The beet webworm Loxostege sticticalis (LS) has eruptive type of population dynamics and high migratory activity. The LS outbreaks are therefore difficult to predict and the pest belongs to the category of highly dangerous pests. However, during periods of depressions this insect is not observed within the most of its range and is very susceptible to infection by pathogens, including various species of microsporidia, some of which are not specific parasites of the order Lepidoptera. The distribution of LS microsporidia in Eurasia is quite extensive. During the study period of LS from 2003 to 2019, we have found 6 species of microsporidia. The parasite list includes not only species known for Lepidoptera such as Nosema sp. and Vairimorpha thomsoni, but also Vairimorpha (Nosema) ceranae as the typical pathogen from Apis mellifera, as well as Endoreticulatus cf poecilimonae, a pathogen similar to Endoreticulatus poecilimonae from Poecilimon thoracicus. Moreover, two isolates from the genus Tubulinosema identified in LS belong to the group of parasites with a very wide host range, including humans. In laboratory experiments, LS proved high sensitivity to microsporidia N. pyrausta from Ostrinia nubilalis and N. tyriae from Tyria jacobaeae. Its susceptibility to Paranosema locustae from Locusta migratoria has also been discovered.
Microsporidia are obligate intracellular parasites that affect the population density of many insect pests. In particular, infection with Nosema pyrausta is one of the major mortality factors for the European corn borer Ostrinia nubilalis, the Asian corn borer Ostrinia furnacalis and the adzuki bean borer Ostrinia scapulalis. The purpose of the work is to compare the susceptibility to N. pyrausta and pathogenesis of three species of moths of the genus Ostrinia. Studies conducted over 2 years have shown that in all three species of host insects under laboratory conditions, both during oral infection and transovarian transmission of infection (in the daughter generations of experimentally infected insects), only diplokaryotic spores formed corresponding to the main morphotype of the genus Nosema. Mean lethal time increased with instar of larvae used for infection but didn’t differ between the three species. The rates of transovarial transmission of N. pyrausta were also similar. Thus, all the insect species examined may equally participate in the parasite persistence in nature and serve as model laboratory hosts for parasitological research and mass propagation of the microsporidium.
Nowadays researchers provide more and more evidence that it is necessary to develop an ecologically friendly approach to pest control. This is reflected in a sharp increase in the value of the biological insecticide market in recent decades. In our study, we found a virus strain belonging to the genus Cypovirus (Reoviridae); the strain was isolated from Dendrolimus sibiricus: that possesses attractive features as a candidate for mass production of biological agents for lepidopteran-pest control. We describe morphological, molecular, and ecological features of the new Cypovirus strain. This strain was found to be highly virulent to D. sibiricus (half-lethal dose is 68 occlusion bodies per second-instar larva) and to have a relatively wide host range (infects representatives of five families of Lepidoptera: Erebidae, Sphingidae, Pieridae, Noctuidae, and Lasiocampidae). The virus strain showed a strong interaction with a nontoxic adjuvant (optical brightener), which decreased the lethal dose for both main and alternative hosts, decreased lethal time, and may expand the host range. Moreover, we demonstrated that the insecticidal features were preserved after passaging through the most economically suitable host. By providing strong arguments for possible usefulness of this strain in pest control, we call on virologists, pest control specialists and molecular biologists to give more attention to the Cypovirus genus, which may lead to new insights in the field of pest control research and may provide significant advantages to compare with baculoviruses and Bacillus thuringiensis products which are nowadays main source of bioinsecticides.
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