Ant behavior in the presence of aphids and aphid predators (Chrysoperla carneia or Coleomegilla maculata): an indicator of ant-aphid mutualism?

Abstract

Ant-aphid systems have been studied for over 100 years, with most studies describing their relationship as mutualistic. Ants (Formicidae) receive nourishment from aphid (Aphididae) honeydew production and it is generally thought that they provide the aphids with protection from natural predators, and other services, in return. This protective benefit often has been studied in terms of change in aphid populations with predation in systems with and without ants. Rarely has this association been studied in from the perspective of ant behavior. We studied ant behavior in the presence of aphid predators in the interest of providing further evidence of this mutualistic relationship. Behavior of ants in ant-tended aphid colonies found on Asclepias syriaca (milkweed) plants was studied on 30 July, 31 July, and 3 August, 2000 at UMBS. One of two predators, Chrysoperla carnea (lacewing larvae) or Coleomegilla maculata (ladybird beetle), was introduced into an area of high ant traffic and ant reactions were categorized into one of five groups and counted for five minutes. This procedure was repeated five times on six plants for each predator. Five trials without predators were also performed on each plant as a control group. The behaviors were condensed into two categories, protective and non-protective, and the distributions of these categories were compared using Chi square tests of goodness of fit and independence. We found that ants generally tend to perform protective behaviors, but they perform protective behaviors even more often in the face of aphid predators. This behavioral study provides further evidence of aphid benefit from ants as a part of a mutualistic relationship.