Biocontrol Agents Of Insect Pests Research Articles

Endophytic entomopathogenic fungi as biological control agents of insect pests.

Entomopathogenic fungi capable of establishing mutualistic endophytic relationships with plants have a tremendous potential as biocontrol agents of insect pests. While fungi have long played an important and highly effective role in pest suppression, the utility of endophytic entomopathogenic fungi in pest management is a relatively new and emerging topic of biocontrol. Here we discuss the relevance of endophytic fungi to plant health in general, synthesize the current knowledge of the effectiveness of endophytic entomopathogenic fungi against diverse insect pests, discuss the indirect plant-mediated effects of endophytic entomopathogenic fungi on arthropods, and describe the diverse benefits of endophytic fungi to plants that are likely to affect herbivores and plant pathogens as well. Lastly, we consider major challenges to incorporating endophytic entomopathogenic fungi in biocontrol, such as their non-target effects and field efficacy, which can be variable and influenced by environmental factors. Continued research on endophyte-insect-plant-environment interactions is critical to advancing our knowledge of these fungi as a sustainable pest management tactic. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Stress tolerance in entomopathogenic nematodes: Engineering superior nematodes for precision agriculture

Entomopathogenic nematodes (EPNs) are soil-dwelling parasitic roundworms commonly used as biocontrol agents of insect pests in agriculture. EPN dauer juveniles locate and infect a host in which they will grow and multiply until resource depletion. During their free-living stage, EPNs face a series of internal and environmental stresses. Their ability to overcome these challenges is crucial to determine their infection success and survival. In this review, we provide a comprehensive overview of EPN response to stresses associated with starvation, low/elevated temperatures, desiccation, osmotic stress, hypoxia, and ultra-violet light. We further report EPN defense strategies to cope with biotic stressors such as viruses, bacteria, fungi, and predatory insects. By comparing the genetic and biochemical basis of these strategies to the nematode model Caenorhabditis elegans, we provide new avenues and targets to select and engineer precision nematodes adapted to specific field conditions.

A global perspective of entomopathogens as microbial biocontrol agents of insect pests

The growing global population has created a significant demand for both quality and quantity of agricultural products, resulting in a significant increase in the use of agrochemicals such as chemical pesticides to counter insect pests. Consumers, on the other hand, have grown increasingly concerned in recent years about the adverse effects of chemical insecticides on human health and the environment. As a result, researchers worldwide have been compelled to conduct research into alternative crop protection solutions. Biological control through entomopathogens has gained prominence among these alternatives, and several microbial biocontrol agents, including baculoviruses, Bacillus , Beauveria , Steinernema , and Heterorhabditis species, have been tested. Microbial biopesticide products are currently being used to combat specific insects that harm crops. The modes of action of entomopathogens, their advantages and constraints are discussed. An overview of processes for their development are highlighted with examples, as well as the issues that impede their development. Finally, special attention was paid to the gaps identified in this sector and the factors limiting their application particularly with respect to market potential. The future potential of entomopathogens may be affected by changing agricultural systems. • Entomopathogens have great potential in controlling insect pest populations in agroecosystems. • Commercial application of a microbial biopesticide necessitates large-scale mass production, formulation with appropriate additives to increase the product's shelf-life, and storage. • Stringent regulatory framework due to biosafety or environmental concerns raises overall costs and delays microbial biopesticide commercialization. • Additional regulatory challenges will be required for the new microbial biopesticide products in order to define low-risk contenders for easy commercialization and free market entry.

