Arthropod Pathogens Research Articles

Metarhizium fungi as plant symbionts

AbstractMetarhizium fungi are pathogens of arthropods, with several early‐diverged species infecting lizards or mushrooms. Most Metarhizium species are also beneficial plant symbionts, and they mainly colonize rhizosphere and rhizoplane with some strains colonizing leaves and stems. The development of Metarhizium and plant association commence either by the attachment of spores to roots or rhizosphere colonization. Rhizosphere hyphae are further attracted to roots by nutrient‐rich root exudates, facilitating rhizoplane colonization. Both undifferentiated and differentiated (characterized by appressorial formation) hyphae can penetrate between root epidermal cells, with sporadical colonization. Plant‐derived reactive oxygen species play a crucial role in limiting root cell colonization by Metarhizium. Metarhizium utilizes plant‐derived sugars and fatty acids for the growth while transferring insect‐derived nitrogen to the plants. Additionally, Metarhizium facilitates plant’s utilization of environmental phosphorus, zinc, and iron via increasing the bioavailability of these nutrients. Metarhizium colonization can improve plant resistance to herbivores, microbial pathogens, and abiotic stresses. Given their versatile benefits to plants, Metarhizium has been developed as insecticides, fertilizers, and plant immunity promoters. In addition to terrestrial ecosystems, recent studies report that Metarhizium also inhabits aquatic and wetland ecosystems, which could further enhance the understanding of their biology and ecology and widen their applications.

Pathogen Binding and Entry: Molecular Interactions with the Insect Gut.

The point of entry for the majority of arthropod pathogens and arthropod-vectored pathogens of plant, animal, and human health importance is the arthropod midgut. Pathogen interaction with the midgut therefore represents a primary target for intervention to prevent pathogen infection and transmission. Despite this key role in pathogen invasion, relatively little is known of the specific molecular interactions between pathogens and the surface of the arthropod gut epithelium, with few pathogen receptors having been definitively identified. This article provides an overview of pathogen molecular interactions in the arthropod midgut, with a focus on gut surface proteins that mediate pathogen entry, and highlights recent methodological advances that facilitate the identification of pathogen receptor proteins.

Reassessing the Diversity of the Arthropod-Pathogenic Genus Pandora Batko (Entomophthoromycotina; Erynioideae)

The fungal order Entomophthorales occurs worldwide, with most species infecting arthropods as pathogens. Species in this order can cause epizootics and change the behavior of infected hosts. Molecular data are available only for 20% of the known species, and distributions of species are seldom summarized. Significant diversity of hosts, poor molecular data availability, and poor resolution of the phylogenetic relationships within this fungal order suggest that the diversity of these fungi is not sufficiently described. The subfamily Erynioideae includes 111 arthropod pathogens, divided among six genera, with the genus Pandora being one of the most diverse genera. Sequences of 18S, 28S, and ITS for two species are used to place these Pandora species in a phylogenic tree of the subfamily; this tree also supports our synonymy of the genus Furia with Pandora. Among the two species specifically covered in this paper, Pandora gloeospora was observed during epizootics occurring in mushroom flies (Diptera: Sciaridae) on Agaricus bisporus cultures in Pennsylvania, Delaware, and Maryland (US) mushroom farms and also in Florida on Pleurotus sp. Outside the US, P. gloeospora was found infecting several Nematocera (Diptera) in Europe (France) and Asia (China). Pandora sylvestris n. sp. was collected during epizootics occurring in larvae of hickory tussock moths, Lophocampa caryae (Lepidoptera: Erebidae), in hardwood forests in Michigan and Vermont.

Potential for Use of Species in the Subfamily Erynioideae for Biological Control and Biotechnology.

The fungal order Entomophthorales in the Zoopagomycota includes many fungal pathogens of arthropods. This review explores six genera in the subfamily Erynioideae within the family Entomophthoraceae, namely, Erynia, Furia, Orthomyces, Pandora, Strongwellsea, and Zoophthora. This is the largest subfamily in the Entomophthorales, including 126 described species. The species diversity, global distribution, and host range of this subfamily are summarized. Relatively few taxa are geographically widespread, and few have broad host ranges, which contrasts with many species with single reports from one location and one host species. The insect orders infected by the greatest numbers of species are the Diptera and Hemiptera. Across the subfamily, relatively few species have been cultivated in vitro, and those that have require more specialized media than many other fungi. Given their potential to attack arthropods and their position in the fungal evolutionary tree, we discuss which species might be adopted for biological control purposes or biotechnological innovations. Current challenges in the implementation of these species in biotechnology include the limited ability or difficulty in culturing many in vitro, a correlated paucity of genomic resources, and considerations regarding the host ranges of different species.

