Research in our lab integrates basic studies on the biology, ecology and behavior of vegetable insect pests and pathogens with applied studies utilizing both novel and traditional pest management approaches.
Phenology of Aphid Vectors of Potato Virus Y (PVY)
Potato virus Y (PVY) is the most important disease issue facing the seed potato industry and it is having an impact on the commercial industry. PVY impacts negatively yield and tuber quality, but more importantly, PVY reduces farm income because seed lots cannot meet virus tolerance limits, and because the emergence of necrotic strains reduce trade market opportunities. Effective on farm PVY management has been realized through our efforts to reduce the potential for aphids to inoculate plants. Aphid populations have also increased, especially with the introduction and establishment of the soybean aphid (Aphis glycines) to the U.S. in the early 2000s. Publicly held, regional and national databases have recently become available to provide information about which aphid species are moving into susceptible seed potato.
Data were compiled from the North Central Region, Aphid Suction Trap Network from over a span of 8 years (2005-2013) and 45 locations comprising over 200 species of aphids and nearly 785K individual captures in the upper Midwestern US. The suction trap information available was initially standardized for each year, location, and week using a random effects modeling approach. Generalized additive models (GAMM) were then fit to the resulting conditional modes of the random effects model, representing the de-seasonalized count data, and have been very effectively used to predict the phenology of each unique aphid species.
The major outcome of this research resulted in our ability to accurately determine the seasonal phenology of dispersing aphid vectors, and further limit risk of PVY transmission by timing the application aphid anti-feedants. Wisconsin Seed Certification quality results have steadily increased over the past 8 years (see figure). This research was supported by a USDA NIFA SCRI in 2009 and has resulted in 3, peer-reviewed publications from our laboratory. New directions in this research have again been supported by the USDA NIFA SCRI program in 2014 through funding support to investigate necrotic virus diseases in potato that limit high quality seed production. Our laboratory is again involved in these investigations with the specific objectives of determining how local landscape composition and agricultural crop compositions can influence the species assemblage and diversity of aphid vector flights as well greater development of our GAMM models to accommodate meteorological variance components.
Determining risk intervals for transmission of aster yellows phytoplasma (AYp)
This project was directed at further enhancing our present understanding of the epidemiology and temporal patterns of aster yellows phytoplasma (AYp) transmission dynamics in Wisconsin muck crops. These AYp strains are transmitted by Macrosteles quadrilineatus, or the aster leafhopper (ALH), which has emerged as a dominant insect pest in susceptible carrot crops due to its ability to vector the pathogen. The AYp has a complex pathogenic relationship with a diverse host range, including members of both monocots and dicots, and is also transported into Wisconsin with the leafhopper vector that makes long distance flights from southern latitudes.
We specifically examined factors that contribute to the variability of aster leafhopper abundance and infectivity and subsequently identified residual trends in these seasonal patterns which could be directly modeled. Nonparametric regression and additive mixed models were used to allow for nonlinear relationships between responses and multiple predictor variables with the outcome of successfully identifying periods of time in the growing season when crop protection is most needed. For integrated pest management practitioners, the identification of temporal trends of abundance and infectivity greatly improved their ability to determine when potentially inoculative leafhoppers were present in susceptible carrot.
We have recently discovered that AYp virulence proteins (effectors) interact with and degrade specific plant transcription factors conserved among plant species, resulting in changes in leaf shape, stem proliferation (witch’s brooms) and flowers that transform into leaves (phyllody). These symptoms are commonly observed in a wide range of plant species infected with AYps suggesting that the effector genes constitute a considerable contribution to AYp epidemiology. The symptomatic plants are often sterile, but are more attractive and better reproductive hosts for the leafhopper vectors, which acquire the phytoplasmas and transmit the parasites to plants. Thus, AYp effector genes have a long reach; they potentially drive AYP epidemics by interacting with conserved plant transcription factors, altering plant development, increasing plant susceptibility to polyphagous insect vectors and modulating insect vector behavior that, taken together, may well empower AYps to infect many plant species and spread over great distances.
