Cute Killing Machines

With their cute little spots and a penchant for crawling amiably around a kid's fingers, ladybugs are a favorite bug for many people. But underneath that happy exterior, ladybugs are cold-blooded killers.

Researchers at Brigham Young University recently studied ladybugs, one of nature's best predators. They found that an imported species of Asian ladybug are even tougher than their North American cousins. The Asian species can tolerate much colder temperatures, which is attractive to farmers searching for natural pesticides.

"Ladybugs are an incredibly important predator," said Gary Booth, a professor of integrative biology at BYU who co-authored the study. "In a given day, ladybugs sometimes consume upwards of two or three times their own body weight. I defy anyone to find another organism on the face of the earth that performs at that level, while also helping humans by saving thousands of dollars in pesticides."

The study pitted native North American ladybugs against Asian ladybugs. Farmers substitute both types of bugs for chemical pesticides, but the Asian variety has steadily been out-surviving its native cousins in the field.

Since ladybugs are sensitive to temperatures, Booth and his colleagues subjected both species to different temperatures to determine how the Asian ladybug is getting a leg up on the competition. While both species did well at high temperatures, Asian ladybugs could maintain ladybug activities in cold temperatures that made their North American cousins sluggish.

"Any kind of creature that can perform better at cooler temperatures, they'll likely displace the species that can't cut it when it's cold," Booth said. "The fact is, species with the ability to metabolize, respire, feed and so forth at lower temperatures means that they're going to be much more competitive. Farmers can use this information to improve their use of ladybugs, and as a biologist, this is an important discovery about how we need to look at an organism in order to understand what's really happening."

This study appears in the current issue of Environmental Entomology.