Biological control by soil predatory mites (Mesostigmata) contributes to important ecosystem services, yet their prey selection and trophic roles in complex soil environments remain poorly understood. For example, functionally different nematode groups, i.e. free-living nematodes (FLN) and plant-parasitic taxa, are food to many predatory soil mites. A dual stable isotope labelling approach was applied to trace these trophic interactions in a short-term pot experiment. Four trophic scenarios were evaluated: predatory mites alone (control), mites with free-living nematodes (FLN + mites), mites with root-knot nematodes (RKN + mites), and mites with both groups of nematodes (FLN + RKN + mites). The 13C signal in the bacterial-feeding FLN Acrobeloides bodenheimeri was achieved by 13CO2-labelling of potted lettuce at the start of the experiment. Mass cultures of 15N marked root-knot nematodes (RKN) Meloidogyne incognita were gained by fertilizing infected tomatoes with 15N-labelled Ca(15NO3)2 and K15NO3. Identical treatments with unlabelled nematodes served as isotopic controls. Dual isotopic labelling allowed tracking the dietary choice of the mite Protogamasellopsis zaheri under semi-natural soil conditions. The mites incorporated 13C when only FLN were available and 15N when only RKN were available, with a clear dietary preference for FLN when both prey types co-occurred. Moreover, 13C-enrichment in treatments with labelled lettuce but without nematodes suggests alternative rhizosphere-linked carbon pathways. Overall, the introduction of two distinct isotopic signals in the diet of a mesofauna predator allowed to identify the relative quantity and composition of specific prey consumed. This demonstrates the power of dual isotope labelling to uncover trophic links in cryptic ecosystems, which cannot otherwise be detected in situ.

As part of a project aimed at harnessing soil food webs for the biological control of root-knot nematodes, specimens of a new species of the gamasine mite genus Macrocheles were found in vegetable fields in Israel. Specimens of this new species were used to initiate laboratory colonies using several species of free-living nematodes and a root-knot nematode as food sources. Females, males, deutonymphs and protonymphs were taken from the colony and morphologically analysed after mounting on slides. Some females and males were also subjected to scanning electron microscopy. Furthermore, 18 female specimens underwent DNA extraction for genetic analysis. The newly discovered species is described and illustrated based on its morphological characteristics and on molecular data obtained from the Barcode of Life Database (BOLD). Finally, an update to the key to distinguish species within the scutatus complex is included.

Long-chain polyunsaturated fatty acids (PUFAs), especially w3 forms, are essential nutrients for many animals and are typically obtained from dietary sources, yet there is limited availability in terrestrial ecosystem. In soil food webs, free-living nematodes are an important source of these PUFAs. Predatory mites (Mesostigmata) play a key role in regulating invertebrate populations, including free-living and plant-parasitic nematodes. Recent studies suggest that diets including nematodes improve the fitness of predatory mites and enhance their function as biological control agents within soil food webs. The predatory mite Parasitus sp. isolated from Mediterranean agricultural fields showed nematode consumption and colony establishment with a mixture of nematode species. This study investigated the effects of single nematode diets on the fitness of Parasitus sp., focusing on the roles of w3- and w6-PUFAs. This included one plant-parasitic and five free-living bacterial-feeding species, mostly cooccurring in the same Mediterranean fields, with one species unable to synthesize w3-PUFAs. The results showed that nematodes rich in w3-PUFAs supported Parasitus sp. development, but those high in w6-PUFAs and deficient in w3-PUFAs did not. However, mite survival and moulting to adulthood were generally low, possibly indicating a need for a specific stimulus or a more varied diet. This study further demonstrated w3-PUFA de novo synthesis in Mesostigmata. Overall, the nematode diets influenced the development of Parasitus sp. differently, which emphasizes the importance of diverse nematode populations to support the fitness of higher trophic levels such as predatory mites.

Numerous lab and field studies have reported the potential of soil predatory mites for the biological control of plant-parasitic nematodes and arthropods pests. Most of these studies have utilized biocontrol agents in augmentative releases, essentially controlling the pest with the released predators. While this may be a valid approach, we hypothesize that conservation of soil mite predators with available, suitable, and accessible free-living nematodes as prey, will provide better agricultural ecosystem performance and long-range sustainability. In this manuscript, we review the relevant studies on soil predatory mite–nematode interactions and highlight their potential for conservation biological control of soil-borne pests. Additionally, we emphasize the importance of implementing environmentally sound soil management practices for the sustainability and conservation of functional soil food webs.

