Predators, ants, and aphids: an investigation of possible mutualism on Populus grandidentata.

Abstract

Interactions between species shape the world in which we live. Mutualism is a type of interaction in which both species involved benefit. A common example of potential mutualism is the relationship between ants (Hymenoptera Formica) and aphids (Homoptera Aphididae). Ants are believed to receive nutrients from honeydew which is secreted anally from the aphids. Homoptera are believed to benefit from the protection from predators by ants and increased reproductive output. Twenty-four samples of Populus grandidentata inhabited by ant-aphid colonies were located on the University of Michigan Biological Station property (T33N R3W sec. 33). In half of these colonies, ants were removed. The remaining plants were used as a control group in which no ants were removed. Hippodamia convergens and Chrysopa carnea, natural predators of aphids, were introduced to both groups of plants. Ants were observed to effectively protect aphids. Predators were removed in 87% of our trials with ants. An aphids was eaten by a predator in only one of the sixty trials in which ants were present. C. carnea ate an aphid faster than H. convergens in the absent of ants. C. carnea were removed more quickly than H. convergens when ants were present. Colonies with high attendance by ants were able to more efficiently remove H. convergens than colonies with low ant attendance. Mature aphids were rarely found in the presence of ants. This may illustrate the opportunity for increased reproductive output due to ants' attendance. Our study illustrated ants' protection of aphids and the possibility of increased reproductive output of mature aphids due to the ants' attendance.