Spatial ecology of Colorado potato beetle resistance
Landscape-scale intensification of individual crops and pesticide use that is associated with this intensification is an emerging, environmental problem that is expected to have unequal effects on pests with different lifecycles, host ranges, and dispersal abilities. We have undertaken new investigates to determine if intensification of a single crop in an agroecosystem has a direct effect on insecticide resistance in a specialist insect herbivore. Using a major potato pest, Leptinotarsa decemlineata, we measured imidacloprid (neonicotinoid) resistance in populations across a spatiotemporal crop production gradient where potato production has increased in Michigan and Wisconsin, USA. We found that concurrent estimates of area and temporal frequency of potato production better described patterns of imidacloprid resistance among L. decemlineata populations than general measures of agricultural production (% cropland, landscape diversity). We are learning that variation in the intensity of neonicotinoid-treated potato in an agricultural landscape can have unequal impacts on L. decemlineata insecticide insensitivity, a process that can lead to resistance and locally intensive insecticide use.
Molecular mechanisms of Colorado potato beetle resistance
An important challenge in understanding L. decemlineata resistance is assessing the genetic mechanisms associated with resistance and classifying up-regulated genes that may be involved in combating an insecticide. We have very recently uncovered trends in imidacloprid phenotypic responses that have developed in Central Wisconsin by estimating the LC50 values among different field populations against a range of imidacloprid doses. The LC50 values collected in 2008-2011, and more recently in 2013 and 2014, show that some field locations remain susceptible to imidacloprid, while nearby fields (<100km) have developed high levels of resistance. We have also uncovered the potential mechanisms of resistance at each field location. We compiled a transcriptome for populations, characterized as phenotypically ‘susceptible’ and ‘resistant’, by isolating mRNA from adult beetles and analyzing gene expression level differences. Strong differences were observed in constituently up and down-regulated genes among different field populations. Most significantly, the up-regulation of 3 cytochrome p450s and a glutathione synthetase related protein in multiple resistant populations provide a mechanistic explanation of resistance evolution in CPB.
Wild bee communities in Central Wisconsin vegetable crops
Pollinator insects like bees are in decline throughout the United States. As these species disappear so too may the billions of dollars’ worth of pollination services they provide annually. Previous research suggests that pollinator decline is being caused by interacting factors, including land use change and agrochemical exposure. These two factors were examined independently in the context of central Wisconsin, where processing vegetable agriculture is a dominant land use. Although bees forage in vegetable fields where they may be exposed to agrochemicals, many of these crops are not pollinator-dependent and have thus been overlooked by previous pollinator research. Furthermore, the heterogeneity of crop types in this region has an unknown effect on pollinator habitat suitability. This study’s objective was to assess the temporal and spatial overlap of pollinator risk factors by examining the seasonal diversity, abundance, and distribution of bee species present in vegetable fields and comparing the results to seasonal changes in insecticide concentration in flower and leaf tissues of crops grown with an at-plant neonicotinoid seed coating.
Neonicotinoid contaminants and water quality issues in Wisconsin’s Central Sands
Neonicotinoids are a popular and widely-used class of insecticides whose water-soluble nature and 20-year usage history has led to questions about their accumulation in groundwater resources. For this study, we investigated the extent to which irrigation water in center-pivot irrigation systems, drawn up from aquifers lying beneath conventional agricultural fields receiving commercial quantities of neonicotinoids, is contaminated by such chemicals. Approximately 300 samples were collected from 92 unique high-capacity irrigation wells and tested for the presence of thiamethoxam, a neonicotinoid, using ELISA kits, with 69% of all samples testing positive for thiamethoxam at a concentration above the analytical limit of quantification of 0.05 ppb. The majority of tested wells possessed low levels of contamination, though five wells showed consistently higher levels of neonicotinoid contamination (> 1.0 ppb). Furthermore, an analysis of the spatial structure of these well detects suggests that the level of contamination is extremely variable from the landscape scale down to the individual field scale, and that the amount of contamination at a particular well can shift by one or two orders of magnitude from year to year and even within a growing season. In this study we also investigated the relationship between these results and certain physical, geographical, and hydrologic factors, and further show how the proportion of landscape surrounding individual wells containing certain individual crops or land use classes can be strongly associated with detections of neonicotinoid compounds in water from these wells.
