Cabbage Caterpillars (Pieris brassicae and Pieris rapae): [Characteristics, Detection, Effects and Treatment]

What are cabbage caterpillars?

One of the pests that most frequently attack cabbage crops are caterpillars, where two species stand out that can ruin the entire harvest: Pieris brassicae and Pieris rapae.

These are species of diurnal butterflies that are capable of wintering as chrysalises, to later appear in spring, when they lay their eggs on the leaves of the plants they invade, in order to reproduce and feed.

The larvae are responsible for great damage to the leaves and combating them is somewhat complicated, because they usually have the ability to reproduce between two to three generations a year, which is why it is very appropriate to take preventive measures.In general, they multiply throughout the year in three generational periods.

The first generation emerges between April and June, after nesting in weeds and wild plant species. Then comes the second generation, which breaks out between July and August and, finally, the last one between the months of September and October, but remaining dormant throughout the winter, and then returning in the spring with tremendous devouring and reproductive activity.

How can we identify them?

It is not very difficult to identify them. Both species have similar characteristics. Let’s see.

1. They measure around 5-6 cm and are white with dark spots, in the butterfly phase.
2. The main evidence of the attack is the appearance of two holes in the leaves of crops. They attack the most superficial ones, but sometimes the voracity is such that barely the central nerve of the leaf remains.
3. They also excrete on the plant, being able to irreducibly damage the fruits.
4. They have a reproductive behavior that is divided into several phases. In the first generation of brassicas, they usually remain in the weeds, but towards the second and third generation they invade the crops, in a period that covers from July to October, when the white butterflies appear, always flying in pairs.
5. Their eggs are quite visible to the naked eye. They are placed on the underside of the leaves in clusters. They are yellow in color and are placed in dozens, in bunches of about 20-50. But this only occurs in the case of Pieris brassicae.
6. Pieris rapae have the peculiarity that they lay individual eggs, so they are difficult to identify.
7. The eggs hatch, on average, about 12 days after laying, giving way to hungry larvae.
8. The larvae have a similar appearance in both species. They are elongated, hairy, about 4 cm long, although they vary in color. The Pieris brassicae has a greenish coloration, with small dark spots on the head and some yellowish lines along the body, while the Pieris rapae, also green, has soft yellow lines and can be camouflaged in the cabbage, because it acquires the same shade of the vegetable.
9. The larvae adhere to the leaves with the help of very fine and sticky threads.
10. When they are young, the caterpillars act in a group, but as they mature, they disintegrate until they act individually. They have an average life of one month.
11. They are also capable of building, in that time of a month, the pupa or chrysalis that will house new members of the next generation of adult butterflies.

What plants do cabbage caterpillars affect?

These two species of caterpillars invade not only crops of the famous Brussels sprouts. They also affect cabbage and cauliflower crops.

How to combat cabbage caterpillars?

Let’s see some of the most important measures to combat the presence of these persistent caterpillars in cabbage crops.

sheet review

It is necessary to always carry out thorough inspections on each plant, as soon as the spring season begins, with a review of the underside of the leaves, in order to detect intruders, which can be removed manually. The same is done with the eggs, which are easily destroyed.

weed removal

Any wild grass growing around the plants should be removed promptly because they become home to the first generation of caterpillars.

They are especially favorable to these species of caterpillars, herbs belonging to the cruciferous, such as Synapsis, Rphanus and Diplotaxis, spontaneous species that become an exquisite food for the caterpillars on which they will develop to bring to the world a second generation of these insects much more numerous than the first, bringing serious damage to crops.

biological controls

If they become a persistent pest, it is convenient to apply biological control treatments so as not to cause chemical impact on the crops.

To do this, it is best to use the natural predator of these caterpillars: the Apanteles glomeratus, a very strong larva that parasitizes the Pieris larvae, causing their death.

The introduction of the bacterium Bacillus thuringiensis kurstaki also works very well, a pathogenic agent that can be applied in a special powder formula that can be diluted in water, easily accessible in specialized stores to be applied with the help of sprays on the leaves.

In the same way, Neem oil with its active ingredient, azadirachtin, works with frequent sprays after being dissolved in water following the instructions in the package insert included by the manufacturer. It does not work to eliminate eggs or adults, but it does in the first stages of the caterpillar.

chromatic traps

With plastic bottles painted blue and smeared with glue, traps can be made that will attract the attention of the butterflies, which can be reduced early because they will remain stuck to the surface, remaining completely immobilized.

Several of these blue traps will need to be placed inside early spring cabbage fields in early spring to prevent female butterflies from starting to scatter their eggs onto plant leaves.

Both products affect the digestive system of the caterpillars, which, unable to feed, then die of starvation.The ideal is to combine them alternately to obtain good results, because they eliminate the larvae early, thus breaking the life cycle of the caterpillar.

What are the best products to eliminate caterpillars from cabbage?

Etofenprox is one of the most effective insecticides to combat the pesticidal behavior of these Lepidoptera, but it also works very well against Diptera, Coleoptera, Thysanoptera and Hymenoptera species.

The downside is that this product contaminates water sources, being toxic to aquatic life in general.Other authorized chemical formulas are pyrethrins, deltamethrin and cypermethrin.

They are applied to crops as insecticides applied to the underside of the leaves with the help of sprays, to control these pests, once it is observed, for example, that the attack threshold reaches 10% of the total crop, it is that is, that it exceeds 15 infected plants, regardless of the type of caterpillar detected.

It should not be forgotten that the critical moment, the moment of greatest care, is when the plants are less developed, when the crop has not yet borne fruit.