Karl Foord of the U of M writes, Each fall brings the challenge of not only what tropical plants to keep over the winter, but also how to keep them healthy in the Minnesota winter home environment. Despite all efforts our plants will provide winter refuge for aphids and mites. It seems like this is the perfect time to use imidacloprid (Merit, Imicide, Grub-ex, Gaucho, Premise). As a systemic it will control the aphids and has no chance of impacting natural populations of insect predators or pollinators in this environment. However, Imidacloprid will not control spider mites. Why not?