Ecologica Montenegrina 32: 1-9 (2020) This journal is available online at: www.biotaxa.org/em http://dx.doi.org/10.37828/em.2020.32.1

Ecological characteristics of pityocampa Denis & Schiffermüller, 1775 (: ) in egg stage in Thasos Island, Greece

MARGARITA GEORGIEVA*, MARIA MATOVA, GERGANA ZAEMDZHIKOVA, IVAILO MARKOFF, PLAMEN MIRCHEV & GEORGI GEORGIEV

Forest Research Institute - Bulgarian Academy of Sciences, 132 ‘St. Kliment Ohridski’ Blvd., Sofia, Bulgaria *Corresponding author: E-mail: [email protected]

Received 22 April 2020 │ Accepted by V. Pešić: 26 May 2020 │ Published online 2 June 2020.

Abstract In September 2017, 96 egg batches of Thaumetopoea pityocampa were collected from Aleppo pine (Pinus halepensis) trees at four sites of Thasos Island in Greece. In the different localities, the average number of eggs in batches varied from 196.5 to 223.9 (212.4 for the Thasos Island). The length of P. halepensis needles with egg batches differed in size - between 84 to 210 mm. Approximately 75% of batches were laid close to the middle of needles, between 121 and 180 mm. The egg masses were formed mainly on two needles (84.4%) and the rest - on one, three or four needles (13.6%) or on fine shoots (2%). In most cases (88.3%), the female started to lay eggs from the tip of the needle. The distance from the base of the needle to the beginning of the egg batches was established between 0 and 180 mm, as most of them (62.7%) were clustered around the average value (87.3 mm) in the diapason of 60-120 mm. The average rate of T. pityocampa survival in egg stage was 48%. The parasitized eggs were 43.8%, and the rest included unhatched eggs, predominately undeveloped eggs with dried-up yolk. No correlation was found between the percentage of parasitized eggs and the distance of the egg batches from the base of needles.

Key words: pine processionary , fecundity, ecology, egg parasitoids, Thasos Island.

Introduction

Pine processionary moth, Thaumetopoea pityocampa Denis & Schiffermüller, 1775 (Lepidoptera: Notodontidae) is one of the most dangerous pests in pine forests in the regions under Atlantic and Mediterranean climates in Europe, Middle East and North Africa (Roques et al. 2015). In Greece, T. pityocampa is distributed from sea level up to 1800 m where its occurrence is only limited by unsuitable weather conditions or geographic island isolation (Avtzis, 1983; Buxton, 1983). It infests both endemic and exotic pine species, with clear preference to Pinus halepensis Mill., P. nigra Arn. and P. radiata Don. Numerous studies were carried out in the country investigating the importance, significance and spatial distribution of T. pityocampa on pine species (Kailidis, 1962a; Avtzis et al. 2016; etc.). Most of them were focused on investigation of effective methods for control the pest distributions and factors regulating density in egg stage (Kailidis, 1962b; Bellin et al. 1990; Schmidt, 1988, 1990; Douma- Petridou et al. 1998; Schmidt et al. 1997a; Mirchev et al. 1999a, 2010; Tsankov et al. 1997, 1999; etc.).

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ECOLOGICAL CHARACTERISTICS OF THAUMETOPOEA PITYOCAMPA IN THASOS ISLAND

Studies on the complex of egg parasitoids were conducted mainly in the continental parts of the country, but also in Hydra Island in Aegean Sea basin (Schmidt et al. 1997a). In 2017, in Thasos Island, an initial study on T. pityocampa egg parasitoids was explored in which four primary species and one hyperparasitoid were reported: Ooencyrtus pityocampae (Mercet, 1921) (Hymenoptera: Encyrtidae), Baryscapus servadeii (Domenichini, 1965), B. transversalis Graham 1991 (Hymenoptera: Eulophidae), Anastatus bifasciatus (Geoffroy, 1785) (Hymenoptera: Eupelmidae) and Trichogramma sp. (Hymenoptera: Trichogrammatidae) (Georgieva et al. in press). In island territories, studies on pine processionary moth are of high interest due to expectations for presence of specific ecological characteristics of the pest populations in isolated areas. Although females are able to fly no more than 2-3 km (Démolin, 1969), genetic exchange in T. pityocampa populations on islands is possible as the male moths fly at a distance up to 50 km (Mirchev et al., 2013). The aim of this investigation was to study the main ecological characteristics of T. pityocampa in egg stage in Thasos Island.

