Characterization of toxicological and neurophysiological effects of natural product based chromenes to Fall Armyworm, Spodoptera frugiperda

Authors: MCCOMIC, SARAH - Louisiana State University; Meepagala, Kumudini; SWALE, DANIEL - Louisiana State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2021
Publication Date: 9/9/2021
Citation: Mccomic, S.E., Meepagala, K.M., Swale, D. 2021. Characterization of toxicological and neurophysiological effects of natural product based chromenes to Fall Armyworm, Spodoptera frugiperda. Journal of Economic Entomology. https://doi.org/10.1093/jee/toab172.
DOI: https://doi.org/10.1093/jee/toab172

Interpretive Summary: The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae), is a pest that has expanded its range from the Americas to nearly 100 countries and continues to threaten the global food supply. Thus, FAW is recognized as one of the most damaging agricultural pests of row crops with economic losses estimated to be at $6 billion dollars annually. FAW control programs depend on a combination of synthetic insecticides and Bacillus thuringiensis (Bt) expressing plants to maintain pest populations below the economic damage threshold. Development of resistance to Bt and most commercialized insecticidal classes has challenged current FAW control paradigms and emphasizes the need to develop new insecticides for FAW management. Natural products (NPs) have served as models for the discovery and development of many commercialized agrochemicals that justifies toxicological analyses of plant secondary metabolites to develop novel insecticidal scaffolds and/or novel mechanisms of toxicity. Overall, chromene natural products have proven to be efficient in their use as potential insecticides. The 13 chromene analogs tested for toxicity against FAW do possess some potential qualities that could be further analyzed into possible insecticides, yet the chemicals studied resulted in relatively low toxicity and had poor in vitro potencies against the CNS nerve firing. The newly synthesized chromenes altered the development of FAW by significantly reducing the number of non-deformed adults upon eclosion and prolonging the larval life stage, indicating the newly synthesized chromene analogs may alter the development of FAW like commercialized insect growth regulators.

Technical Abstract: The development of resistance to most commercialized insecticides has challenged control of fall armyworm (FAW), Spodoptera frugiperda. We previously extracted and purified a chromene amide from Amyris texana and found this scaffold is moderately insecticidal and thus, this study aimed to test the insecticidal properties of 13 synthetically derived chromene analogs to the fall armyworm (FAW, Spodoptera frugiperda). Microinjection of some chromene analogs that were synthesized to FAW exhibited moderate toxicity that was approximately 2- to 3-fold less toxic when compared to permethrin. Alcohol and aldehyde substituted chromene analogs were among the most toxic chromenes. In addition to acute toxicity, three chromenes significantly increased the percentage of developmental defects upon eclosion that prevented adult moths from being capable of flight, suggesting these compounds alter development. Interestingly, microinjection yielded differing signs of intoxication between alcohol and aldehyde substitutions where the alcohol resulted in flaccid paralysis and lethargy whereas the aldehyde led to tonic contractions and hyperactivity. These contrasting sights of intoxication were also observed in electrophysiological assays where alcohol substitutions led to depression of central neuron firing activity and aldehyde substitutions led to hyperexcitation of central neurons. In summary, the chromene amides led to acute lethality and/or altered developmental trajectories of FAW.