Reproduction of Entomopathogenic Nematodes for Use in Pest Control.

The growing interest in the use of entomopathogenic nematodes and their symbiotic bacteria as promising biocontrol agents of many arthropod pests and pathogens has created running technologies to expand their use globally. The related laboratory procedures and tests on these nematodes such as their isolation, count, culture, identification, pathogenicity, virulence, and environmental tolerance should form the solid basis for such an expansion with reliable uses. Extensive practical details of such procedures and tests as well as how to identify and overcome the problems associated with these aspects are addressed in this chapter.

Arthropod microbiota: shaping pathogen establishment and enabling control

Vector-borne diseases (VBDs) pose significant global health threats. The microbiota of arthropod vectors influences their fitness and pathogen acquisition and/or transmission. Here, we review the intricate interplay among the arthropod immune system, the microbiota, and pathogens that limits or favors infection. We focused on the most important arthropod vectors, namely mosquitos, phlebotomines, tsetse flies, triatomines, and ticks, and expanded our analysis to include the nonvector model Drosophila melanogaster for comparison. The microbiota and immune system of arthropod vectors are targets for the development of promising control strategies, such as paratransgenesis and anti‐microbiota vaccines. Further research should focus on elucidating the underlying mechanisms of vector–pathogen–microbiota interactions and optimizing anti-microbiota strategies. These approaches have the potential to combat VBDs and reduce their global impact.

Prevalence and Genetic Diversity of a Microsporidian Parasite in the Black Imported Fire Ant and Its Social Parasitic Ant (Formicidae: Myrmicinae: Solenopsis) in Buenos Aires Province, Argentina.

Microsporidia are natural pathogens of arthropods and have been used as biological control against insect pests. In the United States, efforts to control the invasive Red Imported Fire Ant, Solenopsis invicta, and Black Imported Fire Ant, Solenopsis richteri, have included the use of the microsporidium, Kneallhazia solenopsae. However, there is limited information about the genetic differences among the microsporidian variants found in S. invicta and in S. richteri. In this study, we assessed the prevalence and genetic diversity of K. solenopsae in native populations of S. richteri in Argentina (South America). Additionally, we examined the social parasitic ant, Solenopsis daguerrei, which is found in some S. richteri nests, for the presence of this microsporidium. The survey of 219 S. richteri nests revealed K. solenopsae infections in all five sites analyzed, with 28 colonies (12.8%) positive for the microsporidium. Among the 180 S. daguerrei individuals collected, seven ants (3.9%) from three sites tested positive for K. solenopsae. Phylogenetic analyses of the microsporidian variants present in S. richteri and S. daguerrei based on partial small subunit ribosomal gene sequences (SSU rRNA) showed that both ant species shared the same variant, which is different from the ones found in S. invicta. Further studies are needed to determine the pathogenicity of genetically different K. solenopsae variants among Solenopsis species.

Diversity and Breadth of Host Specificity among Arthropod Pathogens in the Entomophthoromycotina.

A meta-analysis based on the published literature was conducted to evaluate the breadth of host ranges of arthropod pathogens in the fungal subphylum Entomophthoromycotina. The majority of pathogens in this subphylum infect insects, although arachnids (especially mites), collembola, and myriapods are also used as hosts. Most species (76%) have specialized host ranges and only infect arthropods in one host family. The breadth of host ranges in the Entomophthoromycotina is generally greater for species in more basal groups (Conidiobolaceae and Neoconidiobolaceae), where most species are soil-borne saprobes and few are pathogens. The Batkoaceae is a transitionary family in which all species are pathogens and both generalists and specialists occur. Among pathogen-infecting insects, Hemiptera and Diptera are the most commonly infected insect orders. Within the Hemiptera, hosts in the suborder Sternorrhycha were infected by more fungal species than the Auchenorrhyncha and Heteroptera.

