RESEARCH ARTICLE Nitric oxide radicals are emitted by wasp eggs to kill mold fungi Erhard Strohm1*, Gudrun Herzner1, Joachim Ruther2, Martin Kaltenpoth1,3†, Tobias Engl1,3† 1Evolutionary Ecology Group, Institute of Zoology, University of Regensburg, Regensburg, Germany; 2Chemical Ecology Group, Institute of Zoology, University of Regensburg, Regensburg, Germany; 3Insect Symbiosis Research Group, Max Planck Institute for Chemical Ecology, Jena, Germany Abstract Detrimental microbes caused the evolution of a great diversity of antimicrobial defenses in plants and animals. Insects developing underground seem particularly threatened. Here we show that the eggs of a solitary digger wasp, the European beewolf Philanthus triangulum, emit large amounts of gaseous nitric oxide (NOÁ) to protect themselves and their provisions, paralyzed honeybees, against mold fungi. We provide evidence that a NO-synthase (NOS) is involved in the generation of the extraordinary concentrations of nitrogen radicals in brood cells (~1500 ppm NOÁ Á and its oxidation product NO2 ). Sequencing of the beewolf NOS gene revealed no conspicuous differences to related species. However, due to alternative splicing, the NOS-mRNA in beewolf eggs lacks an exon near the regulatory domain. This preventive external application of high doses of NOÁ by wasp eggs represents an evolutionary key innovation that adds a remarkable novel facet to the array of functions of the important biological effector NOÁ. DOI: https://doi.org/10.7554/eLife.43718.001 *For correspondence:
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