Silva Balcanica, 18(1)/2017 Structure OF EGG clusters AND EGG parasitism characteristics OF THAUMETOPOEA SOLITARIA (Freyer) (Lepidoptera: NOTODONTIDAE) IN THE EASTERN RHODOpes, Bulgaria Plamen Mirchev, Georgi Georgiev, Margarita Georgieva Forest Research Institute – Sofia Bulgarian Academy of Sciences Peter Boyadzhiev Department of Zoology, University of Plovdiv, Bulgaria Abstract Egg structure and main characteristics of egg parasitism of pistachio processionary moth (Thaumetopoea solitaria) were studied in six sites in the Eastern Rhodopes in Bulgaria. The results showed that T. solitaria lays eggs on branches with a diameter of 3.6-13.0 mm and the productivity of female butterflies varies between 43 and 187 eggs. Three parasitoids were reared from host eggs: Anastatus bifasciatus (Hymenoptera: Eupelmidae), Ooencyrtus masii and Ooencyrtus sp. nr. indefinites (Hymenoptera: Encyrtidae). A. bifasciatus was the most important parasitoid occupying 81.4-97.3% of the total egg production in different sites. A part of A. bifasciatus population emerged before hibernation. Its emergence period in 2014 was about 100 days, and in 2015 – 69 days. The emergence period of O. masii was shorter but almost coincided with mass emergence of A. bifasciatus. However, Ooencyrtus sp. nr. indefinites appeared after the mass emergence of the other two parasitoids. In 2014 and 2015, its emergence started 15 and 8 days after the completion of mass emergence of O. masii, respectively. Key words: Thaumetopoea solitaria, egg parasitoids, phenology, impact, Eastern Rhodopes, Bulgaria INTRODUCTION The pistachio processionary moth, Thaumetopoea solitaria (Freyer, 1838) (Lepidoptera: Notodontidae) is an East Mediterranean-Turanian species, distributed from FYR Macedonia to Iran, Afghanistan and Israel (Androić, Serafimovski, 1954; Davatchi, 1958; Halperin, 1983; Roques, 2015). In Bulgaria, it is distributed in some regions of southern part of the country (Buresch, 1918-1919; Mirchev еt al. 2004). The host plant of T. solitaria is Pistacia terebinthus L. In this respect, the damage caused by the insect can be assessed as having no economic importance. However, the middle- and old-instar caterpillars possess urticating hairs. The ability of T. solitaria to cause severe allergies to humans and animals decreases or compromises the recreation functions of biotopes attacked in suburban zones and forest parks. 41 Some aspects of biology and ecology of T. solitaria were studied by Davatchi (1958), Serafimowsky (1975), Halperin (1983) and Mirchev et al. (2006). In Bulgaria a disease on larvae caused by Beaveria bassiana (Bals.-Criv.) Vuill. was established (Mirchev et al., 2012). In addition, first record of egg parasitoids of the species was reported (Mirchev et al., 2014a). This paper announces data about bionomics of T. solitaria in egg stage: structure of egg clusters, embryonic mortality, egg parasitoids and their impact on the host in the Eastern Rhodopes in Bulgaria. MATERIAL AND METHODS The study was conducted in 6 sites in the region of the town of Madzharovo (left bank of Arda River), town of Ivaylovgrad (Ivaylovgrad dam, Dupkata protected area, Quarry place), Belopolyane vill. (Likania protected area) and Meden buk vill. (left bank of Byala reka). The main characteristics of study areas are given in another publication (Boyadzhiev et al., 2017). In each site, cuttings of approximate length 4-5 cm from branches of P. terebinthus with egg clusters of T. solitaria were collected on 7 April 2014 and 16 April 2015 in xerophyte forest stands. After collection, the clusters were put singly in test tubes covered with cotton stoppers, and were transported to the laboratory of Forest Research Institute - Sofia. The scales of egg clusters were removed, and the samples were kept at room temperature (20-22ºC) for daily observation. The emerged parasitoids were removed from test tubes and separated in plastic capsules for further determination. Every egg with a hole in the eggshell was opened carefully and the meconia and remains of the emerged or dead insects were determined by a stereomicroscope (40 × magnification) according to Schmidt, Kitt (1994) and Tanzen, Schmidt (1995). The productivity of T. solitaria females was calculated by the number of eggs in different egg clusters. The differences in egg sizes in various samples were determined by F-factor (Schmidt et al., 1999), which indicates the number of eggs per 1 cm egg row length, as follows: e F = , where: r.l e – egg number; r – number of rows; l – cluster length (mm). T. solitaria egg mortality was divided into 5 groups: caterpillars died; undeveloped eggs with dried-up yolk; eggs totally empty; parasitized eggs; and eggs destroyed by predators. 