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United States Department of Agriculture

Agricultural Research Service

Research Project: Managing Insecticide Resistance in the Colorado Potato Beetle and Developing Management Options for Resistant Beetles

Location: Vegetable Crops Research Unit

2012 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:

Monitor resistance in Colorado potato beetle (CPB) to imidacloprid and thiamethoxam and determine field efficacy of new insecticides. CPB populations from commercial potato fields in Eastern, Midwestern, and Western United States locations were tested for resistance to imidacloprid and thiamethoxam using topical applications of technical grade insecticide. High levels of resistance to imidacloprid continue to be present in Maine, New York (Long Island), and Michigan. Resistance to thiamethoxam remains less prevalent than imidacloprid resistance, with only one Michigan population being classified as resistant. Resistance to thiamethoxam is probably increasing more slowly than imidacloprid resistance because imidacloprid is more commonly used than thiamethoxam. Field trials in Virginia, Michigan, and Wisconsin tested effectiveness of currently labeled and novel insecticides against CPB. Several new products were effective. Having a range of compounds from different chemical classes will be important for CPB control as neonicotinoid resistance continues to increase. No indications of resistance to the new products were observed in the field.

Efficacy of alternative insecticides. Registered and experimental foliar insecticides to control CPB and potato leafhopper (PLH) in potato. Experiments were conducted at Hancock Agricultural Research Station (HAES) on a loamy sand soil. Potato, Solanum tuberosum cv. ‘Superior,’ seed pieces were planted and spaced 12 inches apart within rows. Rows were 3 ft apart. The two-row plots were 6 ft wide by 20 ft long, for a total of 0.003 acres. Two guard rows separated plots while 12 ft tilled alleys separated replications. All plots were maintained according to standard commercial practices conducted by HAES staff.

Four replicates of 18 experimental foliar treatments and one untreated control were arranged in a randomized complete block design. The foliar treatments were applied twice in succession when 75-90% of the first generation CPB was within the first and second instar larval stadia.

Control of CPB was assessed by counting the number of egg masses (EM), small larvae (SL), large larvae (LL) and adults per plant on 10 randomly selected plants in each plot. Percent foliage defoliation (%DF) ratings were assessed by visual observation of each plot. Control of PLH, Empoasca fabae, was assessed by counting the number of adults collected from 25 sweep net samples in each plot. Insect counts occurred on several dates and reported means were averaged across those dates.

Populations of CPB were considered average to above-average as measured defoliation in the plots was nearing 5% by the time the initial foliar applications were applied. Increased levels of early larval CPB control were achieved with higher rates of DPX HGW86, Belay, Voliam Flexi, and Coragen compared to the untreated check. Lower than average levels of adult PLH were observed in the experimental plots as no significant differences were observed among registered or experimental compounds. No overt signs or symptoms of phytotoxicity were observed.

Evaluation of systemic insecticides for the control of the CPB, PLH, and aphids in potato. This experiment was conducted at HAES. Potato, Solanum tuberosum cv. ‘Russet Burbank,’ seed pieces were planted and spaced 12 inches apart within rows. Rows were 3 ft apart. The four-row plots were 12 ft wide by 20 ft long, for a total of 0.006 acres. Two untreated guard rows separated plots. Plots were arranged in an 8-tier design with 12 ft alleys between tiers. All plots were maintained according to standard commercial production practices by HAES staff.

Four replicates of 21 experimental treatments and two untreated controls were arranged in a randomized complete block design. All in-furrow treatments were applied in 2.0L of water. Furrows were cut using a commercial potato planter without closing discs attached. Seed treatments were applied in 0.016L of water. Immediately after the in-furrow treatments were applied and all seed piece treatments were placed in open furrows, all seed was covered by hilling.

Stand counts were conducted by counting the number of emerged plants per 20 ft. section of row. Control of CPB, PLH nymphs, and aphids was assessed by counting the number of these insects per plant on 10 randomly selected plants in each plot. Defoliation was evaluated by visual observation of each plot. Percent defoliation was determined for each plot through visual observation. CPB were recorded in the following life stages: adults (A), egg masses (EM), small larvae (SL), large larvae (LL). PLH were recorded as nymphs (N) or adults (A). Adult PLHs were sampled using sweep net. Insect counts occurred on several dates, and means are reported as averages over dates. Insect count averages reflect time periods during the summer when specific life stages peaked in the plots. Experimental plots were mechanically harvested from a single row of the four-row plots and weighed and graded at the HAES.

Populations of CPB in this field trial were considered average to above average as defoliation in the plots was nearing 10% by the time first generation CPB larval numbers began to peak in mid-June. Significant treatment effects were observed relative to the untreated control including CPB larvae and percent defoliation. All treatments except the DPX HGW86 alone provided effective control of PLH adults and nymphs. All treatments resulted in significantly higher tuber yields than the untreated check plots. No signs of phytotoxicity were observed following plant emergence.

Delayed Diapause and Relationships to Resistance. An 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. Field experiments were set-up to investigate the extent of extended diapause or delayed emergence associated with insensitivity among populations. Specifically, experiments consisted of caged beetles 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. The temporal patterns of adult emergence were recorded through the emergence period; the points after which no more adult CPB were emerging. Similar studies were again conducted and here again, populations were collected from sites with a documented history of CPB resistance associated with elevated resistance ratios and the associated emergence phenology will be plotted over time.

This research relates to Objective 1, Develop adapted potato clones with enhanced resistance to major potato diseases, Objective 2, Evaluate exotic potato germplasm for flavor and nutritional components, and introgress valuable genes into the cultivated potato, Objective 3, Examine exotic potato germplasm for resistance to low temperature sweetening and introgress valuable genes into the cultivated potato, and Objective 4, Characterize molecular, physiological and environmental parameters that are determinants of potato quality, especially seed vigor and tuber processing quality.


Last Modified: 8/29/2014
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