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Sex determination is a key developmental event in all organisms. The pathway that regulates sexual fate has been well characterized at the molecular level in the model free-living nematode Caenorhabditis elegans. This study aims to gain a preliminary understanding of sex-determining pathways in a plant-parasitic nematode Meloidogyne incognita, and the extent to which the roles of the sex determination genes are conserved in a hermaphrodite species, C. elegans, and plant-parasitic nematode species, M. incognita. In this study, we targeted two sex-determining orthologues, sdc-1 and tra-1 from M. incognita using RNA interference (RNAi). RNAi was performed by soaking second-stage juveniles of M. incognita in a solution containing dsRNA of either Mi-tra-1or Mi-sdc-1 or both. To determine the effect of RNAi of the target genes, the juveniles treated with the dsRNA were inoculated onto a susceptible cultivar of cowpea grown in a nutrient pouch at 28 °C for 5 weeks. The development of the nematodes was analyzed at different time points during the growth period and compared to untreated controls. Our results showed that neither Mi-sdc-1 nor Mi-tra-1 have a significant role in regulating sexual fate in M. incognita. However, the silencing of Mi-sdc-1 significantly delayed maturity to adult females but did not affect egg production in mature females. In contrast, the downregulation of Mi-tra-1 transcript resulted in a significant reduction in egg production in both single and combinatorial RNAi-treated nematodes. Our results indicate that M. incognita may have adopted a divergent function for Mi-sdc-1 and Mi-tra-1distinct from Caenorhabditis spp. However, Mi-tra-1 might have an essential role in female fecundity in M. incognita and is a promising dsRNA target for root-knot nematode (RKN) management using host-delivered RNAi.

Understanding the diversity of soil organisms is complicated by both scale and substrate. Every footprint we leave in the soil covers hundreds to millions of organisms yet we cannot see them without extremely laborious extraction and microsopy endeavors. Studying them is also challenging. Keeping them alive so that we can understand their lifecycles and ecological roles ranges from difficult to impossible. Functional and taxonomic identification of soil organisms, while possible, is also challenging. Here we present the Smart Soil Organism Detector, an instrument and machine learning pipeline that combines high-resolution imaging, multi-spectral sensing, large-bore flow cytometry, and machine learning to extract, isolate, count, identify, and separate soil organisms in a high-throughput, high-resolution, non-destructive, and reproducible manner. This system is not only capable of separating alive nematodes, dead nematodes, and nematode cuticles from soil with 100% out-of-sample accuracy, but also capable of identifying nematode strains (sub-species) with 95.5% out-of-sample accuracy and 99.4% specificity. Soil micro-arthropods were identified to class with 96.1% out-of-sample accuracy. Broadly applicable across soil taxa, the Smart SOD system is a tool for understanding global soil biodiversity.

Abiotic and biotic factors in soil modulate the efficiency of entomopathogenic nematodes (EPNs) as biological control agents of insect pests. We tested the hypothesis that EPNs associate spatially with a saprophytic fungus Fusarium solani in nature and contribute to both the fungal and nematode population growth, as found in previous laboratory-based studies that measured interactions at a fine spatial scale. Spatial Analysis by Distance Indices (SADIE) revealed highly significant spatial associations between F. solani and EPN communities comprising up to three species (Steinernema diaprepesi, Heterorhabditis indica, and Heterorhabditis zealandica), all of which were measured using quantitative real-time PCR during a 6-month citrus orchard survey. During three successive winter months, the EPNs aggregated in patches where F. solani aggregated during the previous month, although this behavior was not detected during the spring. The F. solani abundance in all plots was also related to that of total EPNs the previous month (one-month time lag; r = 0.17, P = 0.02) and may have resulted, at least in part, from the influence of soil moisture on both organisms. This study is the first report of quantitative relationships between F. solani and EPNs in the field. The results showed that a mutualistic relationship between this saprophytic fungus and EPNs reported previously, may have had measurable, but relatively minor effect on the spatial patterns of either organism at the landscape scale measured in this orchard.

