Dr. Lance J. Meinke
Date of this Version
Dang, T. D. 2021. Characterization of western corn rootworm (Coleoptera: Chrysomelidae) susceptibility to foliar insecticides in northeast Nebraska. M.S. thesis, University of Nebraska-Lincoln, Nebraska.
The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is a major pest of maize in the United States. A variety of tactics are used to manage this pest such as crop rotation, insecticides, and transgenic maize expressing insecticidal proteins from Bacillus thuringiensis (Bt). WCR populations are highly adaptive and have evolved resistance to these management tactics. Management options are limited as few new tactics are available. Research is needed to evaluate the value of existing tactics used within an integrated framework to manage densities/injury and mitigate resistance.
This study evaluated the field performance of formulated foliar insecticides (bifenthrin, chlorpyrifos) targeting adult WCR populations in northeast Nebraska during 2019-2020 with the focus on short and longer-term effects on density. Cohorts of fields were treated with a single application of foliar insecticide or left untreated as controls during the peak adult activity period, then sampled for WCR density before and after treatment. WCR densities, sex ratio, and proportion gravid females were not significantly different in treated and untreated fields prior to insecticide application. Results indicated within-season efficacy of insecticides was excellent as mean adult density was significantly reduced post-application in treated fields compared to control fields. An emergence cage study was conducted the following season to document the effect of foliar insecticides on adult survival. Total adult emergence was significantly reduced the following season in treated fields. Results suggest a single, properly timed insecticide application can reduce build-up of WCR density in continuous maize which would also reduce selection pressure on Bt maize where resistance occurs. A positive relationship between the sampling methods, whole plant counts and unbaited Pherocon AM sticky traps, was derived from the sample data.
Susceptibility of adult WCR populations in northeast Nebraska was further characterized by conducting laboratory vial bioassays with bifenthrin, chlorpyrifos, and dimethoate to develop dose-response curves. Results confirmed that the WCR populations were relatively susceptible to the active ingredients with exception of a few populations exhibiting low levels of resistance. These data will serve as a baseline for comparison in future bioassays and inform WCR management programs.
Advisor: Lance J. Meinke