Location: Vegetable Crops Research2013 Annual Report
1a. Objectives (from AD-416):
Objective 1. Resistance monitoring. Cooperators representing the US potato industry from different US states will receive collection kits including shipping containers and USDA-APHIS permits. Objective 2. Assessing metabolic resistance levels. This objective aims to determine which detoxifying mechanisms are activated in Colorado potato beetle (CPB) in response to insecticides. Objective 3. Efficacy of alternative insecticides. Our goal in this objective is to measure resistance in CPB to novel insecticide action modes such as abamectin, spinetoram, novaluron, rynaxypyr, metaflumizone, and cyazypyr. Objective 4. CPB resistance and diapause. The relationship between CPB diapause intensity and population wide stressors (e.g. insecticide resistance) is currently unknown. Specifically, the goal of this objective is to determine if CPB populations being selected for delayed or protracted emergence from overwintering is related to observed increases in levels of resistance. Objective 5. Plant resistance. We will identify and compare chemicals emitted into the headspace of wild relatives of the cultivated potato that show various levels of resistance to CPB.
1b. Approach (from AD-416):
Resistance monitoring. Cooperators representing the US potato industry from different states will receive collection kits including shipping containers and USDA-APHIS permits. Each CPB population will be screened to determine the relative susceptibility to imidacloprid and thiamethoxam (topical application, 15 adults per concentration, five concentrations, 150 beetles per insecticide). Treated beetles will be placed in Petri dishes lined with filter paper and fed fresh potato foliage and kept at 24°C (±1). Beetle mortality will be assessed 7 days after treatment. Doses lethal to 50% of the beetles (LD50s) for imidacloprid and thiamethoxam will be determined by log dose/probit mortality analysis. LD50s for field populations will be compared to LD50s for susceptible beetles to determine whether resistance to either chemical is increasing in the field. Resistant populations will be mapped to see if resistance appears to be spreading or occurring in new locations. Efficacy of alternative insecticides. Preliminary research with the novel insecticide tolfenpyrad has shown a high level of toxicity to CPB larvae and adults in the lab and field. In 2012, we will conduct bioassays to measure LC50 levels and to determine optimal rates of this chemical to use in the field. In addition, we will evaluate the efficacy of several other novel insecticides including cyantraniliprole, spinetoram, and others. CPB resistance and diapause. We do not know whether resistance acceleration may be occurring as later emerging portions of CPB populations are exposed to sub-lethal, systemic insecticide doses. A proportion of populations may be selected for later emergence when, or if, in-plant insecticide levels decline. Over time, the continual exposure of late emerging insects to sub-lethal doses will aid in hastening resistance development. The long term impacts of a protracted emergence are currently unknown and may compromise the efficacy of current and future systemic registrations. Field experiments in 2010 were set up to investigate the extent to which extended diapause or delayed emergence is associated with insensitivity among populations. Specifically, experiments consisted of caged beetles (approximately 500-1,000 adult CPB / cage) collected from sites with measured levels of neonicotinoid resistance and compared with sites possessing no evidence for insensitivity. To date, we have observed unique differences in the emergence phenology of populations collected from different locations each with unique estimated resistance ratios. During the fall, winter, and spring of 2011-12, we will again monitor the temporal patterns of adult emergence. Here again, populations will be collected from sites with a documented history of CPB resistance associated with elevated resistance ratios and the associated emergence phenology will be examined over the emergence interval.