Metarhizium anisopliae E6 secretome reveals molecular players in host specificity and toxicity linked to cattle tick infection

Although Metarhizium anisopliae is one of the most studied fungal biocontrol agents, its infection mechanism is far from being completely understood. Using multidimensional protein identification technology (MudPIT), we evaluated the differential secretome of M. anisopliae E6 induced by the host Rhipicephalus microplus cuticle. The proteomic result showed changes in the expression of 194 proteins after exposure to host cuticle, such as proteins involved in adhesion, penetration, stress and fungal defense. Further, we performed a comparative genomic distribution of differentially expressed proteins of the M. anisopliae secretome against another arthropod pathogen, using the Beauveria bassiana ARSEF2860 protein repertory. Among 47 analyzed protein families, thirty were overexpressed in the M. anisopliae E6 predicted genome compared to B. bassiana. An in vivo toxicity assay using a Galleria mellonella model confirmed that the M. anisopliae E6 secretome was more toxic in cattle tick infections compared to other secretomes, including B. bassiana with cattle ticks and M. anisopliae E6 with the insect Dysdereus peruvianus, which our proteomic results had also suggested. These results help explain molecular aspects associated with host infection specificity due to genetic differences and gene expression control at the protein level in arthropod-pathogenic fungi.

Practice of integrated vector surveillance of arthropod vectors, pathogens and reservoir hosts to monitor the occurrence of tropical vector-borne diseases in 2020 in Zhejiang Province, China.

Vector-borne diseases have become one of the most serious local public health threats. Monitoring and controlling vectors are important means of controlling vector-borne diseases. However, traditional vector surveillance systems in China mainly monitor vector density, making its early-warning effect on vector-borne diseases weak. In this study, we applied an integrated surveillance system of multiple arthropod vectors and reservoir host containing ecology, etiology, and drug resistance monitoring to obtain better knowledge on vector populations and provide early warning of suspicious vector-borne infectious disease occurrence. An ecology surveillance of mosquitoes, rodents, ticks, and chigger mites, a pathogen infection survey on mosquitoes and rodents, and a drug resistance survey on Aedes albopictus were conducted in 12 cities in Zhejiang Province in 2020. A total of 15,645 adult mosquitoes were collected at a density of 19.8 mosquitoes per Centers for Disease Control and Prevention light trap. Culex tritaeniorhynchus (72.76%) was the most abundant species. The Breteau index of Ae. albopictus was 13.11. The rodent density was 0.91 rodents per hundred traps; the most abundant species was Rattus norvegicus (33.73%). The densities of dissociate and ectoparasitic ticks were 0.79 ticks per hundred meters and 0.97 ticks per animal, respectively. The most abundant tick species was Haemaphysalis longicornis (56.38%). The density of chigger mites was 14.11 per rodent; two species were identified, with the most abundant species being Walchia spp. mite (68.35%). No flavivirus or alphavirus was found in mosquito etiology monitoring, whereas the positivity rates of hantavirus, the pathogenic bacteria Leptospira spp., Orientia tsutsugamushi, and Bartonella spp. detected in rodent etiology monitoring were 1.86, 7.36, 0.35 and 7.05%, respectively. Field populations of Ae. albopictus in Zhejiang Province were widely resistant to pyrethroids but sensitive to most insecticides tested, including organophosphorus and carbamate insecticides. Integrated surveillance systems on multiple arthropod vectors (mosquitoes, ticks, mites) and animal reservoirs (rodents) can provide important information for the prevention and control of epidemic emergencies.

Ambivalent Roles of Oxidative Stress in Triangular Relationships among Arthropod Vectors, Pathogens and Hosts.

Blood-feeding arthropods, particularly ticks and mosquitoes are considered the most important vectors of arthropod-borne diseases affecting humans and animals. While feeding on blood meals, arthropods are exposed to high levels of reactive oxygen species (ROS) since heme and other blood components can induce oxidative stress. Different ROS have important roles in interactions among the pathogens, vectors, and hosts. ROS influence various metabolic processes of the arthropods and some have detrimental effects. In this review, we investigate the various roles of ROS in these arthropods, including their innate immunity and the homeostasis of their microbiomes, that is, how ROS are utilized to maintain the balance between the natural microbiota and potential pathogens. We elucidate the mechanism of how ROS are utilized to fight off invading pathogens and how the arthropod-borne pathogens use the arthropods’ antioxidant mechanism to defend against these ROS attacks and their possible impact on their vector potentials or their ability to acquire and transmit pathogens. In addition, we describe the possible roles of ROS in chemical insecticide/acaricide activity and/or in the development of resistance. Overall, this underscores the importance of the antioxidant system as a potential target for the control of arthropod and arthropod-borne pathogens.

