In 2022, a study was conducted with experimental material from the area of Marikostinovo village, covering various aspects of species bioecology. The stability or changes that have occurred in these bioecological parameters after a 28-31 year period were analysed, with research data from this area conducted in the period 1991-1994. The fecundity of pine processionary moths in the 5 generations compared had a stable level of average values above 214 eggs. The long-term observations and reporting of this indicator gave reason to draw the conclusion that in this region of Bulgaria, the species develops stably, successfully overcoming possible occurrences of extremely high temperatures in July and August. In the egg stage, the most significant factor in reducing the number of T. pityocampa is the impact of parasitoids. Its effect is not a constant value but varies widely, being the difference nearly twice. The relative share of eggs destroyed by predators is insignificant. A distinctive feature of the Marikostinovo site is the high relative proportion of dead caterpillars, sterile and empty eggs, with values significantly higher than those in other areas of the species’ global range. This is the warmest and driest region of Bulgaria. The high values of this indicator are also formed by the large number of unfertilised, sterile eggs, reaching in 1994 up to 1/5 of the eggs in the sample. The dominant species, with constant presence in all samples, is Ooencyrtus pityocampae.