Histopathological and biochemical efficacy of some entomopathogenic nematodes on the greater wax moth, Galleria melonella larvae (Lepidoptera: Pyralidae)

• Penetration rates of four EPN strains on Galleria mellonella larvae were significantly influenced by concentration. • Heterorhabditis bacteriophora showed the highest penetration rates compared to other EPN strains. • Histopathological analysis revealed damage to the cuticle and epidermis at the penetration site. • EPN treatments triggered defense responses in larvae, including hemocyte presence. • EPNs reduced ACP and ALP activities, and increased phenoloxidase activity in treated larvae. The penetration rates of four entomopathogenic nematode (EPN) strains Heterorhabditis bacteriophora (HP88), Steinernema carpocapsae (Sc), Steinernema glaseri (Sg), and Steinernema scapterisci (Ss) were evaluated on last-instar larvae of Galleria mellonella at three concentrations: 20, 50, and 100 infective juveniles (IJ) per larva. Results showed a positive correlation between penetration rate and nematode concentration, with significant differences among strains (P < 0.001). The highest cumulative penetration rates were observed with H. bacteriophora (HP88), ranging from 0.79 ± 0.02 IJ/larva at 20 IJ to 0.98 ± 0.03 IJ/larva at 100 IJ. S. carpocapsae ranged from 0.45 ± 0.03 to 0.83 ± 0.06 IJ/larva, while S. scapterisci had the lowest penetration, from 0.32 ± 0.06 to 0.55 ± 0.03 IJ/larva. Histopathological examination revealed damage to the larvae’s body wall, including disintegration of the cuticular layer, epidermis dissolution, and nematode tunnels in the body cavity. Defense responses, such as hemocyte presence, were observed. Biochemical analysis showed increased acid phosphatase (ACP) after most treatments and alkaline phosphatase (ALP) activities, with acetylcholinesterase (AChE) varying among treatments. Phenoloxidase activity was elevated in all treated larvae. These findings suggest that EPNs, especially H. bacteriophora, are effective against G. mellonella and may be promising biological control agents.