Cruciferous Moths (Plutella xylostella): [Characteristics, Detection, Effects and Treatment]

What are cruciferous moths?

Cruciferous moths or Plutella xylostella, are lepidopteran-type insects, belonging to the Plutellidae family, which have practically conquered the entire world, because although they come from the European Mediterranean region, they also live in America, Asia, Africa and Oceania, that is, it has reached all continents.

It is currently recognized as the pest with a cosmopolitan presence that causes the greatest damage to crops of plants from the Brassicaceae family, in its different varieties, because it has developed great resistance to pesticides and to Bacillus thuringiensis toxins, known as toxins. Bt.

In the tropical and subtropical regions of the planet, this insect abounds in any of the stages that make up its life cycle throughout the year, which implies high resistance and environmental adaptability, because cruciferous plants serve as hosts, since they are also perennial plants that thrive in these ecosystems 365 days a year.

But the same does not happen in temperate zones, because cruciferous plants do not have the capacity to develop throughout the year, which is why the most recent ecological investigations have raised serious suspicions related to the capacity that Plutellas xylostella would have so that their pupae and adults hide inside their hosts in order to survive the winter, after establishing that they have effectively achieved resistance to low temperatures.

The truth of the matter is that these insects never cease to amaze. They survive long distances traveled, being able to move in air currents, maintaining the flight in more than 1,000 km of travel in a single day. That is why they do not have major problems in migrating from warm places to temperate regions.

How can we identify them?

There are many signs related to the morphological characteristics, habits and damage of these small lepidoptera, both in the larval and adult stages. Let’s see.

1. In their adult state, these insects have an approximate standard length of about 15 mm.
2. The head is reddish-brown to black, the body is usually yellow-brown with a longitudinal band across the back. It also has black spots on the prothorax.
3. When it is at rest, it puts its antennae forward, in a kind of extension of its body, which has a narrow and sharp appearance, with a greenish color.
4. It has narrow pale yellow forewings rounded at the tip, but with a full fringed trailing edge. And the hindwings are shorter and more pointed, with more fringes.
5. They are insects of great ability, they move very fast.
6. The pupae are fusiform and about 8 mm long. When they are newborn they are light green and yellow but later they darken.
7. A pupa has a development cycle that lasts around 8 days.
8. They winter as adults as chrysalises and lay eggs in May, when they place up to 6 units on the underside of the leaves, spreading near the nerves of the favorite plants: cabbages, cauliflowers, broccoli, rapeseed, among other cruciferous plants. spontaneous.
9. They come out to eat at night, they have nocturnal habits.
10. The females, throughout their lives, can lay more than 100 eggs and the embryos develop in a short time: a maximum of 8 days will suffice.
11. The young caterpillars are very hard-working and dig galleries or tunnels in the leaves for about a week, to later move on, barely sparing the veins and the epidermis of the bundle. The rest will be fully consumed.
12. At the end of their development cycle, they pupate and will be seen again as moths at the end of June.
13. The nymphosis phase is spent wrapped in a silky and transparent cocoon on the leaves. For this time of pupation, they usually weave a silk cocoon with a loose weave, in places that are not so visible on the plant itself, such as the underside of the leaves.

You have to be very careful with the crops between July and August, because at this time the second generation of these moths appears, which becomes much more aggressive than the first that appears in February.

In this reproductive stage they can even destroy the progress of crops, if they behave as a pest.Towards autumn they begin to hibernate, although they will also do so as chrysalises, but they also damage cruciferous plants quite a bit, because the caterpillars nibble the leaves quite intensely, leaving holes in them.

At this time, they have the habit of destroying the outer leaves first, then go inside the plant and form their chrysalises on the inner leaves.

What plants are affected by cruciferous moths?

This insect is a faithful pest that exclusively attacks crops of the Brassicaceae family in its wild or spontaneous and cultivated varieties.

Various studies have also established that they focus their attention primarily on food plants rich in glucosinolates, such as: varieties of cabbage, cauliflowers, radishes, turnips, Brussels sprouts, kohlrabi, watercress, Chinese broccoli, chestnut mustard, among others. others.

Another important fact to keep them at bay is that due to the lack of cultivated species of Brassicaceae, then they stay in the so-called weeds, so they must be exterminated before the crops begin, since they serve as the perfect home, especially in temperate regions, when they proliferate during the arrival of spring.

How to combat cruciferous moths?

The educational portal Wikipedia points out that from the 70-80s of the 20th century, this moth became the pest with the greatest destructive potential of cruciferous crops on the planet, accusing economic losses of between 4-5 billion people. dollars per year, between damages and expenses derived from control methods that do not end up being as effective at present.

The main cause of this worldwide resistance? Simple: Plutella xylostella do not have natural enemies that can overpower it, apparently because they have a greater ability to fixate on these cruciferous crops than parasitoids, in addition to their admirable migration.

And in addition, it has been determined that they have a high genetic resistance against insecticides and toxins from host plants. It is also believed that the indiscriminate use of insecticides has also favored it because its natural enemies were destroyed and this, evidently, has allowed it to reproduce rapidly anywhere on the planet.

That is why the continued use of healthy cultivation practices is essential to prevent them from becoming a pest that is impossible to control.Some important preventive recommendations are:

1. Elimination of weeds and weeds, because they are favorite hiding places for these moths and their roots are the best food, before they migrate to crops in progress. But in summer, it is especially important to eliminate wild cruciferous plants that tend to sprout under crops in the garden, such as neigh and dandelion, which are recognized by their cross-shaped flowers.
2. Use of certified, guaranteed seeds, free of viruses and diseases. It is also not convenient to carry out transplants and/or plant in places that have previously been punished by pests and bugs.
3. The preparation of the land must go through an intense plowing, where the eggs and larval specimens are eliminated while the fertilizer is sufficiently oxygenated.
4. Crop rotation, especially if the land had previously been infested with pests and diseases.

What are the best products to eliminate cruciferous moths?

Broad-spectrum pyrethroid insecticides such as the brands Opponent from BASF and Guimar from Sarabia, which act by contact and ingestion, help eliminate and control caterpillars and chewing and biting-sucking insects, such as Plutella xylostella moths.

But a scientific team belonging to the CSIC Institute of Agricultural Sciences, together with the Max Planck Institute for Chemical Ecology, have revealed that the so-called Santa Bárbara herb, a cruciferous herb that also includes broccoli and cauliflower, has a fatal power of attraction on moths, because on the surface of their leaves they have chemical compounds capable of killing the larvae, identified as glucosinolates.

This interesting study has found an anti-evolutionary relationship between this moth and the Santa Barbara Grass that could lead to the use of this plant as a trap crop that stops the expansive pretensions of the insect, preventing it from destroying broccoli and cabbage crops.

Although it has not yet been used commercially, the potential of this cruciferous plant to exterminate the moth is great, according to the experiments carried out, which have had very good results, they are encouraging, especially in cases where it is impossible to use insecticides powerful.