Some insects must survive the winter as adults and must have good defenses against fungi and other pathogens. This includes Harmonia axyridis the “Asian” or “Mulitcolored” Lady Beetle. Like most lady beetles, Harmonia feeds on aphids during the summer. In the winter, large numbers, looking for a warm place to spend the winger, can invade homes and annoy homeowners.Harmonia axyridis is more successful and able to out compete some of the Native North American species of Lady Beetle. One advantage for Harmonia axyridis is better resistance to pathogens and parsitoids. This is in part due to high levels of the chemical, harmonine, in the hemolymph. Harmonine is toxic to many types of bacteria. Harmonine is not effective against fungi which can infect our native lady beetles. Harmonia axyridis uses an array of peptides that are toxic to fungi as protections. Native lady beetles have some anti-fungal peptides, but nowhere near the numbers and variety found in Harmonia axyridis. This beetle has expanded its repertoire to over 50 different peptides. The diversity of the peptides increases the likelihood that one of them will protect against a fungal pathogen.
Anti-fungal agents have an important role in human medicine. Pharmaceutical companies are looking for agents that control fungi with few side effects. Anti-fungal peptides of lady beetles are one source of new agents for study and modification.