A parasite called microsporidia lies dormant in the circulatory systems of harlequin ladybirds. But when scientists injected microsporidia into a common European ladybug species, the insects died within two weeks. When the ladybugs were injected with dead microsporidia or a control substance most survived.
Harlequin ladybirds’ immune systems, on the other hand, have learned to deal with microsporidia—which lets the insects use them as biological weapons. Because one way ladybugs compete is by consuming the eggs and larvae of rival species. When European ladybug species eat the harlequin ladybird eggs and larvae, they also consume the microsporidia. And die.
The discovery demonstrates an important role of immunity in evolutionary selection. And it shows that there are many ways to lose a food fight.
—Sophie Bushwick
