A downy killer wages chemical warfare

It may look sweet and fuzzy. But make no mistake. It’s a cold, calculated murderer.

The assassin, a common fungus called Beauveria bassiana, slays with a vast arsenal of chemical weapons, leaving corpses in a fluffy white shroud (including the caterpillar above). And like any trained killer, it quickly moves on to the next victim. “If you’ve got six to eight legs, it is going to go after you,” says molecular biologist and biochemist Nemat Keyhani of the University of Florida in Gainesville. People and other vertebrates are generally safe, he says.

With a cocktail of enzymes, B. bassiana bores through the armor of more than 700 arthropod species worldwide. Once inside a victim, the fungus feasts on the doomed creature’s bloodlike hemolymph, nimbly evading prey defenses with tricks, some unknown to science.

When the fungus is finished dining on hemolymph, usually after a few days, it simply eats its way out

through the insect’s tissue. To ensure that no scavenging microbes share its kill, B. bassiana also spews antimicrobial compounds throughout the dead body. Satiated, the fungus blooms; ivory wisps of fungal strings and tiny spores burst from the carcass’ seams and with any luck, land on the next target.

The bug carnage has seized scientists’ interest at least since 1835, when naturalist Agostino Bassi discovered the fungus knocking off silkworms in Italy. In the decades since, some researchers have tried to train the killer fungus to slaughter unwanted pests such as fire ants, bedbugs,mosquitoes and ticks. Other scientists including Keyhani focus on learning about B. bassiana’s chemical warfare.

Many fungi attack insects. But B. bassiana has provided a rare window into insect countermeasures against assaults. Keyhani and colleagues recently revealed a common grain-eating beetle’s uncommon talent: It can shield itself from the assassin using its own antifungal compound. Although B. bassiana in turn has an enzyme to destroy the compound, the fungus doesn’t produce enough of it to overthrow the beetle’s defense.

The finding, reported June 8 in the Proceedings of the National Academy of Sciences, may be a rare snapshot of an evolutionary competition between insect prey and vicious fungal killer. In this chemical arms race, the beetle is winning — for now.