurseries and at shelter openings when weather conditions allow.
- Install pheromone traps outside the shelter. (1)
- Favor natural enemies in field crops or under open shelters (2).
- Use biopesticides (3).
- Reasoning about chemical protection
(1) Selective trapping with pheromones can be used to limit the parasitic pressure of this insect. The monitoring of the traps will make it possible to follow the evolution of the population of adult moths and therefore to more precisely position the Bt-based treatments.
(2) Certain parasitoid auxiliaries (Hymenoptera and Tachineus fly) allow the larvae of to be controlled naturally Sodoptera eridania .
(3) The use of a product based on the insecticidal bacterium Bacillus thuringiensis (Bt) makes it possible to kill the young larvae of moths which ingest the product by consuming the cabbage leaves. As the sun inactivates Bt-based formulations and the young caterpillars are especially active at night, applications at the end of the day will be preferred to ensure good treatment efficiency. Irrigation by sprinkling the plot should not be started after the treatment, which would otherwise risk being completely washed out.
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