Desiccation tolerance of dauers of entomopathogenic nematodes of the genus Steinernema

For transport of entomopathogenic nematodes to the user, developmentally arrested dauer juveniles (DJ) are mixed with inert carriers at high density. If quiescence is not induced, DJ will quickly lose energy reserves and die. To induce quiescence DJ can be moderately desiccated. This study investigated the desiccation tolerance by measurement of water activity (-value) tolerated by 50% of populations (WA50) of different Steinernema species and strains. DJ were tested with or without prior adaptation to desiccation stress. Stress conditions were produced by exposure to various concentrations of poly(ethylene glycol) 600. Significant differences in desiccation tolerance were recorded between strains and species, but, except for Steinernema abbasi, not within strains of one species. Without adaptation to stress conditions, the most tolerant species was S. carpocapsae (WA50 = 0.836) followed by S. abbasi (0.86). Adaption to stress by exposure to an -value of 0.95 for 48 h increased tolerance to 0.68 and 0.66, respectively. The least tolerant species were S. kraussei, S. glaseri and S. ethiopiense. Tolerance recorded would allow storage at a water activity that would inhibit growth of bacteria but not of fungi. Analysis of water activity tolerated by only 10% of the population indicated potential for genetic improvement by selective breeding for S. carpocapsae, S. abbasi and S. arenarium to reach water activity levels that would also inhibit fungal growth.