An average colony (~200 individuals) consumes 1.5-2.0 kg of needles (dry matter), so that 4-5 nests are enough to defoliate completely a 20-year old tree. However, trees in most cases recover from defoliation, even if it is complete, but grow less and may suffer more attacks of other pests. Recovering can be difficult under extreme dry conditions, such as those of the protective forest belt against desertification in Northern Africa.
 
 
 
 
 
 
 
 

The urticating hairs are present on the larval skin of the 3rd, 4th, and 5th instar larvae, indicatively from October to spring pupation. The 5th instar larva moults inside the cocoon and the skin remains inside, causing the cocoon being full of hairs. The adults emerging from the cocoon may transport on their body some of these hairs.

The hairs are keeping the urticating power for years if maintained at room temperature. The toxin is inactive after exposure at 60°C. A normal washing cycle in home washing machine at 60°C is sufficient to clean off contaminated clothes.

Contact dermatitis (left) and urticating hairs view through electronic microscope (right).
 
   

If contamination occurs, undress ALL clothes and have as soon as possible a shower, wash clothes and shoes at 60°C. In any case do not scrape your skin, you will make things much worse. The irritation will go away in hours or days, depending on the individual susceptibility. There is no need to use medicines, none is effective. In case of strong reaction and pain, consult a doctor. Temporary blindness and paralysis, high blood pressure and other heavy disturbances are known only for people getting in prolonged contact with the caterpillars.

 
 

There are numerous natural enemies, with key species among parasitoids of eggs, parasitoids of larvae and pupae, and larval and pupal predators but competition may limit the overall mortality. In some cases diseases caused by viruses and fungi may induce great mortality, especially when the population density is high and the climate is not favourable to the larval development. Very few species of natural enemies have been found in expansion areas, where mortality levels are generally low.

Hoopoe feeding on pupae.

 

Several control methods have been used against the caterpillars in the past, from the removal of the nests to the spray of chemical insecticides. Nest removal is still a valuable practice in gardens and isolated trees on short trees. The current way to protect the forests from the insect is the application of preparations of the bacterium Bacillus thuringiensis subsp. kurstaki (Btk), which produces toxins specific to Lepidoptera. Thousands of hectares of forest are sprayed each year in EU.

Recently it has been shown that a considerable variation in the susceptibility of the pest to Btk is present in insects from populations recently settled in the Alps, which could be considered as a premise to the development of resistance, especially for those populations subjected to frequent applications. Side effects of Btk applications on non-target Lepidoptera in core areas seem to result in no measurable impacts, likely because the application is usually done in autumn or winter.