ArticlePDF Available

Ecological vs physiological host specificity: the case of the microsporidium Nosema pyrausta (Paillot) Weiser, 1961


Abstract and Figures

The microsporidium Nosema pyrausta (Paillot) Weiser, 1961 plays an important role in the mortality of the European corn borer Ostrinia nubilalis (Hübner, 1796), and shows high virulence to the beet webworm Loxostege sticticalis (Linnaeus, 1761). In contrast, the greater wax moth Galleria mellonella (Linnaeus, 1758) and the gypsy moth Lymantria dispar (Linnaeus, 1758) are referred to as resistant hosts, slightly susceptible to this microparasite. The goal of the present study was to test N. pyrausta against a broad range of lepidopteran species with different taxonomy, physiology, and ecology. The susceptibility to N. pyrausta spores fluctuated greatly among members of various families and super-families of Lepidoptera. As many as 13 species tested were found to be refractory (not able to support the development of the microsporidium), including three species of Yponomeutoidea, four species of Papilionoidea, one species of Pyraloidea, two species of Bombycoidea, and three species of Noctuoi-dea. The species found to be susceptible (with a high proportion of specimens displaying developed infection) included: Evergestis forficalis (Linnaeus, 1758) (Crambidae), Aglais urticae (Linnaeus, 1758) (Nymphalidae), and Dendrolimus sibiricus Chetverikov, 1908 (Lasiocampidae). The species newly found to be highly susceptible (high proportion of infected insects accompanied with high levels of 298 Yuri S. Tokarev et al. / Acta Biologica Sibirica 8: 297-316 (2022) early mortality) were: Spodoptera exigua (Hübner, 1808) (Noctuidae) and Aglais io (Linnaeus, 1758). Large quantities of spores can be produced in vivo using substitute laboratory host A. urticae. These results confirm previous observations that physiological host range of microsporidia (observed under experimental conditions) is broader than the ecological one (observed in nature).
Content may be subject to copyright.
Ecological vs physiological host specicity:
the case of the microsporidium
Nosema pyrausta (Paillot) Weiser, 1961
Yuri S. Tokarev1, Darya S. Kireeva1, Anastasia N. Ignatieva1,
Aleksander A. Ageev2, Aleksei V. Gerus1, Olga N. Yaroslavtseva3,
Anastasia G. Kononchuk1, Julia M. Malysh1
1 All-Russian Institute of Plant Protection, 3 Podbelskogo highway, Pushkin, St. Petersburg, 196608,
2 Center of Forest Pyrology, All-Russia Research Institute of Silviculture and Mechanization of Forestry,
42 Krupskoy st., Krasnoyarsk, 660062, Russia
3 Institute of Systematics and Ecology of Animals SB RAS, 11 Frunze st., Novosibirsk, 630091, Russia
Corresponding author: Julia M. Malysh (
Academic editor: R. Yakovlev| Received 25 June 2022| Accepted 6 July 2022 |Published 9 September 2022
Citation: Tokarev YuS, Kireeva DS, Ignatieva AN, Ageev AA, Gerus AV, Yaroslavtseva ON, Kononchuk AG,
Malysh JuM (2022) Ecological vs physiological host specicity: the case of the microsporidium Nosema pyrausta
(Paillot) Weiser, 1961. Acta Biologica Sibirica 8: 297–316.
e microsporidium Nosema pyrausta (Paillot) Weiser, 1961 plays an important role in the mortality
of the European corn borer Ostrinia nubilalis (Hübner, 1796), and shows high virulence to the beet
webworm Loxostege sticticalis (Linnaeus, 1761). In contrast, the greater wax moth Galleria mellonella
(Linnaeus, 1758) and the gypsy moth Lymantria dispar (Linnaeus, 1758) are referred to as resistant
hosts, slightly susceptible to this microparasite. e goal of the present study was to test N. pyrausta
against a broad range of lepidopteran species with dierent taxonomy, physiology, and ecology. e
susceptibility to N. pyrausta spores uctuated greatly among members of various families and super-
families of Lepidoptera. As many as 13 species tested were found to be refractory (not able to support
the development of the microsporidium), including three species of Yponomeutoidea, four species of
Papilionoidea, one species of Pyraloidea, two species of Bombycoidea, and three species of Noctuoi-
dea. e species found to be susceptible (with a high proportion of specimens displaying developed
infection) included: Evergestis forcalis (Linnaeus, 1758) (Crambidae), Aglais urticae (Linnaeus, 1758)
(Nymphalidae), and Dendrolimus sibiricus Chetverikov, 1908 (Lasiocampidae). e species newly
found to be highly susceptible (high proportion of infected insects accompanied with high levels of
Acta Biologica Sibirica 8: 297–316 (2022)
doi: 10.14258/abs.v8.e19
Copyright Yuri S. Tokarev et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC
BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
298Yuri S. Tokarev et al. / Acta Biologica Sibirica 8: 297–316 (2022)
early mortality) were: Spodoptera exigua (Hübner, 1808) (Noctuidae) and Aglais io (Linnaeus, 1758).
Large quantities of spores can be produced in vivo using substitute laboratory host A. urticae. ese
results conrm previous observations that physiological host range of microsporidia (observed under
experimental conditions) is broader than the ecological one (observed in nature).
Microsporidia, microbial control, bioassay, virulence, lepidopteran pest
Microsporidia are obligate intracellular eukaryotic parasites belonging to a certain
phylogenetic lineage, closely related to Fungi (Bass et al. 2018; Corsaro et al. 2019).
ey are ubiquitous as pathogens of animals and particular species are virulent to
their insect hosts (Issi 2020) and therefore are important for natural density regu-
lation and pest control (Franz and Huger 1970; Lipa and Madziara-Borusiewicz
1976; McManus and Solter 2003; van Frankenhuyzen et al. 2007; Hopper et al. 2016;
Frolov 2019; Andreeva et al. 2021; Malysh et al. 2021). One recent example of suc-
cessful application of microsporidia under eld conditions is that of Myrmecomorba
nylanderiae Plowes, Becnel, LeBrun, Oi, Valles, Jones, Gilbert, 2015 suppressing lo-
cal populations of the tawny crazy ant Paratrechina (Nylanderia) fulva (Mayr, 1862)
in North America (LeBrun et al. 2022). In Lepidoptera, several genera of micro-
sporidian parasites are found (Canning et al. 1985; Cali and Garhy 1991; Andreadis
et al. 1996; McManus and Solter 2003; Malysh et al. 2013, 2018). Among those, one
of the most abundant groups is the genus of Nosema with the type species Nosema
bombycis Nägeli, 1857 from the silkworm Bombyx mori Linnaeus, 1758 (Bomby-
coidea: Bombycidae), which suers devastating epizootics of this pathogen under
conditions of laboratory and industrial mass rearing (Bhat et al. 2009). One of the
closest relatives of this microsporidium is Nosema pyrausta (Paillot) Weiser, 1961, a
widespread pathogen of the European corn borer Ostrinia nubilalis (Hübner, 1796)
(Lepidoptera: Crambidae). Numerous observations indicate that in North Amer-
ica, microsporidia infections play an important role in regulation of O. nubilalis
population density, causing regular epizootics under eld conditions (Lewis et al.