The projects listed below have all been concluded and their descriptions are presented here as an archive. Please note, they have not been updated and may or may not still be accurate. See also: Current Research Projects, Refereed Publications.
Overwintering habitats of the Colorado potato beetle in Wisconsin’s Central Sands production area
Documenting localized Colorado potato beetle movement improves our understanding of how this pest interacts with landscapes beyond the crop. Identification of preferred overwintering sites will provide fundamental research-based information needed to more feasibly and economically apply various cultural management tools (e.g. rotation, trap crops, perimeter sprays, etc).
In temperate potato production regions, preferred CPB overwintering, or diapause, sites, are thought to be outside production fields and along field margins. Late season movement of CPB towards prominent dark, vertical landscape features, such as windbreaks and adjacent forested edges, is hypothesized to occur in many systems.
Understanding behavioral tendencies of adult CPB dispersion from the field will make management practices such as large scale, focused trap crops, trenches, and specific applications of adulticides more efficient and effective. To address these questions, this project has documented and quantified differing bordering landscape elements, consistent with the Natural Resource Initiatives, Managed Ecosystems Project, serving as potential overwintering habitats and has attempted to document the movement and dispersal patterns of overwintered, adult CPB from these areas.
A realization of what, if any, specific non-crop community is preferentially selected by CPB in the Central Sands would be advantageous for several reasons. 1) Unmanaged fallow areas may not provide services and additionally create quality overwintering conditions for beetles. 2) Important native plant communities of particular interest have been identified in the potato growing region through the efforts by the USDA’s Natural Resource Initiatives program. These communities may provide positive ecosystem services such as biological control of pests. 3) Characterization of landscapes which are consistently associated with CPB will promote more effective management solutions.
New insecticide technology for control in potato insect pest management
The Colorado potato beetle continues to be the most serious insect pest found on commercially produced potatoes in Central Sands region of Wisconsin, largely as a result of its resistance to several registered insecticides. The Colorado potato beetle causes damage as a defoliator in both the adult and larval stages. Non-chemical control options for Colorado potato beetle are often limited in scope. Cultural manipulations such as crop rotation, to avoid over wintered populations, can be effective in delaying infestations and decreasing their severity, and trap crops or physical barriers (trenches) have also been employed successfully in other growing regions to delay infestation. Following infestation, however, biological regulation by beneficial insects (predators, parasitoids, etc.) is usually ineffective and growers must relay on chemical control to prevent economic damage.
Thus, although cultural and biological controls can provide some level of population reduction, the Colorado potato beetle must be managed primarily with insecticides. Chemical management programs should be designed to keep Colorado potato beetle populations below damaging levels while avoiding potential problems associated with resistance, non-target toxicity, environmental degradation, and worker safety. This project tests different chemical management programs with registered and experimental insecticides.
A key limiting factor for all cucurbit farmers includes cucumber beetles (Acalymma vittatum) and subsequent transmission of the bacterial wilt pathogen, Erwinia tracheiphila. This project focuses on the development of enhanced IPM practices for cucurbit production employing a combination of novel cultural and pest management practices. A special focus has been to emphasize practices that limit impacts on
domestic and native pollinators. To date, we have documented significant reductions in both populations of cucumber beetles and the bacterial pathogen they transmit in susceptible vine crops using these tactics. Specifically, mean incidence of bacterial wilt was 2-3 X less prevalent among grower cooperators who implemented a combination of IPM-based practices when compared to both commercial and organic farm operators. The seasonal abundance and species composition of insect pollinators did vary among farms locations with Apis and Bombus spp. occurring most frequently. We have demonstrated the ability to significantly reduce the reliance on broad spectrum insecticides by incorporating IPM-based, cultural practices that prevent damaging beetle feeding.
2008 Wisconsin surveys of Colorado potato beetle insensitivity to neonicotinoids
This project is directed at further enhancing our present integrated pest management strategies for key insect pests in potato with a focus on the development of integrated chemical, biological, and cultural management practices. A primary focus of the proposed work has been to accurately identify pest management strategies that reduce the total number of insecticide applications, limit the onset or development of insecticide resistance, and provide novel or refined management tactics for the sequence of insect control measures implemented. An emphasis of this project is to document the occurrence and increase(s) in neonicotinoid resistance among populations of Colorado potato beetle while also providing practical guidance towards implementing an appropriate insecticide resistance management program. Objectives of this project have been designed to address knowledge gaps that must be filled if we are to devise both short and long-term, sustainable management plans to address the key insect pests in potato.