The abundance of three entomopathogenic nematode (EPN) species, seven species of nematophagous fungi, free living nematode competitors of EPNs and a bacterial ectoparasite of EPNs were monitored during approximately two years in four Florida citrus orchards. The objective of the surveys was to identify natural enemies that potentially regulate the temporal abundance of naturally occurring EPNs by using molecular tools. Nematodes were extracted from two soil depths at ∼ monthly intervals, DNA extracted, and target organisms were measured using qPCR. Potentially causal relationships between the temporal patterns of EPNs and their natural enemies were assessed primarily with stepwise regression of variables at various time lags. Drechslerella dactyloides was the only nematophagous fungus species exhibiting evidence of top-down regulation, being inversely related to population change of Heterorhabditis indica at two of three sites. Acrobeloides spp. (EPN competitors) were associated with reduced population growth of Steinernema diaprepesi at two sites and H. indica was associated with reduced abundance of H. zealandica and S. diaprepesi at one site each. A Paenibacillus sp. exhibited significant phase-space, predator-prey dynamics at two of three sites with abundant S. diaprepesi, a species-specific host of the bacterium. The initial abundance of both S. diaprepesi and Paenibacillus sp. explained significant variability in population changes of S. diaprepesi in a multiple regression model at a lag of three months. Controlled experiments showed that pH is directly related to adherence of the bacterial endospores to the S. diaprepesi cuticle. Soil pH in these surveys was directly related to the infestation rate (encumbrance) by Paenibacillus and inversely related to the abundance of S. diaprepesi. Vertical distribution patterns reflected potential routes for avoiding competition and predation between species. Nematode-trapping fungi tended to inhabit shallower soil horizons than did several other nematophagous fungal species and S. diaprepesi and H. indica. The nematophagous fungus Purpureocillium lilacinum was especially abundant in deeper soil horizons and in the flatwoods sites. Depth distribution among EPNs also differed significantly with H. indica > S. diaprepesi > than H. zealandica. These results support soil pH management to conserve the demonstrated services of S. diaprepesi. They also suggest a need to better understand potential non-target effects of practices favorable to nematophagous fungi and bactivorous nematode competitors of EPNs.

Manipulating soil properties to modify the dynamics between nematodes and their natural enemies has been proposed to conserve services such as the biological control of insect pests by entomopathogenic nematodes. Many soil microarthropods including acari mites and collembola are natural enemies of nematodes; however, little is known about the naturally occurring assemblages of these two soil dwelling groups and how they might be influenced by soil conditions. A method to efficiently recover both nematodes and microarthropods from environmental samples would be helpful to characterize communities of these two groups in different habitats. Because samples of nematodes extracted from soil by sucrose centrifugation (SC) also contain soil mites, collembola, protozoans, and fungal and bacterial propagules, the efficiency of SC to recover microarthropods was compared to more conventional methods of microarthropod recovery such as heptane flotation (HF), Berlese funnels (BF), and a modified flotation Berlese method (FBF). Microarthropods were identified using an inverted microscope to class in one experiment and to order in a second. Significantly more microarthropods of all taxa were recovered by SC than with either Berlese method (BF or FBF). In total, 40% more microarthropods comprising seven orders were recovered by HF compared to SC, but the difference was not significant. Ecological indices (diversity, richness, and evenness) derived from HF and SC were congruent and significantly higher than those derived from BF. Excessive organic matter in the HF extractions, compared to those of SC, BF, and FBF, made mite detection and identification difficult and time consuming. Moreover, unlike SC, neither HF nor any Berlese method recovered nematodes. Accordingly, we found SC to be the most efficient method for microarthropod extraction, making it an ideal method for studies of communities of nematodes and many of their natural enemies in the soil.

