Effects of soil type on virulence and persistence of entomopathogenic nematodes in relation to control of Diaprepes abbreviatus (Coleoptera : Curculionidae)

The Diaprepes root weevil Diaprepes abbreviatus (L.) is a major pest of cit rus, ornamentals, and vegetables in Florida and the Caribbean. Entomopathog enic nematodes can provide substantial control of the root feeding larvae, hut their efficacy can be affected by soil type. Our objective was to deter mine the effects of three soil types on the control of D. abbreviatus with Steinernema riobrave (Cabanillas Poinar & Raulston) and Heterorhabditis bac teriophora Poinar. In the laboratory we measured nematode virulence and per sistence in a Marl, Ridge (entisol), and Flatwoods (spodosol) soil. The Mar l soil contains a high silt and clay content (80 and 15%, respectively), wh ereas the other soils are >93% sand and typical soils of citrus production in Florida. The virulence of S. riobrave was greater than H. bacteriophora in all soils. Both nematode species exhibited greater virulence and persist ence in Marl soil compared with sandy soils. Nematode virulence was greater in the spodosol than in the entisol soil. Oxygen levels (in the cups) were not significantly different among the soils. Further research is required to determine the cause of these trends and the applicability of these findi ngs under different water tensions and under field conditions.