Moderator: Fred Springborn, Agriculture & Natural Resources Educator, Montcalm Co. MSU Extension

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1 Great Lakes Fruit, Vegetable & Farm Market EXPO Michigan Greenhouse Growers EXPO December 6-8, 2011 DeVos Place Convention Center, Grand Rapids, MI Potato Where: Gallery Overlook (upper level) Room F Recertification credits: 2 (1B, COMM CORE, PRIV CORE) CCA Credits: NM(0.5) PM(1.5) Moderator: Fred Springborn, Agriculture & Natural Resources Educator, Montcalm Co. MSU Extension 2:00 pm Emergence Phenology of CPB and Its Relationship to Resistance Russell Groves, Entomology Dept., Univ. Wisconsin-Madison 2:30 pm Utilizing Slow Release Nitrogen in Potato Production Kurt Steinke, Crop and Soil Science Dept., MSU 2:50 pm MSU Potato Breeding Update Joe Coombs, Crop & Soil Science Dept., MSU 3:10 pm Transporting Equipment: New Weed and Pest Issues Fred Springborn, Agriculture & Natural Resources Educator, Montcalm Co. MSU Extension 3:30 pm Michigan Disease Update William Kirk, Plant Pathology Dept., MSU

2 Principal Investigator (s) Colorado Potato Beetle Emergence Phenology and Its Relationship to Resistance Russell L. Groves, Assistant Professor and Entomology Extension Specialist, 537 Russell Laboratories, University of Wisconsin, Madison (608) Anders Huseth, Graduate Research Assistant, Department of Entomology, 537 Russell Laboratories, University of Wisconsin, Madison (608) Scott Chapman, Associate Research Specialist, 537 Russell Laboratories, University of Wisconsin, Madison (608) Zsofia Szendrei, Assistant Professor and Entomology Extension Specialist, Department of Entomology, Michigan State University, 439 Natural Science Building, East Lansing MI 48824, (517) Adam Byrne, Research Technician, Department of Entomology, Michigan State University, 439 Natural Science Building, East Lansing MI 48824, (517) Cooperator (s) Wisconsin Potato and Vegetable Growers Association, PO Box 327 Antigo, WI 54409, Office (715) , Fax: (715) Minnesota Area II Potato Growers Association and Research and Promotion Council, th Avenue, Clear Lake, MN 55319, Office (320) , (320) (Fax) Project Abstract. Most insecticides used for control of Colorado potato beetles (CPB) in the Northeast and Midwest US have ultimately failed because of resistance that has developed in populations of this problematic insect. Increasingly, growers rely heavily on a single class of insecticides called the neonecotinoids (i.e.: imidacloprid, thiamethoxam, clothianadin, dinotefuran) for control of CPB (NASS 2006). Imidacloprid resistance appeared in NY in 1997, and is now common in the northeast and appeared in the Michigan in 2004 and in Wisconsin in Growers in these regions of the United States are experiencing serious control problems, including multiple locations in Maine, Michigan, and Wisconsin. This erosion of control with the neonicotinoids threatens the continued effectiveness of current CPB control programs and may seriously alter the economics of potato production. We now also know that CPB resistant to imidacloprid also expresses resistance to new insecticides. The mechanisms of how this resistance has emerged, the extent of this resistance statewide, and the association of this resistance with observation of delayed emergence or extended diapause seems to be of critical importance for the state and the region and further investigation for more practical and long-term CPB control. Background and Rationale. The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), is considered to be among the most destructive arthropods impacting potato production in North America (Gauthier et al. 1981). Physiologically very dynamic in its survivability, the CPB flourishes in many extreme climatic conditions. Reproductively, the CPB possesses the ability to be extremely prolific and fecund. Individual females are capable of producing between eggs and may survive under optimal conditions for days. Eggs are most frequently deposited in masses of approximately eggs/mass on ventral leaf surfaces of Solanum spp.. Larvae of CPB progress through a

