Pathogenicity, prevalence and intensity of a microsporidian infection by Nosema fumiferanae postvittana in the light brown apple moth, Epiphyas postvittana , in California

The Developmental Disorders of Fall Armyworm (Spodoptera frugiperda, Lepidoptera: Noctuidae) Caused by the Infection with Nosema sp. (Microsporidia: Nosematidae)

The fall armyworm (Spodoptera frugiperda), a globally invasive pest, poses substantial threats to corn in China. Microsporidia are a group of obligate intracellular parasitic fungi and are considered to have great potential in biological control. In this article, we investigated the pathology of Nosema sp. infection in S. frugiperda larvae at the organismal, cellular, and molecular levels. At the organism level, this microsporidian significantly prolonged the developmental duration of the host, reduced its body weight, caused molting failure, and led to a high mortality rate at 98.9%, 97.8%, and 64.0%, respectively, in 5 × 105, 5 × 104, 5 × 103 spores/larva doses. Microsporidia infection caused severe damage to midgut cells, including the formation of vacuoles in the cytoplasm, mitochondria, and intercellular spaces, destruction of goblet cells, and partial encapsulation of spores by mitochondria. Transcriptomic profiling revealed significant alterations in gene expression profiles in S. frugiperda larvae following microsporidian infection. The expression levels of genes associated with the chitin synthesis pathway (CHS1, G6PI, GFAT, GNPNA, PAGM, UAP) were inhibited, which may contribute to the effects of Nosema sp. on the growth and development of S. frugiperda.

Identification of Albopleistophora grylli n. gen. n. sp. (Microsporidia) and its impact on crickets (Gryllus spp.) in food-and-feed culture systems

This study provides a comprehensive taxonomic description of a microsporidian parasite infecting crickets, Gryllus bimaculatus and G. assimilis. Our analysis includes gross pathology, histopathology, spore ultrastructure, parasite development cycle, single gene phylogenies, and phylogenomic comparisons. We introduce a new taxon, Albopleistophora grylli n. gen. n. sp., characterised by its unique developmental stages within a sporophorous vesicle, leading to the formation of mature spores measuring 5.7 × 2.8 µm. Although prevalent in commercial cricket cultures, this parasite seemed to have limited effects on cricket survival. Indeed, microsporidia exposure and density assays with the host G. bimaculatus, only revealed density as a significant factor affecting the crickets' survival. Nevertheless, exposure showed significant effect on the crickets' emergence time, where exposed crickets emerged as adults earlier than unexposed individuals. Moreover, exposure to the parasite increased the faeces production and weight gain in cricket males. However, neither exposure nor density significantly impacted the females' fecundity. The absence of spores in non-exposed cricket groups suggested a horizontal transmission, highlighting the importance of controlled rearing practices to eliminate this microsporidium in control groups. The well-known anti-microsporidian drug 'fumagillin' was studied with a higher microsporidia dose of exposure to evaluate any improvement in cricket survival, without showing any significant differences between exposed and unexposed groups. Our findings underscore the nuanced dynamics of host-microsporidia interactions and emphasise the need for ecological context in understanding microsporidian impacts. Even if non-dangerous for its host, monitoring of this parasite seems crucial due to its potential zoonotic transmission by its close phylogenomic relation to human-infecting microsporidia species.

Impact of Nosema maddoxi on the survival, development, and female fecundity of Halyomorpha halys

Nosema maddoxi Becnel, Solter, Hajek, Huang, Sanscrainte, & Estep, a microsporidian species native to the United States, has been found infecting the invasive brown marmorated stink bug, Halyomorpha halys (Stål). Microsporidian infections in insects often shorten lifespans, decrease fecundity, prolong development, and stunt growth. This study was conducted to determine the impact of N. maddoxi on H. halys fitness. Adult females (2 doses) and nymphs (1 dose) drank suspensions of N. maddoxi spores to promote infection. Adult females receiving a high dose died faster than the controls. Nosema maddoxi infections impacted female egg production and egg viability at both doses compared with the controls. Infections were transmitted to 34.9% of adult males caged with infected females. As the number of days after inoculation increased, infection intensity (# spores found within an infected individual) for both adult treatments transitioned from low-intensity to high-intensity. Infected nymphs died significantly sooner than the controls. Of the treated nymphs, 55.9% died before molting into the fourth instar and only 26.5% eclosed to adults. Nymphal development rate and size were not impacted by N. maddoxi infection. These results indicate that N. maddoxi infection can negatively impact the lifespan of adult females, female fecundity, egg viability, and nymphal survival, which we hypothesize would negatively impact H. halys population densities.

A formal redefinition of the genera Nosema and Vairimorpha (Microsporidia: Nosematidae) and reassignment of species based on molecular phylogenetics

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" or "primary" and "environmental"). The Vairimorpha life cycle, in addition to a Nosema-type diplokaryotic 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.

Novel multitrophic interactions among an exotic, generalist herbivore, its host plants and resident enemies in California

What happens when an exotic herbivore invades and encounters novel host plants and enemies? Here, we investigate the impacts of host plant quality and plant architecture on an exotic generalist herbivore, Epiphyas postvittana (Lepidoptera: Tortricidae) and its interactions with resident parasitoids in California. Using artificial diet and five plant species, we found significant effects of diet on the fitness of E. postvittana under laboratory conditions. In the field, based on a common garden experiment with host plants of nine species, we found that larval parasitism varied among plant species by a factor of 2.1 with a higher risk of parasitism on shorter than taller plants. Parasitism of egg masses varied by a factor of 4.7 among plant species with a higher risk of parasitism on taller than shorter plants. In the laboratory, the foraging time of a resident egg parasitoid on excised leaves varied among plant species, but did not correspond to observed egg parasitism rates on these same plants in the field. On leaves of Plantago lanceolata, the probability of egg parasitism decreased with trichome density. Overall, there was a significant effect of host plant on the intrinsic rate of increase of E. postvittana and on the extent of parasitism by resident parasitoids, but no correlation existed between these two effects. The recent decline of E. postvittana in California may be due to the low quality of some host plants and to the many resident enemies that readily attack it, perhaps due to its phylogenetic relatedness to resident tortricids.