Effect of temperature on survival of Australian entomopathogenic nematodes and their virulence against the Queensland fruit fly, Bactrocera tryoni

Entomopathogenic nematodes (EPNs) are commonly used biocontrol agents of insect pests, with a wide range of commercially available isolates targeting specific pests. New isolates are, however, required to improve pest control across a wider range of environmental conditions for target pests, including emerging threats. We assessed the effect of temperature on survival and virulence of 17 Australian isolates of five EPN species (Heterorhabditis bacteriophora, Heterorhabditis indica, Heterorhabditis marelatus, Heterorhabditis zealandica and Steinernema feltiae) against larvae and pupae of the Queensland fruit fly, Bactrocera tryoni. All isolates still infected and killed larvae after infective juveniles (IJ) had been kept without insect hosts at 15 °C, 25 °C or 30 °C for two weeks, indicating their potential to remain viable under field conditions. However, the mean LD50 value ranged from 35 to 150 and was generally lower at 15 °C than at 25 °C and 30 °C. Similarly, after IJs had been kept at 25 °C for 1–3 weeks without insect hosts, all isolates infected B. tryoni larvae, with mean LD50 values ranging from 25 to 144. Interestingly, 15 isolates infected and killed B. tryoni pupae after one week, with a mean LD50 value between 130 and 209, but only two isolates after two weeks, with a mean LD50 value between 229 to 209. No pupal mortality was seen after three weeks. In absence of hosts, EPNs survived longer at 15 °C and 25 °C than at 30 °C. Complete EPN mortality occurred after nine weeks at 30 °C, and after 18 weeks at 15 °C and 25 °C, except for some survival in one S. feltiae isolate (Sf.ECCS). Overall, six isolates of H. indica (Hi.HRN2, Hi.LMI2, Hi.QF6), H. bacteriophora (Hb.HIE), H. zealandica (Hz.NAR1) and S. feltiae (Sf.ECCS) performed best and need further testing as potential biocontrol agents against B. tryoni under semi-field and field conditions.

Characterization of a novel chitinolytic Serratia marcescens strain TC-1 with broad insecticidal spectrum

The Gram-negative rod-shaped bacterium Serratia marcescens is an opportunistic pathogen of many organisms, including insects. We report the identification and optimal in vitro chitinase production conditions of a novel chitinolytic S. marcescens strain TC-1 isolated from a naturally infected white grub (Anomala corpulenta) collected from a peanut field at Nanyang city, Henan province, China. Strain identification was conducted by morphological, physiological, biochemical and molecular analyses. The amplified 16S rRNA gene of TC-1 showed a similarity greater than 99% with multiple strains of S. marcescens. Based on Neighbor-joining phylogenetic tree analysis of bacterial 16S rRNA gene sequences, TC-1 formed a clade with S. marcescens, clearly separated from other Serratia spp. The strain TC-1 showed larvicidal activities against five insect species (A. corpulenta, Plutella xylostella, Spodoptera exigua, Helicoverpa armigera, Bombyx mori) and the nematode Caenorhabditis elegans, but not against S. litura. The operating parameters of chitinase production by TC-1 were optimized by response surface methodology using a three-factor, three-level Box-Behnken experimental design. The effects of three independent variables i.e. colloidal chitin concentration (7–13 g l−1), incubation time (24–72 h) and incubation temperature (24–32 °C) on chitinase production by TC-1 were investigated. A regression model was proposed to correlate the independent variables for an optimal chitinase activity predicted as 20.946 U ml−1, using a combination of colloidal chitin concentration, incubation time and incubation temperature of 9.06 g l−1, 63.83 h and 28.12 °C, respectively. The latter agreed well with a mean chitinase activity of 20.761 ± 0.102 U ml−1 measured in the culture supernatants of TC-1 grown under similar conditions with a colloidal chitin concentration, incubation time and incubation temperature of 9 g l−1, 64 h and 28 °C, respectively. Our study revealed the S. marcescens strain TC-1 with potential as a biocontrol agent of insect pests and nematodes and demonstrated the proposed regression model's potential to guide chitinase production by this strain.

