March 29th - Niranjana Krishnan, Iowa State University. Developing a novel adverse outcome pathway for neonicotinoid insecticides.

Adverse outcome pathways (AOPs) are frameworks that formalize testable hypotheses of how toxic chemicals interact with intracellular molecules to cause harmful effects in individual organisms. In insects, neonicotinoid insecticides are known to act through two AOPs.  In the first AOP, which is neonicotinoid’s primary mode of toxic action, high doses cause neuronal paralysis and death through overstimulation of acetylcholine receptors. In the second AOP, first reported in honey bees (Apis mellifera), lower doses of neonicotinoids alter the neuronal signaling pathway that is responsible for long-term memory, which leads to abnormal foraging behavior and colony failure. In this presentation, the discovery of a third AOP in butterflies and moths is discussed. Neonicotinoids disrupt the larval to pupal molting process and prevent expansion of external body parts, specifically legs, wings, antennae, and proboscis. The doses that cause this effect are two orders of magnitude below doses that act through the primary AOP. Experiments that provided information on the timing of events, along with a review of the literature, indicated that neonicotinoids might be interfering with the function of crustacean cardioactive neurons, which are responsible for successful pupal molt and expansion of external body parts. Mechanisms through which neonicotinoids might be causing this interference are proposed.