The effects of Hymenoptera:Formicidae on the abundance of Homoptera:Aphididae as measured by aphid colony growth rate, predation and sanitation.

Abstract

The nature of a symbiotic relationship is determined by the relative costs and benefits to the symbionts. We examined the relationship between species of Hymenoptera:Formicidae and Homoptera:Aphididae found on Populus balsamifera L. at UMBS in northern lower Michigan. We found that aphid abundance was stabilized in ant-tended colonies and fluctuated in colonies where ants were excluded. Overall, aphid colony growth increased in the antless colonies by 99.3% as compared with a -3.7% overall decrease in the tended colonies over a twelve day period (n=12). The increase in aphid abundance within antless colonies could be attributed to the presence or exclusion of natural predators (-63.2% versus 233.3% growth rate respectively). Induced predators, Crysopa spp., stayed on the leaves of antless colonies more often than on ant-tended colonies. A possible decrease in sanitation, due to increased honeydew and dead aphid accumulation on leaves, was seen in antless colonies. This positive effect of ant presence on aphid abundance in the presence of predators and increase in colony sanitation show that the aphid benefits from this symbiosis.