Onion thrips control using foliar insecticides in dry bulb onion production
Effective, economical, and efficient long term management of onion thrips continues to be a challenge in the production of dry bulb onion. This insect pest continues to be a high pest priority for Wisconsin onion growers. Many of the currently registered products for control of onion thrips are not equally effective against the insect. As a result, thrips management is a top priority and an improved understanding of the ecology and management of this pest is essential towards the development of long-term control methods. The objective of this project is to evaluate currently registered and new, potentially efficacious insecticide foliar treatments to target problematic populations of onion thrips, and also to develop efficacy data in support of future registration of novel insecticides with unique modes of action.
Mint bud mite management in Wisconsin peppermint production: application timing and new tools
Effective, economical, and efficient long term management of mint bud mite continues to be a challenge for specific field locations and the production of black peppermint. In addition to effective crop rotation, bud mites are managed almost exclusively using acaricides. Some acaricides used for control perform adequately, while others continue to perform poorly. Several reasons to explain poor performance include an inappropriate choice of active ingredient, a short residual activity, an application made too late, inadequate application coverage, or a resistant population. Wisconsin mint growers, unlike mint producers in other portions of the US, have a limited number of acaricide management tools for use in controlling mint bud mites. Currently, propargite (Comite® / Omite®) and more recently fenpyroximate (Fujimite) are the only registered acaricides for use in Wisconsin against mint bud mite. Some insensitivity of mint bud mite to propargite combined with concerns regarding environmental persistence, cost, and its listing as a B2 carcinogen make this an increasingly non-viable control option. Spiromesifen (Oberon®) is a relatively new mode of action with both insecticide and acaricide activity which is currently under review with the Federal IR-4 Program. Additional new compounds which may show promise in controlling mint
bud mite include Abamectin, (Temprano™), bifenazate (Acramite® 4SC), and diflubenzuron, (Dimilin® 2L) under optimized spray conditions. The use of these new tools has not been well defined in Wisconsin production systems. The goal of this research will be to refine the use of Fujimite and Comite, and document the potential for Acramite, Dimilin, Oberon, and Temprano as feasible, future control options.
Non crop sources of CMV and implications for management
Recently snap bean (Phaseolus vulgaris L.) and pepper (Capsicum annuum L.) crops in Wisconsin have experienced significant increases in incidence and crop losses associated with infection of cucumber mosaic virus. This increase has anecdotally been linked to the recent introduction and establishment of the soybean aphid (Aphis glycines Matsumura) in the upper Midwest region. Presumably, the unique population biology and dispersal of this species has changed both the spatial arrangement and temporal movement patters previously observed with respect to CMV in the region.
Although significant new information has been developed recently to describe soybean aphid seasonal dispersal, its competence as a virus vector, and the timing of virus increase in susceptible, processing snap bean crops, limited information exists to document the primary inoculum sources where these viruses are acquired. Knowledge of which vector(s) species transmit these viruses to processing snap beans in Wisconsin, where they acquire the viral pathogens, when they move into fields, and when they spread the pathogen to snap beans is critical to understanding and managing the spread of these viral diseases. This project is directed at further enhancing our present understanding of the epidemiology of problematic bean viruses in affected areas of Wisconsin with a focus on factors that influence virus geographical distribution and spread. The objectives are (1) to identify and characterize the seasonal abundance of the primary aphid vectors of CMV and AMV among perennial crops in the agricultural landscape, and (2) to compare the genetic structure of the population of CMV and AMV isolates collected from virus-affected, susceptible succulent bean plantings, dispersing insect vectors, and potential reservoir hosts.