Diversity of Braconid Parasitoids (Hymenoptera: Braconide) of Horticultural Insect Pests from Kolhapur, Maharashtra

Braconids (Hymenoptera: Braconidae) are the potential biocontrol agents of insect pests attacking economically important crop plants. Braconids are exclusively parasitic and are reported mainly on lepidopterous pests. These flies parasitize egg, larval, and pupal stage of the insect pests. Horticultural crops are attacked by lepidopterous pests causing severe damage to crops and there by minimizes crop yield. The use of braconid parasitoids as pest control agents helps to reduce the pest population. The braconids are rearable in laboratories and reared parasitoids can be used in pest control programs. The correct identification, host preference and parasitic potential of the parasitoids plays important role in their utilization in pest control programs. The species reported belongs to genus Cotesia, Apanteles, Bracon, Glyptapenteles, Chilonus, Dolichogenidea, Agathis, Meteorus etc. and have been found parasitizing the insect pests of different horticultural plants. Total 35 species of braconid parasitoids were reported from the Kolhapur district, Maharashtra. The studies will help to add knowledge on number of braconid species found in study area and also explore them to use in biocontrol programs in the region.

Monitoring life cycle stages of axenic cultures of in vitro produced Oscheius L8 MCB in semi-solid state and liquid state and comparative efficacy studies between in vitro and in vivo nematode production against Galleria mellonella

The emergence of entomopathogenic nematodes as biocontrol agents of insect pests has caused a shift of focus towards the use of in vitro methods for commercial production of these organisms for use in agricultural settings. In this study, Oscheius L8 MCB, an insecticidal nematode isolated from Brits in the North West Province of South Africa, was produced in vitro via axenic means in liquid and semi-solid states. Light microscopy was used to monitor and enumerate life cycle stages of this isolate, with special focus given to the yield of the insecticidal Infective juvenile (IJ) stage. Comparative dose–response assays were used to determine the efficacy of in vitro production of Oscheius L8 MCB versus in vivo production against Galleria mellonella. In vitro produced Oscheius L8 MCB consisted of four juvenile stages, with one of the juvenile stages being the non-feeding IJ stage. Adults stages comprised amphimictic males and females, and female hermaphrodites. The semi-solid state produced IJs in three yield peaks of 2.33 × 104 IJs/ml (SEM ± 1922 IJs/ml), 1.93 × 104 IJs/ml (SEM ± 2455 IJs/ml) and 1.92 × 104 IJs/ml (SEM ± 3542 IJs/ml) at days 6, 9 and 11 respectively. In contrast, the liquid state produced a single peak of 3.6 × 104 IJs/ml (SEM ± 1178 IJs/ml) at day 12. In vivo produced Oscheius L8 MCB established at least 50% G. mellonella larvae mortality 24 h post infection, at an infective IJ concentration of 25 IJ/100 µl compared to 0% (semi-solid) and 16.67% (liquid) larvae mortality established by in vitro produced Oscheius L8 MCB at the same concentration after 24 h. The number of IJs emerging from a larvae cadaver may be indicative of field coverage, efficacy, and field persistence. Larvae cadaver infected with in vivo produced IJs produced a maximum of 8.36 × 104 IJs/larvae (SEM ± 3900 IJs/larvae) in comparison to larvae cadaver infected with in vitro produced IJs, which produced maximums of 5.50 × 104 IJs/larvae (SEM ± 2527 IJs/larvae) and 4.44 × 104 IJs/larvae (SEM ± 1803 IJs/larvae) for liquid and semi-solid states respectively. The mortality and IJ emergence in larvae infected with semi-solid state and liquid state Oscheius L8 MCB varied according to infective IJ concentration. However, in conclusion, axenic in vitro culturing of Oscheius L8 MCB may reduce its efficacy against insect hosts.

Evaluation of Native Entomopathogenic Nematode Isolates for the Management of Selected Insect Pests in Nigeria

Native entomopathogenic nematodes (EPNs) were evaluated for the management of three selected pests, Sesamia calamistis, Spodoptera frugiperda and Rhynchophorus ferrugineus in laboratory bioassays. The EPNs were isolated from soils from various locations within Ibadan, Nigeria using the greater wax moth (Galleria mellonella) as insect bait. A two-factor laboratory experimental assay was laid out in a completely randomized design and replicated three times. The EPN suspension was applied on insect larvae with distilled water as control. Number of days to mortality, percentage mortality of insect larvae, and total EPN population of infective juveniles (IJs) recovered from larval cadavers were assessed and reproductive factor (RF) determined. Data were analyzed using analysis of variance, and means were separated using Tukey’s Studentized Range Test at P G. mellonella (5075.08), >S. frugiperda (3957.23), >S. calamistis (742.31). From the results, EPN had the greatest fecundity in G. mellonella and R. ferrugineus showing higher ability to be recycled. This study reveals the potential of native EPNs as a biocontrol agent of insect pests and emphasizes the need for a more environment-friendly and sustainable approach to insect pest management.