2009; Zimmermann et al. 2016). Meanwhile, epizootics in European populations
of Ostrinia moths are less frequent and the average prevalence level typically does
not exceed 10 % (Pelissie et al. 2010; Malysh et al. 2011; Grushevaya et al. 2018).
is discrepancy can be explained by genetic dierences of the European and North
American isolates of the parasite (Tokarev et al. 2015) as well as other ecological
factors diering between the primary (Europe) and the secondary (North America)
areas of the pest.
Host range of a given microsporidium species is an important indicator of its
ability to circulate in nature and inuence insects other than the type host, as well as
its potential for practical implications (Solter et al. 1997, 2010). e beet webworm
Ecological vs physiological host specicity: the case of the microsporidium Nosema pyrausta (Paillot) Weiser, 1961299
Loxostege sticticalis (Linnaeus, 1761), a notorious polyphagous insect belonging to
the same family Crambidae as Ostrinia, was found to be highly vulnerable to N.
pyrausta and demonstrates high mortality rates even at low dosages of the patho-
gen (Malysh et al. 2021). On the contrary, the greater wax moth Galleria mellon-
ella (Linnaeus, 1758) (Pyraloidea: Pyralidae) and the gypsy moth Lymantria dispar
(Linnaeus, 1758) (Noctuoidea: Erebidae) are considered to be the resistant hosts.
In these two insect species, the mean dosage of 2 million (mln) spores per second
instar larva caused infection prevalence at the level of 0-5 %, which could be fur-
ther augmented only by a combination of additional immunosuppressive factors
(Tokarev et al. 2018; Kononchuk et al. 2021). Information concerning susceptibil-
ity of other lepidopteran species to this pathogen could not be found, except for
one study where few larvae of the common buckeye Junonia coenia Hübner, 1822
were tested, resulting in 50 % infection prevalence level (Hall 1952). Meanwhile,
understanding of host ranges and the factors governing host specicity of insect
pathogens, including microsporidia, is inevitable for exploration of patterns of their
natural distribution and for prediction of interplay with other ecosystem compo-
nents upon introduction into new habitats (Jeords et al. 1989; Onstad 1993; Solter
et al. 1997, 2010; Vilcinskas 2019; Issi 2020). Before such species will be considered
for application as microbial control agents, their virulence against crop and forest
pests, as well as interactions with non-target entomofauna, should be carefully ex-
amined to achieve desirable levels of pest management ecacy and to ensure safety
for natural biodiversity.
To explain why dierent insect species vary in their susceptibility levels to a cer-
tain microsporidium, several reasons can be assumed. First, host specicity of the
microparasite may play a certain role, when closely related insects are susceptible to
a certain microsporidium while distant host taxa are less prone to this microparasite
species. In fact, L. sticticalis belonging to the same family Crambidae and subfamily
Pyraustinae as Ostrinia shows high susceptibility to the microsporidium from the
latter host, as opposed by resistant Galleria and Lymantria from other high-level
taxa (see above). Second, insect body size may be of importance, as younger (and
smaller) instars are usually more susceptible to microsporidia and other microbes
as compared to the older (and bigger) ones (Vogelweith et al. 2013). is negative
correlation between the body size and infection susceptibility observed within the
course of individual development of a certain species may also have impact when
dierent insect species are compared. In particular, Loxostege is smaller than Os-
trinia which in turn is smaller than Galleria and Lymantria; and susceptibility to
N. pyrausta is gradually decreasing in this row. ird, feeding behaviour should de-
ne chemical composition of the insect gut juice so that the microsporidium spore
activation is aected (Issi et al. 2005). A polyphagous host is expected to have a
non-specic set of stimuli which potentially might activate the microsporidia spore
extrusion in the midgut lumen. Hence, the polyphagous herbivores Ostrinia and
Loxostege seem to be more suitable as a host for a certain species of microsporidia
300Yuri S. Tokarev et al. / Acta Biologica Sibirica 8: 297–316 (2022)
as compared to the dendrophilic phyllophagous larvae of Lymantria and wax-con-
suming Galleria.
e goal of the present study is to test these assumptions experimentally using
administration of N. pyrausta spores against a broad range of lepidopteran insect
species with dierent taxonomy, physiology, and ecology.
Material and methods
Propagation of the microsporidium
Nosema pyrausta spores were propagated in O. nubilalis under laboratory condi-
tions as described earlier (Grushevaya et al. 2018). Batches of spores were isolated
from the host pupae, washed with distilled water by centrifugation at 1000 g for 5
min and stored prior to experimental assays as pellets in water refrigerated for 1-3
months, which should not impair signicantly their infective potential (Malysh et
al. 2021).
For experimental infection, second instars of lepidopteran insects were used either
collected in nature and assayed directly, propagated as a temporary laboratory cul-
ture, or taken from a permanent laboratory culture.
Directly assayed insects collected in nature as the second instar larvae on their
type host plants were the ermine moths Yponomeuta evonymella (Linnaeus, 1758)
and Yponomeuta malinellus Zeller, 1838, the small tortoiseshell Aglais urticae (Lin-
naeus, 1758) and the European peacock Aglais io (Linnaeus, 1758) in St. Petersburg,
the black-veined white Aporia crataegi (Linnaeus, 1758) in Novosibirsk and the fall
webworm Hyphantria cunea (Drury, 1773) in Krasnodar Area. e cabbage white
Pieris brassicae (Linnaeus, 1758) was available at all developmental stages during
the vegetation season in St. Petersburg, but its larval population is constantly infest-
ed by the parasitoid, Cotesia glomerata (Linnaeus, 1758), at high prevalence levels.
For this reason, eggs were collected in nature and hatched larvae were reared until
second instar larvae under laboratory conditions. ese insects were fed with fresh
leaves of their type host plants or other available species: bird cherry for Y. evony-
mella, apple for Y. malinellus, nettle for Aglais spp., plum for A. crataegi, ash-leaved
maple for H. cunea, and cabbage for P. brassicae.
Temporary cultures were also established to obtain the second instar larvae of
the lial generation reared under laboratory conditions. ese species included
insects either caught as adults (the small white Pieris rapae (Linnaeus, 1758), the
green-veined white Pieris napi (Linnaeus, 1758), and the Indian our moth Plodia
interpunctella (Hübner, 1813) in St. Petersburg) or sampled as the last instar larvae
Ecological vs physiological host specicity: the case of the microsporidium Nosema pyrausta (Paillot) Weiser, 1961301
(the diamondback moth Plutella xylostella (Linnaeus, 1758) in St. Petersburg, the
cotton bollworm Helicoverpa armigera (Hübner, 1808) in Krasnodar Area, the cab-
bage moth Mamestra brassicae (Linnaeus, 1758) in Novosibirsk Region and the Si-
berian moth Dendrolimus sibiricus Chetverikov, 1908 in Krasnoyarsk Region). e
larvae were fed either with their type host plants, such as cabbage leaves (P. rapae, P.
napi, P. xylostella, M. brassicae), and r branches (D. sibiricus), or meridic diet (H.
armigera, P. interpunctella).
As many as three insect species were available as the permanent laboratory cul-
tures. e silkworm B. mori rst instar larvae were purchased from Research Sta-
tion of Sericulture (Stavropol Area) and maintained at the facilities of Slavyansk
Experimental Station of Plant Protection (Krasnodar Area) on mulberry leaves. e
tobacco hornworm Manduca sexta Linnaeus, 1763 eggs were purchased from the
group of companies “T-RexFoods(Moscow) and reared on a commercial meridic
diet (“T-RexFoods”). e beet armyworm Spodoptera exigua (Hübner, 1808) was
propagated at the facilities of the University of Silesia on a meridic diet.
