Effects of pressure differentials on the viability and infectivity of entomopathogenic nematodes

Abstract

During passage through the different components of a spray application system, a nematode suspension will undergo pressure changes. The extent of damage to three species of entomopathogenic nematodes (EPNs) (Steinernema carpocapsae, Heterorhabditis bacteriophora, and Heterorhabditis megidis) in suspension due to the effects of a pressure differential was studied. A French pressure cell and press was used to subject the newly emerged EPN suspensions to a series of pressure differentials ranging from 1283 kPa (186 psi) to 10,690 kPa (1550 psi). Aged suspensions (3 weeks) of H. bacteriophora and H. megidis were also evaluated. Damage was quantified by counting living and dead (whole and pieces) EPNs and by bioassay techniques. As the pressure differential increased, the relative viability of the EPNs decreased. Entomopathogenic nematodes that survived the pressure differential were, in general, able to survive for at least 1 week and maintain infectivity to Galleria mellonella at rates equivalent to EPNs that had not been pressure treated. In general, the relative viabilities of fresh and aged EPNs were equivalent after pressure differential treatments. The relative viability of the treated EPNs remained above 85% for pressure differentials less than or equal to 1283 kPa for H. megidis and 2138 kPa (310 psi) for S. carpocapsae and H. bacteriophora, but decreased rapidly for higher pressure differentials. Greater reductions in relative viability were experienced by Heterorhabditis spp. than S. carpocapsae, indicating that nematode species is an important factor to consider when defining spray operating conditions. We recommend a maximum operating pressure of 1380 kPa (200 psi) for H. megidis and 2000 kPa (290 psi) for S. carpocapsae and H. bacteriophora.