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Impact of Soil Moisture on the Reactivation Capacity of Entomopathogenic Nematodes 1999

Project Leaders: Jennifer A. Grant and Michael G. Villani, Department of Entomology, NYSAES, Geneva

Abstract:

Entomopathogenic nematodes are well adapted to infect larval insect pests living in soil, and have the potential to be important biological control agents in a variety of ornamental and crop production systems. Our studies simulated the natural variations in soil moisture conditions that that occur in the field and explore their effects. The project has broad implications for managing soil dwelling insects with entomopathogenic nematodes in turf, ornamental and crop production systems.

We have been studying the effects of soil moisture on entomopathogenic nematode infectivity under simulated field conditions in the laboratory. Previously we demonstrated the ability of nematodes to be reactivated to infect insects after being held under unfavorable (low soil moisture) conditions. In 1999, we completed a long-term project that evaluated this reactivation capacity over an 18-month period. Two nematode isolates tested (Heterorhabditis bacteriophora Oswego strain and Tuscarora strain) were not active at low soil moistures (below the wilting point of plants), but were reactivated by the addition of water (rehydration) to cause insect mortality levels of 98-100%, throughout the 18 months.

We also investigated the soil moisture contents at which 3 entomopathogenic nematode isolates were deactivated and reactivated. In the deactivation study, we transferred active entomopathogenic nematodes inhabiting high moisture soil to a range of lower moisture soils to determine the moistures at which each nematode species no longer infected insects. In the reactivation study, we determined the soil moisture level to which 3 nematode isolates had to be raised in order to cause insect mortality, after the nematodes had been exposed to low soil moisture conditions.

Practical implications for the use of entomopathogenic nematodes in the field and possible applications in nematode production and storage are discussed.