In two field surveys, high proportions of Galleria mellonella L. (Lepidoptera: Pyralidae) sentinel larval cadavers were infected by Fusarium solani without evidence of concomitant entomopathogenic nematode (EPN) or entomopathogenic fungus (EPF) reproduction. Because F. solani is not considered entomopathogenic, the survey suggested the possibility that F. solani competes with EPNs. We tested the hypotheses that F. solani attracts the EPN, Steinernema diaprepesi, to facilitate infection of Diaprepes root weevils (Diaprepes abbreviatus L.) and thereafter competes with the nematode in the insect cadaver. In two-choice olfactometer assays where one side was treated with F. solani mycelia and conidia, juvenile S. diaprepesi were attracted to the fungus, in either raw soil, or in autoclaved soil in the presence or absence of insects. However, this attraction was attenuated as the habitat became more complex, by using raw soil in combination with insect larvae. Fusarium oxysporum did not recruit the nematode. When soil microcosms were tested with F. solani conidia and S. diaprepesi, the concomitant infection increased the mortality of the insect (P = 0.02) to 83%, compared to 58% and 0% mortality when nematodes or fungi were individually applied, respectively. Concomitant inoculation also increased the number of cadavers that supported nematode reproduction and increased the population density of fungus in soil. The number of IJs entering the host insect was not affected by F. solani. These results support the possibility that F. solani can facilitate the insecticidal efficiency of S. diaprepesi in order to exploit the resources in the cadaver.

The pupal soil cell of the pecan weevil, Curculio caryae (Coleoptera: Curculionidae), was reported previously to exhibit antibiosis to an entomopathogenic fungus, Beauveria bassiana. The objectives of this study were to examine 1) if the antimicrobial effect occurs in other insects that form pupal cells, 2) whether the effect extends to plant pathogenic fungi, and 3) identify the source of antibiosis in pupal soil cells of C. caryae. Antibiosis of pupal cells against B. bassiana was confirmed in-vitro in three additional curculionids, Diaprepes abbreviatus, Conotrachelus nenuphar, and Pissodes nemorensis, all of which had fewer fungal colonies relative to controls. Pupal soil cells were found to suppress phytopathogenic fungi in-vitro, including suppression of Alternaria solani by D. abbreviatus pupal cell, and that of Monilinia fructicola by C. caryae. The detection of antibiosis of soil cells formed by surface-sterilized insects using sterile soil implies the antimicrobial effect stemmed from inside the insect. Further, a novel biotic mechanism was identified: a bacterium related to Serratia nematodiphila was isolated from C. caryae pupal soil cells and was found to be associated with antibiosis. The bacterial cultures with or without autoclave had similar effects but were not as potent as pupal soil cells for suppressing B. bassiana. Also, autoclaved soil cells and autoclaved bacterial culture suppressed M. fructicola but were not as inhibitory as non-autoclaved soil cells. This indicates that antibiosis may be due to bacterial metabolites, although other factors may also be involved. Our findings suggest potential to develop the antibiotic compounds as novel bio-fungicides to control plant diseases.

Entomopathogenic nematode (EPN) species richness merits studies towards making rational decisions for effective management of Caribfly, Anastrepha suspensa (Loew) in southern Florida. Competition for Caribfly and efficacies of EPN biodiversity were examined under laboratory conditions. Similar EPN species treatments to Caribfly-infested fruits, periodically obtained from the ground in groves which were also infested by the parasitoid Diachasmimorpha longicaudata Ashmead (Braconidae), were studied in a series of field trials. Treatments with individual EPN species and their mixtures caused similar mortalities of Caribfly larvae, though the various EPN species competed for larvae in multiple-species treatments. Laboratory trials showed that mortalities of EPN-treated Caribfly pupae were mostly inversely related to EPN diversity. In the field, population densities of emerging adult Caribfly increased with increasing number of EPN species combined in treatments. Thus, single-EPN species treatments proved to be more effective for the management of fruit-to-soil stages of Caribfly. Relative to controls, the proportions of surviving adult Caribfly observed in EPN treatments with Heterorhabditis bacteriophora (exotic in Florida), Steinernema feltiae (exotic EPN) and Heterorhabditis indica (the endemic species) in field plots were 22.5 ± 6, 45 ± 13 and 47 ± 13%, respectively. Number of emerging D. longicaudata in each of EPN species treatments was similar to that observed in control, suggesting that none of the EPN species significantly affected the emergence of D. longicaudata, a parasitoid of Caribfly. Heterorhabditis bacteriophora will be more promising, with insignificant side effects on D. longicaudata in Caribfly-integrated pest management.

