Social Immunity, Worker Investment, and Fungal Resistance in Ants

Abstract

This thesis examines ant pathogen defense at two levels. Chapter 1 reviews behavioral, chemical, symbiotic, and internal immune defenses, emphasizing that social immunity and individual immunity function as interacting layers rather than replacements for one another. Chapter 2 tests whether colony-size-related worker disinvestment extends from morphology to fungal resistance. After screening nine Beauveria isolates against Solenopsis invicta, Beauveria bassiana ARSEF 2597 was selected for comparative assays across 16 ant species and six conidial concentrations. Susceptibility varied among species and doses, and resistance showed phylogenetic signal at high concentrations. Larger-colony species had reduced body-size-corrected cuticle investment, supporting structural worker disinvestment, but fungal resistance was not consistently predicted by colony size, worker size, or cuticle investment. These results suggest that colony size predicts worker structural investment but not individual fungal resistance.