Aphidius ervi and pea aphid (IMAGE) Drexel University Caption Researchers at Drexel University studied how the relationship between pea aphids and their endosymbiont bacteria has evolved to help the aphids fend off parasitic Aphidius ervi. Credit Drexel University/Alex Wild Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.