Biotic resistance: Facilitation between invasive Homoptera and invasive ants limits the establishment of an introduced weed biocontrol agent in New Zealand

► We investigated why boneseed leafroller moth establishment is patchy in New Zealand. ► Establishment failure was correlated with scale insect abundance on boneseed. ► Scale insects were tended by ants, which fed on boneseed leafroller larvae. ► Insect biocontrol agents that feed externally may fail in the presence of ant-tended Homoptera.