First report of the enthomopathogenic nematode Steinernema arenarium (Steinernematidae: Rhabditida) in Bulgaria

Abstract

Steinernema arenarium Artyukhovsky, 1967 (Steinernematidae: Rhabditida) was isolated from alluvial soil at a riverside location near the town of Kresna, at an altitude of 200 m. This is the first report of steinernematids of the glaseri-group for Bulgaria and the Balkan Peninsula. The average ratio c of the infective juveniles of the “Kresna” isolate is 13.8. Such high values of the ratio c (with an average of more than 12) are characteristic of the “glaseri-group” within the genus Steinernema Travassos, 1923, comprising species such as S. diaprepesi Nguyen et Duncan, 2002 [c = 12.1 (10.4-13.2)], S. puertoricense Roman et Figueroa, 1994 (c = 14.2), S. cubanum Mrácˇek, Hernández et Boëmare, 1994 (c = 19), S. glaseri Steiner, 1929 [c = 14.7 (13.6-15.7)], S. boemarei Lee, Sicard Skeie et Stock [c = 13 (12-14)] and S. arenarium. These six species form a distinct monophyletic group within clade V of the genus Steinernema. The ratio c appears to be quite significant for the differentiation of this group. It seems that S. arenarium is widely distributed in some regions of Europe. The species is genetically and phenotypically polymorphic, with preferences for riverside alluvial soils. The establishment of S. arenarium in Bulgaria extends the known area of the species to the southeast. According to the chorotype classification, the distribution of S. arenarium resembles Turano-European. Larvae and adults of insects, mainly of the families Melolonthidae, Rutelidae, Aphodiidae (Coleoptera: Scarabaeoidea), Carabidae and Elateridae (Coleoptera), which probably are among the natural hosts of the species, were isolated from the investigated site. The morphological identification of the species was confirmed by molecular methods.