Material and methods

In the period 6-10 September 2017, a total of 96 T. pityocampa egg batches were collected from Aleppo pine (P. halepensis) trees at four sites of Thasos Island: Skidia (40°36'20.32"N, 24°43'36.12"E, 28 m a.s.l.), Thimonia (40°36'24.62"N, 24°43'14.71"E, 11 m a.s.l.), Alyki (40°36'21.11"N, 24°44'26.43"E, 18 m a.s.l.) and Panagia (40°43'43.00"N, 24°43'50.05"E, 351 m a.s.l.). The collected material was transported to the laboratory of entomology at Forest Research Institute in Sofia, Bulgaria. The scales of egg batches were removed, and the samples were analysed according to the protocol described in Tsankov et al. (1996). Each egg batch was individually placed in a test tube covered by a cotton stopper and kept under laboratory conditions (20-22 °C). In October 2018, the eggs without openings were dissected and analysed under a stereomicroscope (40×). Main characteristics of the collected samples were measured: length and number of needles wrapped by egg batches; distance of egg batches to base of needles; length (determined by two factors: number of rows and number of eggs in them) and diameter of egg batches; orientation of scales on egg batches; ratio of larval emergence, unhatched egg and parasitism ratios. The statistical analysis of obtained data were conducted by MS Excel 2013, Statistica for Windows 12 and Mann-Whitney U test (Hollander & Wolfe, 1973).

Results

A total of 20391 eggs of T. pityocampa were analyzed from four studied sites in Thasos Island (Table 1). The average number of eggs laid in a batch slightly varied from 196.5±65.7 (Alyki) to 223.9±43.1 (Thimonia), with an average of 212.4±51.9 for the Thasos Island. The number of eggs in individual batch, however, significantly ranged - from 34 to 297. Approximately 75% of the eggs were laid between 121 and 180 mm, close to the middle of needles (151.1 mm) (Fig. 1). The egg masses were formed mainly on two needles (84.4%) and single of them - on one, three or four needles as well as on fine shoots (2.0%). The number of rows in egg batches ranged between 6 and 13, with an average of 7.5-7.9 (Table 1). In the individual case of egg batch laid on a fine branch, the number of rows reached up to 15. The large dispersion of the length of egg batches (10-47 mm) correlated with the great variety of eggs in them – from 34 to 297 (Table 1). In most cases (88.3%), the female moths started to lay eggs from the tip of the needle. The distance from the base of the needle to the beginning of the egg batches was between 0 and 180 mm. The majority (62.7%) of the batches were clustered around the average value (87.3±37.9 mm) in a diapason of 60-120 mm (Fig. 2). The average survival of T. pityocampa in egg stage was 48% (Fig. 3). There was a significant deviation from maximal value of hatched larvae in Skidia (55.1%) and the minimal one in Thimonia (37%). The proportion of eggs destroyed by parasitoids and predators varied from 37.7% (Skidia) to 54.3%

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(Thimonia), with an average of 43.8% (Fig. 3). However, the impact of predators was very low – between 0% (Panagia) and 0.13% (Skidia), with an average of 0.07%.

Table 1. Biometric indices of egg batches of T. pityocampa.

Site Parameters Total/ Skidia Thimonia Alyki Panagia Average Total number of egg batches 48 24 22 2 96 Total number of eggs 10280 5374 4324 413 20391 Mean eggs per egg batches ± SD 214.2±48.4 223.9±43.1 196.5±65.7 206.5±54.5 212.4±51.9 Range of eggs per egg batches 65-283 67-297 34-292 168-245 34-297 Average length of needles wrapped by an egg batch, mm 152.0±26.7 159.3±27.5 142.6±22.9 84 151.1±27.2 ± SD Range of length of needles wrapped by an egg batch, mm 85-210 110-210 110-200 84 84-210 Number of needles wrapped by egg batches - on one needle 2 (4.2%) 1 (4.2%) 2 (9.1%) - 5 (5.2%) - on two needles 43 (89.6%) 19 (79.2%) 18 (81.8%) 1 (50.0%) 81 (84.4%) - on three needles 1 (2.1%) 2 (8.3%) 1 (4.5%) - 4 (4.2%) - on four needles 1 (2.11%) 2 (8.3%) 1 (4.6%) - 4 (4.2%) - on twig 1 (2.0%) - - 1 (50.0%) 2 (2.0%) Orientation of scales on egg batches, number - from base to tip needles 44 (93.6%) 19 (79.2%) 20 (90.9%) 0 (0%) 83 (88.3%) - from tip to base needles 3 (6.4%) 5 (20.8%) 2 (9.1%) 1 (100%) 11 (11.7%) Average length of egg batches, mm ± SD 31.4±7.1 31.4±6.4 29.3±7.4 26 30.9±7.1 Range of length of egg batches, mm 10-47 10-44 12-42 16-36 10-47 Average diameter of egg batches, mm ± SD 3.3±0.3 3.4±0.4 3.4±0.5 3.4±0.4 Range of diameter of egg batches, mm; 3.0-4.9 3.0-4.4 3.0-5 3.1-5.2 3.0-5.2 Distance of egg batches to base of needles, mm ± SD 95.1±32.5 81.8±47.8 77.9±35.9 87.3±37.9 Range of distance of egg batches to base of needles, mm; 3-155 5-180 0-138 24 0-180 Average number of egg rows per batch ± SD 7.5±1.2 7.8±1.4 7.9±1.3 7.7±1.5 Range of number of egg rows per batch 6-13 6-11 6-11 7-15 6-15