The attraction of entomopathogenic nematodes (EPNs) to herbivore-injured plant roots has been documented recently to be a common tritrophic interaction. Belowground tritrophic interactions are especially subject to modulation by many abiotic factors including drought. In this study, complementary greenhouse experiments were conducted to understand how drought stress might affect a potato plant’s impact on EPN behavior. In separate trials, the responses of the EPN Steinernema diaprepesi (Nguyen and Duncan) (Rhabditida: Steinernematidae) to root herbivory by larvae of the weevil Diaprepes abbreviatus (Linnaeus) (Coleoptera: Curculionidae), in well-watered and drought stressed potato plants, were measured using soil-matrix olfactometers with two arms. The drought treatments were initiated in 30-d old plants. Drought-stressed potato plants received water when potentiometers read approximately 20 kPa, while for well-watered plants, the number was 8 kPa. Four weeks after initiating the treatments, 400 ml water was added to all pots, immediately before starting the experiments. The experiments revealed that S. diaprepesi infective juveniles (IJs) did not migrate preferentially toward drought-stressed or well-watered plants when neither were subjected to herbivory [t(21) = 1.13, P = 0.269]. However, plants with roots damaged by herbivory attracted more S. diaprepesi IJs if they were well watered than if they were drought stressed [t(24) = 3.19, P = 0.004]. If both plants in the olfactometers were drought stressed, EPNs moved preferentially toward those with root herbivory than those with undamaged roots [t(23) = 3.19, P = 0.004]. No difference was detected in gas chromatography profiles between droughted and well-watered plant roots subjected to herbivory [F(24, 336) = 0.68, P = 0.87]. GC analysis showed that three compounds, including 3-nonanone [t(6) = 4.83, P = 0.003], artemisyl ketone [t(7) = 6.21, P = 0.000], and benzoic acid, 4-ethoxy-, ethyl ester [t(7) = −4.22, P = 0.004] were significantly higher in drought stressed than control plant roots. These results indicate that potatoes, like other plants, can recruit EPNs in response to root herbivory, and that drought stress dampens this tritrophic interaction where choice is involved. Additional research that resolves the mechanisms of these interactions may provide insights to exploit EPNs for crop protection.

In this study, molecular (ribosomal sequence data), morphological and cross-hybridization properties were used to identify a newSteinernemasp. from Florida, USA. Molecular and morphological data provided evidence for placing the novel species into Clade V, or the ‘glaseri-group’ ofSteinernemaspp. Within this clade, analysis of sequence data of the rDNA genes, 28S and internal transcribed spacer (ITS), depicted the novel species as a distinctive entity and closely related toS. glaseriandS. cubanum.Additionally, cross-hybridization assays showed that the new species is unable to interbreed with either of the latter two species, reinforcing its uniqueness from a biological species concept standpoint. Key morphological diagnostic characters forS. khuongin. sp. include the mean morphometric features of the third-stage infective juveniles: total body length (average: 1066 μm), tail length (average: 65 μm), location of the excretory pore (average: 80.5 μm) and the values ofc(average: 16.4),D% (average: 60.5),E% (average: 126) andH% (average: 46.6). Additionally, males can be differentiated fromS. glaseriandS. cubanumby the values of several ratios:D% (average: 68),E% (average: 323) and SW% (average: 120). The natural distribution of this species in Florida encompasses both natural areas and citrus groves, primarily in shallow groundwater ecoregions designated as ‘flatwoods’. The morphological, molecular, phylogenetic and ecological data associated with this nematode support its identity as a new species in theS. glaseri-group.

BACKGROUND Caribbean fruit fly (Caribfly) is a serious economic insect pest because of development of larvae that hatch from eggs oviposited into fruits by female adults. This study assessed the virulence of twelve entomopathogenic nematode (EPN) isolates to Caribfly in laboratory bioassays as a starting point toward evaluation of management strategies for the fruit-to-soil-dwelling stages of A. suspensa in fields infested by Caribfly. RESULTS Inoculation of A. suspensa with 1 mL of ca 200 IJs larva−1 killed Caribfly at either larval or pupal stage. Pupae were more resistant to EPN infections than larvae. Adult emergence from inoculated pupae in soil microcosms was significantly lower than that observed in filter paper assays. Longest or largest steinernematids suppressed emergence of more adult Caribfly from pupae in soils, whereas shorter heterorhabditids were more infectious to Caribfly larvae. The highest mortalities of A. suspensa were caused by exotic nematodes Steinernema feltiae and Heterorhabditis bacteriophora, followed by the native Heterorhabditis indica and the exotic Steinernema carpocapsae. CONCLUSION Entomopathogenic nematodes reduced the development of Caribfly larvae and pupae to adult in our bioassays, suggesting that EPNs have potential for biological control of A. suspensa. Future work will assess management strategies, using the virulent EPNs, in orchards infested by A. suspensa. © 2016 Society of Chemical Industry

