High temperatures will likely limit establishment success of the Brazilian peppertree thrips, Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae) in the USA, despite variation in microhabitat thermal environments

Biological control of the invasive tree, Schinus terebinthifolia Raddi, is under investigation to improve conservation and restoration of native plant communities in the continental USA. Release and monitoring of the Brazilian peppertree thrips, Pseudophilothrips ichini, is ongoing in multiple states and climate zones but establishment has been variable. In particular, establishment has not been confirmed in hot, southern Texas locations despite release of over 150,000 thrips across four locations since 2022. To understand whether thermal limitations may preclude use of P. ichini in some regions, we investigated upper and lower thermal limits of P. ichini. We measured upper limit of chill injury zone (ULCIZ) and lower limit of thermal injury zone (LLTIZ) in the laboratory under multiple combinations of temperature and exposure duration then modeled spatial variation in survival based on detailed weather data over 20 years. Additionally, we documented microhabitat variation in temperature extremes in three release sites in south Texas to evaluate whether thermal refugia exist due to variation in microhabitat conditions. Based on LLTIZ and ULCIZ, thermal injury accumulates rapidly at temperatures above 33.08 ± 0.15 °C and more slowly at decreasing temperatures below 7.85 ± 0.82 °C. Temperatures within the canopy of S. terebinthifolia in the field varied widely and produced a range of predicted mortality, with temperatures at the base of trees that were more moderate in both summer and winter. We determined that, based on the current distribution of S. terebinthifolia in the USA, climate suitability differs between states. Suitability of Florida locations was deemed highly to moderately suitable across seasons, but most Texas locations were unsuitable, including previous release locations in south Texas. These findings suggest releases should continue through most of Florida, in areas of southern California, and locations along the northern gulf coast of Texas. Additionally, augmentative releases of P. ichini during mild seasons may provide opportunities for use of this biological control agent to manage S. terebinthifolia in Texas.