Genotyping, phenotyping and application of entomopathogenic nematodes (Heterorhabditidae and Steinernematidae) for biological control of Psylliodes chrysocephala in oilseed rape

One major threat to rapeseed cultivation in Europe is the cabbage stem flea beetle (CSFB). Pyrethroids are used to control the CSFB, but their continuous use has led to resistance issues, necessitating alternative management solutions.     
Entomopathogenic nematodes (EPNs) have shown effectiveness in controlling various insect pests and could serve as an environmentally friendly alternative for CSFB management. In laboratory and field conditions, different species and strains of EPNs were tested for their susceptibility against CSFB. Among the developmental stages of CSFB, the third larval instar was found to be the most susceptible to Heterorhabditis bacteriophora. Further investigations were conducted to identify the most suitable EPNs species to control CSFB larvae at lower temperatures. Steinernema feltiae proved to be the most efficient species, achieving a maximum reduction of 80% under laboratory conditions.
Despite promising results in controlled conditions, the field performance of EPNs varied, with a maximum reduction of only 34%. This lower efficacy may be attributed to abiotic stresses EPNs face after application, such as UV radiation, low humidity, and colder temperatures. Attempts were made to improve the low-temperature virulence of H. bacteriophora, resulting in the identification of the most virulent strain, SDT1-IL1, which achieved a 45% reduction in the field.    
Genotyping by sequencing (GBS) was used to analyse a collection of wild-type EPN isolates, discovering over 13,000 single nucleotide polymorphisms (SNPs). Association analyses identified SNPs associated with H. bacteriophora low-temperature virulence and tolerance to abiotic stresses. These findings provide valuable information for future breeding and selection approaches to enhance the biocontrol potential of H. bacteriophora using its genetic diversity.


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