Study on Milkweed and Pollinator Population in Virginia- By Jason Robinson

This summer I have been a part of an ongoing study of Asclepias syriaca (Common milkweed) and how changes in population affect known pollinators. To study this, a crew and I traveled to different field sites across Virginia: Blandy Experimental Farms, Sky Meadows State Park and Presquile Wildlife Refuge. At these sites we took plant demographic data (i.e. height, number of flowers, number of leaves, herbivory, etc.) as well as observation videos. The observation videos consisted of 20 minutes of footage focused on a single inflorescence. In addition to observation videos, we conducted and recorded in-person observations. In both sets of observations, the researcher recorded what insect visitors came (if possible, down to species) and how long they stayed. After we collected all the footage, I watched the videos from this summer, last summer, and the summer of 2014.

To analyze what we had gathered, I learned a data analysis programming language called R and used it to synthesize and create detailed graphs that compare the insect visitors between the years and between experimental sites. So far, the most interesting things I have observed are that there are 5 major insects that visit the milkweed plant: brown-beltedbumblebee(Bombus griseocollis), soldier beetle (Chauliognathus marginatus), flies, unknown hymenopterans, and European honeybees (Apis mellifera). Although, from what we have seen the common milkweed beetle, which we previously hypothesized to be a pollinator, is not a significant pollinator. In fact, it’s almost useless as a pollinator. Among the major pollinators, we have also seen inconsistencies in their appearance. For example, while the bumblebee was the most common pollinator in 2014, in 2018 it dropped to fourth in the list of five major pollinators and remained there in 2019 as well.

Previously, a study done by the graduate student in the lab, Nichole Gustafason, related the number of flowers on an inflorescence to the type of pollinators that show up to that plant. Fewer flowers on an inflorescence attracted honeybees while more flowers attracted more soldier beetles, bumblebees, and flies. With further research we may be able to establish similar links between milkweed characteristics and how they influence pollinator behavior.

In addition to the research I have been doing on pollinator behavior, this summer we have been investigating the effects of cardenolides on microbial growth. Cardenolides are toxins in milkweed that deter herbivores by poisoning them. However, sometimes these toxins can end up in the nectar of a plant, (e.g. studies have shown nicotine in the nectar of tobacco plants) which could negatively impact the reproductive success of the plant by repelling pollinators. We are investigating whether cardenolides have antimicrobial properties, providing an advantage to milkweed plants that was previously unknown. The experiments so far have been inconclusive, but this is another study we will continue to pursue during the year.

Attached below is an itemized list of expenses. While we only spent $700.00, the remainder will be spent on computers to replace the inoperative ones in the lab.




September 1st, 2019


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