Entomopathogenic nematodes (EPNs) are widely distributed in soils across all continents except Antarctica. Assessing the EPN community structure in an ecoregion can help reveal their biological control potential against important crop pests. Common methods for detecting EPNs in soil samples include baiting with sentinel insects, direct observation of extracted nematodes, or use of species-specific primer-probe combinations using qPCR. Less well studied is the use of high throughput sequencing (HTS), which has tremendous potential to characterize soil communities of EPNs and natural enemies of EPNs. Here, for the first time, we compared qPCR and HTS to characterize EPN food webs. The frequency and abundance of 10 EPN species and 13 organisms associated with EPNs from 50 orchard and natural area sites in two ecoregions of Portugal were evaluated using qPCR tools, and results were published in 2019. We applied an HTS approach to analyze frozen DNA samples from 36 sites in that study. Universal primers targeting ITS1 were used for nematode detection. All EPN species detected by qPCR were also detected by HTS. The EPN species and nearly all free-living nematodes detected by both processes were highly correlated (P < 0.01). Steinernema feltiae, the dominant EPN species, was detected by HTS in 55% more sites than by qPCR. HTS also detected more EPN species than did qPCR. Sample accuracy, measured by the fit of Taylor's Power Law to data from each method, was significantly better using HTS (r = 0.95, P < 0.01) than qPCR (r = 0.76, P < 0.01). The effect of biotic and abiotic variables on individual EPN species did not differ according to ANOVA and multiple regression analyses of both data sets while the drivers of EPN community structure did not differ when analyzing either data set with CCA. Our results combined with decreasing costs of metabarcoding, suggest that HTS may provide the most cost-effective and accurate means of assessing soil food webs of methods currently available., This study was supported in part by the US-Egypt Project cycle 17 (no. 172) entitled ‘Preparing and evaluating IPM tactics for increasing strawberry and citrus production.’ This article is derived from the Subject Data funded in part by NAS and USAID, and that any opinions, findings, conclusions, or recommendations expressed in it are those of the author alone, and do not necessarily reflect the views of USAID or NAS.

Olfactory signals are critical for soil inhabitants to communicate and respond to the environment. In addition to the well-documented volatile cues from herbivores and herbivory-induced plants, attraction of both entomopathogenic nematodes (EPNs) and insect prey was recently shown to be induced by a saprophytic fungus Fusarium solani. Here, we used headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS), to identify two volatile organic compounds (VOCs), 1-pentanol and 1-octen-3-ol (octenol), from F. solani. In olfactometer bioassays, the infective juvenile stage of the EPN Steinernema diaprepesi was attracted to both VOCs. Although octenol was highly attractive to fungivorous Drosophila melanogaster fruit fly larvae, the non-fungivorous Diaprepes abbreviatus root weevil larvae were repelled by the compound. In soil microcosms, the VOCs delayed the infection of root weevil larvae by S. diaprepesi but facilitated S. diaprepesi infection of fly larvae. Presumably octenol attracted the flies and EPNs to a common locale, while provoking greater separation of EPNs and root weevils than occurred in the absence of the chemical. EPNs may have evolved to exploit these VOCs as a means of encountering fungivorous insects, whereas non-fungivorous arthropods may have evolved to avoid the compounds.

