Elevated CO2 Concentrations Impact the Semiochemistry of Aphid Honeydew without Having a Cascade Effect on an Aphid Predator

Abstract

Honeydew is considered a cornerstone of the interactions between aphids and their natural enemies. Bacteria activity occurring in aphid honeydew typically results in the release of volatile organic compounds (VOCs) that are used by the natural enemies of aphids to locate their prey. Because atmospheric carbon dioxide (CO2) concentration directly impacts the physiology of plants, we raise the hypothesis that elevated CO2 concentrations impact the quantity of honeydew produced by aphids, as well as the diversity and quantity of honeydew VOCs, leading to cascade effects on the foraging behavior of aphids’ natural enemies. Using solid-phase microextraction, we analyzed the VOCs emitted by honeydew from pea aphids (Acyrthosiphon pisum Harris) reared under 450 ± 50 ppm of CO2 (aCO2) or 800 ± 50 ppm CO2 (eCO2). While the total amount of honeydew excreted was only slightly reduced by eCO2 concentrations, we detected qualitative and quantitative differences in the semiochemistry of aphid honeydew between CO2 conditions. Three VOCs were not found in the honeydew of eCO2 aphids: 3-methyl-2-buten-1-ol, 2-methyl-1-butanol, and isobutanol. However, no difference was observed in the searching and oviposition behaviors of hoverfly (Episyrphus balteatus (De Geer)) females exposed to plants covered with honeydew originating from the different CO2 conditions. The present work showed the effect of a particular aspect of atmospheric changes, and should be extended to other abiotic parameters, such as temperature.

Attraction of Female Aedes aegypti (L.) to Aphid Honeydew

“…Crude aphid honeydew seems to have common odor constituents. In crude honeydew of pea aphids feeding on fava bean plants, the same five odorants (2,3-butanedione, 3-hydroxybutanone, 3-methyl-1-butanol, 3-methylbutanoic acid, and 2-methylbutanoic acid) were found by us and a previous study [32], one odorant of which (3-methyl-1-butanol) was again just recently noted [49]. Six odorants identified here (2,3-butanedione, 3-methyl-1-butanol, 3-methylbutanoic acid, 2-methylbutanoic acid, 3-hydroxybutanone, and 2-ehtylhexanol) were also found in honeydew of black bean aphids, A. fabae , feeding on fava bean plants [59], and three of these odorants (2,3-butanedione, 3-methyl-1-butanol, and 3-hydroxybutanone) were noted in honeydew from vetch aphids, Megoura viciae , feeding on fava bean plants [27].…”

Attraction of Female <em>Aedes aegypti </em>(L.) to Aphid Honeydew

“…Crude aphid honeydew seems to have common odor constituents. In crude honeydew of pea aphids feeding on fava beans, the same five odorants (2,3-butanedione, 3-hydroxybutanone, 3methyl-1-butanol, 3-methylbutanoic acid, and 2-methylbutanoic acid) were found by us and a previous study [25], one odorant of which (3-methyl-1-butanol) was again just recently noted [41].…”

“…Six odorants we identified here (2,3-butanedione, 3-methyl-1-butanol, 3-methylbutanoic acid, 2methylbutanoic acid, 3-hydroxybutanone, and 2-ehtylhexanol) were also found in honeydew of black bean aphids, A. fabae, feeding on fava bean plants [50], and three of these odorants (2,3butanedione, 3-methyl-1-butanol, and 3-hydroxybutanone) were noted in honeydew from vetch aphids, Megoura viciae, feeding on fava beans [20]. At least some of these odorants may originate from microbial metabolism of honeydew amino acids [41,52].…”

“…We tested the CHD1 at doses equivalent to 2.5×10 1 µL and 2.5×10 0 µL of crude honeydew (Exps 5,6),. the CHD2 at honeydew equivalent doses of 2.5×10 6 µL, 2.5×10 5 µL, 2.5×10 4 µL, produced by 25 pea aphids per day[41] and that aphid infestations can reach several thousand individuals per m[42,43].2.9 Captures of Mosquitoes in Traps Baited with Synthetic Honeydew Odorant BlendsIn laboratory mesh-cage experiments, we tested captures of mosquitoes in traps baited with synthetic honeydew odorant blends (see below). Each cage (77 × 78 × 104 cm) was wrapped with black cloth except for the top allowing light entry from above.…”

Impacts of Global Warming and Elevated CO2 on Sensory Behavior in Predator-Prey Interactions: A Review and Synthesis

“…Interestingly, elevated CO 2 changes the chemical composition of aphid honeydew, a metabolic byproduct containing kairomones used by aphid predators to detect prey. The qualitative changes in composition were insufficient to impact predator search behavior in this study, suggesting that this interaction is robust to climate change (Boullis et al, 2018). That cue quality may be sufficiently conserved so that behavior is not impacted may be due to the cue being composed of primary metabolites that are the product of fundamental metabolic processes.…”