Miticidal activity of Photorhabdus luminescens for controlling two spider mites, Tetranychus urticae and Tetranychus kanzawai, in Carica papaya

Photorhabdus luminescens (Enterobacterales: Morganellaceae) is a symbiotic bacterium associated with the entomopathogenic nematode Heterorhabditis brevicaudis (Rhabditida: Heterorhabditidae). In this study, the mite-killing activity of the P. luminescens strain 0805-P2R (Pl 0805-P2R) was tested against two species of spider mites, the two-spotted spider mite (TSSM), Tetranychus urticae (Trombidiformes: Tetranychidae), and the Kanzawa spider mite (KSM), Tetranychus kanzawai (Trombidiformes: Tetranychidae). The results showed mortality rates of 78.9 and 65.6% for TSSM and KSM, respectively, at seven days post-inoculation (dp.i) with Pl 0805-P2R bacterial cultures. The major pathological effect of Pl 0805-P2R on TSSM and KSM was identified through the tissue looseness found in multiple tissues, demonstrating the pathological effect of Pl 0805-P2R in both species of spider mites. Porin protein was identified as a major protein in the Pl 0805-P2R culture, suggesting a possible effect on spider mites. Field trials of Pl 0805-P2R bacterial suspension concentrate against spider mites in three papaya fields showed that 1/125-fold Pl 0805-P2R treatment had the highest control rates. However, the control rates of 250-fold Pl 0805-P2R were slightly lower than those of 125-fold Pl 0805-P2R without a significant difference. The control rates of 500-fold Pl 0805-P2R and tebufenpyrad 10% wettable powder (WP) treatments were similar. Therefore, 500-fold Pl 0805-P2R could effectively reduce the leaf pest incidences of papaya, and 250-fold Pl 0805-P2R is a promising candidate for field application to control spider mite damage. In conclusion, P. luminescens 0805-P2R is a potent microbial pesticide with bioactivity against insect and mite pests. These findings highlight the potential of P. luminescens as a sustainable and effective control agent in agricultural systems.