Trilobed uncus taxa of the genus Ostrinia (Lepidoptera, Crambidae) illustrate the complex relationship, at early stages of speciation, between reproductive isolation and differentiation in morphology, resource use and genetic variation. On the basis of behaviour and ecology, we recently hypothesized that individuals with small mid-tibiae belong to two distinct species depending on host plant-O. nubilalis and O. scapulalis sensu Frolov et al. (2007) feeding on maize and on a number of dicotyledons, respectively. Individuals with small, medium or massive mid-tibiae would all belong to O. scapulalis as long as they feed on these dicotyledons. This contrasts with previous taxonomy, which distinguished three species by male mid-tibia morphology, regardless of host plant. Here, we test our hypothesis by examining the genetic structure of Ostrinia populations from regions with mid-tibia polymorphismWestern Russia and Kazakhstan-and comparing it with that of French populations where only small mid-tibiae occur. Results support two predictions: (1) maize-and dicotyledoncollected populations are genetically differentiated from each other like in France, and (2) dicotyledon-collected populations show no genetic evidence of consisting of more than one species. Between-species differentiation was unrelated to geographic distance, despite significant isolation by distance within species. The distinction between two and only two species differing by host plant thus holds at continental scale. Interestingly, one microsatellite locus contributed B10 times more than the others to differentiation between both taxa. This deserves further investigation, as it might reveal a linkage between this outlier and loci involved in host-plant adaptation and/or reproductive isolation.

No abstract

Populations of European corn borer (Ostrinia nubilalis Hübner) from Krasnodar Territory (Southwestern Russia) become regularly infected with Nosema-like microsporidia. To identify the parasite, it was subjected to electron microscopy and small subunit ribosomal RNA (SSU rRNA) gene sequencing. The spore ultrastructure of the parasite was highly similar to Nosema bombycis from China and Nosema pyrausta from the USA. The nucleotide sequence of SSU rRNA gene was identical to a microsporidium isolated from O. nubilalis in southern France (GenBank accession no. HM566196) and closely related to Nosema bombycis (no. AY209011, 99.7 % sequence similarity) from Bombyx mori of Chinese origin and N. pyrausta (no. AY958071) from O. nubilalis of North American origin. As the molecular haplotype of SSU rRNA is fixed for the parasite infecting O. nubilalis across Europe and N. pyrausta was initially described in France as Perezia pyraustae (Paillot CR Acad Sci Paris 185: 673-675, 1927), we conclude that the parasite examined under the present study correspond to the type isolate of N. pyrausta. The microsporidium from O. nubilalis in North America (no. AY958071) corresponds therefore to a closely related, yet distinct haplotype.

The beet webworm Loxostege sticticalis (L.) is a major insect pest that causes serious damage of agricultural crops in Russia, China and adjacent countries. Microsporidia are obligate intracellular parasites that negatively affect population density of many insect hosts including Lepidoptera. In particular, infection with microsporidia is an important mortality factor for L. sticticalis. Special methodology for the identification of microsporidia associated with terrestrial insects is required. In the present paper we report the results of screening beet webworm moths for microsporidia using two techniques, i.e. light microscopy (LM) and PCR. Adult moths were sampled in 2006-2008 in the European part of Russia: Rostov Region, Krasnodar Territory and Republic of Bashkortostan. Microsporidia infections were detected in insects collected from all sampling sites. Examination of smears by LM showed presence of microsporidian spores in 3.4 % of samples (N=98). PCR analysis of the same dataset was positive in 6.7 % of samples, including those containing and not containing spores. The higher infection rate determined by PCR is likely connected with the fact that only mature spores Malysh J. M. at al. / Plant Protection News 2(100) -2019, p. 45-51 can be unequivocally identified by LM, whereas PCR also allows detection of otherdevelopmental stages of microsporidia. Partial sequencing of an amplicon from Krasnodar Territory showed its close relatedness to Endoreticulatus poecilomonae from Poecilimon thoracicus Fieber (Orthoptera: Tettigoniidae).

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.