Experimental infection
e second instars were used for all experimental treatments. e groups of 21-30
larvae of each insect species were maintained for 4-24 hours without feed. en
the starved insects were provided with N. pyrausta-contaminated feed. e plant
leaves (or the r needles) were evenly covered with the spore suspension on both
sides and le for air-drying for several minutes. When necessary, the leaf cuticle was
scratched by a pin to facilitate moistening of the leaf surface. For the insects main-
tained on the meridic diets, a diet portion was mixed with the spore suspension. In
all cases, the amount of spores was adjusted to provide the mean dosage of 1 mln
of spores per larva, taken that 90-100 % of the contaminated feed portion is con-
sumed. Aer contaminated feed consumption, the groups of larvae were split into
three equal groups to represent the repetitions, or maintained as a single repetition.
e pathogen-free feed was provided to the insects for the rest of the experiment.
Control insects were treated similarly but without addition of the microsporidium
spores. Mortality was screened on a daily basis, cadavers were dissected, and inner
tissues examined using light microscopy. In A. urticae, an additional experiment
was performed using the dosage lower by an order of magnitude (0.1 mln spores/
larva). In A. crataegi, two dosages were also used, 0.1 mln and 1 mln spores/larva,
respectively. In this experiment, ten larvae in each variant, including control, were
dissected at 30th day post treatment (d.p.t.). e rest of the insects were transferred
to +4°C for hibernation for four months and then dissected. For M. sexta, P. brassi-
cae and P. rapae, additional series of experiments were performed using insects fed
with the diet (M. sexta) with addition of 1 % phenylthiourea (PTU) or the cabbage
leaves (P. brassicae, P. rapae) sprayed with 1 % PTU one day prior to experimental
infection with microsporidia. is was done to increase insect susceptibility to the
non-specic microsporidium infection (Tokarev et al. 2018). Aer one day feeding
302Yuri S. Tokarev et al. / Acta Biologica Sibirica 8: 297–316 (2022)
on the PTU-treated fodder, the insects were treated with the parasite’s spores as
above. To calculate the spore loads in infected insects, the homogenates were pre-
pared from the individual specimens and amount of spores was quantied using a
Molecular genetic diagnosis
Samples of infected tissues or isolated spores were subjected for DNA extraction,
PCR with microsporidia-specic primers 18f:1047r and sequencing to conrm the
species diagnosis of the parasite (Weiss and Vossbrinck 1999; Malysh et al. 2019).
When necessary, the primers LepF1:LepR1 specic for mitochondrial cytochrome
oxidase subunit I (COI) were used for barcoding of Lepidoptera (Hebert et al.
2004). Sequences were analyzed and compared using BioEdit soware (Hall 1999)
and BLAST utility at the NCBI server (Altschul et al. 1990).
Statistical analysis
Survival analysis, including estimation of median survival time (LT₅₀), was estimat-
ed using Kaplan-Meier procedure followed by log rank test in SigmaPlot 12.5 (Systat
Soware Inc., San Jose, CA, 2011).
Among the three species assayed in Yponomeutoidea, neither Yponomeutidae (the
two species of the ermine moths) nor Plutellidae (the diamondback moth) became
infected with N. pyrausta aer feeding with the spores at early larval stage and
maintainance until pupation or adult emergence.
Among Papilionoidea, four species of Pieridae and two species of Nymphalidae
were tested. None of the P. rapae, P. brassicae, and P. napi, including those pretreated
with PTU for immunosuppression (P. rapae and P. brassicae) became infected. How-
ever, in the group of P. rapae, one larva out of 30 turned out to possess morphol-
ogy (Fig. 1) drastically distinct from that of other Pieridae as the insects grew up.
is specimen did not pupate for as long as three months aer successful pupation
of all other insects in both experimental and control groups. Obviously, another
species was assayed accidentally alongside with P. rapae larvae. e adipose tissue
of this larva was loaded with Nosema-like spores. e tissue sample was used for
both parasite and host identication using molecular genetic tools. As a result, the
parasite was conrmed as N. pyrausta basing upon 100 % identity of the SSU rRNA
gene sequence (852 bp) to Genbank accession # HM566196. Meanwhile, the host
showed 100 % identity of 640 bp long COI sequence to the respective nucleotide
sequence (# GU828662) of the garden pebble moth, Evergestis forcalis (Linnaeus,
1758) (Lepidoptera: Crambidae).
Ecological vs physiological host specicity: the case of the microsporidium Nosema pyrausta (Paillot) Weiser, 1961303
In A. crataegi larvae, specimens positive for Nosema-like spores were found in
all treatment groups dissected both before and aer the hibernation, as well as in the
control, presumably indicating either successful infection with N. pyrausta, includ-
ing contamination of the control group, or natural infection with a microsporidium.
ese spores were elongated oval with blunt ends (Fig. 2A). eir length was in the
range of 3.3-4.5 (mean 3.8) µm, the width was 1.7-2.2 (mean 1.9) µm (number of
measured spores N=20). Meanwhile, the spores of the N. pyrausta isolate used for
the bioassays in the present study were oval with more tapered ends (Fig. 2B). e
N. pyrausta spore length was 3.0-3.9 (mean 3.4) µm, the width was 1.4-1.8 (mean
1.7) µm (N=20 spores). e prevalence level ranged between 20 and 40 % with an
average of 27.7±3.3 % (mean±SE, number of dissected insects N=67). In order to
identify the parasite, SSU rRNA gene fragment was sequenced, which showed 100
% identity (617 bp) to the respective sequence of Nosema sp. CmM2 (# KC836092)
from Cnaphalocrocis medinalis Guenée, 1854 (Lepidoptera: Crambidae). Other
most similar entries found in Genbank with 99.7 % sequence identity belonged to
N. furnacalis (# U26532), N. granulosis (# FN434087), and two isolates of uniden-
tied Nosema species from Spodoptera litura (Fabricius, 1775) (# LC422335) and
Operophtera bruceata Hulst, 1886 (# MG456600). On the other hand, identity to N.
pyrausta (# HM566196) and N. bombycis (# D85503) was below 98 %.
In A. urticae, mortality in control did not exceed 13 % during 25 days of the ex-
periment, and similar dynamics was observed in insects treated with 0.1 mln spores/
larva. On the contrary, the larvae treated with 1 mln spores/larva displayed mortal-
ity of 30 % and 48 % at 10th and 25 d.p.t., respectively. ese values were signicantly
dierent from both the lower dosage and the control groups (Fig. 3). e survived
larvae both in control and treatment groups successfully pupated on 15-20th d.p.t.
Notably, 100 % of perished larvae and survived pupae dissected at 10-30th d.p.i.
showed presence of spores in treatment groups, as opposed to the control group.
Multiple infection loci lled with prespore stages and mature spores were found in
salivary glands and adipose tissue (Fig. 4). e sequencing of SSU rRNA of selected
specimens conrmed the diagnosis of N. pyrausta infection as above. e pupae
from the experimental group infected with 1 mln spores/larva contained from 4 to
625 mln spores, with an average of 246±54.3 spores/pupa (N=12). When A. io was
Figure 1. Full-grown larva of Evergestis forcalis heavily infected with Nosema pyrausta.
