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

## TL;DR

A Chinese strain of Heterorhabditis indica effectively controls the tomato pinworm by suppressing its immune system, showing promise as a sustainable biocontrol method.

## Contribution

The study reveals the molecular mechanisms by which H. indica CQ7-2 suppresses Tuta absoluta's immune response.

## Key findings

- H. indica CQ7-2 has a low median lethal concentration of 1.35 infective juveniles per larva.
- Key immune genes in T. absoluta are suppressed during early and middle stages of infection.
- Despite immune gene upregulation after 18 hours, the host's defense is insufficient to prevent mortality.

## Abstract

The invasive South American tomato pinworm, Tuta absoluta, is a major threat to tomato crops worldwide. As conventional control methods face challenges, there is a growing need for sustainable alternatives. We isolated a native strain of entomopathogenic nematode, Heterorhabditis indica CQ7-2, from local soils and evaluated its potential. Laboratory bioassays demonstrated that this strain is effective at infecting and killing the pest larvae, with a median lethal concentration of only 1.35 infective juvenile nematodes per larva. Further time-course transcriptomic analysis revealed that the nematode impairs the insect’s immune system, preventing it from mounting a successful defense. This work demonstrates the pathogenicity of H. indica CQ7-2 and its association with host immune suppression, supporting its potential as a biocontrol agent for further development.

The South American tomato pinworm, Tuta absoluta, 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, Heterorhabditis indica CQ7-2, against T. absoluta and delineated the host’s molecular immune responses via a time-course transcriptomic analysis. Bioassays revealed that H. indica 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 H. indica 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.