The gypsy moth, Lymantria dispar, is a notorious forest defoliator, and various pathogens are known to act as natural regulators of its population density. As a widespread herbivore with a broad range of inhabited areas and host plants, it is potentially exposed to parasitic microorganisms from other insect hosts. In the present paper, we determined the susceptibility of gypsy moth larvae to the microsporidium Nosema pyrausta from the European corn borer, Ostrinia nubilalis. Gypsy moth samples from two localities of Western Siberia were used. N. pyrausta developed infections in the salivary gland and adipose tissue of gypsy moth prepupae and pupae, forming spore masses after 30 days of alimentary exposure to the second instar larvae. Among the experimental groups, the infection levels ranged from 0 to 9.5%. Effects of a covert baculovirus infection, phenylthiourea pretreatment and feeding insects on an artificial diet versus natural foliage were not significant in terms of microsporidia prevalence levels. Thus, L. dispar showed a low level of susceptibility to a non-specific microsporidium. It can be referred to as a resistant model host and not an appropriate substitute host for laboratory propagation of the microsporidium.

Recently, we found that the spongy moth Lymantria dispar L. is susceptible to infection by a Dendrolimus sibiricus cytoplasmic polyhedrosis virus (DsCPV-1). In the present study, we evaluated the pathogenicity of DsCPV-1 against L. dispar larvae and its impact on surviving insects after the infection. Offspring of virally challenged insects were tested for susceptibility to a stress factor (starvation). In addition, we used light microscopy and quantitative polymerase chain reaction (qPCR) to test the ability of DsCPV-1 to be transmitted vertically. We found insect mortality of the L. dispar parents following the infection was positively associated with DsCPV-1 dose. DsCPV-1 was lethal to second-instar L. dispar larvae with a 50% lethal dose (LD₅₀) of 1687 occlusion bodies per larva. No vertical transmission of DsCPV-1 to offspring larvae was detected, while the majority of insect deaths among offspring larvae were caused by microsporidia (Vairimorpha lymantriae), which was harbored by the parents. The offspring of virally challenged parents exhibited a higher number of detected microsporidia compared to the control. Our findings suggest that the application of DsCPV-1 is effective in controlling pests in terms of transgenerational impact following virus exposure.

Nosemosis type C is a dangerous and widespread disease of the adult European honey bee Apis mellifera and is caused by the spore-forming intracellular parasite Vairimorpha (Nosema) ceranae. The search for new ways of therapy for this disease is complicated due to the seasonal availability of V. ceranae-infected insects as well as the lack of a developed system for the pathogen’s cultivation. By carrying out trials which used different infectious dosages of the parasite, spore storage protocols, host age, and incubation temperatures, we present a simple, safe, and efficient method of V. ceranae propagation in artificially infected worker bees in the laboratory. The method is based on feeding the groups of adult worker bees with microsporidian spores and insect maintenance in plastic bottles at 33 °C. The source of the spores originated from the cadavers of infected insects from the previous round of cultivation, in which the infective spores persist for up to six months. An analysis of five independent cultivation rounds involving more than 2500 bees showed that the proposed protocol exploiting the dosage of one million spores per bee yielded over 60 million V. ceranae spores per bee, and most of the spore samples can be isolated from living insects.

Background. Microsporidia are ubiquitous parasites of animals, most abundant in arthropods and fishes. Many species of these parasites are important from standpoints of medicine, veterinary and agriculture. Microsporidium Nosema pyrausta is an important disease agent in corn borer populations causing adverse effect on host fitness. Genotyping of this parasite is necessary for proper species identification and intraspecific polymorphysm studies. Materials and Methods. Microsporidia-infected larvae of corn borers of the genus Ostrinia were recovered from Krasnodar Territory in Russia and Gomel Region in Belarus. Small subunit ribosomal RNA (SSU rRNA) was amplified and sequenced directly, while intergenic spacer (IGS) was amplified, cloned and sequenced (1-5 clones per sample) for four isolates of microsporidia. Sequences were aligned and compared using standard bioinformatics tools (Clustal W and BLAST). Results. SSU rRNA genotyping showed allocation of all four isolates to N. pyrausta with 100% identity to each other and 99.7% similarity to Nosema bombycis, the type species of the genus Nosema. High levels of IGS sequence variation (61-74%) is observed both between isolates of different species and populations of microsporidia as well as between molecular clones within parasite isolates from individual hosts. Conclusion. N. pyrausta is widespread in corn borer populations and its genetic structure is complicated, as in other species of these parasites. Further studies of molecular markers are needed for genetic differentiation of geographic isolates of N. pyrausta.