Ruler division = 1 mm.
304Yuri S. Tokarev et al. / Acta Biologica Sibirica 8: 297–316 (2022)
assayed, this species also showed 100 % infection with N. pyrausta spore masses
(N=23), though exact mortality and spore load data were not collected. It can only
be noted, that on 7th d.p.t., as many as 12 out of 30 larvae perished (40.0±5.77 %)
with zero mortality in control. Among those perished larvae, microsporidia preva-
lence level reached 100 % and the spore load averaged 5.9±0.14 spores/larva.
Figure 2. Bright eld light microscopy of the spores of Nosema sp. from Aporia crataegi (A)
and Nosema pyrausta from Ostrinia nubilalis (B).
Figure 3. Mortality dynamics in Aglais urticae aer feeding with Nosema pyrausta at the
dosages of 0.1 or 1 million spores per second instar larva. Dierent letters indicate mortality
curves with signicantly dierent median lethal time at p<0.01. For raw data, see supple-
mentary material, Table 1.
Ecological vs physiological host specicity: the case of the microsporidium Nosema pyrausta (Paillot) Weiser, 1961305
In Pyraloidea, the only species assayed within the frames of the present study
was P. interpunctella, while data for other Pyralidae and Crambidae have been re-
trieved from published literature. In this stored grain pest, only a limited sample
of 13 larvae was available for N. pyrausta treatment assay, and 12 in control. Early
larval mortality within 10-14 d.p.t. reached as much as 25-33 % in both groups,
followed by pupation of the survivors within 15-45 d.p.t. In one pupa from the N.
pyrausta treatment group, formed by 34th d.p.t., few oval Nosema-like spores were
detected. In another pupa from 43rd d.p.t., both few Nosema-like spores and multi-
ple oval spores of smaller size in packets by 8 were observed, the latter referred to
as the octospores (Fig. 5). e Nosema-like spores measured 3.5 × 1.7 µm, length/
width ratio of 2.1 (N=18) while the octospores measured 2.5 × 1.5 µm, length/width
ratio of 1.7 (N=18). None of the control insects were infected (N=12). Sequencing of
SSU rRNA of both the Nosema-like spores and the octospores resulted in the iden-
tical reads, up to 802 bp long (#ON256647), with 99.4 % identity to the reference
sequence of Vairimorpha carpocapsae (Paillot, 1938) (# AF426104).
Figure 4. Bright eld light microscopy of Nosema pyrausta infection in salivary glands (A-
C) and adipose tissue (D) of the small tortoiseshell Aglais urticae with clearly seen prespore
developmental stages (pds), immature (is) and mature spores (ms).
306Yuri S. Tokarev et al. / Acta Biologica Sibirica 8: 297–316 (2022)
Table 1. Raw data on the mortality of the small tortoiseshell, Aglais urticae aer treatment
of II instar larvae with Nosema pyrausta spores at two dosages
Repetion # Sample
Number of insects perished on days 5-25
5 10 15 20 25
Control 1 10 0 1 1 0 0
2 10 0 0 0 0 0
3 10 0 0 2 0 0
0.1 mln 1 7 0 0 0 0 0
2 7 0 0 1 0 0
3 6 0 1 0 0 0
1 mln 1 10 0 3 0 1 2
2 10 0 4 0 0 0
3 9 0 2 0 1 1
Figure 5. Bright eld light microscopy of the Nosema-like spores (Nls) and the octospores
(os) of Vairimorpha cf carpocapsae detected in Plodia interpunctella.
In Lasiocampoidea, D. sibiricus was the only species assayed. In control, as
many as 6.7±4.55 % larvae perished by 3rd d.p.t., and mortality remained at this
level throughout the 60 days of the experiment. When challenged with N. pyrausta
spores (2 mln spores/larva), larval mortality steadily increased, reaching 33-71 %
within 10th-50th d.p.t. (Fig. 6). LT50 was 30.0±13.73 days. Both perished (starting
from 7th d.p.t.) and survived larvae were dissected, showing prevalence of the mi-
crosporidium at 92 % (N=26). Sequencing of amplicons obtained from ve selected
specimens (collected at 10th, 20th, 30th, 40th, and 50th d.p.t.) using microsporidia-
specic primers conrmed the diagnosis of N. pyrausta.
In Bombycoidea, two representatives of two respective families, B. mori (Bom-
bycidae) and M. sexta (Sphingidae) were assayed, both showing no changes in mor-
tality levels and pupation speed as compared to control, and no infection with mi-
Ecological vs physiological host specicity: the case of the microsporidium Nosema pyrausta (Paillot) Weiser, 1961307
Figure 6. Mortality dynamics in Dendrolimus sibiricus aer feeding with Nosema pyrausta
at the dosage of 2 million spores per second instar larva. Dierent letters indicate mortality
curves with signicantly dierent median lethal time at p<0.01. For raw data, see supple-
mentary material, Table 2.
Table 2. Raw data on the mortality of the Siberian moth, Dendrolimus superans aer treat-
ment of II instar larvae with Nosema pyrausta at the dosage of 2 mln spores/larva
Treatment Repetition # Sample
Number of insects perished on days 5-60
5 10 15 20 25 30 35 40 45 50 55 60
Control 1 10 1 0 0 0 0 0 0 0 0 0 0 0
2 10 1 0 0 0 0 0 0 0 0 0 0 0
3 10 0 0 0 0 0 0 0 0 0 0 0 0
N. pyrausta 1 21 4 3 3 0 0 1 1 0 1 2 0 0
In Noctuoidea, representatives of two families were tested. Development of H.
cunea from Erebidae was not aected by N. pyrausta treatment challenging and
no infection was observed. Among Noctuidae, two species, H. armigera and M.
brassicae, were not aected by N. pyrausta challenging. On the contrary, S. exigua
displayed 100 % mortality of larvae challenged both with 1 and 0.1 mln spores/larva
within 10-12 d.p.t., which was by an order of magnitude higher as compared to con-
trol. Tissues of perished larvae were lled with N. pyrausta spores, as shown by light
microscopy and conrmed by PCR and sequencing as above.
308Yuri S. Tokarev et al. / Acta Biologica Sibirica 8: 297–316 (2022)
Susceptibility to N. pyrausta varied greatly across families and higher rank taxa of
Lepidoptera. As many as 13 species assayed in the present study were found to be re-
fractory, i.e. not able to support development of the microsporidium, including the
representatives of Yponomeutoidea (3 species), Papilionoidea (4 species of Pieri-
dae), Bombycoidea (4 species), and Noctuoidea (2 species). Resistant hosts, which
could become infected only at low prevalence levels, were found in our previous
studies among Pyralidae, namely G. mellonella (Tokarev et al. 2018), and Erebi-
dae, represented by L. dispar (Kononchuk et al. 2021). Susceptible species with high
proportion of specimens displaying developed infection include the type host O.
nubilalis and its congeners (Grushevaya et al. 2020). In the present study, new cases
of susceptible hosts are A. urticae and D. sibiricus. Moreover, in spite of occasional
observation and the limited sample size (N=1), it can also be indicated that E. for-
calis is susceptible to infection with N. pyrausta. Finally, highly susceptible species,
displaying high proportion of insects with developed infection accompanied with
high levels of early mortality, are also found across higher rank taxa. e new cases,
in addition to the previously reported L. sticticalis (Malysh et al. 2021), include A.
io and S. exigua.
