A bstract In the low-energy effective action of string theories, non-abelian gauge interactions and supergravity are augmented by infinite towers higher-mass-dimension operators. We propose a new method to construct one-loop matrix elements with insertions operators D 2 k F n R in tree-level type-I type-II superstrings. Inspired ambitwistor our is based on forward limits moduli-space integrals ...