Biological control of Tetranychus urticae in watermelon using two predatory mites and spatial distribution patterns of Tetranychus urticae in commercial watermelon fields
Date
2023
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Publisher
University of Delaware
Abstract
Watermelon is a major specialty produce crop grown on the Delmarva Peninsula. The Two-Spotted Spider Mite (Tetranychus urticae) (TSSM) is an important pest that feeds on leaves and affects the plant’s ability to photosynthesize. Current management relies heavily on miticide applications, which runs the risk of local mite populations developing resistance. Mite populations were collected from several fields in 2020 and 2021 to evaluate whether susceptibility differences were evident among populations to abamectin, fenpyroximate, and spiromesifin. The contact bioassays suggested that all tested miticides should be very effective even at low doses. If this were to change in the future, integrating additional management strategies for mite management would be necessary. Implementation of biological control agents and strategies may help to reduce the risk of resistance. Understanding mite movement in fields can also aid in making targeted applications of miticides or biological control agents. Two predatory mite species (Phytoseiulus persimilis and Neoseiulus fallacis) (Acari: Phytoseiidae) were tested to determine if one was more efficient than the other and to determine how insecticides might affect predators and TSSM populations. There were no clear differences among predators in terms of efficacy, but in 2021, plots with predators had greater yield than plots without. Predatory mite populations were reduced due to infiltration of other predators and duration of establishment. Spatial mapping of spider mite populations in fields indicated that some fields may have been infested by spider mites early, possibly from greenhouses. Most fields were infested from weedy edges. Maps created for each field indicated that the edges of fields would require monitoring and applications of biological or chemical treatment to prevent spider mite populations from increasing drastically as they move into the field. Establishing efficient biological control methods will require more research but knowing where and when to apply control methods and having effective chemical control available as a last resort will be helpful in future research.
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Keywords
Bioassay, Biological control, Neoseiulus fallacis, Phytoseiulus persimilis, Spatial distribution, Tetranychus urticae, Watermelon, Delmarva Peninsula, Mite populations, Insecticides