Caterpillars (larval stage) are covered with stinging hairs that break off and float in the air, so they can cause irritation in the ears, nose and throat in humans, and severe allergic reactions. The substance that gives this urticante capability is a heat-labile toxin called Thaumatopina.
Adult individuals in the form of butterflies mate in summer. The female lays eggs on the tops of the trees forming characteristics set very spirally around one or two needles. Between 30 and 40 days later are born tracked (Usually in the months of September-October), which will pass through five larval states in cold areas it can last up to eight or nine months.
The caterpillars have social behavior, mode throughout their larval life normally they establish cooperative interactions with her sisters start. Also in general, they develop all their larval life on the same tree, and just abandon him to the procession of pupa or to find an adjacent pine if they have exhausted all the needles of pine where they were born (this only happens in feet very small size or when several put on a tree not much porte).
Immediately after the larvae hatch out and begin to feed on acículas trees (genus Pinus mainly), causing defoliation. The first, by its size and activity level food and moderate defoliation. From the first instar caterpillars colonies jointly build small silk bags feature of collective shelter.
From the third instar caterpillars on trees build a more dense and conspicuous pockets, which spend the winter. They spend the day periods and come out to feed at dusk. In the fifth instar caterpillars they are extremely voracious. After feeding for about 30 days between February and April, the caterpillars in this last phase down to the ground from the trees, features rows Indian (hence its common name "processionary").
The cause is unknown but is always found to be a female (a larva cause a female adult) that guides the procession. Finally they buried in the ground, where they pass pupation or chrysalis. In summer they hatch pupae and emerge butterflies whose lifespan is very short (one to two days), they mate, beginning the cycle again. It is in this last phase of the cycle where pheromone traps are effective.
Damage and control methods
Even though stocks Thaumetopoea pityocampa reaches very high levels and are able to defoliate trees intensely, they can hardly grow into a forest pest. At best they can actually reduce the growth of pine plantations. In locations where damage timber production can be taken into account. In places with strong water stress defoliation these can be very little relevance on the growth of trees, taking into account the strong growth restrictions imposed by the climate.
The main negative effect are the possible harm to people (especially children) caused by populations located in the vicinity of recreational areas frequented by campers or places. It is therefore a public health problem and not a forest pest. This approach must be taken into account in managing it.
To control populations of this species physical, chemical and biological means are used. Physical means pass through the elimination of the pockets, when the tracks are provided, these are cut, stacked and incinerated destroying larval populations. In the past it was fired on pockets. Chemical control is authorized spraying insecticides (pyrethroids and chitin and Bacillus thuringiensis) Should apply on the larval stages in the early stages of development, before stinging hairs develop the third stage.
They can be applied using ground means. Until September 15, 2012 air assets were used, but these have been banned in the EU and in Spain since that date, following the publication of Royal Decree 1311/2012, of 14 September, establishing the framework for action is set to achieve a sustainable use of plant protection products..
The main method of biological control, perhaps the most effective considering effectiveness / effort involves using pheromone traps to capture adult males reducing the chances of copulation. By capturing only males traps are only effective with low population densities. They are also used to assess population levels of adults.