Location: Vegetable Crops Research Unit
Project Number: 3655-21220-002-11
Start Date: Aug 31, 2011
End Date: Sep 30, 2014
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.