Pest suppression is one of the desirable functions of a healthy soil. Predatory Mesostigmata soil mites, with their high degree of omnivory, are one of the most remarkable groups performing this beneficial role. Food web bottom-up effects are important for the fitness of these predators, which ultimately affects their potential as biocontrol agents. In below-ground systems, free-living nematodes (FLN) are an important diet for mites, providing essential nutrients such as omega 3 long-chain polyunsaturated fatty acids (ω3-LC PUFAs). Here we assess the food quality of nematodes for the maintenance of predator fitness, i.e. development, reproduction and lipid content. We selected two mite species, different in size and morphology, collected from vegetable crops in Israel. Additionally, five species of FLN were isolated from the same fields. Additionally, one plant-parasitic species, common across arable sites in Israel, and maintained on tomato as host, was tested. Depending on species and trophic group, nematodes varied in fatty acid profile, and both mite species generally reflected the fatty acid pattern of their diet. All nematode species were able to produce ω3-LC PUFA de novo, except the bacterial feeder Acrobeloides bodenheimeri, which had the highest proportion of ω6-PUFA. Interestingly, the latter lacking ω3-LC PUFA, was the best diet for both mites. Macrocheles aff. scutatus, a medium-sized mite with a holodorsal shield, fed and developed on all nematodes except the entomophilious Oscheius tipulae. It was able to complete its development feeding on the plant parasitic Meloidogyne incognita, yet the reproduction was almost zero. The smaller and slender Protogamasellopsis zaheri, with a split dorsal shield, developed and reproduced with all nematodes, with M. incognita as an intermediate diet. Our results demonstrate that nematode species vary in their nutritional quality as prey. However, food quality is predator species dependent, likely affecting biocontrol efficacy. Besides ω3-LC PUFA, ω6-PUFA can play an important role in the reproductive and developmental parameters of mesostigmatid mites; yet, other factors such as nematode size and behaviour have to be considered.

Gamasellodes garybauchani sp. nov. Rueda-Ramírez & Santos is described based on specimens collected at the Beltsville Agricultural Research Center (BARC) (Maryland, USA). Twenty-one specimens were used for the description, of which five were subjected to low temperature scanning electron microscopy (LTSEM), followed by DNA extraction for genetic analysis and subsequent slide mounting. The remaining 16 specimens were subjected to only DNA extraction for genetic analysis and subsequent slide mounting. Morphological characters of the new species observed both in the images obtained in LTSEM and in the observation of the mounted specimens are detailed. Molecular information available on the Barcode of Life Datasysetm (BOLD) is presented. An update to the recent key to the Gamasellodes species is provided.

Mites of the genus Rhizoglyphus (Acari: Acaridae) are serious pests of plants belonging to the orders Liliales and Asparagales such as onions, garlic, lilies, and tulips. Their control by synthetic pesticides is becoming problematic as a result of resistance development in these mites and environmental and health issues. New pest control methods thus need to be developed. This review provides an overview of studies related to bulb mite management. Entomopathogenic fungi and generalist predatory mites are prospective agents for biological control of these pests while entomopathogenic nematodes and the metabolites of their symbiotic bacteria seems to be less effective. There are, however, many more organisms in the soil that might play important roles in biological control of bulb mites as well as other soil pests of these bulbous plants. Therefore, a holistic approach based on the understanding of food webs in the soil environment and their ecological services is essential for developing effective control of bulb mites. For the rehabilitation and conservation of soil biodiversity supporting these ecosystem services, emphasis must be placed on sustainable soil management (e.g., ensuring green coverage, minimal soil disturbance and high content of organic matter).

Species of soil predatory mites feed on a diverse diet making them excellent candidates for conservation biological control programs. Free living nematodes (FLNs) are commonly found in soils at all trophic levels and serve as prey for many soil predatory mites (SPMs) in a functional soil food web. Here we present highlights of two case studies and the preliminary results of one ongoing study, all with the common aim of improving the conservation of soil predatory mites for the control of soil pests. In the first study, we used Macrocheles embersoni for housefly control (Azevedo et al., 2019), in the second, Stratiolaelaps scimitus for the control of the root knot nematode (RKN) Meloidogyne incognita (Azevedo et al., 2020), and in the third, we use frass of black soldier fly Hermetia illucens as an organic amendment for harnessing the local soil food web for the control of RKN. In the first two studies, complementing the diet of predatory mites with the FLN Rhabditella axei in their culture medium resulted in higher predator abundance and better biological control, compared to the negative control and the release of predators without FLNs and microbiota. In the third study the effect of the soil amendment on soil biota and RKN control differed among soils. We expect that soil amendments alter biocontrol efficacy, and that these effects are dependent on the biodiversity of soil biota as well as abiotic soil properties, and that caring for soils is a pre-requisite for successful conservation biological control.

