Silva Balcanica, 19(3)/2018 DOI: 10.6084/m9.figshare.8198273

ZONE AND RATE of PINE PROCESSIONARY MOTH (Thaumetopoea pityocampa) EXPANSION in

Gergana Zaemdzhikova1, Ivailo Markoff1, Plamen Mirchev1, Georgi Georgiev1, Margarita Georgieva1, Rumen Nachev2, Mariana Zaiakova2, Maria Dobreva2 ¹Forest Research Institute – Bulgarian Academy of Sciences ²Forest Protection Station -

Abstract

Data records of Forest Protection Station – Plovdiv were used to study the zone and rate of expansion of pine processionary moth (Thaumetopoea pityocampa) in Central Bulgaria. In 1995, the first pest outbreaks were registered on the territory of two State Forest Enterprises - and Sahrane (now Mazalat). The spreading of T. pityocampa has increased gradually - three gradation periods were recorded, the last one started in 2015 and is ongoing, affecting small areas all over the Regional Forest Directorate of . In this area, the pest is spreading predominantly eastward. Newly infested areas are predominantly close to already infested ones. New infested forest stands occurred far away from the reported ones but they were rare and appeared usually in gradation years. The species settled new range quite slowly and its attacks are still concentrated near the initial outbreaks. In order to prevent T. pityocampa to affect the whole territory of the Directorate it is obviously necessary to control its initial outbreaks. Because of its pupal diapause, the attacked stands should be treated for several consecutive years, even at low population density. Key words: Thaumetopoea pityocampa, expansion, rate of spread, pine plantations

INTRODUCTION

Pine processionary moth, Thaumetopoea pityocampa (Denis et Schiffermüller, 1775) (Lepidoptera: Notodontidae) is one of the most common defoliator insects widespread in the Mediterranean regions of Southern Europe, Asia Minor and North Africa (Battisti et al., 2015). The northern boundary of its range passes through Bulgaria. The pest attacks exclusively pines (Pinus spp.) and Cedrus spp. It is the most dangerous defoliator in black (Pinus nigra Arn.) and Scots (P. sylvestris L.) pine plantations in Bulgaria. For the period 1951-2017, the area affected by T. pityocampa amounted to 1 145 378 ha, or 17 500 ha per year (Mirchev et al., 2018). Over the last decades, a vertical and horizontal expansion of species’ world range has been established to the north and to higher altitudes (Battisti et al., 2005; 2006). The range of pine processionary moth’s expansion was a subject of numerous studies, and models forecasting the process of extension were presented (Huchon, Demolin, 1970; Battisti et al., 2005; Robinet, 2006; Robinet et al., 2007; Mirchev еt al., 2011). Higher winter temperatures influence pine processionary moth’s survival (Battisti

13 et al., 2005). In recent years, global climate warming has been observed (IPCC, 2007), and the same ongoing process was manifested in Bulgaria (Grunewald et al., 2009; Raev et al., 2010). In addition to this global phenomenon, the local site conditions also influence the species’ outbreaks and enlargement of its range, especially the presence of appropriate trophic base. In France, a significant increase of pine-afforested stands was reported during the last century (Robinet et al., 2007), and in Bulgaria, the afforestations reached the highest rate during 1960s and 1980s - the area occupied by P. nigra plantations enlarged over 5 times, and by P. sylvestris – 2.5 times (Mirchev еt al., 2000). The process of pine processionary moth’s expansion in Bulgaria started in 1990s. Until 1995, the species’ range covered the slopes of Pirin and the Rhodopes. It was limited to the ‘southern-frontier forest vegetation region’, characterized by transitional Mediterranean climate. No attacks have been recorded yet in Strandzha Mountain and along the Black Sea coast, although these zones come under the same region of forest vegetation. In 1995, the pest occupied new territories in Central Bulgaria - on the southern slopes of the Balkan range and on Mountain, beyond the pest’s original range (Mirchev et al., 2011). A sustainable new area of the pine processionary moth’s infestation emerged in the ‘Thracian forest vegetation region’, where the climate is considered as transitional-continental. Currently, pest’s expansion zone coincides with the administrative boundaries of the Regional Forest Directorate (RFD) Stara Zagora, and it is not established yet in the region of State Forest Enterprise (SFE) , situated on the north-east outskirts of the Directorate’s territory. In this area, the coniferous stands amounts to 44 459 ha that is 6.5% of the total pine plantations in Bulgaria (EFA, 2010). The forests include exclusively Scots and black pine plantations (99%), with a slight predominance of the black pine. Most of the pine plantations (75%) were planted at altitudes below 800 m a.s.l. providing abundant trophic base for the pine processionary moth in this region. The aim of the present study is to investigate the spread of pine processionary moth in the zone of its expansion in Central Bulgaria: outline the new zone boundaries, amount the frequency of pest’s attacks and the rate of its enlargement.

