Professor Purdue University West Lafayette, Indiana
The western corn rootworm (WCR) Diabrotica virgifera virgifera Leconte is a major pest of maize in the United States. Currently, it is principally managed using Bt-toxin expressing hybrids and neonicotinoid seed treatments (NSTs), which were concurrently introduced in the early 2000s. This simultaneous release, and subsequent rapid adoption, created a situation in which Bt maize hybrids were never rigorously assessed in the absence of NSTs, and vice versa. Consequently, neonicotinoids’ influence on refuge function, primarily whether these insecticides aid, or hinder, the production of a sufficient population of susceptible beetles to delay resistance, has not been evaluated. Moreover, a mounting suite of detrimental environmental effects of NSTs have been documented, lending some urgency to questions about their necessity.
To determine NSTs’ influence on refuge function, untreated and treated Bt maize fields were planted with 5% untreated refuge marked with 15N and adults were collected and analyzed to determine their natal host plant. Based on our results, the numbers of refuge beetles produced by the 5% seed blend are likely insufficient in producing mating rates to delay resistance development. Four treatments (1. Untreated, Bt seed; 2. NST, Bt seed; 3. Untreated, non-Bt seed; 4. NST, non-Bt seed) were also compared to determine the effect of using NSTs in combination with Bt maize at managing secondary soil pests in the Midwest. Each sampling year documented low abundance of soil pests and minimal effect of NSTs on maize yield.