RAPHAEL DE CAMPOS CASTILHO1, DIANA RUEDA-RAMÍREZ2 & ERIC PALEVSKY3 Escola Superior de Agricultura Luiz de Queiroz (ESALQ), Universidade de São Paulo (USP), 13418 900 Piracicaba, São Paulo, Brazil. E-mail: raphael.castilho@usp.br; Institute of Biology, Ecology Group, Humboldt Universität zu Berlin, Germany. E-mail: dianaru@gmail.com; 3Newe-Ya'ar Research Center, Agricultural Research Organization, Ministry of Agriculture, Israel. E-mail: palevsky@volcani.agri.gov.il

Biological control is an important ecosystem service for soil and plant health and has been successfully exploited, especially through augmentative biological control programs, for above-ground agricultural pest control often using predatory mites of Mesostigmata. Similar success has not been achieved for below-ground systems. Predatory mites are an important part of soil food webs, in which they have a regulatory impact. While this is mediated by the predator on the prey, recent studies suggest that biocontrol efficiency can be enhanced in the mid to long term for generalist predators by the presence of complementary prey. In below-ground systems, nematodes are an important food source and numerous species of predatory mites in soil may prefer them. Thus, nematodes are a viable and accessible alternative prey for these natural enemies. Our aim was to review the studies on mite-nematode trophic interactions and how these interactions affect the regulatory activity of predatory mites in soil. We found ca. 170 publications reporting a predator-prey interaction. The majority of the studies were conducted in the laboratory (149 studies), but important correlations between nematode and mite densities have been observed in greenhouses and in the open field. Most reports involved free-living nematodes (FLN), followed by plant-parasitic nematodes (PPN) and finally animal-parasitic nematodes (APN). These reports are for Astigmatina, Endeostigmata, Prostigmata, Oribatida (non-Astigmatina) and Mesostigmata, the latter group being the one in which most nematophagous species are known. The family with the most reports of nematophagy is Ascidae (46 species), followed by Macrochelidae and Laelapidae (both with 30 species). In many cases, a positive effect on reproductive parameters and developmental times of mite species has been observed with a nematode-based diet, especially FLN. Although still scarce, studies on species of Laelapidae, Macrochelidae, Parasitidae and Rhodacaridae have shown that supplementing FLN in the diet can favor reproduction and development, even though preference may change at different stages of development. Also, recent studies have shown that some organic amendments can increase the density and diversity of mites, FLN or both, enhancing top down forces by predatory mites in the soil food web. Although some steps have been taken, future studies should focus on transferring laboratory research to field and semi-field conditions. For this, a multidisciplinary approach is essential.

Current and future legislation requiring the reduction of pesticides use, coupled with global initiatives for the promotion of soil health and conservation of soil biodiversity are creating opportunities for studies aimed at highlighting ecosystem services provided by functioning soil food webs in agricultural systems, including soil predatory mites. However, the key personnel for performing such studies are expert taxonomists, who are already spread very thin. To meet this demand, we propose an integrative approach where scientists (without expertise in taxonomy) play a significant role in supporting expert taxonomists. Soil samples were collected at the USDA ARS Farming Systems Project (FSP) at the Beltsville Agricultural Research Center, either incubated or not, followed by extraction of mites and nematodes. Improved modified Berlese funnels and an extraction protocol were utilized to improve sequencing success. Incubation dramatically enhanced the number of extracted individuals per sample whilst the daily freezing of extracted mites substantially improved the sequencing success rate compared to previous studies. Taken together, this led to the addition of records for eight Mesostigmata and ten Oribatida BINs to BOLD (Barcode of Life Datasystem). Fifteen species of Mesostigmata species were found, with three dominant species, Cycetogamasus diviortus (Athias-Henriot, 1967) (Parasitidae), Lasioseius youcefi Athias-Henriot 1959 (Blattisociidae) and a new species of Gamasellodes (Ascidae). LTSEM imaging followed by molecular identification contributed further details to the published descriptions of C. diviortus and L. youcefi. In line with our general aim, collecting, extracting, identification to morpho-species, sample preparation for DNA barcoding and uploading relevant information to BOLD was performed by trained personnel, but without taxonomic expertise. Whereas our skilled taxonomists focused on the morphological identifications using light microscopy, expanding on existing descriptions using LTSEM images and in a subsequent manuscript the description of a new species. We believe this division of tasks and labor will set the stage for further collaborative integrated studies between ecologists, biocontrol specialists and expert taxonomists for the identification, evaluation, and description of known and novel soil acarine biological control agents (BCAs).

