The dataset provides the date of procession in situ and the date of emergence in a common garden for caterpillars sampled in 6 sites located along an altitudinal gradient in Mont Ventoux, France, for the pine processionary moth Thaumetopoea pityocampa. The experimental protocol was followed yearly between 1970 and 1984. Due to prolonged diapause, some of the individuals emerged up to 4 years after field sampling.

Study sites Six sites were chosen across an altitudinal gradient along the D974 road in the Vaucluse Department between Malaucène and the Mont Ventoux Station (France), namely G (Portail St Jean, 444.93 m above sea level (a.s.l.), lat. 44.164 long. 5.141 dd ), C (2ème Plateforme, 670.90 m a.s.l., lat. 44.159 long. 5.153 dd), B (Bramefam, 696.92 a.s.l., lat. 44.162 long. 5.158 dd), A (Le Camp, 687.83 m a.s.l., lat. 44.164 long. 5.155 dd), F (Fribouquet, 781.41 m a.s.l., lat. 44.168 long. 5.177 dd) and R (Les Ramayettes, 922.79 m a.s.l., lat. 44.169 long. 5.196 dd). The 4 first ones were on the territory of the municipality of Malaucène while F and R were in the municipality of Beaumont-du-Ventoux.

Monitoring and sampling of processions The same protocol was followed yearly from 1970 to 1984. At each study site, up to 10 Austrian pine trees (Pinus nigra) were selected and equipped with a wire and a net strapped on the trunk down to the ground to trap the caterpillars leaving the tree in procession in search for a pupation site and prevent them from burying. The number of trees selected depended on the density of nests each year. When PPM density was very low, nests were sampled on other trees in the vicinity and grafted on the selected pines. All the sites were visited everyday from January 1st to May 31st each year. The caterpillars trapped at the base of each tree were thus sampled and counted everyday. The larvae were then separated, put individually in a glass tube and identified with a unique code. Caterpillars sampled from the same tree at the same date were identified as belonging to the same batch; note that they might originate from different nests of the same tree, and thus belong to several families.

Monitoring of adult emergence The sampled larvae were brought back everyday to Malaucène (altitude 340 m a.s.l., lat. 44.192 long. 5.1403, dd) and let in a laboratory under natural photoperiod at room temperature (not recorded). A month after pupation, cocoons were taken from the tubes and were put into plastic boxes filled with untreated sawdust; individuals from the same batch were grouped in the same box, with 100 individuals maximum per box. The boxes were checked daily from the 1st of June to the 30th of September, to record emergences. In case all individuals did not emerge, the box was monitored again the following year to allow recording of the date of emergence of the diapausing pupae, until the fifth year.