Aphids cause serious damage in greenhouses, where conditions are favorable for their development throughout the year and where they can reach high density over a short period of time. The damage caused by aphids may lead to deterioration of the ornamental qualities of infested plants and sometimes even death. One of the most important and serious consequences is virus transmission.

Currently, there is no extensive research on ornamental plants in greenhouses in Bulgaria, which prompted the current study. The only survey on this topic was conducted by Tashev (1962). He reported 6 aphid species: Aulacorthum (Neomyzus) circumflexum (Buckton, 1876); Macrosiphoniella sanborni (Gillette, 1908); Macrosiphum euphorbiae (Thomas, 1878); Myzus (Myzus) ornatus Laing, 1932; Myzus (Nectarosiphon) ascalonicus Doncaster, 1946; Myzus (Nectarosiphon) persicae (Sulzer, 1776).

The results of our survey contribute to the scientific knowledge in the investigated field, but also have a practical application, benefitting producers of ornamental crops. The purpose of this study was to identify the species composition of aphids on greenhouse ornamentals, their host range and the most frequently infested ornamental species in Bulgaria.

The investigation was conducted over a period of five years, from 2008 to 2012. Twenty greenhouses, located in the regions of Sofia, Plovdiv, Smolyan, Pavlikeni, Varna and Burgas, were observed. Several types of greenhouses were included: for growing and propagation of ornamentals, for landscaping (annuals, perennials, rooting cuttings), for acclimatization of imported plants, for winter preservation of cold-tender species and for plant collections.

The observed greenhouses are designated as follows:

Greenhouses with a permanent plant composition: Greenhouses of University of Forestry (GL); Greenhouses of Bulgarian Academy of Science (GB); Greenhouses of the University Botanic Gardens (GS); Greenhouses of Euxinograd park (GE); Greenhouses of Vrana park (GV); Greenhouses of Krichim park (GK); Ravda (R1);

Greenhouses with a constant circulation of plant species: private greenhouses in Sofia (S1, S2, S3, S4, S5, S6); Varna (V1, V2); Burgas (B1); Ravda (R2); Pavlikeni (PV); Plovdiv (PL); Smolyan (SM).

Aphids were collected in plastic bags together with the infested plant parts. Larvae were reared in laboratory conditions to the stage of adults.

The species identification was carried out using permanent microscope slides, after the traditional method of Hille Ris Lambers (1950). Identification keys included Blackman and Eastop (1994, 2000, 2006), Shaposhnikov (1964) and Stroyan (1984).

The total number of collected samples of aphids on ornamental plants during the observed five-year period was 279.

In total, 33 aphid species and one subspecies from 13 genera and 5 subfamilies (Lachninae, Chaitophorinae, Calaphidinae, Aphidinae and Eriosomatinae) were identified. Four species were identified only to the generic level but they are included in a total number of species because of the presence of clear distinguishing characters proving that they are separate species. Fourteen species belong to genus Aphis (42 %) and three species belong to genus Myzus (9 %). Genera Aulacorthum, Brachycaudus, Macrosiphum and Rhopalosiphum are represented by 2 species. Genera Cinara, Idiopterus, Macrosiphoniella, Ovatus, Periphyllus, Prociphilus and Tinocallis are represented by 1 species.

All aphid species and their host plants, including the data of Tashev (1962), are presented in alphabetical order in Table 1.

Twenty three of all recorded aphid species (69.7 %) have been reported on indoor ornamental plants (Weiss 1916, Cichocka and Goszczynski 1975, Achremowicz et al. 1986, Cichocka 1992, Łabanowski 2008, Rafi et al. 2010) and only six (18.2 %) have been found on ornamentals in Bulgarian greenhouses (Tashev 1962).

Twenty one of all recorded aphid species are polyphagous, 9 are oligophagous and only one is monophagous (Blackman and Eastop 1994, 2000, 2006). Seven of the polyphagous species were observed more frequently (Fig. 1).

During the survey, the most common species, represented by the highest numbers of samples, was Myzus persicae, found throughout the year in 13 greenhouses (61 samples, 21.9 %) (Fig. 1), followed by Aulacorthum solani (10 greenhouses, 51 samples, 18.3 %), Aulacorthum circumflexum (3 greenhouses, 33 samples, 11.8 %), Aphis gossypii (9 greenhouses, 26 samples, 9.3 %), Aphis spiraecola (4 greenhouses, 11 samples, 3.9 %), Macrosiphum euphorbiae (3 greenhouses, 9 samples, 3.2 %) and Aphis fabae (3 greenhouses, 8 samples, 2.9 %). All other species were found very rarely and were represented by 5 or less samples (< 1.8 %).

The present study indicates that in greenhouses with a permanent plant composition, aphid infestations are more frequent, more widespread, and are caused by a greater variety of species compared to infestations in greenhouses with a constant circulation of plant species (Fig. 2).

The widest host range was shown by Myzus persicae (43 hosts, 38 %), Aulacorthum solani (32 hosts, 28 %), Aulacorthum circumflexum (23 hosts, 20 %), Aphis gossypii (9 hosts, 8 %), Aphis spiraecola (8 hosts, 7 %), Aphis fabae (7 hosts, 6 %) and Macrosiphum euphorbiae (6 hosts, 5 %).

Periphyllus californiensis and Aphis (Aphis) fabae mordvilkoi are reported for the first time for Bulgaria. Furthermore, Aphis spiraecola has been found in new localities and has widened its host range in this country. So far, this species had been reported only on apple by Rasheva and Andreev (2007). All hosts reported in the present study for Aphis spiraecola are new for Bulgaria.

The list of host plants includes 114 species from 95 genera and 58 families. The most frequently infested plant species belong to Asteraceae (50 samples) and Malvaceae (37 samples). Eighteen samples were collected from Araceae; 16 samples from Apocynaceae; 15 samples from Araliaceae; 13 samples from Geraniaceae; and 10 samples from Acanthaceae, Solanaceae and Rosaceae.

The most frequently infested plants belong to the genera Hibiscus (12.9 %, 36 samples), Dendranthema (6.8 %, 19 samples), Chrysanthemum (5 %, 14 samples) and Pelargonium (4.7 %, 13 samples).

The highest diversity of aphid species was observed on Hibiscus rosa-sinensis and consists of 9 species (from 29 samples). Five species were identified on Dendranthema sp. (19 samples), Chrysanthemum hybridum (13 samples) and Anthurium andreanum (6 samples). Four species were found on Cyclamen persicum, Shefflera arboricola and Syngonium podophyllum. Three species were recorded on Aptenia cordifolia, Bougainvillea glabra, Chlorophytum comosum, Hebe sp., Hedera helix, Hibiscus syriacus, Mandevilla sanderi and Vinca major.

The aphids established on ornamental plants in greenhouses in Bulgaria comprise 33 species and one subspecies from 13 genera and 5 subfamilies.The most widespread aphid species is Myzus persicae, followed by Aulacorthum solani and Aphis gossypii. The widest host ranges were shown by Myzus persicae, Aulacorthum solani and Aulacorthum circumflexum.

The list of host plants includes 114 species from 95 genera and 58 families. The most infested plants belong to the genera Hibiscus and Dendranthema. The largest number of aphid species was detected on Hibiscus (9 species).