3 series of 4 instars in days depending on environmental conditions. The final instar crawls from the canopy and burrows into the soil for pupation which lasts approximately 10 after which they emerge as an adult beetle. In Wisconsin, CPB typically undergo 2 successive generations per growing season. Moreover, the CPB has been credited with being largely responsible for creating the modern insecticide industry. Since 1864, hundreds of compounds were tested against this pest, and application equipment was specifically invented to aid their delivery. Currently, insecticides still remain the foundation of the CPB control on commercial potato farms. More than 30 active ingredients are currently registered for use against this pest in the United States. Not surprisingly, high selection pressure eventually resulted in a large number of insecticide-resistant CPB populations, with resistance rapidly progressing since the middle of the last century. Potato growers continue to struggle to control this problematic insect pest, and maintaining control of this insect remains at the forefront of our efforts to protect potato from damaging insect pests. A high predisposition to resistance development is probably caused by a number of factors. First, plants in the family Solanaceae have high concentrations of toxic glycoalkaloids in their foliage resulting in the requisite development of the physiological capability to detoxify or tolerate poisons. Next, high beetle fecundity not only increases the probability of random mutations, but also ensures the rapid build-up in resistant mutants once mutations have occurred. Thirdly, the beetles have a narrow host range and a limited dispersal range, such that both larvae and adults feed on the same host plants and often in a very discrete geographic area. And finally, growers rely almost exclusively on insecticides for adequate beetle control because other control techniques often provide insufficient levels of control. Taken together, these factors increase the selection pressure towards resistance within this species. Resistance problems reached critical levels in the United States in the early to middle 1990s, when growers in several potato-producing regions were nearly out of chemical control options. Arrival of neonicotinoid insecticides in 1995 brought a period of relief in areas where the beetles had developed resistance to recent chemistries, the most recent being the synthetic pyrethroids. However, the first instances of resistance to imidacloprid were soon reported from commercial potato farms in several locations including NY, ME, and NJ. While a number of new chemistries have recently been registered, there is no reason to believe that any of them will break the seemingly endless resistance cycle that is increasing becoming commonplace in CPB management. Current Neonicotinoid Resistance in Wisconsin. In the field, insecticide resistance can initially be observed as only a minor reduction in the observed level of control. It is often only until resistance has become fixed in the population when we begin to see full-scale field failures. In the laboratory, resistance is typically measured with a bioassay as an increase in the dose (LD50) or concentration (LC50) of the toxin required to kill 50% of the test population. Bioassays normally consist of preparing serial dilutions of tested chemicals and then applying them to beetles originating from populations of interest. Estimated LD50 or LC50 values are then determined using a probit transformation of percent mortality data regressed against log 10 doses. Over the past 4 production seasons, the Wisconsin Potato and Vegetable Growers Association has supported our laboratory in conducting surveys to measure the insensitivity among populations of CPB to the neonicotinoid class of insecticides in Wisconsin. Adult CPB were collected from sites with successive, within-season generations to compare changes in insensitivity between overwintered beetles and summer adults. Briefly, adult bioassays were performed by treatments with a topical application of technical grade insecticide dissolved in acetone, 60 beetles/dose, 5 doses causing between 0 and 100% mortality, plus 30 beetles treated only with acetone. Measured responses are assessed for selected, in-state populations and compared directly to a highly susceptible, reference control strain of CPB obtained from a laboratory colony in New Jersey and results from our 2010 surveys are provided (Table 1). It is important to note that sites were not selected at random across these areas. A portion of candidate populations evaluated in this survey were selected with the prior knowledge that some were difficult to control with neonicotinoid tools.

