Baseline Seasonal Inventory of Arthropods Within Endangered Physaria thamnophila (Zapata Bladderpod) Habitat in Tamaulipan Thornscrub of South Texas

Physaria thamnophila (Zapata bladderpod) is a federally endangered plant restricted to southernmost Texas and northeastern Mexico. We conducted a seasonal inventory of arthropods in occupied habitat at the Arroyo Ramirez Tract of the Lower Rio Grande Valley National Wildlife Refuge. Arthropods were sampled from 40 plots during summer and fall 2024 and winter and spring 2025 using sticky cards, pitfall traps, and vacuum collections. Specimens were classified into higher-level taxa, primarily orders, with Coleoptera, Hymenoptera, and Lepidoptera additionally identified to family. Seasonal differences in abundance, taxonomic richness, and diversity were evaluated using repeated-measures mixed models, supplemented by plot-level cluster bootstrapping. We collected 23,721 arthropods representing 20 higher-level taxa. Total abundance was significantly higher in spring (8098 specimens) and winter (6925) than in summer (4952) and fall (3746). Hymenoptera, Diptera, Coleoptera, and Thysanoptera accounted for 86.6% of specimens. Order-level richness peaked in spring (9.23 orders per plot), whereas Shannon diversity was significantly lower in winter (1.23) than in other seasons. Coleoptera abundance peaked in winter, predominantly among Buprestidae, although beetle family richness and diversity peaked in spring. These findings demonstrate seasonal variation in arthropod abundance, composition, richness, and diversity, providing a baseline for future studies of plant–arthropod interactions and P. thamnophila conservation.