Dispersal of spicebush (Calycanthus occidentalis, Calycanthaceae) by yellow jackets (genus Vespula; Hymenoptera: Vespidae)

Authors: BURGE, DYLAN - University Of California; Beck, John

Submitted to: Madrono
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2019
Publication Date: 8/6/2019
Citation: Burge, D.O., Beck, J.J. 2019. Dispersal of spicebush (Calycanthus occidentalis, Calycanthaceae) by yellow jackets (genus Vespula; Hymenoptera: Vespidae). Madrono. 66(2):41-46. https://doi.org/10.3120/0024-9637-66.2.41.
DOI: https://doi.org/10.3120/0024-9637-66.2.41

Interpretive Summary: Although a rare occurrence, wasps of the family Vespidae are known to seek out and disperse the seeds of at least two North American and two Asian plant species. Attraction of the wasps to the seeds is likely due to the release of odors that signal availability of a fleshy appendage of the seed (eliaiosome) that is rich in protein and fat, and the wasps remove before releasing the seed. Here, we present our findings on dispersal of spicebush (Calycanthus occidentalis) seeds by wasps of the genus Vespula. A private industry scientist in collaboration with an ARS scientist in Gainesville, FL observed and performed experiments with the goals of discovering: how geographically widespread this interaction is; what the reward system is, if any; and, how wasps detect the achenes. Eight populations of C. occidentalis in northern California were used to observe wasps and plants, and to perform experiments on wasp attraction to the achenes. In all examined populations, workers of Vespula pensylvanica were observed entering mature Calycanthus receptacles, removing the seed, taking flight with them, and successfully transporting the seed through the air. Nutritional analysis and experiments suggested that wasps were attracted to the organ of the seed which is high in fat and protein. Further experiments using solvent extracts of the achenes suggests that the attraction is chemical in nature, and likely mediated by odors emitted by the seed. Basic research such as this helps understand the plant-insect interactions of plant-visiting insects and apply this knowledge toward pollinators of agricultural commodities.

Technical Abstract: Carnivorous wasps of the family Vespidae are known to seek out and disperse the diaspores of at least two North American and two Asian plant species. Attraction of the wasps to the diaspores is likely due to the release of volatile compounds that signal availability of an eliaiosome rich in protein and fat, which the wasps remove before releasing the diaspore. It is thought that this interaction between carnivorous wasps and plants is rare, occurring in just a few plant species. Here, we present our findings on dispersal of spicebush (Calycanthus occidentalis Hook. & Arn.) achenes by carnivorous wasps of the genus Vespula. Observations and experiments were performed with the goals of discovering: how geographically widespread this interaction is; what the reward system is, if any; and, how wasps detect the achenes. Eight populations of C. occidentalis in northern California were used to observe wasps and plants, and to perform experiments on wasp attraction to the achenes. In all examined populations, workers of western yellowjacket (Vespula pensylvanica [de Saussure, 1857]) were observed entering mature Calycanthus receptacles, removing achenes, taking flight with them, and successfully transporting achenes through the air. Receptacles were found to open upward at an average angle of 458 (SD . 298), preventing the achenes from falling to the ground when mature. No animals other than wasps were observed visiting the receptacles during the observations. Experiments suggest that wasps are attracted to an elaiosome-like organ of the achene. Nutritional analysis shows that this organ is high in fat and protein. Further experiments using solvent extracts of the achenes suggest that the attraction is likely mediated by volatile compounds.