Combined Elevation of Temperature and CO2 Levels Impacts the Production and Sugar Composition of Aphid Honeydew
Abstract Honeydew is the keystone of many interactions between aphids and their predators, parasitoids, or mutualistic partners. Despite the crucial importance of honeydew in the aphid-ant mutualism, very few studies have investigated the potential impact of climate change on its production and composition. Here, we quantified changes in the sugar compounds and in the amount of honeydew droplets released by Aphis fabae reared on Vicia faba plants, under elevated levels of temperature and/or CO2. A combined elevation of these two abiotic factors increased honeydew production as well as the total amount in sugars, in particular the concentration of fructose and melezitose. Increased amount of sugars in phloem sap under elevated CO2 conditions, along with a raise of aphid metabolism and sap ingestion to compensate for water loss under elevated temperatures might explain these observed changes increase in honeydew production and sugar content. A higher amount of excreted honeydew coupled with a higher concentration in melezitose and fructose are expected to enhance both the feeding behavior and the laying of a recruitment trail by ant foragers, thereby reinforcing the ant-homopteran mutualism under a scenario of elevated temperature and CO2 levels. We discuss about the enhancing and counteracting effects of climate change on other biological agents (gut microorganisms, predators, parasitoids) that interact with aphids in a complex multitrophic system.