Entomopathogenic nematodes (EPNs) are insect parasites used as biological control agents. Free-li... more 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. Entomopathogenic nematodes (EPNs) are insect-killing parasites used in biological control and are a model system for studying host-parasite interactions. EPNs can infect and kill a host within 48 hours and are commercially available for use in home gardens and industrial agriculture 1, 2. In the EPN life cycle, free-living infective-juveniles (IJs) encounter a host (either uninfected or possibly at an early stage of infection) (Fig. 1A), and then decide whether or not to invade the host. Once an IJ invades a host it releases symbiotic bacteria (Fig. 1B), which proliferate and help to both kill the host and provide a food source for the growing nematodes 3 (Fig. 1C). Steinernema spp. are gonochoristic, requiring a male and female in order to produce offspring 4. Within the host approximately 2–3 generations of nematodes can be produced (Fig. 1D), but eventually resources begin to run out inside the insect cadaver 2. As resources are depleted, the L2 juveniles will associate once more with the bacteria and take an alternative developmental pathway, becoming infective juveniles (IJs) rather than L3 juveniles. These IJs will then emerge and search for a new host to infect 2, 5 (Fig. 1E). In their search for a new host there are two host-seeking strategies–employed by IJs–which represent endpoints of a continuous spectrum. The first is a cruise foraging strategy where the IJ spends the majority of its time actively moving in search of a host 6, 7. The second strategy is an ambush foraging strategy where the IJ employs a sit-and-wait approach, waiting for a potential host to pass close by, allowing the IJ to attach and invade 7, 8. Between these two endpoint foraging strategies there are species of EPNs that have been classified as intermediates 6, 9. These foraging strategies are employed by individuals within a population and it has been shown that even for a species like S. carpocapsae. which is described as an ambush forager, a small proportion of individuals are cruise foragers and have been referred to as " sprinters " 8. Here, we worked with four species of Steinernema: S. carpocapsae, an ambush forager 6, 8 ; S. glaseri, a cruise forager 6, 9 ; and S. riobrave and S. feltiae, which are described as intermediate foragers 6, 9. EPN foraging strategies and the decision of whether or not to infect certain hosts is informed by olfactory and mechanosensory cues. Previous work has shown that volatile odorants emitted by uninfected insects elicit host-seeking behavior in EPN IJs 10–12. IJs rely on chemical cues in the environment to locate, identify, and evaluate their hosts 7. It has been shown that EPNs can distinguish between uninfected and infected hosts, and even Published: xx xx xxxx OPEN
Entomopathogenic nematodes (EPNs) are insect parasites used as biological control agents. Free-li... more 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. Entomopathogenic nematodes (EPNs) are insect-killing parasites used in biological control and are a model system for studying host-parasite interactions. EPNs can infect and kill a host within 48 hours and are commercially available for use in home gardens and industrial agriculture 1, 2. In the EPN life cycle, free-living infective-juveniles (IJs) encounter a host (either uninfected or possibly at an early stage of infection) (Fig. 1A), and then decide whether or not to invade the host. Once an IJ invades a host it releases symbiotic bacteria (Fig. 1B), which proliferate and help to both kill the host and provide a food source for the growing nematodes 3 (Fig. 1C). Steinernema spp. are gonochoristic, requiring a male and female in order to produce offspring 4. Within the host approximately 2–3 generations of nematodes can be produced (Fig. 1D), but eventually resources begin to run out inside the insect cadaver 2. As resources are depleted, the L2 juveniles will associate once more with the bacteria and take an alternative developmental pathway, becoming infective juveniles (IJs) rather than L3 juveniles. These IJs will then emerge and search for a new host to infect 2, 5 (Fig. 1E). In their search for a new host there are two host-seeking strategies–employed by IJs–which represent endpoints of a continuous spectrum. The first is a cruise foraging strategy where the IJ spends the majority of its time actively moving in search of a host 6, 7. The second strategy is an ambush foraging strategy where the IJ employs a sit-and-wait approach, waiting for a potential host to pass close by, allowing the IJ to attach and invade 7, 8. Between these two endpoint foraging strategies there are species of EPNs that have been classified as intermediates 6, 9. These foraging strategies are employed by individuals within a population and it has been shown that even for a species like S. carpocapsae. which is described as an ambush forager, a small proportion of individuals are cruise foragers and have been referred to as " sprinters " 8. Here, we worked with four species of Steinernema: S. carpocapsae, an ambush forager 6, 8 ; S. glaseri, a cruise forager 6, 9 ; and S. riobrave and S. feltiae, which are described as intermediate foragers 6, 9. EPN foraging strategies and the decision of whether or not to infect certain hosts is informed by olfactory and mechanosensory cues. Previous work has shown that volatile odorants emitted by uninfected insects elicit host-seeking behavior in EPN IJs 10–12. IJs rely on chemical cues in the environment to locate, identify, and evaluate their hosts 7. It has been shown that EPNs can distinguish between uninfected and infected hosts, and even Published: xx xx xxxx OPEN
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Papers by Dong-Hwan Choe