Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2002
Publication Date: 2/1/2003
Citation: Fife, J.P., Derksen, R.C., Ozkan, H.E., Grewal, P.S. 2003. Effects of Pressure Differentials on the Viability and Infectivity of Entomopathogenic Nematodes. Biological Control. 27:65-71. Interpretive Summary: Laboratory research has shown that Entomopathogenic nematodes (EPNs) can be effective in biological management of some insect pests. Field results have not been as positive. To treat large fields, farmers rely on traditional equipment to deliver spray solutions containing EPNs. Delivery of EPNs in this traditional manner can create conditions, such as large pressure differentials, which may damage or even kill the EPNs. In this study, EPN suspensions were evaluated for their ability to withstand pressure differentials ranging from 1283 to 10,690 kPa. Species evaluated included Steinernema carpocapsae, Heterorhabditis bacteriophora and Heterorhabditis megidis. Pressure differential tests were conducted by placing samples in a French cell press and releasing a small volume after pressure within the chamber had been achieved. The numbers of living and damaged EPNs following treatment were used to quantify differences observed between test conditions and species. Bioassay techniques were used to assess the relative viability and relative infectivity of EPNs following treatment. Approximately 85% of H. megidis survived at pressure differentials less than or equal to 1283 kPa. Similar viability levels were observed at pressures of 2138 kPa or less for S. carpocapsae and H. bacteriophora. Relative viability decreased rapidly at higher pressure differentials. Tests indicate that there are differences in how different EPN species may be able to withstand pressure changes in a traditional sprayer delivery system. Operating guidelines developed from this research will give growers more confidence to use EPNs as biological control alternatives and reduce dependence on traditional insecticides.
Technical Abstract: Entomopathogenic nematodes (EPNs) have been found to control soil-dwelling insect pests. Improvements in production and formulation technology have made access to and use of insecticidial EPNs more feasible for commercial use. However, lack of knowledge about how to handle and deliver EPNs may be limiting their use in the commercial marketplace. Tests were conducted to determine the extent of damage that may occur due to the effects of a pressure differential that may develop in traditional spray delivery systems. Separate suspensions of Steinernema carpocapsae, Heterorhabditis bacteriophora and Heterorhabditis megidis were placed in a French pressure cell and subjected to pressure differentials ranging from 1283 to 10,690 kPa. Damage to the EPNs was assessed by quanitifying the number of living and damaged EPNs. In addition, bioassay techniques were used to assess the relative viability and relative infectivity of EPNs following treatment. Increasing pressure differential decreased the relative viability but it was species dependent. The relative viability of fresh and aged (three weeks) EPNs were not significantly different. S. carpocapsae generally had greater viability than Heterorhabditis spp. Relative viability remained greater than 85% for pressure differentials less than or equal to 1283 kPa for H. megidis and 2138 kPa for S. carpocapsae and H. bacteriophora. Relative viability decreased rapidly at higher pressure differentials. These tests not only point out differences in how different EPN species may survive delivery through a commercial spray system but they also provide guidance on defining operating conditions that will minimize loss of EPN viability.