It's cute, it's bright, and it gobbles aphids, but the harlequin ladybird can be hard to love. That's because the beetle, originally from Asia, has multiplied so wildly in the United States and Europe that swarms invade houses in the fall. Now, scientists have uncovered one of the harlequin's secrets to success: It cooks up a pharmacy's worth of antimicrobial compounds to protect itself against disease. Scientists collected wild harlequin ladybirds from infested homes—including the home of the mother of one of the authors—and injected some with bacteria or yeast. DNA sequencing of the ladybird's protein-coding genes revealed roughly 50 that help manufacture antimicrobial peptides, compared with 16 such genes identified in the red flour beetle, which the researchers examined for comparison. Two of the harlequin's protective peptides squelched growth of bacteria and an insect-killing fungus. The harlequin's array of germ-fighting chemicals helps it shrug off pathogens when it invades new territory, the researchers report today in the Proceedings of the Royal Society B.
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