Bulb crops are attacked by various soil-dwelling pests and pathogens. Entomopathogenic (EPFs) and mycoparasitic fungi (MPFs) which are distributed in natural and agricultural soils worldwide can play an important role as natural enemies of bulb pests. The species richness and density of these fungi in onion and garlic fields have not been investigated. The aim of this study was to determine the occurrence of EPFs and MPFs in soils where these crops were grown and compared the data from sites of the Czech Republic and Israel. Methods of fungi isolation and quantification were based on elution of soil samples by water and cultivation using selective media with dodine for EPFs and cultivation using potato dextrose agar with chloramphenicol for MPFs. Entomopathogenic fungi Beauveria spp., Isaria spp., Lecanicillium spp., Metarhizium spp., Purpureocillium spp. and mycoparasitic fungi Trichoderma spp. were isolated from soil samples in both countries. The highest density was observed in the genus Metarhizium in both countries. Metarhizium spp. were most abundant in the site Mlýn Podhora in the Czech Republic. The average density of colony-forming units (CFU) per 1 mL of soil sample was 1.47 × 104. The lowest density was observed in the genus Beauveria in both countries, up to 5.93 × 102 CFU per 1 mL of soil sample. Soils in the Czech Republic contained about ten times higher number of EPFs compared to Israel. Rather higher prevalence of MPFs was also found in the Czech Republic. Possible reasons for within and between countries variability in EPFs and MPFs occurrence are discussed.

The bulb mite, Rhizoglyphus robini, is a serious pest of garlic, onion and other crops. The mite is usually found in association with dangerous fungal pathogens such as Fusarium spp. Control of this pest has relied upon the use of synthetic acaricides but chemical control of the bulb mite is difficult because it is able to develop resistance quickly. Thus, alternative control methods, e.g. biological control, need to be developed and implemented. The aim of this study was to assess efficacy of selected strains of entomopathogenic fungi (EPF) against adult females of R. robini under laboratory conditions. New EPF strains were isolated from soil samples collected in onion and garlic fields in the Czech Republic and Israel using soil elution and cultivation on selective media. Fungal species were determined using macroscopic, microscopic and molecular markers. The efficacy against R. robini females was tested in 17 isolated and 3 reference strains of EPF. Results revealed high variability among species and strains. The highest efficacy against R. robini mites was found in strains of Metarhizium anisopliae isolated from soil samples collected in the Czech Republic which caused mortality up to 99.3%, and a Metarhizium indigoticum strain from Israel causing 98.3% mortality after four days of bioassay. Isaria fumosorosea strains did not caused mortality higher than 40%. The lowest virulence was found in Beauveria spp. strains causing mortality of mites between 5 and 25%. Median lethal time (LT50) and median lethal concentration (LC50) in the three most virulent strains ranged between 2 and 4 days and between 1.01×104 and 2.36×105 spores/ml, respectively. The concentration-response models indicated that the M. indigoticum strain is more lethal than M. anisopliae strains. The present study showed that some strains of entomopathogenic fungi, especially from the genus Metarhizium, could be perspective biocontrol agents against R. robini.

Under reduced solar UV radiation, such as in polycarbonate-covered nurseries, the two-spotted spider mite Tetranychus urticae is a major pest of all citrus cultivars, while under natural solar radiation, only sensitive cultivars are infested. We hypothesized that citrus resistance to T. urticae is induced by UV. We infested seedlings of Citrus volkameriana rootstock with T. urticae under natural and under UV-screened solar radiation, along with non-infested control seedlings. We then monitored the establishment of the spider mites and analyzed the volatile leaf profile using GC-MS. The density of spider mites was reduced dramatically on seedlings exposed to solar UV. Overall, ninety volatile compounds (47 monoterpenes, 35 sesquiterpenes, and 8 aldehydes) were detected in the leaves, many of them known to be herbivore-induced and/or UV enhanced. Their levels were affected not only by solar UV radiation or by mite infestation independently. Synergistic interaction of these two factors resulted in 90% of the volatiles suppressed by T. urticae infestation in the absence of UV radiation. This suggests that plant induced resistance is dependent on exposure to UV radiation.

