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," said Emory University biologist Dr. Nicole Gerardo, who led the study."Aphids have some components of an immune system, but they are missing the genes that we thought were critical to insect immunity." One hypothesis is that aphids may compensate for their lack of immune defenses by focusing on reproduction. From birth, a parthenogenic female aphid contains embryos that also contain embryos. This is called "telescoping of generations." "She is born carrying her granddaughters," Dr. Gerardo said. "In a lab, a female aphid can produce up to 20 copies of herself per day. About 10 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, Dr. Gerardo noted. "A key question is whether these microbes could have changed the aphid genome, or changed how the aphid uses its genes." Further study of how the aphid immune system interacts with microbes could yield better methods for controlling them in agriculture. Pea aphids are major agricultural pests and also important biological models for studies of insect-plant interactions, symbiosis, 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.
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