A couple years ago I (Raechel) stumbled upon a scientific paper about nitrogen and insecticide tolerance that lives rent-free in my brain now. It’s best described in a diagram from the paper:
The 2022 article is “High nitrogen in maize enriches gut microbiota conferring insecticide tolerance in lepidopteran pest Spodoptera litura” by Hu, Lin et al. (iScience, Volume 25, Issue 1, 103726), and the article is available Open Access at that link. Spodoptera litura is Tobacco cutworm, and while that is not an insect we generally worry about in corn in the Midwest, I would doubt this response is only limited to one species, and may not be limited to just lepidopterans (butterflies/moths).
This was followed up with another article published in 2024: High nitrogen application in maize enhances insecticide tolerance of the polyphagous herbivore Spodoptera litura by induction of detoxification enzymes and intensification of cuticle (Wang et al. Pesticide Biochemistry and Physiology, Volume 203, 2024), which is unfortunately not available in full Open Access (the abstract and highlights are).
That’s two mechanisms that excess nitrogen can cause insects to be resistant to insecticides: 1) by promoting the gut microbiome to degrade the chemical, and 2) by triggering changes in the insect itself (breaking down the chemicals and thickening it’s skin).
When those of us at BASS talk about lowering N inputs, it’s not just because of runoff and saving money. Nitrogen has been having other effects inside of our fields that we haven’t been studying as closely. It’s time we rethink what we really need (and maybe replace some high-needs hybrids with BASS Hybrids that actually like less N).