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 Colorado potato beetle (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.
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. Volatiles that are specific to and are abundantly produced by CPB resistant Solanum species will be evaluated for CPB behavior modifying activity. Wild species clones selected for the production of behavior modifying volatiles will be crossed to the cultivated potato. The hybrid offspring will be selected for adaptation, fertility and resistance to CPB. Resistance bioassays will be carried out in the laboratory and the field. We will identify volatiles from resistant plants and use this to inform potato breeders about an unattractive or repellent potato volatile profile, which can be combined with traits that reduce CPB development, increase CPB mortality and slow the development of insecticide resistance. Our ultimate goal is to combine multiple resistance mechanisms into a clone that delays CPB resistance development and provides long lasting broad-spectrum crop protection.
Potato plants, as all other plants, emit volatiles that regulate their interactions with pests, such as the Colorado potato beetle. We studied the headspace chemical composition of cultivated potatoes (cv. Snowden) and different wild potato species that are resistant Colorado potato beetle. We found that the headspace of cultivated potatoes is different from that of wild species and that there are differences in headspace composition among wild species. The tested wild species were: Solanum oplocense, S. chacoense, and S. pinnatisectum. When examining qualitative differences in headspace samples, we discovered that S. oplocense, S. chacoense, and S. pinnatisectum, all emit monoterpenes (e.g., limonene) not found in the cultivated potato. When comparing the cultivated potato to wild Solanum species, we also discovered that beta-caryophyllene and (E)- beta-farnesene make up 35-40% of the volatiles from cultivated potato, whereas in the wild Solanum species they comprise only 6-20% of the total emissions.
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.