3. Progress Report:
This project was renumbered from 3655-21000-049-28S to 3655-21220-002-11S. In 2012, insensitivity to neonicotinoids was measured at 6 field locations in the commercial and seed production regions of the state of Wisconsin. Populations included in the bioassay were selected based on grower reports of neonicotinoid tolerance in the field. Additionally, a single population was collected from potato at the Arlington Agricultural Research Station, Arlington, Wisconsin. This site is outside the primary potato production regions of the state and represents a susceptible field population. At each location insensitivity was measured, adult insects were collected into plastic cups (0.94 L) from the potato canopy, and transported in coolers on ice directly to the University of Wisconsin-Madison campus. Upon arrival, insects were released in screen cages onto untreated, greenhouse-grown potato maintained in an environmental chamber at 24°C and a photoperiod of 16:8 (L:D) for three days. Resistance to neonicotinoids was assessed with topical imidacloprid bioassays. Technical grade imidacloprid was dissolved into pesticide grade acetone, then serially diluted to a range of doses between 0.001-10 ppm. Between five and nine doses were chosen based on preliminary bioassays resulting in 0-100 percent mortality. Adult beetles were divided into equal numbers per dose, each containing no fewer than fifteen insects per replicate. Collected individuals were treated with 1 µL of insecticide solution applied to the first abdominal sternite using a 50 µL syringe equipped with a repeating dispenser. Control insects received a 1 µL dose of pesticide grade acetone alone. Treated insects were placed into 100x15 mm polystyrene Petri dishes with filter paper. Insects were maintained on fresh, greenhouse-grown potato foliage in an environmental chamber at 24°C and a photoperiod of 16:8 (L:D). Bioassay response was measured at day three, five, and seven post-treatment. Insects were classified as alive, intoxicated, or dead. Intoxicated beetles were unable to grasp the tip of a pencil with all six legs and walk one body length up the pencil. Intoxicated or dead insects were pooled for statistical analyses. Efficacy of Insecticides. The objective of this experiment was to assess the efficacy of foliar insecticides applied to control insect pests in potato. The trial consisted of 38 main effect treatments arranged in a randomized complete block design (RCBD) with four experimental replicates. Potato was machine planted on 26 April 2012 at the Hancock Agricultural Research Station in central Wisconsin. Experimental plots consisted of 2 row plots measuring 6 ft wide and 20 ft in length with unplanted guard rows on each side. Rows were planted on 36 inch row centers with 12 inches between plants with 12 ft alleys separating replications. All foliar treatments were applied at 20 gallons per acre (gpa) using a four nozzle, 6 foot boom equipped with a flat fan spray tip powered by a CO2 backpack sprayer operating at 30 pounds per square inch (psi). Foliar treatments were applied twice in succession when 75-90% of the first generation Colorado potato beetle (CPB) was within the first and second stadia. Foliar applications of novaluron were initiated 7 June 2012, one week earlier than all other treatments. The first foliar application occurred between 7:45am – 8:30am hours on 14 June 2012, and application conditions were recorded as a southwest wind at 9.2 mph, 60.1°F (15.6°C), 51% RH, under clear skies. A second application occurred on 21 June 2012 between the hours of 7:00am and 8:00am. Application conditions were recorded as a west wind at 8.1 mph, 64°F (17.8°C), 87% RH, under cloudy skies. All plots were maintained according to standard commercial practices. CPB adults (AD), egg masses (EM), small larvae (SL), large larvae (LL) as well as potato leaf hopper (PLH) adults and nymphs were assessed by counting the number of each life stage on 10 randomly selected plants from the center two rows in each plot. CPB counts occurred five times during June and July. The first set of counts occurred on 18 and 21 June 2012 after the first application. The second set of counts occurred on 28 June 2012, 3 and 10 July after the second application. PLH counts were performed on the same 5 dates. Count data were log10 transformed prior to analysis. Means were separated using the least squared difference option in an analysis of variance (ANOVA). Populations of CPB were already established by the first foliar application, as defoliation estimates approached 5% in most plots. Experimental treatments were often significantly different than untreated check in the control of CPB adult, larval, and associated defoliation, although some treatments were more effective at controlling immature CPB. Adult PLH pressure was moderate, and the neonicotinoid containing compounds plus the synthetic pyrethroids provided the most effective control of PLH adults. No signs of phototoxicity were observed. This research relates to objectives 1 and 3 through neonicotinoid bioassays and efficacy of insecticides.