No Small Potatoes: Molecular and Landscape Approaches to Understanding Beet Leafhopper Populations and Pathogen Transmission in the Columbia River Basin

Jillian Joyce Foutz

doi:10.7273/000005243

The beet leafhopper (BLH; Circulifer tenellus (Baker); Hemiptera: Cicadellidae) is a serious pest of potato and other crops in the Columbia River Basin. This insect is the primary vector of multiple plant pathogens, historically including beet curly top virus and, more recently, “Candidatus Phytoplasma trifolii.” BLH is known to be highly polyphagous and develops largely on non-crop weedy host plants. Current management practices for BLH and the pathogens it transmits consist of applications of insecticide on a regular schedule throughout the growing season. BLH are heavily monitored for population and pathogen outbreaks, but many questions remain about where and when they develop, and what role host plants play in the epidemiology of pathogens spread by BLH. Here, I examine different trapping methodologies and seasonal trends in BLH host plant use and pathogen presence to determine how management practices could be improved with a better understanding of BLH behavior. First, I used different trap types and placements to assess BLH capture rates and incidence of pathogens. BLH adults and nymphs were monitored in four trials at different times of year with commonly-used yellow sticky card traps and prototype 3D-printed preservative traps, each placed at ground level or 1 m height. I found that traps at ground level consistently captured more BLH, and that sticky cards generally captured significantly more BLH than preservative traps except in autumn. There were not significant differences in pathogen prevalence between trap types, but sticky cards captured more insects at times when pathogen incidence was higher. Results indicate that multiple factors, such as life stage, infection status, and seasonality may be interacting to affect BLH trap attraction. Trends observed highlight the need to understand the behavior of BLH and other vectors with respect to accurate monitoring. Next, I surveyed weedy sites adjacent to potato fields in the Columbia River Basin in 2019, 2020, and 2021. BLH adults and nymphs were sampled from weeds present seasonally at each site and were screened for the presence of Ca. P. trifolii along with plant tissue samples. I observed seasonal trends in BLH non-crop host plant use and phytoplasma infection. Results suggest that BLH likely infect potato and other crops when key spring weed hosts senesce, forcing BLH to disperse and search for summer hosts. Understanding the seasonal use and infection status of important BLH host plants may allow for improved monitoring techniques and earlier detection of population and pathogen outbreaks.

No Small Potatoes: Molecular and Landscape Approaches to Understanding Beet Leafhopper Populations and Pathogen Transmission in the Columbia River Basin

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