TRIPLE-IJ and SHIFT as a coupled framework for characterising entomopathogenic nematode performance under abiotic stress

Christopher Tobe Okolo

Entomopathogenic nematodes (EPNs) of the families Steinernematidae and Heterorhabditidae are widely recognised as promising biological control agents, yet the translation of laboratory-demonstrated virulence into consistent field-scale efficacy remains an unresolved challenge. A central reason for this gap is the fragmented way EPN performance is conventionally characterised: infectivity and reproductive output are measured as isolated endpoints, and the ecological fitness of infective juveniles (IJs) following cadaver emergence is rarely integrated into the same analytical framework. This paper proposes two conceptually linked frameworks to address this limitation. TRIPLE-IJ (Temperature Response in Infectivity and Progeny Leading to EPN-IJ dynamics) provides a structured, eight-parameter approach to characterising the dual effects of temperature on EPN performance, separating the infectivity phase (time to death, larval mortality, infection intensity, and proportion of larvae producing IJs) from the reproductive phase (latency to first emergence, emergence duration, IJ yield, and cadaver productivity). SHIFT (Stress Hurdles and IJ Foraging Traits) organises post-emergence ecological fitness across three major abiotic stress categories, namely desiccation, hypoxia, and oxidative stress, in relation to the foraging strategies governing host-seeking capacity. Integrated as a sequential two-gate performance filter, the frameworks generate four biologically meaningful isolate archetypes that can guide screening, selection, and deployment decisions in biocontrol programmes. Both frameworks were derived retrospectively from empirical work on indigenous Nigerian EPN isolates evaluated against Spodoptera frugiperda but are proposed as broadly applicable tools for EPN characterisation across host systems and agroecological contexts. Their adoption as a minimum reporting standard would improve cross-study comparability and strengthen the evidence base for EPN deployment in tropical and subtropical biocontrol programmes, with particular relevance for sub-Saharan Africa where indigenous isolate screening is expanding rapidly.