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):
Objective 1. 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. Objective 2. Assessing metabolic resistance levels. CPB adults were collected from three VA locations in 2011 and assayed for baseline levels of three metabolic enzymes (esterase, glutathion-S-transferase, and cytochrome P450 monooxygenase) associated with detoxification mechanisms. A total protein content assay was also conducted on the three VA populations as well. The results from these baseline assays will be compared to enzyme assays conducted after exposing CPB adults from the same fields in 2012 to sub-lethal doses of different insecticides. These trials should indicate which detoxifying mechanisms are activated in CPB. The results of these experiments may provide insight into the potential resistance development of CPB. Objective 3. 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.
3. Progress Report:
This project was renumbered from 3655-21000-049-27S to 3655-21220-002-10S. Colorado potato beetle (CPB) populations from commercial potato fields in Eastern, Midwestern, and Western United States locations were tested at Michigan State University and the University of Wisconsin 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 Colorado potato beetle. Several new products were effective. Having a range of compounds from different chemical classes will be important for Colorado potato beetle control as neonicotinoid resistance continues to increase. No indications of resistance to the new products were observed in the field. In Virginia, potato leaf-dip bioassays were completed in 2011 showing that the novel insecticide tolfenpyrad is highly toxic to CPB larvae. The insecticide is also toxic to CPB adults indicating that tolfenpyrad is about 40x more toxic to CPB larvae than adults. Additional field efficacy evaluations with commercially-formulated tolfenpyrad conducted on the Eastern Shore of Virginia revealed that this insecticide is highly efficacious on CPB larvae. In the interest of insecticide resistance management, it is imperative that we continuously monitor the efficacy of currently used insecticides as well as assess the efficacy of new ones on CPB. Progress relates to objectives 1, 2, 3, and 4 by monitoring resistance in Colorado potato beetle to imidacloprid and thiamethoxam and determining field efficacy of new insecticides and evaluating the affect of alternative insecticides.