OVER WORLD DISTRIBUTION OF STEINERNEMATIDAE AND HETERORHABDITIDAE ( NEMATODA , PANAGROLAIMIDA ET RHABDITIDA ) ENTOMOPATHOGENIC NEMATODES

State of the diversity of helminths and groups of other parasites of vertebrate animals, their systematics and biology in standard and anthropogenically transformed ecosystems View project State of the diversity of helminths and groups of other parasites of vertebrate animals, their systematics and biology in standard and anthropogenically transformed ecosystems View project Yegor Yakovlev National Academy of Sciences of ... 14 PUBLICATIONS 1 CITATION


INTRODUCTION
The entomopathogenic nematodes (EPN) is an ecological group of invertebrates consisting of nematode parasitoids of insects from Steinernematidae and Heterorhabditidae (Nematoda: Panagrolaimida and Rhabditida) families.The study of EPN is important for developing a perspective biological method [6].Every year, new species of the entomopathogenic nematodes are described in the arithmetic progression due to a progress of the molecular technique.It is interesting to study the distribution of EPN on the Earth in connection with climatic and biogeographic factors, plant distribution etc. [10,11].
This study has proved a necessity of fundamental studies in different countries to fill in the gaps in the EPN distribution through the world.

MATERIALS AND METHODS
The study is based on data obtained from publications on distribution of the entomopathogenic nematodes in different countries.Part of the reports on EPN's distribution until 2002 was included in the performed analysis according to Hominick [10].
In a statistical analysis the cluster analysis from PAleontological STatistics v.2.17 program [9] was applied.The Bray-Curtis model was chosen for tree construction.In the analysis the presence/absence of Steinernema Travassos, 1927, and Heterorhabditis (Poinar, 1976) species were included in the studied countries.The area of each country in square kilometers (five groups, 0-1,000; 1,000-100,000; 100,000-1,000,000; 1,000,000-5,000,000; >5,000,000) belonging to the biogeographic regions (Palearctic: Western and Eastern; Oriental; Afrotropical; Nearctic; Neotropical; Australasian), and botanical continents according to the World Geographical Scheme for Recording Plant Distributions definition (Europe; Asia-Temperate; Asia-Tropical; Africa; Northern America; Southern America; Australasia) were used.For countries with an unidentified state of discovered EPN (e.g., Steinernema sp.),only the identified species were accepted as '1' value.
ISO 3166-1 alpha-3 codes [12] were applied for the abbreviated names of the countries (including the updated RUS1 for the European part of Russian Federation and RUS2 -for the Western part).
The world distribution map (Fig. 1) on the high resolution blank map of the world from the Wikimedia [19] was created.

RESULTS AND DISCUSSION
The entomopathogenic nematodes are distributed in all biogeographic regions excluding the Arctic, Antarctic and Subantarctic islands.According to recent studies, 120 species of the entomopathogenic nematodes (Steinernema and Heterorhabditis) were found in 72 countries (see Table ).
The entomopatogenic nematodes are widely spread in the Oriental (46 species from three genera) and Palaearctic regions (32 species of Steinernema and 5 species of Heterorhabditis) (see Table ).EPN are scarcely presented in the Australasian region -2 species of Steinernema and 4 of Heterorhabditis.The distribution of entomopathogenic nematodes depends on different abiotic and biotic factors: temperature [13,16], density, humidity [18] and chemical composition of substrate [3,14,15]; composition of phytocenosis [2,7]; climatic factors of a region; host finding strategy [4,8] and climatic preferences of nematodes [5], etc.

