Insect pollinator crossing of international border barriers along the U.S.-Mexico border

Abstract

Infrastructure along the U.S.-Mexico Border may not be equally permeable to all types of insect pollinators with potential implications for pollen and gene flow between plant populations. Pollinators were observed on their approach to two types of border barriers (slatted and cemented) along the U.S.-Mexico Border from March 2023 to January 2024. Near the barrier, four insect behaviors were observed including 1) flying over the barrier, 2) crossing through the slats of the barrier, 3) not crossing the barrier, or 4) flying parallel to the barrier without crossing. Overall, 90.2% of the pollinators crossed the barrier. Butterflies were most often observed flying over the barrier (86.8%) or sometimes moving through the slats in the barrier (6.8%). It was more common for moths to crawl through the slats than to fly over the barrier based on the occurrence model. On windy days, both butterflies and moths sometimes flew parallel to the barrier without crossing (1.2% and 27.3%, respectively), although moth crossing behavior was not related to the abundance model. Butterfly abundance increased in higher temperatures and decreased in higher wind speeds. Other insect pollinators were also observed (bee, skipper, wasp) but their crossing behavior was not significantly related to the model. Because pollinators support endangered plant species, strategies to facilitate their barrier crossing could support plant conservation in South Texas.