Factors affecting the fitness of an entomopathogenic nematode (Heterorhabditis bacteriophora SUP strain) for use in biocontrol in a horticultural area of Argentina

The optimum conditions for storage, infectivity and multiplication of the nematode Heterorhabditis bacteriophora SUP strain, isolated from horticultural soils in Argentina, were determined for later use in biocontrol. This strain was able to kill Tenebrio molitor larvae (over 90%) at 16 and 25 degrees C, after 7 and 4 days, respectively, with mortality being significantly higher at 25 degrees C. No infectivity was reported at 4 and 11 degrees C. Higher concentrations (over 150 infective juveniles (IJ) insect(-1)) produced higher percentages of mortality. However, increasing inoculum density reduced offspring production and increased emergence time. Storage density between 2500 and 7500 IJ ml(-1) had no effect on survival of IJ. Survival of IJ maintained at 4 and 16 degrees C was around 80% after 4 weeks storage and 30% after 32 weeks. However, at 25 degrees C, a 60% IJ survival was observed at 4 weeks, decreasing to around 10% after 16 weeks and with no survival at 24 weeks. An overall significant decrease in virulence was observed after 90 and 120 days of storage but this was more pronounced at a storage temperature of 4 degrees C than at 16 and 25 degrees C. IJ stored at 4 degrees C had reduced virulence after 90 and 120 days, but not after 60 days. This study provides useful information about some fundamental environmental conditions influencing important nematode traits of the species H. bacteriophora.