42 RESULTS Structure of egg clusters The egg productivity of T. solitaria females varied between 43 and 187 eggs (Table 1). The difference between the average egg number in clusters of samples with highest values established (Ivaylovgrad dam, 153.9) and those with the lowest (Likania, 116.6) was 24.2%. The sample from Quarry collected on7 April 2014 showed the greatest dispersion, and that from Madzharovo collected on 16 April 2015 was the most compact. The egg clusters were laid on branches with a diameter of 3.6-13.0 mm. Their mean diameter varied between 5.1 and 6.9 mm (Table 1). The length of egg clusters varied between 7.0 and 28.0 mm. The parameters of three main indicators of egg clusters (egg number, length of egg clusters, and row number), are mutually dependent. As concerns to average length of egg clusters, a difference of 25.3% has been registered between the values from Ivaylovgrad dam (22.1) and Likania (16.5) – the samples with the greatest differences in average egg number in 1 egg cluster. The number of rows in them (5-9) was less variable than both indicators already discussed. The difference in the average number of rows (6.4-7.1) was 9.9%. Factor F in samples averaged 10.35-10.82 (Table 1). The difference between the highest and the lowest values established was 4.3%, i.e. almost 6 times lower than the differences between the highest and the lowest values for the average egg number in one cluster. The diameter of one visible egg on a cluster was 0.98 mm. The survival rate of T. solitaria in egg stage is determined by influence of biological and ecological factors. The average number of hatched caterpillars varied between 63.6 and 87.6% (Table 1). The differences in average values of emerged caterpillars can be defined as substantial and it can be assumed that here the influence of ecological factors has been decisive, whereas the health and physiological condition of the butterflies has probably been the reason for the enormous difference from 6.6% to 100.0% in individual egg clusters. T. solitaria egg mortality The analyses showed that some larvae died during hatching, i.e. a presence of exit openings and dead caterpillars in the eggs was observed (Table 2). Other dead larvae were found in the eggs without exit openings – an indication that the death had occurred before the emergence period. In a part of dead caterpillars and undeveloped eggs with dried-up yolk presence of fungal mycelium was established, but the pathogen and the pathogenesis had not been identified. The parasitoids’ impact has the highest share in mortality at the egg stage. It approximate distribution among different groups was as follows: a half part was due to parasitization; a quarter part - to undeveloped eggs with dried-up yolk; and the remaining quarter part was divided among the above-mentioned factors. In almost all samples, the parasitized eggs were over 50%, and Ivaylovgrad dam sample reached close to this value – 46.3%. In eight samples – Ivaylovgrad dam being the exception again – eggs destroyed 43 Table 1. Structure of egg clusters and rate of hatching of caterpillars in various regions of the Eastern Rhodopes, Bulgaria Meden Site of collection Madzharovo Dupkata Quarry Dam Likania buk 7 April 16 April 7 April 16 April 7 April 16 April 16 April 7 April 7 April Date of collection 2014 2015 2014 2015 2014 2015 2015 2014 2014 Code M 1 M 2 D 1 D 2 Q 1 Q 2 D L Mb Number of egg clusters 18 8 44 29 26 38 8 35 16 Total number of eggs 2523 1108 5658 3569 3158 4463 1231 4081 1921 Mean 140.2 138.5 128.3 123.1 121.5 117.4 153.9 116.6 120.1 ±SD 18.9 14.5 24.0 23.8 30.8 29.1 27.2 23.3 17.2 44 Minimum 104 118 66 73 48 43 95 56 91 Maximum 169 155 178 165 170 173 187 166 153 Diameter of branches on which egg clusters were deposited Mean (mm) 5.5 5.1 5.9 5.9 6.9 5.8 5.8 6.4 5.8 ±SD 1.2 0.9 1.4 1.1 2.8 1.6 0.9 1.7 1.6 Minimum (mm) 4.1 4.0 3.7 4.5 3.6 3.9 4.5 3.6 3.8 Maximum (mm) 8.0 6.2 10.0 9.0 13.0 10.2 7.1 10.0 8.7 Length of egg clusters Mean (mm) 19.2 20.1 17.6 18.0 17.5 17.0 22.1 16.5 16.7 ±SD 2.1 2.3 3.0 3.0 3.7 3.8 3.6 3.1 2.5 Minimum (mm) 16.0 17.0 9.8 10.0 8.0 7.0 16 9.0 14 Table 1. Continued Meden Site of collection Madzharovo Dupkata Quarry Dam Likania buk 7 April 16 April 7 April 16 April 7 April 16 April 16 April 7 April 7 April Date of collection 2014 2015 2014 2015 2014 2015 2015 2014 2014 Code M 1 M 2 D 1 D 2 Q 1 Q 2 D L Mb Maximum (mm) 22.0 24.0 25.0 25.0 24.0 24.0 28 23.2 22.3 Number of egg rows per cluster Mean 6.7 6.5 6.7 6.4 6.5 6.5 6.5 6.7 7.1 ±SD 0.5 0.5 0.9 0.8 0.9 1.0 0.9 0.9 0.8 Minimum 6 6 5 5 5 5 6 5 6 45 Maximum 7 7 9 8 9 9 8 9 8 Factor F Mean 10.82 10.66 10.82 10.63 10.62 10.80 10.72 10.7 10.35 ±SD 0.41 0.81 1.02 1.04 1.05 1.03 0.54 0.89 1.1 Minimum 9.76 9.21 7.33 7.40 7.93 7.89 9.9 7.95 7.65 Maximum 11.39 11.57 13.15 12.50 11.96 12.50 11.47 12.64 11.34 Caterpillars hatched, % Mean 75.9 63.6 87.6 83.4 77.9 81.2 80.3 77.5 76.1 ±SD 13.7 22.5 10.9 11.8 19.2 14,2 10.7 19.89 14.5 Minimum 50.7 21.2 59.5 53.3 0.7 28,2 57.9 6.6 40.2 Maximum 96.7 91.5 100.0 99.2 96.6 97,7 91.3 99.1 93.8 by predators were found, although not in large quantities.