Представленість ентомопатогенних нематод у біогеографічних областях
Genera's resistance to the influence of all those factors is different [13,17] and can influence their distribution.
As discussed by Adams, Peat and Dillman [1], such differences in number of Steinernema and Heterorhabditis species and their distribution can be associated with different time of origin of these species.According to the age of symbiotic organisms Xenorhabdus spp., molecular and morphological evidences, the Steinernematidae family had appeared 350 million years ago opposite to the Heterorhabditidae family which is younger and had less time to produce species.
The calculated tree for Steinernema and Heterorhabditis distribution shows the nominal division of the represented countries into two big clusters A (Fig. 2, A) and B (Fig. 2, B).Cluster A is divided into two sub-clusters: A1, with the European countries in 96 % of cases and A2 with a mixed composition.o a1-2-3 with common species of H. bacteriophora, S. affine and S. carpocapsae, and a1-2-4 in the most of medium-sized countries.The medium size of countries and the presence of S. feltiae are general for both sub-groups.A2 sub-cluster is divided into two groups, both with countries of the Palaearctic region and Asia-Temperate botanical continent: • a2-1, with S. feltiae, in Canada and Japan, the presence of S. carpocapsae and S. kraussei is similar; • a2-2, with most common species of H. bacteriophora, S. carpocapsae, and rarely -H.indica and S. feltiae.Cluster B is divided into two sub-clusters, B1 and B2.B1 sub-cluster has countries with big territory and highly endemic EPN fauna.
B2 sub-cluster is characterized by a spread of H. indica and is divided into the following parts: • b2- It is clear that presence of the EPN species in the studied countries and their belonging to biogeographic regions were inherent for the tree construction.In the cases of low diversity of EPN fauna, the belonging to botanical continents and land area is of prime importance.For example, Spain, France and Italy are classified as medium-sized countries in the Western Palaearctic region, all belonging to the European botanical continent.All these countries have similar species of EPN in fauna: obvious S. affine, S. carpocapsae, S. feltiae, H. bacteriophora and partly S. arenarium (Artyukhovsky, 1967) Wouts, Mráček, Gerdin et Bedding, 1982.Besides, forming of mutual diversity of EPN species contributes to France bordering with Spain and Italy overland.
Since some countries possess huge land areas, the intensive process of describing new species stands apart (Republic of China, South Africa, United States of America, India and Vietnam).
Unfortunately, the analysis is indirectly related to national borders, temperature and moisture conditions, landscape relief and the level of studying of EPN, and, thus cannot be claimed as completely objective.However, it was shown indirectly by the land size (which could be a perspective for complete study) of countries and their belonging to the botanical continents and biogeographic regions (depending on climatic features, phytocenose compositions and indirectly to fauna of insect hosts).
According to current study, the level of investigation of EPN presence on different territories is of great importance.Information about the distribution of EPN's or related studies in 127 countries are not available.High number of gaps in distribution of the main genera of EPN's nearby or within the densely populated countries was noted.

Fig. 1 .Рис. 1 .
Fig. 1.Data on the distribution of Steinernema (A) and Heterorhabditis (B) in the world.The right column shows a relation between colors on map and number of species per country; "n/a" meaning: information is not available or research has not been carried out Рис. 1. Розподіл родів Steinernema (A) та Heterorhabditis (B) у світі.Колонка справа демонструє зв'язок між кольорами на карті та кількістю видів у країнах, "n/a" означає: інформації немає або дослідження ще не про водили The highest rate of distribution of Steinernema species has been registered in China (19 species) and the highest rate of distribution of Heterorhabditis (7 species) -in the United States of America.The highest number of EPN's of both genera has been found in China, that is 23 species in total.The most common EPN species are: S. feltiae (Filipjev, 1934) Wouts, Mráček, Gerdin et Bedding, 1982 (37 countries), H. bacteriophora Poinar, 1976 (32 countries) and S. carpocapsae (Weiser, 1955) Wouts, Mráček, Gerdin et Bedding, 1982 (31 countries).More rare are H. indica Poinar, Karunakar et David, 1992 (20 countries), H. megidis Poinar, Jackson et Klein, 1987 (17 countries), S. affine (Bovien, 1937) Wouts, Mráček, Gerdin et Bedding, 1982 and S. kraussei (Steiner, 1923) Travassos, 1927 (14 and 13 countries).96 species of Steinernema and Heterorhabditis have been found only in one country per species.The distribution of entomopathogenic nematodes depends on different abiotic and biotic factors: temperature[13,16], density, humidity[18] and chemical composition of substrate[3,14,15]; composition of phytocenosis[2,7]; climatic factors of a region; host finding strategy[4,8] and climatic preferences of nematodes[5], etc.Genera's resistance to the influence of all those factors is different[13,17] and can influence their distribution.As discussed by Adams, Peat and Dillman[1], such differences in number of Steinernema and Heterorhabditis species and their distribution can be associated with different time of origin of these species.According to the age of symbiotic organisms Xenorhabdus spp., molecular and morphological evidences, the Steinernematidae family had appeared 350 million years ago opposite to the Heterorhabditidae family which is younger and had less time to produce species.The calculated tree for Steinernema and Heterorhabditis distribution shows the nominal division of the represented countries into two big clusters A (Fig.2, A) and B (Fig.2, B).Cluster A is divided into two sub-clusters: A1, with the European countries in 96 % of cases and A2 with a mixed composition.