The gene functions to maintain the structure of the vitelline membrane in implying its co-option into axis formation.

Axis specification is a fundamental developmental process. Despite this, the mechanisms by which it is controlled across insect taxa are strikingly different. An excellent example of this is terminal patterning, which in Diptera such as occurs via the localized activation of the receptor tyrosine kinase Torso. In Hymenoptera, however, the same process appears to be achieved via localized mRNA How these mechanisms evolved and what they evolved from remains largely unexplored. Here, we show that , known for its role in terminal patterning, is instead required for the integrity of the vitelline membrane in the hymenopteran wasp We find that other genes known to be involved in terminal patterning, such as and , also do not function in embryonic development. These findings extended to orthologues of vitelline membrane proteins known to play a role in localizing Torso-like in ; in these are instead required for dorso-ventral patterning, gastrulation and potentially terminal patterning. Our data underscore the importance of the vitelline membrane in insect development, and implies phenotypes caused by knockdown of must be interpreted in light of its function in the vitelline membrane. In addition, our data imply that the signalling components of the terminal patterning systems were co-opted from roles in regulating moulting, and co-option into terminal patterning involved the evolution of a novel interaction with the vitelline membrane protein Torso-like.This article has an associated First Person interview with the first author of the paper.