Dispersal and Repulsion of Entomopathogenic Nematodes to Prenol.

Chemosensory cues are crucial for entomopathogenic nematodes (EPNs)-a guild of insect-killing parasitic nematodes that are used as biological control agents against a variety of agricultural pests. Dispersal is an essential element of the EPN life cycle in which newly developed infective juveniles (IJs) emerge and migrate away from a resource-depleted insect cadaver in order to search for new hosts. Emergence and dispersal are complex processes that involve biotic and abiotic factors, however, the elements that result in EPN dispersal behaviors have not been well-studied. Prenol is a simple isoprenoid and a natural alcohol found in association with EPN-infected, resource-depleted insect cadavers, and this odorant has been speculated to play a role in dispersal behavior in EPNs. This hypothesis was tested by evaluating the behavioral responses of five different species of EPNs to prenol both as a distal-chemotactic cue and as a dispersal cue. The results indicate that prenol acted as a repulsive agent for all five species tested, while only two species responded to prenol as a dispersal cue

Touch-stimulation increases host-seeking behavior in Steinernema Carpocapsae.

Previous research demonstrated that Steinernema carpocapsae infective juveniles (IJs) exposed to a host cuticle were more attracted toward certain host-associated volatile odors. We wanted to test the specificity of attraction that results from exposure to host cuticle. Host recognition behavior was analyzed after stimulating IJs by allowing them to physically interact with Galleria mellonella cuticles. The subsequent behavioral response and the proportion of the population participating in chemotaxis to multiple host odors were measured. We found that exposure to host cuticles resulted in a significantly higher percentage of the population participating in host-seeking behavior, with threefold more nematodes participating in chemotaxis. We tested whether exposure to live or dead host cuticle resulted in a different response and found that a higher percentage of IJs exposed to a live host cuticle participated in chemotaxis than IJs exposed to a dead host cuticle, but that IJs exposed to a dead host demonstrated significantly higher participation than was observed for non-stimulated IJs. To test whether the increase in IJ participation in host-seeking behaviors after exposure to a live host cuticle was specific, we exposed stimulated IJs to a known repulsive odor, a neutral odor, and two predicted attractants. We found that stimulation of IJs through physical contact with a host cuticle induces a specific enhancement of host-seeking behavior to host-specific odors rather than a general increased chemotactic response to all volatile stimuli. However, the nematodes displayed an enhanced response to multiple host-specific odors. Future work should focus on the mechanism through which contact with live host cuticle stimulates increased behavioral response.Previous research demonstrated that Steinernema carpocapsae infective juveniles (IJs) exposed to a host cuticle were more attracted toward certain host-associated volatile odors. We wanted to test the specificity of attraction that results from exposure to host cuticle. Host recognition behavior was analyzed after stimulating IJs by allowing them to physically interact with Galleria mellonella cuticles. The subsequent behavioral response and the proportion of the population participating in chemotaxis to multiple host odors were measured. We found that exposure to host cuticles resulted in a significantly higher percentage of the population participating in host-seeking behavior, with threefold more nematodes participating in chemotaxis. We tested whether exposure to live or dead host cuticle resulted in a different response and found that a higher percentage of IJs exposed to a live host cuticle participated in chemotaxis than IJs exposed to a dead host cuticle, but that IJs exposed to a dead host demonstrated significantly higher participation than was observed for non-stimulated IJs. To test whether the increase in IJ participation in host-seeking behaviors after exposure to a live host cuticle was specific, we exposed stimulated IJs to a known repulsive odor, a neutral odor, and two predicted attractants. We found that stimulation of IJs through physical contact with a host cuticle induces a specific enhancement of host-seeking behavior to host-specific odors rather than a general increased chemotactic response to all volatile stimuli. However, the nematodes displayed an enhanced response to multiple host-specific odors. Future work should focus on the mechanism through which contact with live host cuticle stimulates increased behavioral response

Host seeking parasitic nematodes use specific odors to assess host resources.

Entomopathogenic nematodes (EPNs) are insect parasites used as biological control agents. Free-living infective juveniles (IJs) of EPNs employ host-seeking behaviors to locate suitable hosts for infection. We found that EPNs can differentiate between naïve and infected hosts, and that host attractiveness changes over time in a species-specific manner. We used solid-phase microextraction and gas chromatography/mass spectrometry to identify volatile chemical cues that may relay information about a potential host's infection status and resource availability. Among the chemicals identified from the headspace of infected hosts, 3-Methyl-2-buten-1-ol (prenol) and 3-Hydroxy-2-butanone (AMC) were selected for further behavioral assays due to their temporal correlation with the behavioral changes of IJs towards the infected hosts. Both compounds were repulsive to IJs of Steinernema glaseri and S. riobrave in a dose-dependent manner when applied on an agar substrate. Furthermore, the repulsive effects of prenol were maintained when co-presented with the uninfected host odors, overriding attraction to uninfected hosts. Prenol was attractive to dauers of some free-living nematodes and insect larvae. These data suggest that host-associated chemical cues may have several implications in EPN biology, not only as signals for avoidance and dispersal of conspecifics, but also as attractants for new potential hosts