From the presented dataset (Table 3), this can be judged that the susceptibility
to a given species of a microsporidian parasite (exemplied here by N. pyrausta)
does not follow a strict high-rank taxonomy-driven pattern in Lepidoptera. Indeed,
susceptible hosts are found in four dierent superfamilies. Moreover, both the re-
fractory and susceptible, as well as highly susceptible species could be found within
a given superfamily (Papilionoidea) and family (Noctuidae).
Table 3. Summary of susceptibility data of lepidopteran insect hosts to Nosema pyrausta
infection under experimental conditions
Insect host Trophic
to Nosema
Species Wingspan,
16-25 Oligophagous:
Prunus, Sorbus
- is paper
16-20 Oligophagous:
- is paper
Plutellidae Plutella
15 Oligophagous:
- is paper
Ecological vs physiological host specicity: the case of the microsporidium Nosema pyrausta (Paillot) Weiser, 1961309
Insect host Trophic
to Nosema
Species Wingspan,
45-60 Oligophagous:
- is paper
Pieris rapae 45-50 Oligophagous:
- is paper
Pieris napi 45-55 Oligophagous:
- is paper
75 Oligophagous:
Rosaceae, Salix,
-** is paper
Aglais urticae 45-62 Monophagous:
+ is paper
Aglais io 50-55 Oligophagous:
++ is paper
Junonia coenia 50-65 Oligophagous:
+ Hall 1952
Pyralidae Plodia
18-28 Grain-feeding -** is paper
30-41 Wax-feeding ± Tokarev et
al. 2018
Crambidae Ostrinia
26-30 Polyphagous,
+ Grushevaya
et al. 2020
26-30 Polyphagous,
+ Grushevaya
et al. 2020
26-30 Polyphagous,
+ Grushevaya
et al. 2020
24-29 Polyphagous,
++ Malysh et
al. 2021
25-28 Oligophagous:
+ is paper
Lasiocampidae De ndr oli mus
60-120 Oligophagous:
Abies sibirica
Ledebur, 1833,
+ is paper
Bombycidae Bombyx mori 40-50 Monophagous:
- is paper
Sphingidae Manduca
95-120 Oligophagous:
- is paper
310Yuri S. Tokarev et al. / Acta Biologica Sibirica 8: 297–316 (2022)
Our idea that the polyphagous lepidopteran larvae may be more susceptible to
infection with microsporidia as compared to the oligophagous and the monopha-
gous ones, does not nd a conrmation as well. In particular, among polyphagous
herbivorous noctuids, only one out of three tested species turned out to be (highly)
susceptible, while the others two were refractory. On the other hand, monophagous
A. urticae, as well as oligophagous J. coenia, D. sibiricus, and E. forcalis, were sus-
ceptible while oligophagous A. io was highly susceptible.
e size of the insect host species also does not seem to directly dene levels of
larval susceptibility to N. pyrausta, as can be seen from comparison of the small-
est (refractory, P. xylostella) vs one of the largest (highly susceptible, D. sibiricus)
of the tested insects. On the other hand, P. xylostella is known to be a very fast de-
veloping species (Andreeva et al. 2021) while D. sibiricus development is very slow
(Kirichenko et al. 2009) and this might have been a clue to understanding why the
former species is refractory, and the latter is highly susceptible. is assumption,
however, can be opposed by the case of the fast developing L. sticticalis which is
highly susceptible.
Results of microsporidia testing against insects originating from nature should
always be treated with care and veried using appropriate methods of pathogen
species identication to exclude the cases of natural infection, especially in isolates
Insect host Trophic
to Nosema
Species Wingspan,
Erebidae Hyphantria
25-42 Polyphagous,
- is paper
37-62 Polyphagous,
± Kononchuk
et al. 2021
Noctuidae Helicoverpa
30-40 Polyphagous,
- is paper
26-32 Polyphagous,
++ is paper
34-50 Polyphagous,
- is paper
* e insect species is referred to as a) refractory (-) when it develops no infection; b) resistant (±) when
low proportion of insects with developed infection or low intensity of infection is observed; c) susceptible
(+) when high proportion of specimens display developed infection; and d) highly susceptible (++) when
high proportion of insects with developed infection is accompanied with high mortality level.
** e data should be treated as preliminary due to presence of naturally occurring microsporidia which
might have inuenced interactions of the test insects with the experimentally applied pathogen.
Ecological vs physiological host specicity: the case of the microsporidium Nosema pyrausta (Paillot) Weiser, 1961311
and species with similar morphology, as shown for A. crataegi and P. interpunctella.
Presence of a natural infection might have inuenced interactions of the test insects
with the experimentally applied microsporidium. On the one hand, inherent mi-
crosporidia may prevent from infection with an externally applied pathogen species
due to competition. On the other hand, application of a non-specic microsporid-
ium, which cannot infect the insect itself, may however induce activation of other
microsporidia which are present in the covert form (Issi 1986). Anyway, such results
should be considered cautiously and require additional studies using microsporid-
ia-free colonies of the test insects.
In spite of observed infectivity of N. pyrausta to a broad range of Lepidoptera,
it has not been reported in those or similar host species under natural conditions
when extensive surveys were performed. For example, in the Illinois Natural History
Survey (INHS) Collection, none of the 30 microsporidia samples from Crambidae,
Pyralidae, Erebidae, Lasiocampidae, Noctuidae, and other families, showed reliable
identity with N. pyrausta (Tokarev et al. 2020). Similarly, among 161 microsporidia-
positive specimens of S. litura in Japan, none displayed infection with N. pyrausta
(Shigano et al. 2015). Additionally, the survey of the Gebank database indicated
absence of entries which can be identied as N. pyrausta from hosts other than O.
nubilalis. e obtained data are in good agreement with the previous observations
that physiological host range of microsporidia, observed under experimental con-
ditions, is broader than the ecological one, observed in nature (Solter and Maddox
1998). In case of N. pyrausta, one logical explanation is the cryptic lifestyle of the
host larvae, preventing them from excessive exchange of parasite burden with other
Experimental evidence of microsporidian host range is of great importance both
for elucidation of factors which dene insect interactions with eukaryotic micro-
parasites and for evaluation of microsporidia potential for microbial pest manage-
ment, including susceptibility of possible target pest species, suitability of certain
laboratory models for large-scale propagation of the entomopathogens and their
side eects on the non-target entomofauna. In this study, the ability of N. pyrausta
to infect lepidopteran larvae was found to vary depending upon the insect species.
Susceptible hosts are found within dierent taxonomic and ecological groups. High
mortality levels induced in S. exigua suggest N. pyrausta could be a promising agent
to control the pest. Meanwhile, spore yield indices observed in A. urticae indicate
the prospects of in vivo mass production of the pathogen in this host species. By
this research, we encourage other scientic groups to gather as much information as
possible concerning host ranges of microsporidian species they work with.
