Dietary road salt and monarch butterflies: minimal effects on larval growth, immunity, wing coloration, and migration to Mexico

• DOI: 10.1101/2023.09.04.554310
• Publication Date: 2023-09-05T03:20:15Z
• Authors: Amanda K Hund; Timothy S. Mitchell; Isabel Ramirez; Amod Zambre; Lili Hagg; Anne Stene; Karilyn Porter; Adrian Carper; Lauren Agnew; Alex Shephard; Megan Kobiela; Karen Oberhauser; Orley R. Taylor; Emilie Snell-Rood
• Keywords: Monarch butterfly

Abstract The spectacular migration of the monarch butterfly is under threat from loss habitat and decline their milkweed host plants. In northern part range, roadsides could potentially produce millions monarchs annually due to high densities milkweed, however roadside can accumulate chemicals roads, such as sodium road salt. Controlled lab studies have shown mixed effects on development: small increases be beneficial an important micronutrient in brain muscle development, but large sometimes decrease survival. It unclear how dietary affects performance ecologically relevant conditions, itself. this experiment, we raised outdoors, migration-inducing sprayed with three levels chloride. We released 2500 tagged held additional 250 for further assays. While our recovery rates wintering grounds were low (N = 7 individuals), individuals all chloride treatments made it Mexico. Butterflies reared control salt concentrated tissues, while those diets excreted sodium, suggesting above a physiological optimum. There no treatment wing coloration, survival, body size, immunity, or parasite prevalence. Taken together, results suggest that are robust milkweeds found along roadsides, which promising respect conservation efforts promote habitat. Significance Statement Monarch butterflies flagship species pollinator conservation, recently being listed endangered by IUCN. Roadside target breeding they often hostplant. However, also pollutants, deicing treatments. caterpillars treated milkweeds, measuring suite measures, releasing nearly migration. little effect Mexico, development time, prevalence, coloration. Monarchs appear supporting possibility