Figure 1. Length distribution of P. halepensis needles with eggs batches of T. pityocampa.

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Figure 2. Distribution of egg batches by distance from the base of the needle.

Figure 3. Hatching rates and mortality of T. pityocampa larvae.

Eggs with unhatched larvae, without impact of parasitoids and predators, ranged from 7.2% (Skidia) to 10% (Alyki), with an average of 8.2% (Fig. 3). Among them, the eggs with dried-up yolk varied between 2.4% and 5.7% (an average of 4.1%), followed by eggs without openings but with died larvae in them – 1.7-3.9% (2.1%), eggs with larvae died with openings – 0.9-1.8% (1.5%) and empty (sterile) eggs – 0.3-1.0% (0.5%). The percentage of parasitism was not depended on the location of T. pityocampa egg batches on pine needles. Divided by the mean distance of egg batches from the base of needle (87.3 mm), Mann- Whitney U test (0.3) showed practically the same level of parasitism in lower and upper half of egg batches.

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The significant dispersion of the degree of parasitism around the mean value (43.8%) was due to the large number of additional influencing factors and explains the low value of the factor R² = 0.0171 (Fig. 4).

Figure 4. Dependence of the egg parasitism by the location of egg batches on the needles.

Discussion

Fecundity is a quantitative indicator characterizing T. pityocampa status in studied sites. Female moth usually lays only one egg batch (Douma-Petridou, 1990), so the number of eggs in them corresponds to the fertility of the species in different areas. Fecundity is not a constant for a given region – it is determined by environmental factors in studied period and population cycle of pine processionary moth. In present study, there are small differences in T. pityocampa average fecundity in four sites in Thasos Island (196.5-223.9 eggs). Similar results were reported for localities from the continental part of Greece (Mirchev et al. 1999a, 2010) and Marikostino village in Southwestern Bulgaria (Tsankov et al. 1998b). Some authors (Tiberi & Roversi 1987; Özkazans, 1987) conclude that T. pityocampa fecundity decreases with decreasing of habitat altitude. Masutti & Battisti (1990) point out that climatic conditions, population cycle, host plants and especially biochemical composition of pine needles also influence this biological indicator (Carvalho et al. 1999; Moura et al. 1999). The chemical composition of metabolites influences the mortality of larvae (Roussis et al. 1994). Devkota & Schmidt (1990) found that the host plant had an effect on survival, weight of pupae and pupal diapause. Buxton (1990) reported that in mixed plantation of P. radiata and P. pinaster, the pine processionary moth prefers the first species on which the larvae are larger that would correlate with higher fertility. The behaviour patterns of T. pityocampa female moths during egg laying differs significantly in the individual host plants. Mirchev (2005) found that 98% of egg batches of T. pityocampa on P. nigra, P. sylvestris and P. brutia were laid on a pair of needles, which is probably due to the greater thickness of the needles and the more loose crowns of the trees. In P. halepensis, 63.7% of egg batches were laid on a pair of needles, and the rest ones – on thin twigs, single or three-six needles, that have been observed by other authors, as well (Démolin, 1969; Schmidt, 1988, 1990; Belin et al. 1990; Kit & Schmidt 1993).

