HOST MATTER: Parasite infection drives chemical reconfiguration of decomposing host and shapes insect behavioral responses.

1. Host-parasite interactions shape ecosystems by driving species dynamics, yet their influence is typically considered in terms of host mortality rather than the chemical environments generated during infection and decomposition.
2. Here, we show that parasitic infection actively reconfigures the chemical phenotype of decomposing hosts, reshaping ecological interactions through volatile-mediated signaling. Using soil-dwelling parasites -entomopathogenic nematodes (EPNs) and their symbiotic bacteria- as a model system, we integrate behavioral assays, comprehensive volatolomic characterization, and CO2 quantification across three insect orders and two EPN species over four post-mortem intervals.
3. We demonstrate that infection generates a distinct and conserved volatile signature dominated by carboxylic acids, sulfur-containing compounds, and unsaturated hydrocarbons, accompanied by elevated CO2 emissions.
4. These infection-derived blends elicit contrasting behavioral responses: they repel non-natural hosts while consistently attracting natural hosts, indicating that infected cadavers function as chemically structured information hubs. In contrast, frozen-killed insects exhibit fermentation-type profiles, and bacteria-only treatments produce simplified alkane-dominated blends, demonstrating that the full chemical phenotype emerges from the nematode-bacteria complex.
5. Our findings reveal parasitic infection as a process that reorganizes decomposition chemistry with measurable behavioral consequences, uncovering a previously underappreciated mechanism by which parasites structure soil food webs and