Compatibility of the entomopathogenic nematode, Steinernema carpocapsae, with Bacillus spp. used in the biological control of plant pathogens

Entomopathogenic nematodes in the order Rhabditida are bacteria-carrying nematodes that possess the ability to infect a variety of insects. They have generated interest due to their potential use as biological control agents of insects. Biological control of plant pathogens has also received increasing attention in recent years. Several Bacillus spp. can improve plant growth by suppressing major and minor pathogens and possibly by direct stimulation of plant growth.

The compatibility of entomopathogenic nematodes and Bacilli with biological control activity against plant pathogens, are examined in this research project. The objective of the first experiment was to determine whether bacterial isolates "with biological control activity against plant pathogens would attract or repel an entomopathogenic nematode, Steinemema carpocapsae . A choice test was used with culture medium plugs cut from plates inoculated with Bacillus spp., or bacteria-free nutrient agar plates. Approximately 200 to 400 infective juveniles were released at a point distant from these plugs. Nematodes in the vicinity of the control or treatment plugs were counted at 4 and 8 hours after release. The average percentage of infective juveniles that were attracted to the treatments was 31%, with a range of 20 to 43%. Bacillus isolate BA77 was least attractive to the nematodes and E69 was the most attractive. The nine Bacillus isolates with biological control activity against plant pathogens attracted S. carpocapsae, but only minimally.

The objective of the second experiment was to monitor the development and reproduction of S. carpocapsae on four of the Bacillus isolates tested in the previous iv experiment (BA77, E69, E727, and E61). Steinemema carpocapsae population growth was adversely affected in the presence of BA77, and the other isolates supported minimal nematode development when feeding on the tested bacteria. The results indicate that S. carpocapsae may not be able to develop and reproduce on the tested bacteria.

Entomopathogenic nematodes should not be introduced into soils containing the Bacillus isolate BA77, and to some degree E727. To integrate isolates E69 or E61 with entomopathogenic nematodes, the nematodes should probably be introduced first. Further investigations are necessary before the type of relationship (competition, antagonism, synergism) between entomopathogenic nematodes and the Bacilli examined is determined.