Arboreal Tiger Beetles Recorded from Lowland Crop Cultivations in Sri Lanka

Purpose : Thirty-one species of arboreal tiger beetles are known from Sri Lanka of which 25 species are endemic. However, their habitat types are poorly documented and the available records are far outdated. Therefore, a survey of tiger beetles was carried out to determine their present occurrence with emphasis on agricultural habitat types. Research Method : Forty-six locations of the country, covering eighteen districts, all provinces, representing a majority of bioclimatic zones except those in Montane Sri Lanka were surveyed for arboreal tiger beetles. Sampling was conducted using the visual encounter method. Collected beetles were identified using taxonomic keys and descriptions. Findings : Eight species of arboreal tiger beetles were collected from the survey. Majority of the species (06) were collected from crop cultivations of coconut and also from tea, fruit farms, betel leaf, cinnamon and pepper. Four species of Derocrania and two species of Tricondyla were recorded from the cultivations and all had fused elytra and hence unable to fly. Derocrania scitiscabra was the dominant arboreal tiger beetle species in the crop cultivations. Originality/ Value : The study documents hitherto unrecorded habitat types for a poorly documented important beetle group of Sri Lanka. It further provides information for future research on the possibility of using arboreal tiger beetles as bio-control agents of insect pests of agricultural crops.

Preservative Media for Beauveria Bassiana (bals.) Vuill Storage

Beauveria bassiana is an important entomopathogenic fungus that used as a biocontrol agent of insect pests. Maintaining and preserving B. bassiana cultures is essential for the effective evaluation of its potential as microbial agent against insect pest, for biodiversity studies and also for exchange of fungal material between laboratories. In the present work we evaluated the suitability of four preservation materials based on gelatin and rice to maintain the viability of B. bassiana to be used as baits for insect’s control. The gelatin amended with sugar recorded the maximum viability after 70 days of storage as 98.3% compared to 63.3% on rice media. Effective control of 80% of the ants was observed after 10 days of feeding on gelatin amended with sugar and rice bait. The results demonstrated that treatment with formulations containing conidia of B. bassiana presents insecticidal activity against ant in addition of acting as preservation materials.

Preservative Media for Beauveria Bassiana (bals.) Vuill Storage

Beauveria bassiana is an important entomopathogenic fungus that used as a biocontrol agent of insect pests. Maintaining and preserving B. bassiana cultures is essential for the effective evaluation of its potential as microbial agent against insect pest, for biodiversity studies and also for exchange of fungal material between laboratories. In the present work we evaluated the suitability of four preservation materials based on gelatin and rice to maintain the viability of B. bassiana to be used as baits for insect’s control. The gelatin amended with sugar recorded the maximum viability after 70 days of storage as 98.3% compared to 63.3% on rice media. Effective control of 80% of the ants was observed after 10 days of feeding on gelatin amended with sugar and rice bait. The results demonstrated that treatment with formulations containing conidia of B. bassiana presents insecticidal activity against ant in addition of acting as preservation materials.

Population structure of Cydia pomonella granulovirus isolates revealed by quantitative analysis of genetic variation.

