INTERACTIONS BETWEEN BEAUVERIA-BASSIANA AND THE ENTOMOGENOUS NEMATODES, STEINERNEMA-FELTIAE AND HETERORHABDITIS-HELIOTHIDIS

The nematodes Steinernema feltiae and Heterorhabditis heliothidis and the fungus Beauveria bassiana possess broad and overlapping host ranges. The impact of B. bassiana and nematodes on host period of lethal infection (PLI) and on nematode and fungus progeny production in a single host was investigated. B. bassiana was applied initially and one species of nematode applied simultaneously or sequentially (1 to 5 days later) to last instar Galleria mellonella larvae. In general, the PLI for larvae exposed to nematodes and B. bassiana simultaneously was shorter than that for larvae exposed to either pathogen alone, or exposed to both sequentially. Even though infection with both pathogens decreased host PLI, B. bassiana and nematodes rarely coproduced progeny in dually infected hosts. In treatments with nematodes alone, or B. bassiana and nematodes applied at the same time or 1 day later, Xenorhabdus, the bacterium mutualistically associated with the nematodes, was observed in host hemolymph 12 hr after the application of the nematodes. Xenorhabdus or nematodes prevented or inhibited the growth of B. bassiana in the insect if nematodes were applied within 24 hr after the application of B. bassiana. B. bassiana was detrimental to the development of S. feltiae and H. heliothidis when applied to the insect more than 48 hr before nematodes. Temperature influenced the outcome of development in dually infected larvae. In early sequential treatments B. bassiana was more likely to develop to the exclusion of nematodes at 15°C, while nematodes were more likely to develop in these treatments at 22° and 30°C. Even though dual infections can result in a decreased PLI compared to singly infected hosts, antagonistic interactions between B. bassiana and entomogenous nematodes in dually infected hosts can adversely affect pathogen development and progeny production. © 1990.