MATERIALS AND METHODS

The main data sources of the pine processionary moth’s attacks in the territory of RFD Stara Zagora included the archive documents of Forest Protection Station (FPS) – Plovdiv and the electronic models of Forest Management Plans (FMPs) published on the website of the Executive Forest Agency (EFA, 2018). The FMPs contain specific attributive information for the forest type, tree species, height density, as well as other environmental attributes such as elevation, soil type etc. An amount of 6305 ‘signal sheets’ recording the signals for the size of area attacked by T. pityocampa at the territory of RFD Stara Zagora for the period 1995- 2017, have been reviewed. The Gauss–Krüger (GK) coordinate system was used to indicate all attacked stands at the Directorate’s area, as well as the inventory data for

14 their dendrometric characteristics were presented. An electronic database was created to summarize and analyze all comprehensive data. All infested stands have been included, i.e. there was no sampling. Th erefore, only descriptive statistic has been applied.

RESULTS General data For the period 1995-2017, the area attacked by T. pityocampa on the territory of RFD Stara Zagora amounts to 36 244 ha. According to the statistics of EFA, for the same period, the total area of attacks in Bulgaria was assessed as 546 633 ha. Th us, 6.6% of the area aff ected by the pest for the last 23 years have occurred in its expansion zone. About 10% of aff ected forests area was degreed as ‘strongly attacked’. Th is percentage has remained relatively constant for years. Th e attacked area is the sum of reported area attacked by pine processionary moth which is not equal to the infested area – the amount of aff ected forests, as frequently the same stands are repeatedly attacked for a long period of years. Th e area of attacks is well known and currently used to plan control measures whereas the infested area is still to be established by using GIS. Amount of attacked area in the expansion zone At the territory of RFD Stara Zagora, forest stands attacked by T. pityocampa were recorded on the region in fi ve out the six SFEs (Fig. 1). Th e heaviest infestations have mainly occurred in two enterprises where the pest’s fi rst penetration was registered in 1995 - Mazalat (Sahrane) and Chirpan, altogether occupied 92.2% of the total attacked area. Th e lowest amount of attacks is situated in the region of SFE . Th is region is the easternmost area in the country infested by the pine processionary moth. Attacks of the pine processionary moth are registered in the lands of 48 settlements,

fig. 1. Total area of attacks by SFEs

15 fig. 2. Total number of attacks in the expansion zone indeed villages, on the total area of 4905 ha. Among them, the most aff ected ones were Osetenovo (1364 ha), Manolovo (930 ha), followed by Aleksandrovo, Tazha and Kolyu Marinovo vills. (507-536 ha) (Fig. 2). On the territory of these settlements occurred approximately 80% of all registered attacks. Th e attacks of the pine processionary moth areas are still concentrated near the initial outbreaks where attacks began in 1990s in the territory of RFD Stara Zagora. Dynamics of attacks in T. pityocampa expansion zone Dynamics of T. pityocampa attacks on P. nigra and P. sylvestris stands was presented for a twenty-three-year period (Fig. 3). During the entire period, three pronounced peacks are expressed – in 2004, 2012 and 2016. Th ere is a noticeable cyclic population dynamics, with a lower rate of infestations for a period of seven to ten years between the eruptive gradation phases. Until 2000, the pine processionary moth’s infestation in pine stands on the territory of RFD Stara Zagora remained insignifi cant – between 100 and 330 ha per year were attacked. Since 2000, the fi rst signifi cant increase in attacked area was established, marking the beginning of species’ gradation, with a peak of 2540 ha in 2004 (Fig. 3). For the next 5-year period, the size of infested area stayed relatively constant with amount between 1280 and 1700 ha per year. In 2012, a new pest’s gradation was recorded with a peak of 2112 ha infested area. Th e last drastic increase of attacks was recorded in 2016, when the size of aff ected area amounted to 3950 ha that is 9% of the pine plantations on the Directorate’s territory. Enlargement of T. pityocampa range Th e fi rst attacks of T. pityocampa in Central Bulgaria were registered in 1995 on the territory of two SFEs Mazalat (Sahrane) and Chirpan. Until 2009, pest’s infestation was registered only on the territory of these enterprises (Fig. 4). Afterwards, new pest’s

