Frequency of occurrence and identification of nematodes among entomopathogenic organisms in agrocoenoses of Ukraine

Abstract

The research objects were entomopathogenic organisms (Nematoda, Fungi, Bacteria, and Insecta) collected in agrocoenoses in different regions of Ukraine during 2016–2018 and 2020–2021. The following research materials were used: soil samples, soil live-traps, specimens of Galleria mellonella L., 1758 (Lepidoptera: Pyralidae) and potential host insects (Coleoptera: Elateridae, Tenebrionidae, Melolonthinae; Lepidoptera: Noctuidae). We analysed 312 samples (220 soil + 92 live-trap samples) and >100 specimens of potential host insects. Our data demonstrate that in soils of agrocoenoses, favourable conditions are created for the dispersal of entomopathogenic organisms. We report the frequency of occurrence of insect-pathogenic nematodes in agrocoenoses of Ukraine, and describe their identification and the specifics of pathology they cause to the insect Galleria mellonella in the context of other entomopathogenic organisms. The frequency of occurrence (% of samples) of entomopathogenic nematodes (genus Steinernema Travassos, 1927 and genus Heterorhabditis Poinar, 1976) in agrocoenoses was the highest among other organisms that caused infectious and parasitic diseases of insects and were found in 15% of the samples. Three species of entomopathogenic nematodes—Steinernema carpocapsae (Weiser, 1955) Wouts et al., 1982, Steinernema ex gr. ‘glaseri‘, and Heterorhabditis bacteriophora Poinar, 1976—have been identified. We have found 8% of samples to contain fungal disease-causing agents (genera Beauveria Vuill., 1912, Metarhizium Sorokin, 1879, and Akanthomyces Lebert, 1858). The frequency of occurrence (%) of all remaining causative agents of infectious and parasitic diseases of insects, namely bacterial diseases and myiasis (infection of a fly larva) (Diptera: Tachinidae) were 3% and 2%, respectively. A mixed infection was detected in 2.5% of the total number of analysed samples; nematodoses-mycoses mixed infections were most often recorded. We have recorded the phenomenon of hyperparasitism with nematodosis-entomosis co-infection inside dead G. mellonella larvae for the first time.