All for One Health and One Health for All: Considerations for Successful Citizen Science Projects Conducting Vector Surveillance from Animal Hosts.

Simple SummaryVector-borne diseases are often zoonotic and so a One Health approach must be employed in order to investigate and control them. Therefore, surveillance of arthropod vectors and pathogens among animal populations should complement human disease surveillance. Since traditional surveillance methods to collect arthropod vectors and conduct pathogen testing from animals can be challenging, data collection can be supplemented with citizen science approaches, where the general public is actively involved in collecting animals and/or samples. In this review, we discuss considerations for researchers to create a successful vector surveillance program using citizen science approaches with different stakeholders who own, have interests in, or work with animals.Many vector-borne diseases that affect humans are zoonotic, often involving some animal host amplifying the pathogen and infecting an arthropod vector, followed by pathogen spillover into the human population via the bite of the infected vector. As urbanization, globalization, travel, and trade continue to increase, so does the risk posed by vector-borne diseases and spillover events. With the introduction of new vectors and potential pathogens as well as range expansions of native vectors, it is vital to conduct vector and vector-borne disease surveillance. Traditional surveillance methods can be time-consuming and labor-intensive, especially when surveillance involves sampling from animals. In order to monitor for potential vector-borne disease threats, researchers have turned to the public to help with data collection. To address vector-borne disease and animal conservation needs, we conducted a literature review of studies from the United States and Canada utilizing citizen science efforts to collect arthropods of public health and veterinary interest from animals. We identified common stakeholder groups, the types of surveillance that are common with each group, and the literature gaps on understudied vectors and populations. From this review, we synthesized considerations for future research projects involving citizen scientist collection of arthropods that affect humans and animals.

Molecular Detection and Differentiation of Arthropod, Fungal, Protozoan, Bacterial and Viral Pathogens of Honeybees.

The honeybee Apis mellifera is highly appreciated worldwide because of its products, but also as it is a pollinator of crops and wild plants. The beehive is vulnerable to infections due to arthropods, fungi, protozoa, bacteria and/or viruses that manage to by-pass the individual and social immune mechanisms of bees. Due to the close proximity of bees in the beehive and their foraging habits, infections easily spread within and between beehives. Moreover, international trade of bees has caused the global spread of infections, several of which result in significant losses for apiculture. Only in a few cases can infections be diagnosed with the naked eye, by direct observation of the pathogen in the case of some arthropods, or by pathogen-associated distinctive traits. Development of molecular methods based on the amplification and analysis of one or more genes or genomic segments has brought significant progress to the study of bee pathogens, allowing for: (i) the precise and sensitive identification of the infectious agent; (ii) the analysis of co-infections; (iii) the description of novel species; (iv) associations between geno- and pheno-types and (v) population structure studies. Sequencing of bee pathogen genomes has allowed for the identification of new molecular targets and the development of specific genotypification strategies.

Feasibility of developing classical biological control solutions for the herbaceous weed Allium triquetrum in Australia

ABSTRACT Allium triquetrum L. (Amaryllidaceae), a bulbiferous monocot, is native to the Mediterranean. It was introduced to Australia in the early 1900s, where it has subsequently become a significant invader of temperate forests throughout south-eastern Australia. Intensive chemical and mechanical control methods can suppress A. triquetrum infestations at the local scale for short periods of time but remain ineffective at sustainably curtailing its invasion at landscape and regional scales. In this context, we undertook field surveys across the Mediterranean (mainland France, Corsica, Sardinia) to determine the feasibility of developing classical biological control solutions for A. triquetrum in Australia. Despite extensive sampling (i.e. 30 surveys at 18 sites over three growing seasons), very few phytophagous arthropod and fungal pathogen taxa were detected on A. triquetrum. The most common arthropod species were the flies Phytomyza gymnostoma and Delia hirticrura, the weevil Oprohinus consputus and the moth Hysterophora maculosana. All identified arthropod taxa were considered generalists, having been found on other plant species, and some are known pests of cultivated Allium species. Twenty-one different fungal isolates were recovered from A. triquetrum, with most considered as saprophytic, secondary/opportunistic pathogens that probably infected already-damaged A. triquetrum leaves. Only four fungal taxa were found to be primary pathogens of A. triquetrum but have been recorded to infect other plant species. None of these enemy taxa were deemed to be suitable candidate biocontrol agents to help manage A. triquetrum invasion in Australia. Future research directions for improved A. triquetrum management in Australia are discussed in this paper.

