Identification and biocontrol potential of Oscheius nematodes and their associated bacteria from Florida tropical fruit orchards against selected pests in laboratory conditions

Some species of Oscheius nematodes (Rhabditidae) are insect parasites and exhibit potential as biological control agents against insect pests. These nematodes are associated with endosymbiotic bacteria with insecticidal properties. Using Galleria mellonella as bait to isolate nematodes, three Oscheius species, O. tipulae , O. carolinensis and O. myriophilus , were identified from soil samples collected from Florida fruit tree orchards. 16S marker analysis revealed six bacterial strains isolated from the nematode’s internal tissues, including Providencia rettgeri , Proteus mirabilis , Clostridium senegalense and Brucella anthropic . We cultured each Oscheius species using the specific bacterial strain originally isolated from that nematode. We investigated the parasitic efficacy of these nematodes and their associated bacteria against three key pests of fruit trees, including tea shot hole borer ( Euwallacea perbrevis ), two-spotted spider mite ( Tetranychus urticae ) and a polyphagous mealybug ( Dysmicoccus grassii ) under in vitro conditions. Results showed that O. myriophilus and O. tipulae caused over 50% mortality in tea shot hole borer after 72 h of exposure at a concentration of 50 infective juveniles (IJ). Notably, O. tipulae achieved a 93% mortality rate against mealybug, while O. myriophilus caused 100% mortality in spider mite within the same timeframe. Oscheius -associated bacterial treatments resulted in significantly higher mortality than non-treated controls. Mortality reached 100% in spider mite within 48-72 h for all bacterial isolates, while mealybug was highly susceptible (90-100% after 72 h), particularly to Providencia rettgeri isolate 3 and Clostridium senegalense . The tea shot hole borer was less affected, with moderate mortality (45-67% after 72 h); P. rettgeri isolate 2 (66.8%) and B. anthropi (58.3%) were the most effective. Overall, P. rettgeri isolate 3 demonstrated the strongest pathogenicity across all pest hosts. Further research is required to evaluate the effectiveness of these nematodes and their associated bacteria, with a view to identifying the most promising bio-pesticide combination for controlling insect and mite pests.