Signaling by AWC Olfactory Neurons Is Necessary for Caenorhabditis elegans' Response to Prenol, an Odor Associated with Nematode-Infected Insects

Chemosensation plays a role in the behaviors and life cycles of numerous organisms, including nematodes. Many guilds of nematodes exist, ranging from the free-living Caenorhabditis elegans to various parasitic species such as entomopathogenic nematodes (EPNs), which are parasites of insects. Despite ecological differences, previous research has shown that both EPNs and C. elegans respond to prenol (3-methyl-2-buten-1-ol), an odor associated with EPN infections. However, it is unclear how C. elegans responds to prenol. By utilizing natural variation and genetic neuron ablation to investigate the response of C. elegans to prenol, we found that the AWC neurons are involved in the detection of prenol and that several genes (including dcap-1, dcap-2, and clec-39) influence response to this odorant. Furthermore, we identified that the response to prenol is mediated by the canonically proposed pathway required for other AWC-sensed attractants. However, upon testing genetically diverse isolates, we found that the response of some strains to prenol differed from their response to isoamyl alcohol, suggesting that the pathways mediating response to these two odorants may be genetically distinct. Further, evaluations leveraging natural variation and genome wide association revealed specific genes that influence nematode behavior and provide a foundation for future studies to better understand the role of prenol in nematode behavioral ecology

Odors and Genetic Pathways Influencing Resource-Seeking in EPNs and Free-Living Nematodes

Entomopathogenic nematodes (EPNs) are insect-killing parasitic worms that are utilized in agriculture and home-garden use against a variety of insect pests. It is the infective juvenile stage (IJ) of the EPN life cycle responsible for locating, infecting and colonizing a new insect host to continue the life cycle and produce progeny. My research revealed that EPN species within the genus Steinernema, responded to host volatiles, in species—specific patterns with regard to both behavioral trends to the progression of infection, as well as overall participation. Analysis of host-odor profiles- for both naive and infected hosts (including recently infected and long-term, resource depleted insect cadavers) produced a variety of odors and one of the more notable odors produced was 3-methyl-2-buten-1-ol (prenol). EPN IJs were found to be repelled by prenol at a variety of doses (ranging from 2M to 20mM) and prenol yielded age-dependent increases in dispersal, implicating prenol as a potential IJ dispersal cue. However, lack of molecular tools in EPNs prevented investigations into the molecular underpinnings of how prenol is detected and translated into the observable repulsion. To overcome this obstacle, we leveraged the model organisms: Caenorhabditis elegans which exhibits attraction to prenol. Through use of natural variation, genome-wide association, and leveraging multiple genetic resources in the C. elegans community we identified the involvement of the AWC neuron in detection and response to prenol as well as eight genes that influence responses to prenol, including genes that have not previously been shown to affect chemotactic behaviors: dod-17, clec-39, dcap-1 and dcap-2. For many of these genes, we have found EPN orthologs exist, meaning we have uncovered information that potentially could be utilized to better understand EPN behavioral ecology such that EPNs may be improved or utilized more effectively in the future

Odors and Genetic Pathways Influencing Resource-Seeking in EPNs and Free-Living Nematodes

Entomopathogenic nematodes (EPNs) are insect-killing parasitic worms that are utilized in agriculture and home-garden use against a variety of insect pests. It is the infective juvenile stage (IJ) of the EPN life cycle responsible for locating, infecting and colonizing a new insect host to continue the life cycle and produce progeny. My research revealed that EPN species within the genus Steinernema, responded to host volatiles, in species—specific patterns with regard to both behavioral trends to the progression of infection, as well as overall participation. Analysis of host-odor profiles- for both naive and infected hosts (including recently infected and long-term, resource depleted insect cadavers) produced a variety of odors and one of the more notable odors produced was 3-methyl-2-buten-1-ol (prenol). EPN IJs were found to be repelled by prenol at a variety of doses (ranging from 2M to 20mM) and prenol yielded age-dependent increases in dispersal, implicating prenol as a potential IJ dispersal cue. However, lack of molecular tools in EPNs prevented investigations into the molecular underpinnings of how prenol is detected and translated into the observable repulsion. To overcome this obstacle, we leveraged the model organisms: Caenorhabditis elegans which exhibits attraction to prenol. Through use of natural variation, genome-wide association, and leveraging multiple genetic resources in the C. elegans community we identified the involvement of the AWC neuron in detection and response to prenol as well as eight genes that influence responses to prenol, including genes that have not previously been shown to affect chemotactic behaviors: dod-17, clec-39, dcap-1 and dcap-2. For many of these genes, we have found EPN orthologs exist, meaning we have uncovered information that potentially could be utilized to better understand EPN behavioral ecology such that EPNs may be improved or utilized more effectively in the future