Tick Saliva and Salivary Glands: What Do We Know So Far on Their Role in Arthropod Blood Feeding and Pathogen Transmission.

Ticks are blood-sucking arthropods that have developed myriad of strategies to get a blood meal from the vertebrate host. They first attach to the host skin, select a bite site for a blood meal, create a feeding niche at the bite site, secrete plethora of molecules in its saliva and then starts feeding. On the other side, host defenses will try to counter-attack and stop tick feeding at the bite site. In this constant battle between ticks and the host, arthropods successfully pacify the host and completes a blood meal and then replete after full engorgement. In this review, we discuss some of the known and emerging roles for arthropod components such as cement, salivary proteins, lipocalins, HSP70s, OATPs, and extracellular vesicles/exosomes in facilitating successful blood feeding from ticks. In addition, we discuss how tick-borne pathogens modulate(s) these components to infect the vertebrate host. Understanding the biology of arthropod blood feeding and molecular interactions at the tick-host interface during pathogen transmission is very important. This information would eventually lead us in the identification of candidates for the development of transmission-blocking vaccines to prevent diseases caused by medically important vector-borne pathogens.

Dispersion of adeleid oocysts by vertebrates in Gran Canaria, Spain: report and literature review.

Within the family Adeleidae, Adelina spp. belong to a group of arthropod pathogens. These parasites have been reported to have a wide geographic distribution, however, there are no reports of these protists in the Canary Islands, Spain. One of the peculiarities of the life cycle of Adelina spp. is the participation of a predator, because fecundation and sporulation occur inside the body cavity, and so necessitate destruction of the definitive host. The involvement therefore of a ‘dispersion host’, which eats the definitive host and spreads the oocysts through its faeces, is critical for the maintenance of certain Adelina spp. On the island of Gran Canaria, adeleid oocysts have been found in stool samples from four animals, three California kingsnakes (Lampropeltis californiae), and one feral cat. These animals were part of a larger coprological study of vertebrate parasites (117 snakes, 298 cats), where pseudoparasitic elements were also recorded. L. californiae and feral cats are invasive species which are widespread across the island and this novel finding of Adelina spp. oocysts in their faeces suggests that they could also serve as potential sentinel species for arthropod parasites.

Land-Use Type Drives Soil Population Structures of the Entomopathogenic Fungal Genus Metarhizium.

Species of the fungal genus Metarhizium are globally distributed pathogens of arthropods, and a number of biological control products based on these fungi have been commercialized to control a variety of pest arthropods. In this study, we investigate the abundance and population structure of Metarhizium spp. in three land-use types—arable land, grassland, and forest—to provide detailed information on habitat selection and the factors that drive the occurrence and abundance of Metarhizium spp. in soil. At 10 sites of each land-use type, which are all part of the Swiss national soil-monitoring network (NABO), Metarhizium spp. were present at 8, 10, and 4 sites, respectively. On average, Metarhizium spp. were most abundant in grassland, followed by forest and then arable land; 349 Metarhizium isolates were collected from the 30 sites, and sequence analyses of the nuclear translation elongation factor 1α gene, as well as microsatellite-based genotyping, revealed the presence of 13 Metarhizium brunneum, 6 Metarhizium robertsii, and 3 Metarhizium guizhouense multilocus genotypes (MLGs). With 259 isolates, M. brunneum was the most abundant species, and significant differences were detected in population structures between forested and unforested sites. Among 15 environmental factors assessed, C:N ratio, basal respiration, total carbon, organic carbon, and bulk density significantly explained the variation among the M. brunneum populations. The information gained in this study will support the selection of best-adapted isolates as biological control agents and will provide additional criteria for the adaptation or development of new pest control strategies.

