The Impact of Cu Ion, Two Novel Schiff Base Ligands and their Copper (II) Complexes on the Biological Activity of the Entomopathogenic Nematodes

Background: Many biotic and abiotic soil components affect entomopathogenic nematode (EPN's) activity, infectivity, host finding ability and the rate of reproduction. Since, copper being an essential element, could be toxic at its elevated concentrations in soils, the study was aimed therefore to evaluate the biological effect of Cu ion and safer alternatives, i.e. Schiff base ligands and their copper complexes on EPN's juveniles. Methods: Two novel Schiff base ligands of 2-amino 3- cyano 1, 5 diphenylpyrrole and salicylaldehyde (HL1) or 2- hydroxy11-naphthylaldehyde (HL2) and their copper (II) complexes were synthesized and characterized. Their effect on the infectivity and reproduction potential of the Egyptian entomopathogenic nematodes (EPN's) Heterorhabditis bacteriophora and the imported Steinernema carpocapsae were tested at 1.5 mg/l and 11.0 mg/l. Results: The infectivity of Cu (II) ion treated H. bacteriophora and S. carpocapsae juveniles (at low and high concentrations) generally reduced, (33.30 % and 11.50%) and (88% and 75%) respectively, as compared with that of control. The infectivity of the ligands and complexes treated H. bacteriophora and S. carpocapsae juveniles at both concentrations matches that of the non-treated nematodes (100%). The reproduction of H. bacteriophora and S. carpocapsae decreased with increasing concentrations of copper (II), the ligands (HL1, HL2) and complexes (C1, C2) except in HL1 for H. bacteriophora and C2 for S. carpocapsae. The difference in reproduction potentials of the tested EPN's due to the dose variations of the agents was observed to be insignificant. Conclusions: Although the pollution of soil with copper (II) ions affects nematode infectivity and reproduction potential, Schiff base ligands and their copper complexes were found to be less harmful and hence the latter could be used in combination with fertilizers to overcome one of the abiotic factors enhancing the field efficacy of EPN.