Caribbean fruit fly, also known as Caribfly or Anastrepha suspensa , is a major tephritid pest of guavas. A virulent entomopathogenic nematode (EPN) species was investigated to suppress the fruit-to-soil stages of Caribflies, which are also attacked by the koinobiont parasitoid Diachasmimorpha longicaudata in south Florida. The main objective was to develop a feasible and cost-effective EPN-application method for integrated pest management (IPM) of Caribfly to improve guava production. Naturally infested guavas were treated with increasing Heterorhabditis bacteriophora infective juvenile (IJ) concentration or rate (0, 25, 50, …, 1,600 IJs cm -2 ) in field trials to measure the optimum IJ rate and then examine sensitivity of producing guavas to inclusion of Heterorhabditis bacteriophora in Caribfly IPM plans. Relative survival of Caribfly in treatments significantly decreased with increasing IJ rate from 0 to 100 IJs cm -2 . Similarly, probability of observing large numbers of parasitoid wasps ( Diachasmimorpha longicaudata ) in EPN treatments significantly declined with increasing IJ rate (0-100 IJs cm -2 ), even though the non-target effects of Heterorhabditis bacteriophora on relative survival of Diachasmimorpha longicaudata could not be determined because of few emerging parasitoid wasps. Optimum suppression (⩾ 60%) of Caribfly was consistently achieved at 100 IJs cm -2 or 17,500 IJs fruit -1 . Profitability analysis showed that Heterorhabditis bacteriophora can be included in Caribfly IPM tactics to produce guavas. Costs of EPNs in Caribfly IPM are minimized if Heterorhabditis bacteriophora is strategically applied by spot treatment of fruit. Repayment of costs of EPN-augmentation by spot treatments appears achievable by recovering 5.71% of the annual yield losses (⩾1,963 kg ha -1 ≈ US$ 8,650 ha -1 ), which are largely due to Caribfly infestation. Hectare-wide EPN-augmentation (or broadcasting) method requires more fruit recovery than the total annual yield losses to repay its high costs. Profitability of guava production in south Florida will not be very sensitive to marginal costs of the spot treatment method, when compared to the field-wide broadcasting of Heterorhabditis bacteriophora .

Amphimictic populations of root-lesion nematodes with numerous males and females having three lip annuli, a functional spermatheca and non-areolated lateral field occur on sword fern (Nephrolepis exaltata) in Florida. Identified for decades asPratylenchus penetrans, they appeared to be a morphologically separated species on the basis of a longer stylet (17.8-18.3 μm) thanP. penetrans(15-17 μm) and different lip pattern inen faceview (rectangularvsdumb-bell inP. penetrans). Morphologically similar amphimictic root-lesion nematodes have also been detected on flax lily in Costa Rica. Subsequent morphological observations indicated that these amphimictic root-lesion nematodes from fern and flax lily are closely related to the parthenogenetic speciesP. bolivianus, which has areolated lateral fields. In spite of the reproductive and morphological dissimilarities between these populations, their separation into different species was not supported by the results of molecular analyses of their DNA sequences. The populations used in these analyses included those that are amphimictic from Florida and Costa Rica and others that are parthenogenetic from the type locality in Bolivia, and geographically distant localities in Chile, China, Colombia and Europe. Phylogenetic analyses of the ITS and D2-D3 expansion segments of the 28S rRNA gene indicated that they belong to the same species,P. bolivianus, which consists of two morphotypes,P. bolivianus(am) amphimictic andP. bolivianus(pm) parthenogenetic, herein described and illustrated. Contradictory results were obtained by the analyses using a portion of thehsp90gene. The phylogenetic study, which included sequences of other root-lesion nematodes, a topotype and geographical distant populations ofP. zeae, revealed thatP. bolivianusandP. zeaeformed highly supported clades in the majority consensus trees. PCR with species-specific primers for rapid diagnostics ofP. bolivianusandP. zeaewere developed and tested.

An emerging organic citrus industry in Florida could benefit greatly from effective, non-conventional methods to mitigate losses from pests and diseases. We studied part of a soil food web in an organic orchard to learn ways to conserve and enhance biological control of insect pests by native entomopathogenic nematodes (EPNs). We evaluated two OMRI (Organic Materials Review Institute) approved cultural practices: (i) a mulch of commercially pelleted chicken manure, (ii) a commercial formulation of Purpureocillium lilacinus, and (iii) an un-amended control. Several soil nutrients (i.e. nitrogen, phosphate, and potassium) were affected by the amendments, but initial equilibrium values (T0) were restored by the last sampling time (T12). The plant parasitic nematode Tylenchulus semipenetrans increased in both treatments compared to the untreated control at T3 (. P

Florida is unique in the continental USA for its subtropical and tropical climates. The state is a major producer of fresh fruits, vegetables and ornamentals, in addition to its most renown crop, citrus. Nationally, Florida ranks first in production of citrus, sugarcane, tomato, cucurbits such as watermelon, cucumber and squash, and second in the value of ornamental or floriculture products, strawberry, bell pepper, sweet corn, and avocado. The warm, humid climate and porous soils permit extended nematode population growth with short overwintering, often resulting in extensive crop damage by one or multiple nematode species, including tropical nematodes not encountered elsewhere in North America. Although Florida has been accurately described as a nematologist’s paradise, here we focus on five genera that are of primary agricultural importance, while noting additional economically important species that occur in the state.

