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. Please contact us if you are interested in collaborating on any of our ongoing projects.
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.
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.
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.