Australian entomopathogenic nematodes against the yellow mealworm, Tenebrio molitor: isolate-specific variation in virulence, establishment rate and reproductive potential

The yellow mealworm, Tenebrio molitor (L.) (Coleoptera: Tenebrionidae), is a significant stored-product pest, a valuable insect for animal feed production and a study system for immunology and entomopathogens, including entomopathogenic nematodes (EPNs). However, the efficacy and biocontrol potential of Australian EPN isolates against this host remain unexplored. We evaluated the virulence, establishment rate and reproductive potential of 17 Australian EPN isolates of Heterorhabditis and Steinernema in T. molitor larvae under laboratory conditions. All isolates successfully infected, killed and reproduced within T. molitor larvae, although their performance varied markedly. Heterorhabditis indica Hi.LMBT, Hi.LMI2 and Hi.HRN2 emerged as the most virulent isolates. EPN establishment rate in the host differed strongly among isolates, ranging from 5.8 to 17.2%, with Steinernema feltiae Sf.ECCS and Heterorhabditis marelatus Hm.ENCB showing the greatest establishment rate in the host. Reproductive potential ranged from ∼56,000 to ∼140,000 IJs per larva, with S. feltiae Sf.Y13 and Heterorhabditis zealandica Hz.NAR4 showing the highest reproduction. Multivariate and correlation analyses indicated substantial within-species variation for EPN species represented by multiple isolates, and that virulence, establishment rate and reproductive potential in T. molitor were not correlated with each other among isolates. Our results highlight considerable potential of Australian EPN isolates for mealworm control, while showing that candidate selection should not rely on virulence alone. Instead, effective screening should integrate virulence, establishment rate and reproductive potential to identify promising isolates that warrant further evaluation under realistic stored-product conditions.