Threshold Concentrations of Nucleopolyhedrovirus in Soil to Initiate Infections in <Emphasis Type="Italic">Heliothis virescens</Emphasis> on Cotton Plants |
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Authors: | James R Fuxa |
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Institution: | (1) Department of Entomology, Louisiana State University, 404 Life Sciences Bldg., Baton Rouge, LA 70803, USA |
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Abstract: | The purpose of the research was to determine threshold concentrations of nucleopolyhedrovirus (NPV) in soil for abiotic transport
to cotton plants in the field and under conducive and nonconducive conditions in the greenhouse. Under the assumption that
2% mortality would suffice to initiate foci of infection in Heliothis virescens larvae on the plants, thresholds ranged from 25 to 2,311 viral occlusion bodies (OB)/g soil in the greenhouse. Thresholds
generally were smaller for rain on sandy soil and wind on clay soil than for wind on sand or rain on clay. Thresholds generally
increased with height of the plant above the soil surface. In field plots, percentage mortality in bioassays of cotton plants
was greatest on leaves versus other tissues, and mortality increased with soil dosage and decreased with plant height and
over time. Season-long soil-NPV-transport thresholds for 2% plant-bioassay mortality of larvae ranged from 1 OB/g to 7.4 × 108 OB/g soil based on the amounts of NPV applied to the soil at planting time, and they ranged from 8 OB/g to 1.2 × 105 OB/g soil based on bioassays of soil samples collected concurrently with plant samples throughout the growing season. These
results should contribute to NPV epizootiology, biological control, and risk assessment through better understanding of viral
soil-to-plant transport. |
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