Genetic diversity of viruses is driven by genomic mutations and selection through its host, resulting in differences in virulence as well as host responses. For baculoviruses, which are naturally occurring pathogens of insects and which are frequently sprayed on hundred thousands to millions of hectares as biocontrol agents of insect pests, the phenomenon of virus–host co-evolution is of particular scientific interest and economic importance because high virulence of baculovirus products is essential and emergence of host resistance needs to be avoided as much as possible. In the present study, the population structure of twenty isolates of the Cydia pomonella granulovirus (CpGV), including twelve isolates from different geographic origins and eight commercial formulations, were studied on the basis of next-generation sequencing data and by analyzing the distribution of single nucleotide polymorphisms (SNPs). An entirely consensus sequence-free quantitative SNP analysis was applied for the identification of 753 variant SNP sites being specific for single as well as groups of CpGV isolates. Based on the quantitative SNP analysis, homogenous, heterogenous as well as mixed isolates were identified and their proportions of genotypes were deciphered, revealing a high genetic diversity of CpGV isolates from around the world. Based on hierarchical clustering on principal components (HCPC), six distinct isolate/group clusters were identified, representing the proposed main phylogenetic lineages of CpGV but comprising full genome information from virus mixtures. The relative location of different isolates in HCPC reflected the proportion of variable compositions of different genotypes. The established methods provide novel analysis tools to decipher the molecular complexity of genotype mixtures in baculovirus isolates, thus depicting the population structure of baculovirus isolates in a more adequate form than consensus based analyses.

Molecular and Phenotypic Characterization of Heterorhabditis indica (Nematoda: Rhabditida) Nematodes Isolated During a Survey of Agricultural Soils in Western Uttar Pradesh, India.

Entomopathogenic nematodes (EPNs) are important biocontrol agents of insect pests. To increase the availability of locally adapted entomopathogenic nematode isolates for biocontrol programs, a survey of several agricultural soils in Western Uttar Pradesh, India was conducted. Eight hundred and sixty soil samples from the districts Meerut, Bulandshahr, Baghpat, and Bijnor were collected and examined for the presence of entomopathogenic nematodos using the "Galleria baiting method". Steinernema and Heterorhabditis nematodes were recovered. The isolated Heterorhabditis nematodes were molecularly, and morphologically characterized, and their biocontrol potential was evaluated against Spodoptera litura. Finally, the geographical distribution of entomopathogenic nematodes was studied based on the analysis of ITS GenBank records. A small proportion of the collected soil samples were positive for Heterorhabditis and Steinernema nematodes. Twelve soil samples were positive for the presence of Heterorhabditis nematodes, and 29 samples were positive for Steinernema. The Heterorhabditis nematodes were identified as Heterorhabditis indica based on morphological, morphometrical and molecular analyses. No other species of Heterorhabditis were isolated from the soil samples analyzed, suggesting that this species is dominant in the western part of Uttar Pradesh, India. The morphology of the nematode isolates was somewhat similar to the morphology of the H. indica isolate used for the original description of this species, with a notable exception mucrons were present in the hermaphrodite and female specimens we collected, but this structure was not observed in the specimens used for the original description of the species. Principal component analyses (PCA) show small inter- and intraspecific morphological variability between the nematodes species of the "Indica" clade. The insecticide properties of one isolate, CH7, were evaluated against Spodoptera litura, and the results show that this isolate effectively killed this pest under laboratory conditions, demonstrating its potential as a biocontrol agent. This study sets the basis for establishing new biocontrol agents to be used in future pest management programs in India.

Genetic diversity of Beauveria bassiana in semi natural and agricultural habitats and its biocontrol potential against cowpea aphid, Aphis craccivora Koch.

Information on the biology and ecology of Beauveria bassiana in different habitats could provide essential knowledge in their development as biocontrol agents of insect pests. In this study, phylogenetic and genotypic information was used to evaluate the genetic diversity of B. bassiana within semi natural and agricultural habitats in Karnataka State of South India and assessed their extracellular chitinase activity and pathogenicity against cowpea aphid, Aphis craccivora. Multilocus phylogeny and microsatellite genotyping of B. bassiana conjointly resolved three phylogenetic species, Bb_1, Bb_2, and Bb_3, in semi natural and agricultural habitats. None of the three phylogenetic species of B. bassiana were associated with crop plants in agroecosystem or insect hosts in semi natural habitat. All the three phylogenetic species were detected with four genotypes each. All isolates of B. bassiana were pathogenic to A. craccivora in greenhouse bioassays. Isolate GKVK 01_13 caused a significantly high mortality of aphids and detected with an increased level of chitinase activity. The study results suggest that application of indigenous virulent strain of B. bassiana could provide effective control of native insect pest A. craccivora.

