(Systemic) Insecticides in plants: Phytotoxicity, bioactivation, or hormesis?

Insecticides are commonly associated with insects as the target of their activity. Curiously, the fact that insects are seldom the target of insecticide application is the object of frequent neglect, potentially leading to undesirable consequences. This concern is even more troubling when systemic insecticides are considered because the use of such compounds is on the rise and the popularity of preemptive seed coating with these compounds has greatly increased during the last decades. Thus, insecticide action is not limited to insects, but also affects crop plants, especially when systemic insecticides are considered. Plants are the primary target of application and venue to reach the arthropods targeted by the insecticidal molecule. Thus, they can retain and distribute insecticides and their byproducts, and eventually exhibit the consequences of such exposure. Consequently, phytotoxicity and/or bioactivation may ensue. The former response is better known although more frequently explored when herbicides are considered, while the latter is sparking more attention recently. These potential insecticide-mediated responses, particularly when systemic insecticides are considered, are here discussed individually and as a part of a biphasic continuum of response based on the hormesis phenomenon and its implications.