Ants as social insects live in groups, which increases the risk of contagious diseases. In response to the threat of pathogens, ants have evolved a variety of defense mechanisms, including incorporating antimicrobial chemicals into nest material for nest hygiene. Crematogaster rogenhoferi is an arboreal ant, building its nest using plant tissues. It is still unclear how C. rogenhoferi is protected against pathogens in its nest. Two main chemicals, 2,2'-methylenebis[6-(1,1-dimethylethyl)-4-methyl-phenol] (MP) and lup-20(29)-en-3-one (LP), isolated from nest materials of C. rogenhoferi were used to investigate ants' anti-pathogenic activity against the entomopathogenic fungus Beauveria bassiana and the entomopathogenic bacteria Serratia marcescens. The results showed that MP and LP can inhibit the growth of B. bassiana through direct contact and fumigation. However, neither MP nor LP had any negative effect on S. marcescens growth. Subsequent analysis showed that MP was found in both the abdomen part and the head part of C. rogenhoferi workers, and LP was not detected in C. rogenhoferi workers. Since LP is a common plant secondary metabolite, it is implied that LP may originate from the plant tissue of C. rogenhoferi nest materials. Our results showed that C. rogenhoferi capitalizes on its own antimicrobial chemicals and probably the chemical defenses which have evolved in plants to protect itself against pathogens.
Keywords: Crematogaster rogenhoferi; GC-MS; ant nest extract; antibiosis; immune defense.