An undescribed Ophelimus gall wasp species that causes damage to Eucalyptus trees was found in Taiwan in a recent investigation. The major hosts of this Ophelimus sp. are Eucalyptus grandis (Myrtaceae), E. urophylla, and E. camaldulensis. Analysis by Tukey's test showed no significant difference in mature gall volumes among the 3 host plants, regardless of differences in gall color or shape. An evaluation of galling preferences and host susceptibility of the hybrid strains from the 3 major hosts showed that the most preferred host to galling adults was the (E. urophylla × grandis) × E. camaldulensis hybrid, followed by the (E. grandis × urophylla) × E. camaldulensis hybrid. The (E. grandis × urophylla) × (E. tereticornis × grandis) hybrid had the lowest infestation rate, and it was found that mixing non-host species with suitable hosts to build resistant hybrid strains could be a workable management tool for plantation pest control. Previous research on host preferences and host ranges of known invasive wasps on eucalypts was also reviewed in this study, which may help choose ideal strains to alleviate attacks from this Ophelimus wasp in the future.