Spring 2010: Of Note

Tiny Aphids, Big Surprises

These tough little bugs could teach us a lot

By Carol Clark

Pea aphids, expert survivors of the insect world, appear to lack major biological defenses, according to the first genetic analysis of their immune system. “It’s surprising,” says Emory biologist Nicole Gerardo, who led the study, published in February in Genome Biology. “Aphids have some components of an immune system, but they are missing the genes that we thought were critical to insect immunity.”

Pea aphids are major agricultural pests, yet important biological models for studies of insect-plant interactions, virus vectoring, and genetic plasticity. These resilient insects thrive despite a host of enemies, including parasitic wasps, lady bugs, fungal pathogens, and frustrated farmers and gardeners the world over. So, given their lack of immune defenses, how do they protect themselves?

Perhaps by focusing on reproduction: from birth, a female aphid contains embryos that also contain embryos. “She is born carrying her granddaughters,” Gerardo says. “In a lab, a female aphid can produce up to twenty copies of herself per day. About ten days later, those babies will start producing their own offspring.”

Over 50 million years, aphids have evolved complex relationships with beneficial bacteria that supply them with nutrients or protect them from predators and pathogens. It’s possible that the weak immune response in aphids developed as a way to keep from killing off these beneficial microbes. Further study of how the aphid immune system works could yield better methods for controlling them in agriculture and provide insights into human health.

“We need beneficial bacteria for proper digestion in the gut and to protect against cavities in the teeth,” Gerardo says. “Some people feel sick when they take antibiotics because the drug kills off all the beneficial bacteria. If we can study the process of how to keep beneficial bacteria while clearing out harmful bacteria across several organisms, including aphids, we might be able to understand it better.”