the pine processionaries Episode IV

Our means of combating this dangerous species:

– Descent traps,
– Pheromone traps and treatments,
– Weeding.
Currently: This is the time to take bags from drop traps and destroy their contents.

Why now ?

Due to the life cycle of the pine processionary, Thaumetopoea pityocampa.

Butterflies fly in our region in July (reference Grenoble agglomeration) with some variations depending on the climatic zones.
For owners, tenants, operators, technical services who have chosen to trap the caterpillars when they descend because the process is very effective, the caterpillars, which descend in March April, are now all in the nests but in a month, can -be less, they will be transformed into butterflies which will fly away to lay eggs on the surrounding pines and cedars.
It is therefore time to destroy them if we want to limit the appearance of new nests.
I say limit because not all buried caterpillars turn into butterflies the first year. This is spread out gradually and in a decreasing manner over three years.

Incineration is the best method.

– Question: But we are not allowed to burn plants in our gardens?
– Answer: Caterpillars are not green waste, so they do not come under this regulation (Ministry of Health). So we can incinerate them. The mayor of the commune has the possibility of taking an order to regulate the burning of processionary caterpillar nests.
– Q: Are there other solutions?
– A: As these caterpillars are sensitive to extreme cold (we rarely find them above 1000 meters in our region) and for a few bags, it is possible to let them spend a few weeks in the freezer, but by enclosing them hermetically. in another bag to avoid putting stinging hairs in the freezer.
On the other hand, it is forbidden to put them in household waste collections, such as in recycling centers.
– Q: Why don’t we leave the bags hanging on the trees?
– A: With the new shapes of the traps which make it easier to collect the caterpillars, the butterflies can easily go the opposite way and get out of the traps.
– Q: Will we get rid of the nests next winter?
– A: There will certainly be a lot less, but probably still a little over the next 2 winters because in the first year only 50 to 60% of the butterflies hatch. The second year is about 30% and there is still a small 20% for the third year.
But you have to take into account the contamination coming from the neighborhood, hence the need to encourage those around you to trap or treat the caterpillars.

At the Green Spaces Service in Grenoble, the number of weeded nests fell by 95% in three years when the service implemented a control method combining monitoring* and treatment supplemented by trapping for trees that were impossible to treat.

*Monitoring: This method consists of installing pheromone traps before the butterflies emerge. These traps are fitted with a sticky cardboard inside which helps to estimate the number of males trapped. These traps are counted and emptied at regular intervals (weekly) and the count is plotted on a graph. The curve obtained shows a very clear peak which represents the period of “great flight” when fertilization takes place, followed very quickly by spawning. It is known that the hatching of eggs occurs about 1 month after this time. By adding 2 to 3 weeks for the time of the first pupal stage, we obtain an ideal period for Bacillus Thuringian treatments.
NB, the caterpillars do not feed at the time of their moult, by targeting the second larval stage which lasts longer than the first, the chances of success of the treatment are optimal.

Ask all your questions during the gardening program on Sunday morning on France bleu Isère from 9 a.m. to 10 a.m. by calling 04 76 46 45 45.