Ant-aphid relationship: commensalism or protocooperative?

Abstract

Past documentation reveals that ant and aphid interaction is either commensalistic or protocooperative. Our purpose was to determine what type of symbiotic relationship Formicidae and aphids Homoptera share. The experiment included nine Populus grandidentata saplings with ant (Formicidae) and aphid (Homoptera) populations present on their axis of the stem. There were three additional saplings in the study with ant and aphid populations on the dorsal side of the leaves. The 12 saplings were divided into three treatment groups: 1.) aphids only, 2.) aphids plus ants, and 3.) aphids plus a predator (Coccinellidae). Saplings with aphids along their axis were measured per mm2 each day for five days. Saplings with aphids on the dorsal side of their leaves were individually counted. A Wilcoxon-Mann-Whitney test showed a significant (n1=4,n2=4, U'=16, p<=0.05) decrease in the population size on a sapling with aphids plus lady-bird beetles. The ants may provide the protection against intensive predation and natural predators.