A closer look at the chemical relationship between a beetle and its microscopic cronies has turned up a selective antifungal compound (Science 2008, 322, 63). The finding could be broadly used to decipher complex biological relationships and may lead to new drugs. Cameron R. Currie at the University of Wisconsin, Madison; Jon Clardy at Harvard Medical School; and colleagues examined the southern pine beetle, a notorious pest that bores into tree bark and leaves ravaged pine forests in its wake. These beetles harbor a slew of interacting species, including a beneficial fungus that feeds beetle larvae and an antagonistic fungus that wipes out that larval food supply. By combining scanning electron microscopy with extensive chemical analysis of beetle extracts, Currie and Clardy's team figured out how the beetles stop the antagonistic fungus: They carry a bacterium that uses mycangimycin, a polyunsaturated peroxide, to selectively disable the bad fungus. Mycangimycin is too unstable to be a viable drug candidate but studying other beetle-bacteria associations might unearth potent drug leads, Clardy says.