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In P. nigra and P. sylvestris trees, the laying of eggs always started from the base of the needles, whereas in P. halepensis and P. brutia in some cases it started from the tips, with higher proportion in P. halepensis (13.5%) (Mirchev, 2005). This percentage is largely consistent with the results of the current study in Thasos Island (11.7%), but it is significantly lower than that reported by Schmidt (1990b) in Southern Greece (one-third of egg batches). In France, the females of T. pityocampa, as a rule, start to form egg batches near the base of needles (Démolin, 1969; Huchon & Demolin 1970). In , Thaumetopoea wilkinsoni Tams 1926 lays eggs only from the base, and most often on a pair of needles, even though the host plant is P. halepensis (Kit & Schmidt 1993). As concerns the egg batches of Thaumetopoea pinivora (Treitschke, 1834) on P. sylvestris in Baltic Sea region, 97% of them were deposited from the tip to the base of the needles (Tsankov et al. 1993). The survival of T. pityocampa in egg stage (expressed by the relative proportion of hatched larvae) in studied four sites ranged between 37% and 55.1%, with an average of 48% for the Thasos Island. In a twelve-year study with experimental material from many regions of Bulgaria, , Northern Macedonia, Albania and Greece, the percentage of hatched larvae varied from 44.1% to 95.8%, with the highest values in Bulgaria in P. sylvestris plantations at a relatively high altitude (Mirchev, 2005). These results showed that T. pityocampa survival depended on many factors that most probably indirectly create favourable conditions for the development of egg parasitoids – the most significant regulator of T. pityocampa in egg stage. In Thasos Island, the parasitoids destroyed 37.7-54.3% (an average of 43.8%) of host eggs. The parasitism is a dynamic variable that has varied widely over the years. In Kurtovo locality in Bulgaria, in 1991, the effect of egg parasitoids was 24.5% (Tsankov et al. 1996) and five years later, it decreased to 4.4% (Mirchev & Tsankov 2001). The values of parasitised eggs of pine processionary moth in some Mediterranean countries are too heterogeneous: Portugal - 9.9% (Mirchev & Tsankov 2000); Spain - 11.3-31.7% (Schmidt et al. 1999); Morocco - 21.4% (Schmidt et al. 1997b); Algeria - 33.7% (Tsankov et al. 1995); Italy - 6.0-72.0% (Tiberi, 1990). In this study, the percentage of dead larvae in the eggs averaged 8.2%. Data from other studies were also within this range, rarely exceeding 15% (Mirchev & Tsankov 2000; Mirchev, 2005; Tsankov et al. 1995). Mirchev (2005) reported that microbiological analyzes did not reveal the presence of pathogens responsible for larval death, and probably the causes of mortality were abiotic, such as high temperatures, low atmospheric humidity, etc. In Bulgaria, the entomopathogenic fungus Beaveria bassiana (Bals.-Criv.) Vuill. was found in newly hatched larvae of Thaumetopoea solitaria (Freyer, 1838) (Lepidoptera: Notodontidae) (Mirchev et al. 2012). In Thasos Island, undeveloped eggs with dried-up yolk in studied localities ranged between 2.4% and 5.7%. Such results were found in all 49 analyzed samples from different sites in Balkan Peninsula, with their share in most cases were below 10% (Mirchev, 2005). Sterile eggs made up 0.3-1.0%. Similar results (below 1%) were reported in Greece (Bellin et al. 1990), Morocco (Schmidt et al. 1997b), Portugal (Mirchev & Tsankov 2000), etc. In conclusion, it should be noted that due to the close location of Thasos Island to the continental part, there is a lack of isolation capable to create conditions for formation of specific population of pine processionary moth that would differ significantly in its biological features from the population inhabiting continental part of Greece.

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).

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Tsankov, G., E. Douma-Petridou, P. Mirchev, G. Georgiev, A. Koutsaftikis (1997) Comparative studies of populations of the pine processionary moth (Thaumetopoea pityiocampa Den. & Schiff., Lepidoptera: Thaumetopoeidae) in Bulgaria and Greece. I. Biometrical and ecological indices of the species at the egg stage from the biotopes in Marikostinovo, Bulgaria and Kalogria-Achaia, Greece. Acta entomologica bulgarica 1/2, 77-85. Tsankov, G., G.H. Schmidt, P. Mirchev (1998b) Studies on the egg parasitism in Thaumetopoea pityiocampa over a period of four years (1991-1994) at Marikostino/Bulgaria. Anzeiger für Schädlingskunde, Pflanzenschutz, Umweltschutz 71, 1-7. Tsankov, G., E. Douma-Petridou, P. Mirchev, G. Georgiev, A. Koutsaftikis (1999) Spectrum of egg parasitoids and rate of parasitism of batches of the pine processionary moth Thaumetopoea pityiocampa (Den. & Schiff.) in the Northern Peloponnes/Greece. Journal of the Entomological Research Society 1 (2), 1-8.

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