Seasonal infectivity of aster leafhoppers in carrot
Each year, Wisconsin growers produce carrots on an average of 4200 acres grossing over $6 million dollars in revenues (USDA-NASS, 2007 annual bulletin). Unfortunately, carrot fields are threatened annually by the occurrence of aster yellows phytoplasma (AYp), which is obligately transmitted by the aster leafhopper (Macrosteles quadrilineatus Forbes). Current control practices strictly utilize insecticide sprays that target the aster leafhopper. Spray timing is guided by an aster yellows index that is based on the proportion of infective leafhoppers present in a field at a given point in time. Crop scouting and molecular diagnostic tools have decreased the inherent lag between finding inoculative leafhoppers and prescribed sprays. However, yield losses of 5-20% resulting from AYp are still commonplace (1). A more comprehensive and sustainable, multi-tactic control strategy is warranted to lower inoculum pressure in the areas surrounding susceptible crops. The management of off-crop habitats in ways that minimize the persistence and decrease the accumulation of AYp inoculum in the local environment has the potential to contribute to the sustainability of carrot production primarily through reductions in pesticide.
The primary focus of this research is to improve our knowledge of where leafhoppers acquire the pathogen, when they move into susceptible fields, and when they spread the pathogen to crops. Specifically, our focus has been to 1) accurately identify primary inoculum sources of AYp of greatest epidemiological significance in non-crop habitats surrounding carrot fields and 2) to compare the genetic structure of the population of AYp from reservoir hosts to that within carrot and to determine if genotype variability relates to either prevalence or infectivity potential of the pathogen. Ultimately, this project will provide accurate, new information about the relative importance of AYp sources in the habitat surrounding carrot fields. This information can then be used to evaluate the local AYp risk and, in turn, management practices can be developed to decrease the accumulation and local persistence of the pathogen.
Long-term storability of potato virus Y infected tubers
In recent years, Potato Virus Y has reemerged as a serious disease problem in many potato production areas in the northern United States and eastern Canada. Asymptomatic cultivars which express mild or no symptoms when infected with PVY combined with an increase in recombinant strains of this virus prevent accurate field identification and rouging of infected plants. There is a lack of effective strategies to reduce the incidence of PVY infected plants and tubers, and there is a need to improve cost-effective methods of determining PVY levels in seed lots and further understanding the impact of current season virus infection on tuber storage and quality attributes.
Limited information currently exists to document the impact of PVY infection on quality aspects tuber storage performance. In the first year of preliminary research, we have documented significant reductions in storage quality parameters including percent solids and shrinkage. This area of investigation seems extremely important towards limiting continued storage losses and further assessing the impact of plant disease (PVY infection) on seed tuber physiological age.
Seasonal flight dynamic of aphid species in occurrence with potato virus Y infection in commercial potato fields
Potato virus Y (PVY), once managed effectively by strict seed certification practices, has re-emerged as a serious disease problem in the seed potato crop in many areas of the United States and Canada. New variants of PVY that cause tuber necrosis further threaten tuber quality in both seed and commercial crops. Managing levels of PVY in seed and eliminating the tuber necrotic strains will require an adjustment of seed certification practices and a more aggressive use of on-farm management strategies by both seed and commercial potato growers.
The goal of this project has been to document the seasonal phenology of aphid vector species and their relationship to PVY incidence in the field. Replicated field plots were set up in Wisconsin using green tile pan traps and sentinel potato plants. Sentinel plants were left in the field for a week, then held in an aphid-proof greenhouse for PVY disease development and detection. Membrane ELISA was used to test for the presence of PVY. Over a similar sample interval, aphids were collected from green tile pan traps and identified to species. Correlating aphid movement with PVY disease progress will help to define the relative importance of specific aphid vectors in driving recent PVY disease cycles. Moreover, we hope to define the periods of greatest risk for PVY transmission and the necessity for deployment of targeted, best management practices to limit PVY spread.
The contribution by native pollinators towards pollination has been studied in several crops requiring insect-mediated pollination including watermelon, pumpkin, and sunflower. However, there is a scarcity of research regarding the level of wild bee visitation to open cucumber flowers. We will sample the native bee communities in
pickling cucumber in the Central Sands and Driftless Region of Wisconsin. This study will determine if the landscape surrounding a field impacts the species diversity and abundance of native bees. It is expected that a greater level of natural habitat near cucumber fields can offer alternative floral resources and undisturbed nesting sites for wild pollinators. Additionally, this project will examine if the species assemblage of native pollinators varies based on the date of planting and the distance from field edges.