Biocontrol potential of entomopathogenic nematodes against the grey maize weevil Tanymecus dilaticollis (Coleoptera: Curculionidae) adults.

The grey maize weevil, Tanymecus dilaticollis, is a polyphagous species, which is among the most important pests of maize in Southeastern Europe. The efficacy of commercial products with two species of entomopathogenic nematodes (EPNs), Steinernema carpocapsae and Heterorhabditis bacteriophora, was investigated against adults of the grey maize weevil under laboratory conditions. Nemastar®, containing S. carpocapsae was more effective on T. dilaticollis adults than Nematop® containing H. bacteriophora, when applied uniformly to the surface of the soil, on Petri dishes containing T. dilaticollis adults. Results showed that S. carpocapsae rates of 83-333 infective juveniles/adult caused > 94% mortality in T. dilaticollis adults, whereas H. bacteriophora caused 27-61%, adult mortality, after exposure of insects to the commercial products of EPNs for 15 days. The infection rates of EPNs increased with concentration applied and ranged from 70-83% and 19-64% for Nemastar® and Nematop®, respectively. Subsequent field and semi-field tests were conducted with Nemastar® (application rate of 50 million S. carpocapsae per 100 m2) in maize crops with biological (mycoinsecticide Naturalis®, biofungicides and fertilizers) and chemical seed treatment (Gaucho® FS 600; active ingredient: imidacloprid) in Knezha, Bulgaria. Nematodes were found only in the dead specimens, in open plots and cages sprayed with the commercial nematode product. Nematode sprayings contributed for higher maize yields in the open maize plots in the fields with different seed treatments. We suggest that the use of powder formulation of S. carpocapsae in combination with biologically treated maize seeds can contribute to minimize the use of chemical insecticides against the grey maize weevil. The results obtained can be used as a base to further tests to ascertain the efficacy of EPNs products before they can be recommended for use in the integrated approach to T. dilaticollis management.

Phytophagous larvae occurring in Central and Southeastern European oak forests as a potential host of Entomophaga maimaiga (Entomophthorales: Entomophthoraceae) - A field study.

We evaluated the presence and impact of Entomophaga maimaiga on both target and non-target phytophagous larvae. All six study plots, with low gypsy moth population density, were situated in Central and Southeastern European oak forests and E. maimaiga had previously been reported from these plots. Totally, 45 of 4,045 (1.13%) collected non-target larvae died due to fungal infections. No non-target insect specimen was infected by E.maimaiga, although the presence of the pathogen could not be fully excluded in three cadavers. Out of 1,780L.dispar larvae collected, 15individuals (0.84%) were infected by E.maimaiga.

Natural occurrence of microsporidia infecting Lepidoptera in Bulgaria.

We examined 34 lepidopteran species belonging to 12 families to determine presence and prevalence of microsporidian pathogens. The insects were collected from May 2009 to July 2012 from 44 sites in Bulgaria. Nosema species were isolated from Archips xylosteana, Tortrix viridana, Operophtera brumata, Orthosia cerasi, and Orthosia cruda. Endoreticulatus sp. was isolated from Eilema complana. The prevalence of all isolates in their hosts was low and ranged from 1.0% to 5.3%. Phylogenetic analyses of the new isolates based on SSU rDNA are presented.

Review of the genus Endoreticulatus (Microsporidia, Encephalitozoonidae) with description of a new species isolated from the grasshopper Poecilimon thoracicus (Orthoptera: Tettigoniidae) and transfer of Microsporidium itiiti Malone to the genus.

The historic genus Pleistophora (Plistophora) is a highly polyphyletic clade with invertebrate Microsporidia reassigned to several new genera since the 1980s. Two genera, Endoreticulatus and Cystosporogenes, clearly separate into distinct but closely related clades based on small subunit ribosomal RNA analysis but are included in different families that are each polyphyletic. A microsporidium with morphology resembling the Endoreticulatus/Cystosporogenes clade was isolated from the grasshopper Poecilimon thoracicus from a site in Northwest Bulgaria. It produced intense infections in the digestive tract of the host but no behavioral changes were noted in infected individuals. Prevalence of the microsporidium increased over the active feeding season yearly. Mature spores were oval and measured 2.58±0.21 µm×1.34±0.24 µm, with 16 to approximately 32 spores in a parasitophorous vacuole. The spores were uninucleate and polar filament coils numbered 8-9 situated in a single row. The spore polaroplast consisted of an anterior lamellar section and a posterior vesicular section, and the posterior vacuole was reduced. Analyses of a 1221 bp partial SSU-rRNA sequence indicated that the isolate is more closely related to the Endoreticulatus clade than to Cystosporogenes, but shows earlier phylogenetic separation from species infecting Lepidoptera and represents a new species, Endoreticulatus poecilimonae. To compare sequences of Endoreticulatus spp. from Lepidoptera to those infecting other insect orders, an isolate, Microsporidium itiitiMalone (1985), described from the Argentine stem weevil, Listronotus bonariensis, was sequenced. Like the grasshopper isolate, the weevil isolate is closely related but basal to the lepidopteran Endoreticulatus clade. The original description combined with the new sequence data confirms species status and permits transfer of the isolate from Microsporidium, a genus erected for microsporidian species of uncertain taxonomic status, to Endoreticulatus.