The First Isolation of Microsporidia from Dragonflies in Japan.

Entomopathogenic microsporidia are pathogens of various arthropods and therefore cause disease in important host species ranging from agricultural pests to beneficial insects. Here, we investigated three genera of entomopathogenic microsporidia from dragonflies； these were isolated in Kanagawa, Japan, in 2014. In total, the infection rate was 0.85%（16 of the 1,886 surveyed dragonfly adults）. Four strains of microsporidia selected from infected Orthetrum albistylum speciosum（Uhler）（Odonata: Libellulidae）adults were measured for spore size and analyzed at the molecular level. According to spore size, the four strains were roughly divided into two groups. Analysis of small-subunit ribosomal RNA sequences indicated that the microsporidia strains belonged to the Trachipleistophora, Vavraia, and Paranosema clusters. Microsporidia species that are closely related to the strains isolated in this study have previously been reported to infect insects other than dragonflies. Therefore, we suggest the possibility that the microsporidian strains we isolated in O. albistylum speciosum may also infect other insect species.

Biopesticide Research and Product Development in Africa for Sustainable Agriculture and Food Security – Experiences From the International Centre of Insect Physiology and Ecology (icipe)

Arthropod pests and vectors constrain the livelihood opportunities of people in Africa by debilitating production of crops and livestock and through transmission of vector-borne diseases. In the absence of effective alternative management options to tackle these pests and vectors, there is extensive dependence on synthetic pesticides for their management on crop and livestock systems, with significant negative impacts on animal and human health, and the environment. Biopesticides are effective and environmentally sustainable alternatives to synthetic pesticides. At the International Centre of Insect Physiology and Ecology (icipe), the Arthropod Pathology Unit (APU) was established for effective biopesticide research-for-development (R4D), underpinned by a large repository of arthropod pathogens, protocols for lab bioassays and field efficacy testing, and an effective public-private partnership to generate new biopesticide products. The focus of icipe’s APU has gradually transformed from basic to applied research leading to innovative, commercial products. Among the insect pathogens, greater focus has been placed on fungi, especially Metarhizium anisopliae, against key crop and livestock pests. Presently, three biopesticides based on M. anisopliae strains researched by icipe have been commercialized by Real IPM (Thika, Kenya) and are used on 132,994 ha in sub-Saharan Africa, with registration of additional products against animal ticks and the fall armyworm Spodoptera frugiperda pending. Our R4D activities on arthropod pathogens increasingly include bacteria, microsporidia, entomopathogenic nematodes and viruses. Recently, icipe is expanding R4D towards plant endophytes and rhizosphere inhabitants. The Centre also embarked on understanding the diversity, roles and possible exploitation of insect symbionts in key plant pest and disease vectors. In addition, key entomopathogens of reared insects for human food and animal feed need to be identified and controlled through high hygiene standards during rearing. Further, research is aimed at integrating biopesticides not only with other integrated pest management (IPM) technologies but also with pollination services.

A comparison of weed, pathogen and insect pests between low tunnel and open-field grown strawberries in New York

While growing strawberries under plastic low tunnels is an increasing trend in the northeastern U.S., the effect of low tunnels on the incidence and severity of arthropod pests, pathogens, and weeds is largely unknown and presents a possible barrier to commercial adoption. During 2018 and 2019, we identified and quantified pest abundance on low tunnel versus open field grown strawberries at a research site in Geneva, New York, and compared these trends under three plastic types in 2019. Overall, we found that while yield and fruit marketability increased under tunnels of all plastic types compared to the open-field, ground-dwelling and foliar herbivores (mostly Tetranychus urticae) abundance was higher under low tunnels compared to open plots. In contrast, herbivores caught on clear sticky cards were more prevalent in open plots than under tunnels. A neutral effect of tunnels was present for Lygus lineolaris density and weed biomass during both years, although damage by L. lineolaris decreased under UV-limiting plastics. Tunnels also reduced infestation by Drosophila suzukii and several pathogens on foliage and fruit. This study provides needed information on pest communities of low tunnel strawberry in the Northeast, and could be used as an essential foundation for future IPM research.