4 Table 1. Estimated LD 50 values (µg/beetle), 95% fiducial limits, and calculated resistance ratios for adult Colorado potato beetle populations collected and assayed in Wisconsin, County Site ID (P<0.0001) (α=0.05) Estimated slope (± SE) LD 50 (± 95% CL) Resistance Ratio 1 Adams A (P=0.0008) 12.6% ± ( ) / (25.7) B (P=0.0451) 9.9% ± ( ) / (18.2) C (P=0.0103) 8.2% ± ( ) / (14.5) D (P=0.0284) 6.8% ± ( ) / (3.0) E (P=0.0095) 8.3% ± ( ) / (2.5) F (P=0.0128) 7.7% ± ( ) / (6.1) Columbia G (P<0.0001) 10.8% ± ( ) / (0.6) Langlade H (P=0.0983) 5.9% ± ( ) / (4.0) I (P=0.0127) 9.1% ± ( ) / (7.7) Portage J (P=0.0062) 7.1% ± ( ) / (1.7) K (P=0.0077) 9.4% ± ( ) / (4.8) L (P=0.0517) 11.2% ± ( ) / (2.0) M (P=0.0789) 4.9% ± ( ) / (1.3) Waushara N (P=0.0192) 6.1% ± ( ) / (7.7) O (P=0.0522) 7.9% ± ( ) / (11.0) P (P=0.0003) 8.1% ± ( ) / (8.4) Q (P=0.0803) 9.4% ± ( ) / (14.9) R (P=0.0104) 7.4% ± ( ) / (12.9) 1 Resistance ratio estimates calculated against a New Jersey reference control strain of Colorado potato beetle adults (LD50 = 0.024). Delayed Diapause and Relationships to Resistance. Another important and recent observation surrounding the emergence of neonicotinoid resistance is the concept of extended emergence, or delayed diapause. Diapause is a genetically determined behavior of an insect s lifecycle designed to synchronize its biology with seasonal variation in the environment. Insects inhabiting more dynamic or unstable environments with unpredictable resources may extend diapause for longer periods, resulting in delayed emergence. Portions of Wisconsin s resistant CPB populations may be temporally avoiding the highest titers of in plant insecticide by emerging later. Emergence and colonization over longer periods of time will result in extended egg deposition, resulting in multiple resistant life stages present simultaneously in the crop. Anecdotal evidence suggests several of Wisconsin s insensitive populations are smaller, less fit, and may emerge over a longer period. Acceleration of resistance will occur as later emerging portions of populations are exposed to sub-lethal systemic insecticide doses. Population scale selection for later emergence will coincide with reduced in-plant insecticide levels. Over time, the continual exposure of late emerging insects to sub-lethal doses will produce even greater resistance issues. If true, rapid natural selection may fix the protracted emergence trait in the gene pool. Long term impacts of protracted emergence will compromise the efficacy of current and future systemic registrations. Exploitation of phenotypic fitness costs with judicious, reduced risk insecticide application, altered use patterns, and cultural controls will significantly reduce fixation of multiple resistance mechanisms in Wisconsin. Mechanisms for Resistance in CPB. Known mechanisms of Colorado potato beetle resistance to insecticides include enhanced metabolism involving esterases, carboxylesterases and monooxigenases, target site insensitivity, as well as reduced insecticide penetration and increased excretion. Resistance mechanisms may be highly diverse even within a relatively narrow geographical area. Cytochrome P450 is involved in the metabolism of internal hormones and lipids in insects, and also participates in the metabolism of xenobiotic compounds such as pesticides. In the Colorado potato beetle, the P450 dependent monooxygenase system is the most common mechanism of resistance across many populations from diverse geographical origins. Of significant importance, the pre-treatment by an oxygenase inhibitor, piperonyl

5 butoxide (PBO), has previously been demonstrated to reduce resistance of adult beetles resistant to organophosphates, carbamates, and synthetic pyrethroids. Importantly, imidacloprid-resistant beetles from Long Island, New York showed greater than a 3X reduction in resistance with PBO treatment. Specifically, the insect metabolism of imidacloprid leads to the production of an olefin metabolite that is less toxic to the insect than the parent compound and this phenomenon has been observed in both susceptible and resistant strains, but to a greater extent in the resistance strains. Project Purpose. Our ongoing research has been directed at further enhancing our present integrated pest management strategies for key insect pests in potato with a focus on the development of integrated resistance management (IRM) practices to lower Colorado potato beetle (CPB) pest populations below economic thresholds. The primary focus of the proposed work will be to accurately identify the regional and statewide scope of neonicotinoid resistance, the relationship of resistance to CPB emergence phenology, and the predominant mechanisms of resistance which have developed in CPB. These knowledge gaps must be filled to devise both short and long-term, sustainable management plans to address emerging resistance in populations of the CPB. Continued increases in measured insensitivity to the neonicotinoid class insect control products could dramatically increase the cost of adult Colorado potato beetle control using foliarbased products exclusively. Complete loss of these compounds could result in significant losses on an areawide basis which may threaten the viability of the potato production industry in the region. Populations of CPB with modified emergence patterns may further confound current control practices by limiting the efficiency of current systemic insecticide-based control programs. A longer-term goal of this research is to enhance current insect management programs in potato, which rely on a very few water-soluble and systemically mobile insecticides, with an economically viable and improved system. Potential Impact. Research objectives outlined in this study are anticipated to benefit agricultural producers, crop consultants, University of Wisconsin Specialists and County Educators, and other stakeholders and will be essential for properly timing insect population control measures and cultural practices to limit resistance development. Promotion of innovative resistance management within the USDA and NRCS s Environmental Quality Incentive Program (EQIP) may further promote greater awareness and acceptance of these practices through economic incentives. With EQIP, potato growers experiencing elevated neonicotinoid resistance and insecticide loss may optimize pest management by adopting innovative management for greater farm profitability, resource conservation, environmental assessment, and biodiversity restoration. Moreover, the outcomes of the generated research will (1) begin to build a more comprehensive picture of the extent of neonicotinoid resistance in the upper Midwest production region, (2) the potential for neonicotinoid resistance to influence CPB emergence phenology, and (3) the predominant mechanism(s) of resistance present in the selected populations.