Interaction Between The Biocontrol Agents; Entomopathogenic Nematodes, Serratia Marcescens, and Beauveria Bassiana Isolated From Palestine

Biological control agents, such as nematodes, bacteria, and tungi have been successfully used as alternatives of chemical pesticides. Their use involves in some cases a combination of two or more agents. The combined agents may interact with one another during their application either outside or inside the target insect leading to either increased or decreased efficiency of the biological control process. The nature of such interactions and their effect on the efficacy of each biocontrol agent has not been given an adequate attention yet. In this work. we isolated, identified, and characterized a new isolate of entomopathogenic bacterium S. marcescens. We studied the effect of the new isolate and another entomopathogenic fungal isolate Beauveria bassiana on the invasion and recovery of the insect-pathogenic nematode Heterorhabditis, strain Bethlehem 11. Both of the fungal isolates and nematode strain were isolated at the UNESCO Biotechnology Center at Bethlehem University. The insect used in this study was last instar larvae of the wax moth Galleria mellonella. Experiments aiming at studying in-vitro interactions showed that the survival of the nematode Infective juveniles (IJs) stage is not affected by incubation in S. marcescens or B.bassiana cultures for 48 hours at continuous shaking. However, the survival of the Juvenile 4stage (J4) was substantially reduce by both pathogens. Infection of G. mellonella larvave for 24 hours with S. marcescens larvae or B.bassiana before nematode infection slightly decreased insect mortality, and dramatically reduced the invasion of ncinatode l.ls into the insect. That is; when the insect larvae were infected with nematode l.ls alone (control), the penetration reached 7.37% . However, when the Galleria larvae were preinfected with S.marcescens or B.bassiana for 24 hours the penetration was restricted to 1.16% and l.72% respectively. Similar effect of preinfecting the insect was obtained on the recovery of nematode infective Juveniles into adults. The recovery of IJs in larvae preinfected with either S. marcescens or B.bassiana was 0.61% and 1.2% respectively, compared to 7.0% recovery in the control. Also, the total production of nematodes was suppressed by preinfection for 24 hours with S. marcescens or B. bassiana. While preinfection with the first pathogen totally hindered nematode production, preinfection with the second pathogen restricted nematode production to 2.l x 10³ individuals/larvae, compared to 106x10³ individuals/larvae in control. Moreover, preinfecting larvae with the fungal pathogen tor periods of 48, 72, and 96 hours totally inhibited nematode production. These findings should be taken in consideration when we evaluate the efficacy and sustainability of EPNs biocontrol agent when applied simultaneously with S. marcescens or B. bassiana or in fields previously treated with these agents.