312Yuri S. Tokarev et al. / Acta Biologica Sibirica 8: 297–316 (2022)
Authors are indebted to Yuliya V. Volodartseva and Alsu M. Utkuzova (All-Russian
Institute of Plant Protection, St. Petersburg, Russia) for assistance with stock insect
cultures’ maintenance and to Sergei G. Udalov (ibidem) for capturing insect macro
photographs (Fig. 2). e bioassays using S. exigua could not be possible without
cooperation with Alina Kafel (University of Silesia, Katowice, Poland). e research
was performed using the equipment of the Core Centrum “Innovative Technologies
of Plant Protection” at the All-Russian Institute of Plant Protection and the Core
Centrum "Genomic Technologies, Proteomics and Cell Biology" of the All-Russian
Institute of Agricultural Microbiology (St. Petersburg, Russia). e research was
supported by Russian Science Foundation under grant # 20-66-46009.
Altschul SF, Gish W, Miller W, Myers EW, Lipman DJ (1990) Basic local alignment search
tool. Journal of Molecular Biology 215 (3): 403–410.
Andreadis TG, Maier CT, Lemmon CR (1996) Orthosomella lambdinae n. sp. (Microspor-
ida: Unikaryonidae) from the Spring Hemlock Looper, Lambdina athasaria (Lepidop-
tera: Geometridae). Journal of Invertebrate Pathology 67 (2): 169–177. https://doi.
Andreeva IV, Shatalova EI, Khodakova AV (2021) e diamondback moth Plutella xylostel-
la: ecological and biological aspects, harmfulness, population control. Plant Protection
News 104: 28–39. [In Russian]
Bass D, Czech L, Williams BAP, Berney C, Dunthorn M, Mahé F, Torruella G, Stentiford GD,
Williams TA (2018) Clarifying the Relationships between Microsporidia and Crypto-
mycota. Journal of Eukaryotic Microbiology 65 (6): 773–782.
Bhat SA, Bashir I, Kamili AS (2009) Microsporidiosis of silkworm, Bombyx mori L. (Lepi-
doptera-Bombycidae): a review. African Journal of Agricultural Research 4 (11): 1519–
Cali A, Garhy ME (1991) Ultrastructural study of the development of Pleistophora schubergi
Zwölfer, 1927 (Protozoa, Microsporida) in larvae of the spruce budworm, Choristoneura
fumiferana and its subsequent taxonomic change to the genus Endoreticulatus. Journal
of Protozoology 38 (3): 271–278.
Canning EU, Barker RJ, Nicholas JP, Page AM (1985) e ultrastructure of three micro-
sporidia from winter moth, Operophtera brumata (L.), and the establishment of a new
genus Cystosporogenes n.g. for Pleistophora operophterae (Canning, 1960). Systematic
Parasitology 7 (3): 213–225.
Corsaro D, Wylezich C, Venditti D, Michel R, Walochnik J, Wegensteiner R (2019) Fill-
ing gaps in the microsporidian tree: rDNA phylogeny of Chytridiopsis typographi
Ecological vs physiological host specicity: the case of the microsporidium Nosema pyrausta (Paillot) Weiser, 1961313
(Microsporidia: Chytridiopsida). Parasitology Research 118 (1): 169–180. https://doi.
van Frankenhuyzen K, Nystrom C, Liu Y (2007) Vertical transmission of Nosema fumif-
eranae (Microsporidia: Nosematidae) and consequences for distribution, post-diapause
emergence and dispersal of second-instar larvae of the spruce budworm, Choristoneura
fumiferana (Clem.) (Lepidoptera: Tortricidae). Journal of Invertebrate Pathology 96 (2):
Franz JM, Huger AM (1970) Microsporidia causing the collapse of an outbreak of the green
tortrix Tortrix viridana L. in Germany. Proceedings: 4th International Colloquium on
Insect Pathology. College Park, MD, 48–53.
Frolov AN (2019) Patterns of pest population dynamics and phytosanitary forecast. Plant
Protection News 3 (101): 4–33.
Grushevaya IV, Ignatieva AN, Malysh SM, Senderskiy IV, Zubarev IV, Kononchuk AG (2018)
Spore dimorphism in Nosema pyrausta (Microsporidia, Nosematidae): from morpho-
logical evidence to molecular genetic verication. Acta Protozoologica 57: 49–52. ht-
Grushevaya I, Ignatieva A, Tokarev Y (2020) Susceptibility of three species of the genus Os-
trinia (Lepidoptera: Crambidae) to Nosema pyrausta (microsporidia: Nosematida). BIO
Web of Conferences 21: 00040.
Hall TA (1999) BioEdit: a user-friendly biological sequence alignment editor and analysis
program for Windows 95/98/NT. Nucleic Acids Symposium Series 41: 95–98.
Hall IM (1952) Observations on Perezia pyraustae Paillot, a microsporidian parasite of the
European corn borer. Journal of Parasitology 38: 48–52.
Hebert PD, Penton EH, Burns JM, Janzen DH, Halwachs W (2004) Ten species in one: DNA
barcoding reveals cryptic species in the neotropical skipper buttery Astraptes fulgera-
tor. Proceedings of the National Academy of Sciences USA 101 (41): 14812–14817. ht-
Hopper JV, Huang WF, Solter LF, Mills NJ (2016) Pathogenicity, morphology, and char-
acterization of a Nosema fumiferanae isolate (Microsporidia: Nosematidae) from the
light brown apple moth, Epiphyas postvittana (Lepidoptera: Tortricidae) in California.
Journal of Invertebrate Pathology 134: 38–47. jip.2016.01.001
Issi IV (1986) Microsporidia as a phylum of parasitic protozoa. Protozoology 10: 1–136. [In
Issi IV (2020) Development of Microsporidiology in Russia. Plant Protection News 103:
161–176. [In Russian]
Issi IV, Dolgikh VV, Sokolova YY, Tokarev YS (2005) Factors of pathogenicity of Micro-
sporidia, the intracellular parasites of insects. Plant Protection News 3: 15–23. [In Rus-
Jeords MR, Maddox JV, McManus ML, Webb RE, Wieber A (1989) Evaluation of the over-
wintering success of two European microsporidia inoculatively released into gypsy
moth populations in Maryland, USA. Journal of Invertebrate Pathology 53: 235–240.
314Yuri S. Tokarev et al. / Acta Biologica Sibirica 8: 297–316 (2022)
Kirichenko NI, Baranchikov YN, Vidal S (2009) Performance of the potentially invasive
Siberian moth Dendrolimus superans sibiricus on coniferous species in Europe. Agri-
cultural and Forest Entomology 11: 247–254.
Kononchuk AG, Martemyanov VV, Ignatieva AN, Belousova IA, Inoue MN, Tokarev
YS (2021) Susceptibility of the gypsy moth Lymantria dispar (Lepidoptera: Erebi-
dae) to Nosema pyrausta (Microsporidia: Nosematidae). Insects 12: 447. https://doi.
LeBrun EG, Jones M, Plowes RM, Gilbert LE (2022) Pathogen-mediated natural and manip-
ulated population collapse in an invasive social insect. Proceedings of the National Acad-
emy of Sciences USA 119 (14): e2114558119.
Lewis LC, Bruck DJ, Prasia JR, Raun ES (2009) Nosema pyrausta: Its biology, history, and
potential role in a landscape of transgenic insecticidal crops. Biological Control 48 (3):
Lipa J, Madziara-Borusiewicz K (1976) Microsporidians parasitizing the green tortrix (Tor-
trix viridana L.) in Poland and their role in the collapse of the tortrix outbreak in Puszc-
za Niepolomicka during 1970–1974. Acta Protozoologica 15: 529–536.
