Cell-free supernatants from entomopathogenic bacteria as a potential alternative for managing Tetranychus urticae in tomato.

Tetranychus urticae is a cosmopolitan pest that causes significant yield losses in tomato crops. Entomopathogenic bacteria of the genera Photorhabdus and Xenorhabdus produce diverse secondary metabolites with acaricidal properties. This study aimed to evaluate the acaricidal and deterrent effects of cell-free supernatants (CFSs) of Photorhabdus luminescens, Xenorhabdus szentirmaii and Xenorhabdus doucetiae against T. urticae in tomato. In Petri dishes, each CFS was sprayed onto leaflets infested with females or eggs. The deterrent activity was assessed through dual-choice bioassays. Furthermore, the acaricidal effect of these bacterial metabolites was validated under field conditions over two growing seasons. After 72 h, CFSs of P. luminescens, X. szentirmaii and X. doucetiae caused mortality rates of 80.7%, 93.5% and 85.0% in laboratory bioassays, respectively. Furthermore, egg viability was significantly reduced. In choice bioassays, the Repellency, Leaf Damage and Oviposition Indices demonstrated greater pest activity on untreated plants than on those treated with bacterial compounds. In field trials, X. szentirmaii supernatant reached a 65.4% mortality rate and significantly reduced leaf damage. Secondary metabolites produced by P. luminescens, X. szentirmaii and X. doucetiae exhibited both acaricidal and deterrent activity against T. urticae, representing a promising tool for the integrated pest management in tomato production.