The plague of the month of November

So far we have reviewed the pests that attack our orchard, the pantry or garden but today we go beyond our own house or farmland to enter the forest and know a little more about the most disgusting caterpillar, the processionary.

The pine processionary is the caterpillar of a nocturnal butterfly (Thaumetopoea pityocampa Schiff) named because it travels in groups forming characteristic processions when they are going to bury. We speak of a defoliator insect that attacks the needles of the pines to feed and that can weaken the trees.

Life cycle and biology

Adult females lay eggs (between 120 and 300) on pine needles and are able to discern between different species of pine trees thanks to the aroma, thickness, and length of the needles. The wingspan of female butterflies is 36 to 49 mm, males are slightly smaller 31-39 mm and have abundant golden scales.

So far we have reviewed with Inés Perales the pests that attack our orchard, the pantry or garden but today we go beyond our own house or farmland to enter the forest and know a little more about the most disgusting caterpillar, the processionary.

The pine processionary is the caterpillar of a nocturnal butterfly ( Thaumetopoea pityocampa Schiff) named because it travels in groups forming characteristic processions when they are going to bury. We speak of a defoliator insect that attacks the needles of the pines to feed and that can weaken the trees.

Life cycle and biology

Adult females lay eggs (between 120 and 300) on pine needles and are able to discern between different species of pine trees thanks to the aroma, thickness, and length of the needles. The wingspan of female butterflies is 36 to 49 mm, males are slightly smaller 31-39 mm and have abundant golden scales.

In addition, after the molt, the larva acquires its definitive typical appearance, which varies depending on the climatic conditions of each zone, so that the color of the tegument becomes darker as the locality is colder. Also in this phase, the stinging darts are formed, which can cause serious allergies in humans and hives.

During the 4th and 5th larval stage the caterpillars become larger and stinging. They leave the nest at night to feed while they are weaving the bags. The duration of the 4th stage varies depending on the climate of the area, so it is longer in cold areas, in which this phase usually lasts until the end of winter, while in warm areas it can be reduced to one month. This stage of intense feeding is when the tree may be in danger.

Some pines are tastier than others.

Depending on the susceptibility to processionary attacks, the species of pines can be divided into two groups, the first group consisting of Pinus nigra, Pinus canariensis and Pinus sylvestris. The second group is Pinus pinaster, Pinus halepensis, and Pinus pinea.

When the processionary is already installed and during the first years, the infestation only affects specific trees that remain partially deflated but after two generations, if the climatic conditions are favorable, the forest mass can be totally defoliated. It is at this point that there is high mortality of larvae due to lack of food. However, the process does not have to occur exactly like this because it can be stopped, receded or advanced depending on the environmental conditions.

Treatment

The most direct way to control this pest is the destruction of the bags: cutting, burning, crushing or shotgun shooting when the height of the trees makes them inaccessible. The synthesis of the sex pheromone of the processionary female has allowed the use of traps for the massive capture of males to maintain low levels of the insect population. These traps are distributed at the edges of the pine forest and in the less dense areas, which are the flight zones of the males.

The following method is very ingenious: the first group pines placed in the reforestation in small stands dispersed in the dough would act as baits, so it would only be necessary to treat these pines annually to keep the entire dough clean.

Massive chemical treatments are performed with growth inhibitors used on the larvae in the first stage. As for the microbiological insecticides based on Bacillus thuringiensis, they are applied to the first three larval stages.

As you can see, we also don’t get rid of pests in the forests so if you visit parks, gardens or any pine with processionary, beware! Let your pet sound eat no larvae.

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