Ecological characterization of Steinernema rarum

Entomopathogenic nematodes are used for inundative biological control of insect pests but also have potential for use in augmentative and/or inoculative biological control. Numerous new species are being described but generally, little information is provided on their ecology. Moreover, many species have been described previously without subsequent ecological information. This paper presents a number of simple experiments examining a nematode's physiological host range, host-foraging behavior, thermal activity range, and soil moisture activity range that provides the basic information necessary for further studies of a new species as a biological control agent. We suggest that any taxonomic description of new species should be combined with such an ecological study. This kind of information should also be generated for species in which no ecological studies have been done. In our study, we found that the entomopathogenic nematode Steinernema rarum which was described in 1986 infected a wide range of arthropod species under laboratory conditions but appeared to be best adapted to lepidopteran larvae as hosts. It used an intermediate foraging strategy infecting both mobile hosts on the soil surface and sedentary hosts below the soil surface efficiently. The range of soil moisture at which S. rarum was effective suggested an adaptation to the fluctuating soil moisture in the upper soil layers. Its temperature optimum of 25 degrees C corresponded well to the warm temperate climate of its area of origin in Argentina. The optimal storage temperature was around 15 degrees C. Our study suggests that S. rarum is well adapted to lepidopteran hosts with larvae spending part of their live on the soil surface and/or that pupate in the soil.