Influence of insect larvae and seedling roots on the host-finding ability of Steinernema feltiae (Nematoda: Steinernematidae)

The ability of nematode foragers to locate appropriate insect hosts is essential to their performance as successful biological control agents. We investigated the host-finding ability and chemotaxis of Steinernema feltiae in the presence of cues from Galleria mellonella larvae and tomato and radish seedling roots, given individually and in combination, over 120 min. In agar arena tests, infective juveniles of S. feltiae responded positively to unsterilized and sterilized larvae and tomato seedling roots and negatively to unsterilized radish seedling roots, This negative response changed following surface sterilization of these seeds. The response of the infective juveniles to a combination of larva and seedling roots depended on the nature of the individual cues and their proximity to each other. For example, the response of the nematodes to a combination of cues from a sterilized larva and an unsterilized tomato seedling root placed adjacent to each other was intermediate to the separate responses to cues from a sterilized larva and an unsterilized tomato seedling root given individually. However, the response of the nematodes to a combination of adjacent cues from a sterilized larva and an unsterilized radish seedling root was not significantly different from that to cues from an unsterilized radish seedling root given individually, When the cues from the larva and seedling roots were separated by a distance, the response of the nematodes favored the larva. However, this positive effect was lessened when the larva was surface sterilized as compared with the response to the unsterilized larva, The altered responses of the infective juveniles to target cues following surface sterilization suggest that cues from the larval cuticle and seedling roots, such as those associated with their surface microflora, may significantly influence their host-finding ability. The use of entomopathogenic nematodes as biological control agents under field applications can be improved by careful consideration of the application protocols and by the recognition that chemical alterations of the soil rhizosphere may influence their host-finding ability. (C) 2000 Academic Press.