Abstract
Entomopathogenic nematodes (EPNs) are potent insect parasites and have been used for pest control in agriculture. Despite the complexity of the EPN infection process, hosts are typically killed within 5 days of initial infection. When free-living infective juveniles (IJs) infect a host, they release their bacterial symbiont, secrete toxic products, and undergo notable morphological changes. Collectively, this process is referred to as “activation” and represents the point in a nematode’s life cycle when it becomes actively parasitic. The effect of different host tissues and IJ age on activation, and how activation itself is related to virulence, are not well understood. Here, we employed a recently developed bioassay, which quantifies IJ activation, as a tool to address these matters. Appreciating that activation is a key part of the EPN infection process, we hypothesized that activation would positively correlate to virulence. Using the EPNs Steinernema carpocapsae and S. feltiae we found that EPN activation is host-specific and influenced by infective juvenile age. Additionally, our data suggest that activation has a context-dependent influence on virulence and could be predictive of virulence in some cases such as when IJ activation is especially low.
Highlights
Entomopathogenic nematodes (EPNs) are a guild of insect-parasitic nematodes that kill their hosts rapidly and utilize pathogenic bacteria to facilitate their parasitic lifestyle [1,2]
We found that Infective juveniles (IJs) activation is species-specific and host-specific (Figure 1)
Whereas S. carpocapsae demonstrated highest activation when exposed to waxworm homogenate and lowest activation when exposed to house cricket homogenate (Figure 1)
Summary
Entomopathogenic nematodes (EPNs) are a guild of insect-parasitic nematodes that kill their hosts rapidly and utilize pathogenic bacteria to facilitate their parasitic lifestyle [1,2]. EPNs have applied uses such as the biological control of pests [3,4], but they are useful models for studying a wide variety of biology including bacterial-host symbiosis [5,6], and as potential models for vertebrate parasites [7]. We used the same technique to understand the activation dynamics of S. carpocapsae and S. feltiae IJs when exposed to the tissue of a variety of potential insect hosts. We assessed the predictive value of IJ activation by conducting virulence assays on sand crickets, superworms, and soldier fly larvae. It is not yet understood what triggers
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