Biocontrol Mechanisms of a Chinese Heterorhabditis indica Strain Against Tuta absoluta: Virulence Assay and Time-Course Transcriptomics of Host Immune Responses

The South American tomato pinworm, <i>Tuta absoluta</i>, is a devastating invasive pest that threatens global tomato production, while entomopathogenic nematodes (EPNs) represent promising biocontrol agents. Because a detailed understanding of the molecular basis of the insect immune response is crucial for uncovering how hosts detect and counteract nematode infection, such knowledge may reveal weaknesses exploitable for improved control strategies. However, the molecular mechanisms governing the immune interaction between this pest and EPNs remain poorly understood This study investigated the biocontrol potential of a native Chinese EPN strain, <i>Heterorhabditis indica</i> CQ7-2, against <i>T. absoluta</i> and delineated the host's molecular immune responses via a time-course transcriptomic analysis. Bioassays revealed that <i>H. indica</i> CQ7-2 LC₅₀ was 1.35 IJs per larva. Comparative transcriptome profiling of larvae revealed that the EPN infection was associated with transcriptional patterns consistent with immunosuppression. Key genes involved in humoral and cellular immunity were significantly suppressed during the early and middle infection stages. Although a widespread upregulation of immune genes occurred after 18 h post-infection (hpi), it was insufficient to prevent host mortality. These findings demonstrate that the virulence of <i>H. indica</i> CQ7-2 is underpinned by associated with modulation of key immune pathways, leading to an ineffective defense response. This work provides deep insights into the molecular arms race between an invasive pest and a native EPN, supporting CQ7-2 as a promising biocontrol agent and providing a framework for understanding host-EPN interactions.