Malysh YM, Tokarev YS, Sitnikova NV, Kononchuk AG, Grushetskaya TA, Frolov AN (2011)
Incidence of microsporidian infection of stem borers of the genus Ostrinia (Lepidop-
tera: Crambidae) in the Krasnodar Territory. Parazitologiia 45: 234–244. [In Russian]
Malysh JM, Tokarev YS, Sitnicova NV, Martemyanov VV, Frolov AN, Issi IV (2013) Tu-
bulinosema loxostegi sp. n. (Microsporidia: Tubulinosematidae) from the beet webworm
Loxostege sticticalis L. (Lepidoptera: Crambidae) in Western Siberia. Acta Protozoolog-
ica 52: 299–308.
Malysh JM, Ignatieva AN, Artokhin KS, Frolov AN, Tokarev YS (2018) Natural infection of
the beet webworm Loxostege sticticalis L. (Lepidoptera: Crambidae) with three Micro-
sporidia and host switching in Nosema ceranae. Parasitology Research 117: 3039–3044.
Malysh JM, Kononchuk AG, Frolov AN (2019) Detection of microsporidia infecting beet
webworm Loxostege sticticalis (Pyraloidea: Crambidae) in European part of Russia in
2006–2008. Plant Protection News 2: 45–51.
Malysh JM, Chertkova EA, Tokarev YS (2021) e microsporidium Nosema pyrausta as a
potent microbial control agent of the beet webworm Loxostege sticticalis. Journal of In-
vertebrate Pathology 186: 107675.
McManus ML, Solter L (2003) Microsporidian pathogens in European gypsy moth popula-
tions. Proceedings: Ecology, survey, and management of forest insects. USDA Forest
Service, Northeastern Research Station - General Technical Report NE-311: 44–51.
Onstad DW (1993) resholds and density dependence: the roles of pathogen and insect
densities in disease dynamics. Biological Control 3: 353–356.
Pelissie B, Ponsard S, Tokarev YS, Audiot Ph, Pelissier C, Sabatier R, Meusnier S, Chaufaux
J, Delos M, Campan E, Malysh JM, Frolov AN, Bourguet D (2010) Did the introduction
of maize into Europe provide enemy-free space to O. nubilalis? – Parasitism dierences
Ecological vs physiological host specicity: the case of the microsporidium Nosema pyrausta (Paillot) Weiser, 1961315
between two sibling species of the genus Ostrinia. Journal of Evolutionary Biology 23:
Shigano T, Hatakeyama Y, Nishimoto N, Watanabe M, Yamamoto Y, Wijonarko A, Ohba-
yashi T, Iwano H (2015) Variety and diversity of microsporidia isolated from the com-
mon cutworm Spodoptera litura in Chichijima, Ogasawara Islands. Journal of Insect
Biotechnology and Sericology 84 (3): 69–73.
Solter LF, Maddox JV (1998) Physiological host specicity of microsporidia as an indicator
of ecological host specicity. Journal of Invertebrate Pathology 71 (3): 207–216. https://
Solter LF, Maddox JV, McManus ML (1997) Host specicity of microsporidia (Protista: Mi-
crospora) from European populations of Lymantria dispar (Lepidoptera: Lymantriidae)
to indigenous North American Lepidoptera. Journal of Invertebrate Pathology 69: 135–
Solter LF, Pilarska DK, McManus ML, Zúbrik M, Patočka J, Huang WF, Novotný J (2010)
Host specicity of microsporidia pathogenic to the gypsy moth, Lymantria dispar
(L.): Field studies in Slovakia. Journal of Invertebrate Pathology 105: 1–10. https://doi.
Tokarev YS, Malysh JM, Kononchuk AG, Seliverstova EV, Frolov AN, Issi IV (2015) Rede-
nition of Nosema pyrausta (Perezia pyraustae Paillot 1927) basing upon ultrastructural
and molecular phylogenetic studies. Parasitology Research 114: 759–761. https://doi.
Tokarev YS, Grizanova EV, Ignatieva AN, Dubovskiy IM (2018) Greater wax moth Gal-
leria mellonella (Lepidoptera: Pyralidae) as a resistant model host for Nosema pyrausta
(Microsporidia: Nosematidae). Journal of Invertebrate Pathology 157: 1–3. https://doi.
Tokarev YS, Huang WF, Solter LF, Malysh JM, Becnel JJ, Vossbrinck CR (2020) A formal
redenition of the genera Nosema and Vairimorpha (Microsporidia: Nosematidae) and
reassignment of species based on molecular phylogenetics. Journal of Invertebrate Pa-
thology 169: 107279.
Vilcinskas A (2019) Pathogens associated with invasive or introduced insects threaten the
health and diversity of native species. Current Opinion in Insect Science 33: 43–48. ht-
Vogelweith F, iery D, Moret Y, Moreau J (2013) Immunocompetence increases with larval
body size in a phytophagous moth. Physiological Entomology 38: 219–225. https://doi.
Weiss LM, Vossbrinck CR (1999) Molecular biology, molecular phylogeny, and molecu-
lar diagnostic approaches to the Microsporidia. In: Wittner M, Weiss LM (Eds) e
Microsporidia and Microsporidiosis. ASM Press, Washington, 129–171. https://doi.
Zimmermann G, Huger AM, Langenbruch GA, Kleespies RG (2016) Pathogens of the Euro-
pean corn borer, Ostrinia nubilalis, with special regard to the microsporidium Nosema
pyrausta. Journal of Pest Science 89: 329–346.
316Yuri S. Tokarev et al. / Acta Biologica Sibirica 8: 297–316 (2022)
Genbank accession numbers: (will be made publicly available when
the paper will be published; available at authors by request)
... When a microsporidium is applied against insect species other than their natural host, its virulence indices may drastically change. In the case of N. pyrausta, though the majority of tested lepidopterans were less vulnerable as compared to Ostrinia, certain species turned out to be highly susceptible, including the polyphagous pests such as the beet armyworm Spodoptera exigua (Hübner, 1808) (Noctuoidea: Noctuidae) (Tokarev et al., 2022) and the beet webworm Loxostege sticticalis (Linnaeus, 1761) (Pyraloidea: Crambidae). In the latter case, effective trans-generational transmission of the parasite followed by a gradual decrease of the insect fertility is also observed (Malysh et al., 2021). ...
Full-text available
The microsporidium Nosema pyrausta (Paillot) Weiser, 1961 is an important mortality factor of the stem borers of the genus Ostrinia and may be used to control other lepidopteran pests. Rearing conditions (temperature regime and diet composition) of the laboratory host Ostrinia furnacalis (Guenée, 1854) (Pyraloidea: Crambidae) were compared in terms of their influence on N. pyrausta spore production, estimated as the mean spore number per host pupa. At lowered temperature (+20 °C), most of the experimental insects died at the larval stage, and in survived pupae, the microsporidium spore yield was below 8 × 106 spores/pupa. At the temperature of +24 °C, which is supposed to be the optimal for the insect laboratory culture exploited, N. pyrausta spore yield was about 50 × 106 spores/pupa. At increased temperature (+28 °C), the parasite spore yield was not higher than 28 × 106 spores/pupa. The mean spore yield values were significantly different between the variants of the three thermal regimes at 99% confidence level. The microsporidium spore production was further compared in insects fed with a standard corn flour-based diet vs modified diet (corn flour mixed with soybean flour at an equal proportion), reared at + 24 °C. Insect feeding with the modified diet caused an increase of the average spore yield by 35% (70 × 106 vs 52 × 106 spores/pupa obtained using the standard diet). Similarly, the weight of the pupae reared on the modified diet was 33% higher (0.0721 g vs 0.0542 g on the standard diet). Both the spore yield and the pupal weight values were significantly different between the two diet types at 95% confidence level. This provides one logical explanation of the parasite spore production increase as conditioned by the insect host weight increment. These observations indicate that +24 °C is the optimal thermal regime for N. pyrausta spore production which can further be augmented by supplementing diet of infected Ostrinia furnacalis larvae with soybean flour.
