State Size Features
Larva Up to 40 mm - Typical noctuid form: 3 pairs of thoracic legs and 5 pairs of false abdominal legs. It is green to brown. Sometimes it has several yellow longitudinal lines.
Adult 30 mm (wingspan) - Wings grayish brown. S. Exigua has two characteristic orange spots. The hind wings are clear the brown ribs and rim.
The adults appear in the spring, mate and the females deposit the eggs grouped preferably on the underside of the leaves. Next they cover the setting with scales of their abdomen that serve as protection. The eggs hatch and the caterpillars begin to feed, gregariously at first. After completing all its stages, the caterpillar weaves a cocoon of silk and pupa inside, buried in the ground. New adults will give rise to future generations, usually 3, although it depends on the climate. In the greenhouse generations can happen throughout the year. Populations tend to be maximum in the fall.
Symptoms / Damage
They cause defoliation when biting the leaves. When the caterpillar is small it destroys the underside, repeating the epidermis of the leaf. As it grows, its jaws are larger and you can eat the leaf from top to bottom.
If the caterpillar destroys the apical growth bud, the plant becomes blind and will not develop.
The remains of excrement in the plant will serve to evindeciar the presence of this or other caterpillars.
In harvestable crops such as lettuce, the caterpillars are introduced inside destroying it, although externally the symptoms are not appreciable. In other crops depreciate the fruit by gnawing the bark, as in watermelon.
The larva feeds on the foliage of the plants and can be eaten completely by the small ones. The smaller larvae devour the parenchyma of the leaves, so that all that remains is a thin epidermis and veins. Larger larvae tend to open holes through thicker areas of plants. For example, they will make a direct hole in the heart of a lettuce instead of eating the tissue of a particular leaf, which makes the product unfit for trade. They attack buds and buds, preventing flowering, the appearance of new leaves and the development of plants. In their wandering, the smaller larvae leave a silk trail, entangling the leaves with a silvery film.
The critical period is in post-planting, when the plants are underdeveloped. We must focus on destroying the caterpillars in their first stages, when they are more sensitive, and try to do so mainly with natural products so as not to eliminate the auxiliary fauna.
There is a large amount of active materials that can be used to combat this pest depending on the crop.
There are predators (Orius spp., Lacewings), hymenoptera parasitoids, viruses and fungi, which are important allies in the control of this insect.
- Cultural measures
Placement of pheromone traps, both for this species and for other noctuids such as heliotis. These traps are used to capture adults and are essential to determine the exact moment at which to start treatments.
It is convenient to eliminate the weeds that serve as refuge.