16 fig. 3. Dynamics of T. pityocampa attacks in RFD Stara Zagora

fig. 4. Enlargement of T. pityocampa attacked area in RFD Stara Zagora outbreaks and range enlargement were established in SFEs Stara Zagora and , remaining insignifi cant until 2015. During the period of the last species’ gradation (2015-2017), the amount of aff ected stands in SFE Kazanlak reached ones in Chirpan and Mazalat, and in 2016, for fi rst time, an emergence of distant new outbreak ofT. pityocampa was registered at the territory of SFE Maglizh. Th e pine processionary moth has been expanding its range to east since 1995, and is now infesting areas near SFE Maglizh. Applying the GK coordinates of the attacked areas, simplifi ed maps of T. pityocampa attacks on the Directorate’s territory were presented. Th e locations of the primary foci of attacks as well as the locations of secondary outbreaks, derived from distant transmission, are quite clearly seen on the maps. Th e expansion began before 2000 in two centers (Fig. 5) – one in north, in SFE Sahrane (former Pavel Banya and Mazalat) and a second one - in SFE Chirpan, in the south. Since 2000, the outbreaks expanded to east, in the direction of prevailing winds and reached to SFE Maglizh. Th e predominant direction of the pine processionary moth’s spreading remained the same in the following seventeen years (Fig. 6). Almost all new outbreaks were

17 Правилната фиг. 6 в статията в Silva Balkanica 19(3)/2918 EXPANSION ZONE AND EXPANSION RATE OF THE PINE PROCESSIONARY MOTH (THAUMETOPOEA PITYOCAMPA) IN BULGARIA

Zaemdzhikova G¹, I. Markoff ¹, P. Mirchev¹, G. Georgiev¹, M. Georgieva¹,

R. Nachev2, M. Zaiakova2, M. Dobreva2

е, както следва:

fig. 5. Enlargement attacked areas in RDF Stara Zagora in 1990s

fig. 6. Enlargement of T. pityocampa attacked areas in RDF Stara Zagora by decades established in east direction from the old ones. Some scattering in the north and south directions were also noticed. Migrations to the west were very rare. T. pityocampa settles its new range quite slowly and its attacks are still concentrated near the initial outbreaks.

DISCUSSION

In Bulgaria, pine processionary moth was established for fi rst time in the beginning of the 20th century (Buresh, 1915; Drenovski, 1923), but fi rst severe attacks were recorded only in the 1920s (Ruskov, 1929-1930).

18 In Central Bulgaria, from 1999 to 2018, it has advanced 46.3 km, from the ridge of hills to the surroundings of Maglizh, indicating the range of expansion of around 2.6 km per year (Mirchev et al., 2018). In a flight, the average distance of males is up to 50 km (Mirchev et al., 2013), and for females – up to 2-3 km (Démolin, 1969b). The extension of species’ range is undoubtedly determined by the perimeter of females’ flights, so the rate of natural expansion could be expected to be slow. With females dispersal capacity up to 2-3 km, the fragmentation of the pine stands in this region is an important obstacle for pine processionary moth’s spreading. Robinet et al. (2006) emphasized that the spread of the pest depends on such factors as roadside and landscape afforestation in the settlements and roads, attracting the moths by passing car lights at night. The eastward spreading of pine processionary moth in the investigated area coincides with the direction of the prevailing winds in this part of Bulgaria. The high Balkan range prevents the pest’s spreading to the north. The role of wind and other factors (mountains, motorways, fragmentation of the pine forests) requires further research. In this study, the zones of expansion and the temporal data for T. pityocampa attacks were established, but the impact of the terrain characteristics and the location of the pine forests on the territory of RFS Stara Zagora has yet to be studied through GIS. Data obtained in current study shows that T. pityocampa has settled new area relatively slowly. So far, the attacks were rare in the eastern part of the Directorate’s territory. In order to prevent T. pityocampa to affect the whole territory, it is necessary to control its initial outbreaks. Limiting its spread by applying the appropriate pest control is extremely difficult because of its biological feature - prolonged pupal diapause (Georgiev, 1959). In time of it, a part of pupae remains in the soil and emerges in up to six years (Démolin, 1969а). Thus, even with a 100% effect of pest control treatment, in the next year, the pest could appear again from the dormant pupae. Therefore, in the enlarged pest range, the attacked stands should be treated for several consecutive years, even at low population density.

Acknowledgements: This study was supported by the project ‘Expansion of pine processionary moth (Thaumetopoea pityocampa(Denis et Schiffermuller, 1775) (Lepidoptera: Thaumetopoeidae) in Bulgaria – a dangerous allergen and economically important pest in the pine ecosystems’ funded by the National Scientific Fund (DN01/17, 22.12.2016).

REFERENCES

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