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Moisture Effects on Entomogenous Nematodes 1997

Project Leaders: Jennifer A. Grant and Michael G. Villani

Objectives:

1. Determine the survival, infectivity, and persistence of two species of entomogenous nematodes-Steinernema glaseri (SG) and Heterorhabditis bacteriophora (Oswego strain) (HB)-under varying soil moisture levels in the laboratory.

2. Determine the infectivity and persistence of entomogenous nematodes in the field, under soil conditions manipulated to vary in moisture levels.

Results:

Objective 1: In the first week insect mortality was very high (80-100%) in all but the driest (6% soil) nematode treatments. Mortality declined quickly in the drier soils over the first four weeks in treatments with both species. Storage temperature had minimal effect on insect mortality. After rehydration, infectivity rebounded to nearly 100% in all but one of the treatments (6% soil with SG). Over the following 14 weeks infectivity declined in all treatments, with HB in higher moisture content soils and having been stored in cooler conditions remaining infective the longest.

Objective 2: HB nematodes were applied to silt loam, sandy loam, and sand soil plots with 6, 9, 12, and 15% moisture content. Waxmoth larvae were also buried in the plots. Half the plots were maintained with high irrigation levels and half with low levels, based on 100% and 65% evapotranspiration, respectively. Soil collected from the plots one day after nematode application showed high mortality of waxmoth larvae (75-90%) in all but the low-irrigation sand plots. At eight days, mortality dropped to <35% in all treatments.