Targeted Host Sampling Strategy Reveals Hidden Diversity of Gall-Inducing Insects on Asteraceae

The remarkable habits of gall-inducing insects make them valuable subjects for ecological and evolutionary research. However, comparative studies across regions are often constrained by uneven sampling efforts, both spatially and temporally. To overcome this limitation, we developed a new sampling methodology, the “Target Host Sampling Strategy” (THSS), which leverages insect-host plant associations derived from ecological networks in neighboring zoogeographical regions to guide systematic sampling in the focal areas. We validated the THSS through a case study of gall-inducing insects associated with Asteraceae in subtropical Taiwan, where species diversity has likely been underestimated due to inconsistent survey efforts. In total, we documented 53 gall morphotypes on 23 plant species, of which approximately 77% (41 morphotypes) represent new records. These findings demonstrate that THSS is a powerful approach for uncovering previously overlooked gall-inducing insects, especially those forming inconspicuous galls on herbaceous hosts. Four orders of gall-inducing insects are recognized in this study, i.e., Diptera (Cecidomyiidae and Tephritidae), Hemiptera (Triozidae and Aphidoidea), Lepidoptera and Hymenoptera. To support future taxonomic and ecological studies, we also provided an updated checklist of gall morphotypes on Taiwanese Asteraceae.