Since 2005, the Florida citrus industry has faced the need to control the devasting bacterial disease huanglongbing (HLB). Advanced production systems (APS) were designed to grow citrus trees more quickly than conventional citriculture (CC) methods in order to mitigate the impact of HLB. Daily fertigation required by APS produces changes in the soil physical–chemical properties compared to those in conventionally managed orchards. We used real-time PCR in an ongoing field experiment to compare the effects of APS and CC on more than a dozen metazoan and microorganism species in soil food webs that affect larvae of a major arthropod pest of citrus, Diaprepes ab b reviatus . Soil chemical properties, citrus performance, weevil occurrence, and abundance of free-living and plant-parasitic nematodes were also evaluated. The effects of polypropylene mulch that provides a barrier to soil entry by D. abbreviatus larvae were also investigated in each of the two cultural systems. Trees grew significantly larger in APS and mulching increased tree growth and reduced tree mortality, thereby increasing fruit yield per ha. APS increased the fruit yield in 2011; however, by 2013 the number of fruit per tree was not affected by any of the treatments. Root mass density increased in APS, but decreased under mulch. The numbers of plant-parasitic and free-living nematodes and some natural enemies of nematodes such as Catenaria sp. and Paecilomyces lilacinus were more abundant in the treatments with greater root mass density. Both organisms in the D. abbreviatus – Phytophthora nicotianae pest–disease complex were more abundant in APS than in CC, whereas fewer steinernematid entomopathogenic nematodes (EPNs) that prey on insect larvae occurred in APS. By contrast, heterorhabditid EPNs tended to be more numerous in APS than in CC, although they comprised

Since its first detection in 2005, the bacterial disease huanglongbing (HLB or citrus greening) has emerged as a critical threat to the citrus industry in Florida. An “Advanced Production System” (APS) could mitigate the impact of HLB by bringing citrus trees into production more quickly and economically than conventional citriculture methods. However, unlike conventional practices, APS fertigates plants daily, thereby changing the soil properties in ways that might impact soil biota. We tested the hypothesis that changes to soil properties caused by APS would affect the abundance of native entomopathogenic nematodes (EPNs) and/or the survival of augmented EPNs. The densities of organisms at different trophic levels were measured by real-time qPCR in three experiments conducted in an ongoing field experiment. Target organisms included 6 entompathogenic nematodes, 5 nematophagous fungi (NF) and a phoretic bacterium, Paenibacillus sp. Soil properties, free-living nematodes and citrus fibrous roots were also measured. Compared to soil under conventional citriculture (CC), APS increased soil pH and Mg content, while reducing the electrical conductivity, and content of K, Mn and Fe. The naturally occurring EPN Steinernema diaprepesi was 5 times less abundant in APS plots where these nematodes were more heavily encumbered by the phoretic bacterium Paenibacillus sp., which limits the foraging success of EPNs. In general, when EPNs were augmented in either treatment, fewer Steinernema riobrave than Heterorhabditis indica were recovered and recovery of both species declined rapidly over time. As seen with native S. diaprepesi, fewer augmented S. riobrave were recovered from APS plots in two of the three experiments, whereas the management system did not affect the recovery of H. indica. More of some endoparasitic and trapping NF were recovered from soil augmented with S. riobrave than with H. indica. However, variation in the responses of NF to the management systems suggests that these NF species were not primarily responsible for the steinernematid responses to APS. Although APS has the potential to reduce EPN populations and exacerbate herbivory by subterranean pests such as the root weevil Diaprepes abbreviatus, additional study of the physical causes of this effect may reveal ways to avoid the problem.