Entomopathogenic nematodes as biocontrol agents of insect pests in orchards.

Abstract Entomopathogenic nematodes (EPNs) are increasingly being used as biological control of insect pests due to their successful biocontrol activity against various economically important insect pests. Despite the growing success of EPNs, their effective use in orchards remains rather scarce. The principal limiting factors for the practical implementation of EPNs in Integrated Pest Management (IPM) programmes in orchards are their reduced control activity and persistence due to low-temperature regimes and desiccation, in particularly when applied against aboveground pest stages. However, recent advances in formulation technology, application strategy (with emphasis on improved persistence of the applied EPNs) and gradually acquired knowledge on optimal implementation strategies already have extended - and in the future most likely will further expand - the practical adoption of EPNs in pest management programmes in orchards. A successful implementation of EPNs in orchards requires that their usage fits into an IPM strategy. Interactions between EPNs and other biological or chemical control agents can be synergistic, additive or antagonistic, depending on the specific chemical and biological agents, as well as their rates and timing and host species. In this article, the most important aspects and features of EPN applications in orchards are reviewed.

De novo characterization of venom apparatus transcriptome of Pardosa pseudoannulata and analysis of its gene expression in response to Bt protein

BackgroundPardosa pseudoannulata is a prevailing spider species, and has been regarded as an important bio-control agent of insect pests in farmland of China. However, the available genomic and transcriptomic databases of P. pseudoannulata and their venom are limited, which severely hampers functional genomic analysis of P. pseudoannulata. Recently high-throughput sequencing technology has been proved to be an efficient tool for profiling the transcriptome of relevant non-target organisms exposed to Bacillus thuringiensis (Bt) protein through food webs.ResultsIn this study, the transcriptome of the venom apparatus was analyzed. A total of 113,358 non-redundant unigenes were yielded, among which 34,041 unigenes with complete or various length encoding regions were assigned biological function annotations and annotated with gene ontology and karyotic orthologous group terms. In addition, 3726 unigenes involved in response to stimulus and 720 unigenes associated with immune-response pathways were identified. Furthermore, we investigated transcriptomic changes in the venom apparatus using tag-based DGE technique. A total of 1724 differentially expressed genes (DEGs) were detected, while 75 and 372 DEGs were functionally annotated with KEGG pathways and GO terms, respectively. qPCR analyses were performed to verify the DEGs directly or indirectly related to immune and stress responses, including genes encoding heat shock protein, toll-like receptor, GST and NADH dehydrogenase.ConclusionThis is the first study conducted to specifically investigate the venom apparatus of P. pseudoannulata in response to Bt protein exposure through tritrophic chain. A substantial fraction of transcript sequences was generated by high-throughput sequencing of the venom apparatus of P. pseudoannulata. Then a comparative transcriptome analysis showing a large number of candidate genes involved in immune response were identified by the tag-based DGE technology. This transcriptome dataset will provide a comprehensive sequence resource for furture molecular genetic research of the venom apparatus of P. pseudoannulata.

Dynamics of transcriptomic response to infection by the nematode Heterorhabditis bacteriophora and its bacterial symbiont Photorhabdus temperata in Heliothis virescens larvae.

Entomopathogenic nematodes in the Heterorhabditis genus and their symbiotic Photorhabdus bacteria are important biocontrol agents of insect pests and models for the study of microbe-host interactions. In this work, we used larvae of the tobacco budworm (Heliothis virescens) as a model to study its defensive mechanisms against Heterorhabditis bacteriophora nematodes carrying symbiotic Photorhabdus temperata. We first determined time points of initial nematode entry and release of bacteria into the haemolymph to perform transcriptional analysis of insect gene expression during these steps in the infective process. RNA-Sequencing analyses were then performed to profile differential gene expression in the insect during nematode invasion, bacterial release and final steps of infection, relative to the untreated controls. Our results support the theory that insect immune response genes are induced upon nematode invasion, but themajority of these genes are suppressed upon the release of bacteria by the nematodes into the haemolymph. Overall, these findings provide information onthe dynamics of the insect's response to a progressing infection by this entomopathogenic nematode-bacteria complex and facilitate development of Hel.virescens as a pest model for future functional studies of the key insect defence factors.

