The pine processionary moth is advancing into Northern Bulgaria and could reach the Black Sea coast within the next 50 years

The pine processionary moth is advancing into Northern Bulgaria and could reach the Black Sea coast within the next 50 years, experts have predicted during a discussion in Gabrovo on the species’ spread. The meeting, organised by the local administration, brought together specialists from the Forest Research Institute at the Bulgarian Academy of Sciences, representatives of state institutions, and local mayors from the Gabrovo region.

The species poses a risk to humans and animals due to the allergic reactions it can trigger, and it is also considered a significant indicator of climate change. Experts noted that climate shifts are allowing the pest to thrive at higher altitudes than previously observed.

The pine processionary moth is a Mediterranean species first recorded in Bulgaria in 1906 in the Sofia region, with its presence noted in Dupnitsa in 1909. Historically, it was mainly found in southwestern Bulgaria, in the lower regions of the Rila and Rhodope Mountains, up to approximately 1,350 metres above sea level.

“Currently, the species is found at elevations of up to around 1,500 metres, which is an indication of climate change, something also observed in other countries,” said Professor Georgi Georgiev, Director of the Forest Research Institute. He added that, over the past 50–60 years in Italy, the upper limit of its range has increased by 100–150 metres.

In Bulgaria, conditions for the spread of the pine processionary moth exist across the entire country, the specialists noted. The species can survive for 1–2 days at temperatures as low as minus 25 degrees Celsius.

“A forecast has been made regarding the spread of the pine processionary moth. The Stara Planina ridge presents a significant barrier to the species’ distribution. However, it could penetrate Northern Bulgaria through the Iskar Gorge. The forecast indicates a west-to-east expansion, with the species expected to reach the Black Sea coast within about 50 years,” Georgiev added.

Its arrival in the areas of Troyan, Gabrovo, and Tryavna is thought to have occurred via adult moths landing on vehicles, while its entry into Northern Bulgaria likely took place through the Troyan Pass.

The species’ population dynamics are complex. The pine processionary moth goes through five developmental stages, varying in size. From the third stage onwards, the caterpillars begin to release substances that can trigger severe allergic reactions in humans. Experts reassured, however, that there are no recorded fatalities in Bulgaria resulting from human contact with the species.

“There are other species in the country that also cause severe allergies, such as the oak processionary moth and another processionary species found in the southernmost regions of Bulgaria,” Professor Georgiev explained.

He noted that there are effective means of controlling the species’ population. Ground-level activity of the caterpillars can be limited using traps, which are suitable for deployment in urban areas.

Experts confirmed that research has been conducted on the three species responsible for allergic reactions.

During the discussion, questions were raised about when the processionary moth is most susceptible to treatment and at which stages it can be eradicated. Applying chemical treatments to the pupae only affects a single microhabitat, they explained. Control efforts are mainly targeted at larvae in their first to third instars. While pesticides have never achieved complete eradication of the species, mortality rates of up to 80% have been reported. Experts stressed that this does not mean treatment of pupae in the soil should be discontinued.

“The nests are visible and are usually located on the southern side of the tree crowns. The species is thermophilic,” Professor Georgiev said.

When asked about the reliability of traps against the pine processionary moth in urban environments, experts stated that, in theory, such traps should be 100% effective.

The pine processionary moth is a type of moth whose name derives from the caterpillars’ characteristic behaviour of moving in a line, one after another, in a procession. It causes serious damage not only to pine species (Pinus spp.) but also poses a health risk to humans and other mammals, as the hairs of the caterpillars release irritating toxic substances that can trigger severe allergic reactions.