The long proboscis of the aphid Stomaphis yanonis (Aphididae Lachninae) is advantageous for avoiding predation by tending ants.

Whether in ant-aphid mutualism the ants exert evolutionary selection pressure on aphid morphology has not yet been fully tested. Here, we tested whether the long proboscises of Stomaphis yanonis (Aphididae Lachninae) aphids confer an advantage in preventing predation by the tending ants. Specifically, we tested the hypothesis that aphids with a shorter proboscis would excrete less honeydew, making them more likely to be preyed upon by ants.