Full-text available
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.
Full-text available
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.
Full-text available
Прогноз фитосанитарного состояния в защите растений рассматривается как вероятностное научно-обоснованное суждение о динамике популяций вредных объектов в будущем, базирующееся на выявленных закономерностях в прошлом. При этом достоверность и точность прогнозов зависят от степени изученности факторов динамики численности объекта прогнозирования. Анализ полученных в ВИЗР результатов многолетних работ, посвященных изучению динамики популяций особо опасных вредителей в том числе с использованием таблиц выживаемости, а также мировой и отечественной литературы по проблеме, свидетельствует о ведущей роли биоценотической регуляции в динамике численности вредных членистоногих. Хотя в отличие от природных биогеоценозов, агробиоценозы возникли в результате хозяйственной деятельности человека, они также представляют собой сложные эволюционирующие системы. Очевидно, одним из основных направлений их эволюции является формирование и укрепление механизмов, обеспечивающих способность к саморегуляции, то есть к стабилизации динамического равновесия элементов, относящихся к разным трофическим группам. Соответственно, относительный вклад в динамику численности вредных объектов погодно-климатических факторов начинает постепенно ослабляться. Очевидно, прогресс в области фитосанитарных прогнозов, отвечающих требованиям сходимости, достоверности, качества и точности, должен в полной мере учитывать эффекты регулирующих механизмов, причем не столько в качестве уточняющего или корректирующего фактора, сколько в роли ключевого прогностического критерия.
Full-text available
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 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).
Full-text available
Insect populations are declining even in protected areas, but the underlying causes are unclear. Here, I consider whether the factors driving the loss of insect diversity include invasive and/or introduced insects transmitting pathogens to less-resistant native species. The introduction of insects into new areas for biocontrol, to promote pollination, or for mass rearing in insect farms, threatens the health and diversity of indigenous insects by the co-introduction of entomopathogens whose spillover is difficult to control. Even less virulent pathogens or covert infections can become lethal if environmental stressors weaken the resistance of indigenous host species in an additive, potentiating or synergistic manner. More research is needed to develop effective strategies that protect the health and diversity of native insects.
Изучение микроспоридий (М) и микроспоридиозов диких животных начато в России в 60-ые годы прошлого века. В европейской части страны изучались М, паразитирующие у насекомых – вредителей сельского хозяйства (ВИЗР), у пресноводных членистоногих и рыб (ГосНИОРРХ) и у таких кровососущих насекомых как слепни (Биолог. Ин-тут АН, Петрозаводск). В Западной Сибири изучали М кровососущих комаров (Томский ун-тет). В итоге до 2000 года у 100 видов животных описано 118 видов и 47 родов М, из них 20 новых. На современном этапе исследований с применением молекулярно-филогенетического анализа ведется описание новых и переописание ранее описанных видов. Получены принципиально новые данные по видообразованию, подтверждена коэволюция паразитов и их насекомых-хозяев на примере М и кровососущих комаров. При изучении строения и физиологии М впервые выявлены: миграция секреторных белков М в ядро клетки хозяина, факторы подавления паразитом апоптоза клетки хозяина, наличие энергетических органелл – митосом не в развивающихся стадиях, а в спорах М. Впервые показана роль аппарата Гольджи в образовании аппарата экструзии, а также отсутствие у М везикулярного секреторного транспорта. Впервые для России выявлены случаи заражения М ВИЧ-инфицированных пациентов. В настоящее время внимание обращено на разработку новой универсальной системы М, сочетающей молекулярные характеристики с описанием особенностей строения и развития каждого паразита.
Significance Invasive social insects are among the most damaging of invasive organisms and have proved universally intractable to biological control. Despite this, populations of some invasive social insects collapse from unknown causes. We report long-term studies demonstrating that infection by a microsporidian pathogen causes populations of a globally significant invasive ant to collapse to local extinction, providing a mechanistic understanding of a pervasive phenomenon in biological invasions: the collapse of established populations from endogenous factors. We apply this knowledge and successfully eliminate two large, introduced populations of these ants. More broadly, microsporidian pathogens should be evaluated for control of other supercolonial invasive social insects. Diagnosing the cause of unanticipated population collapse in invasive organisms can lead to applied solutions.
The microsporidium Nosema pyrausta is an important mortality factor of the European corn borer, Ostrinia nubilalis. The present study was aimed at N. pyrausta virulence testing to the beet webworm (BW), Loxostege sticticalis. This agricultural pest, L. sticticalis, was highly vulnerable to N. pyrausta. The parasite’s spores were located in salivary glands, adipose tissue, and Malpighian tubules of the infected specimens. Infection was transmitted transovarially through at least 3 laboratory generations, in which BW fitness indices were lower than in the control, and moth emergence and fertility decreased prominently. Transovarial infection was most detrimental to female egg-laying ability, resulting in zero fertility in F3. When propagated in BW, the microsporidium tended to increase its virulence to L. sticticalis, as compared to t Ostrinia isolates. The parasite’s ability to infect this host at low dosages and transmit vertically should guarantee its effective establishment and spread within BW populations. In conclusion, N. pyrausta is a promising agent against BW, which is a notorious polyphagous pest in Eurasia.
The microsporidian genera Nosema and Vairimorpha comprise a clade described from insects. Currently the genus Nosema is defined as having a dimorphic life cycle characterized by diplokaryotic stages and diplosporoblastic sporogony with two functionally and morphologically distinct spore types ("early" and "environmental"). The Vairimorpha life cycle, in addition to a Nosema-type diplokarytic sporogony, includes an octosporoblastic sporogony producing eight uninucleate spores (octospores) within a sporophorous vesicle. Molecular phylogeny, however, has clearly demonstrated that the genera Nosema and Vairimorpha, characterized by the absence or presence of uninucleate octospores, respectively, represent two polyphyletic taxa, and that octosporogony is turned on and off frequently within taxa, depending on environmental factors such as host species and rearing temperature. In addition, recent studies have shown that both branches of the Vairimorpha-Nosema clade contain species that are uninucleate throughout their life cycle. The SSU rRNA gene sequence data reveal two distinct clades, those closely related to Vairimorpha necatrix, the type species for the genus Vairimorpha, and those closely related to Nosema bombycis, the type species for the genus Nosema. Here, we redefine the two genera, giving priority to molecular character states over those observed at the developmental, structural or ultrastructural levels and present a list of revised species designations. Using this approach, a series of species are renamed (combination novum) and members of two genera, Rugispora and Oligosporidium, are reassigned to Vairimorpha because of their phylogenetic position. Moreover, the family Nosematidae is redefined and includes the genera Nosema and Vairimorpha comprising a monophyletic lineage of Microsporidia.