Metarhizium brunneum is a generalist entomopathogenic fungus known to be virulent against Acari. We investigated Metarhizium brunneum-7 (Mb7) interactions in three systems of phytophagous mites and their respective plant hosts: Volkamer lemon (Citrus volkameriana) and the citrus rust mite Phyllocoptruta oleivora; common bean (Phaseolus vulgaris) and the two-spotted spider mite Tetranychus urticae; and spring onion (Allium cepa) and the bulb mite Rhizoglyphus robini. All three mite species were susceptible to directly applied Mb7 conidia. Results obtained using the standard method for studying endophytic colonization vs. live confocal imaging of plant tissues using the green fluorescent protein (GFP)-transformed fungus differed markedly, demonstrating that microscopy validation was more definite than the standard process of recovery from plant tissue. Endophytic colonization was observed in conidium-infiltrated citrus leaves and in roots of onion plants treated with soil-drenched conidia, but not in common bean treated by either spray or drench of conidia. Endophytic colonization of citrus leaves did not affect the citrus mite population. Drench application in common bean reduced two-spotted mite population. Similarly, drench application in onion reduced bulb mite population. This study emphasizes the importance of the host plant effects on Mb7 control efficacy of mite pests, and the merits of live-imaging techniques in studying endophytic interaction.

Soil predatory mites feed on a diverse diet making them excellent candidates for conservation biocontrol. Free-living nematodes (FLN) are commonly found in soils and serve as prey for many acarine predators. Our goal was to determine whether conservation biological control of plant-parasitic nematodes by predators could be enhanced by provisioning FLN with their culture medium (FLNCM) under semi-field conditions. We conducted two experiments on dwarf tomato plants, the first until the beginning of flowering and the second until harvest. The treatments evaluated were with and without: 1) the root-knot nematode Meloidogyne incognita, 2) the predator Stratiolaelaps scimitus, and 3) the FLN Rhabditella axei in its culture medium. In both experiments, gall abundance was lowest in the combined treatment of FLN and predators. Similar reduction in gall abundance occurred when only predators or only FLNCM was added to the soil mix. Additionally, in the FLNCM treatment, foliar macronutrients N and K were significantly higher than the negative control. Our original aim was to use FLN as a supplementary food source for predators in conservation IPM. Based on the significant reduction in gall numbers, and the increase in foliar macronutrients, it is clear that the FLNCM treatment played additional roles. Finally, for demonstration, the predation of M. incognita was visualized in high resolution imaging using a low-temperature-scanning electron microscope. Accordingly, we recommend that future research focus on identifying soil amendments that will foster the establishment of beneficial microbiota, FLN and soil predators for the conservation biological control of soil pests.

Journal Article Focus on Nematodes: Microscopic Roundworms Get access Gary Bauchan, Gary Bauchan US Department of Agriculture, Agricultural Research Service, Beltsville, Maryland, United States Search for other works by this author on: Oxford Academic Google Scholar Joseph Mowery, Joseph Mowery US Department of Agriculture, Agricultural Research Service, Beltsville, Maryland, United States Search for other works by this author on: Oxford Academic Google Scholar Ron Ochoa, Ron Ochoa US Department of Agriculture, Agricultural Research Service, Beltsville, Maryland, United States Search for other works by this author on: Oxford Academic Google Scholar Eric Palevsky, Eric Palevsky Israel Agricultural Research Organization, Ramat Yishay, Tel Aviv, Israel Search for other works by this author on: Oxford Academic Google Scholar Lynn Carta Lynn Carta US Department of Agriculture, Agricultural Research Service, Beltsville, Maryland, United States Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 26, Issue S2, 1 August 2020, Page 2002, https://doi.org/10.1017/S1431927620020103 Published: 01 August 2020

Because of its ability to expedite specimen identification and species delineation, the barcode index number (BIN) system presents a powerful tool to characterize hyperdiverse invertebrate groups such as the Acari (mites). However, the congruence between BINs and morphologically recognized species has seen limited testing in this taxon. We therefore apply this method towards the development of a barcode reference library for soil, poultry litter, and nest dwelling mites in the Western Palearctic. Through analysis of over 600 specimens, we provide DNA barcode coverage for 35 described species and 70 molecular taxonomic units (BINs). Nearly 80% of the species were accurately identified through this method, but just 60% perfectly matched (1:1) with BINs. High intraspecific divergences were found in 34% of the species examined and likely reflect cryptic diversity, highlighting the need for revision in these taxa. These findings provide a valuable resource for integrative pest management, but also highlight the importance of integrating morphological and molecular methods for fine-scale taxonomic resolution in poorly-known invertebrate lineages.