Host coexistence in a model for two host-one parasitoid interactions.

Building from a continuous-time host-parasitoid model introduced by Murdoch et al.(Am Nat 129:263-282, 1987), we study the dynamics of a 2 host-parasitoid model assuming, for the sake of simplicity, that larval stages have a fixed duration. If each host is subjected to density-dependent mortality in its larval stage, we obtain explicit conditions for the existence of an equilibrium where the two host species coexist with the parasitoid. However, if host demography is density-independent, equilibrium coexistence is impossible. If at least one of the 1 host-parasitoid systems has an oscillatory dynamics (which happens under some parameter values), we found, through numerical bifurcation, that coexistence is favoured. Coexistence between the two hosts may occur along a periodic solution even without density-dependence. Models of this type may be relevant for the use of parasitoids as biocontrol agents of insect pests.

Temperature-dependent changes in the host-seeking behaviors of parasitic nematodes.

BackgroundEntomopathogenic nematodes (EPNs) are lethal parasites of insects that are of interest as biocontrol agents for insect pests and disease vectors. Although EPNs have been successfully commercialized for pest control, their efficacy in the field is often inconsistent for reasons that remain elusive. EPN infective juveniles (IJs) actively search for hosts to infect using a diverse array of host-emitted odorants. Here we investigate whether their host-seeking behavior is subject to context-dependent modulation.ResultsWe find that EPN IJs exhibit extreme plasticity of olfactory behavior as a function of cultivation temperature. Many odorants that are attractive for IJs grown at lower temperatures are repulsive for IJs grown at higher temperatures and vice versa. Temperature-induced changes in olfactory preferences occur gradually over the course of days to weeks and are reversible. Similar changes in olfactory behavior occur in some EPNs as a function of IJ age. EPNs also show temperature-dependent changes in their host-seeking strategy: IJs cultured at lower temperatures appear to more actively cruise for hosts than IJs cultured at higher temperatures. Furthermore, we find that the skin-penetrating rat parasite Strongyloides ratti also shows temperature-dependent changes in olfactory behavior, demonstrating that such changes occur in mammalian-parasitic nematodes.ConclusionsIJs are developmentally arrested and long-lived, often surviving in the environment through multiple seasonal temperature changes. Temperature-dependent modulation of behavior may enable IJs to optimize host seeking in response to changing environmental conditions, and may play a previously unrecognized role in shaping the interactions of both beneficial and harmful parasitic nematodes with their hosts.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-016-0259-0) contains supplementary material, which is available to authorized users.

Variation in the susceptibility of Drosophila to different entomopathogenic nematodes.

Entomopathogenic nematodes (EPNs) in the genera Heterorhabditis and Steinernema are lethal parasites of insects that are of interest as models for understanding parasite-host interactions and as biocontrol agents for insect pests. EPNs harbor a bacterial endosymbiont in their gut that assists in insect killing. EPNs are capable of infecting and killing a wide range of insects, yet how the nematodes and their bacterial endosymbionts interact with the insect immune system is poorly understood. Here, we develop a versatile model system for understanding the insect immune response to parasitic nematode infection that consists of seven species of EPNs as model parasites and five species of Drosophila fruit flies as model hosts. We show that the EPN Steinernema carpocapsae, which is widely used for insect control, is capable of infecting and killing D. melanogaster larvae. S. carpocapsae is associated with the bacterium Xenorhabdus nematophila, and we show that X. nematophila induces expression of a subset of antimicrobial peptide genes and suppresses the melanization response to the nematode. We further show that EPNs vary in their virulence toward D. melanogaster and that Drosophila species vary in their susceptibilities to EPN infection. Differences in virulence among different EPN-host combinations result from differences in both rates of infection and rates of postinfection survival. Our results establish a powerful model system for understanding mechanisms of host-parasite interactions and the insect immune response to parasitic nematode infection.