Using Herbivory Blocks to Test Herbivory’s Effect on Sexual Reproduction of the Common Milkweed

For the final leg of the field research, we embarked on another ambitious task.  Throughout the observations, we did not see any red milkweed beetles with pollinia attached, so they probably are not acting as pollinators.  However, that is not the only way these beetles could affect sexual reproduction.  In order for the milkweed to engage in procreation, the plant must attract pollinators to remove the pollinia and take the pollinia to pollinate another milkweed.  That is why most plants, including milkweed, produce nectar.  There is a slight wrinkle in milkweed however; they are poisonous.  They produce cardenolides to resist herbivory.  Those chemicals are found throughout the plant, from the seeds to the leaves to the flowers.  That means herbivory by the red milkweed beetles could ramp up the milkweeds cardenolide production, which could drive off pollinators.  If that were true, herbivory could lead to decreased pollination.

To test this, we set up what we called “herbivory blocks”.  What we did was select three milkweed in close proximity to each other.  For each block, we established three tiers of herbivory.  One was the control plant, one was medium herbivory, and one was heavy herbivory.  For each, we covered the plant with a mesh covering.  For the control, no beetles were added into the cage.  For the medium herbivory, we added four beetles to the cage.  For the heavy herbivory, we added eight beetles.  These were left for twenty-four hours to allow for the beetles to dine on the milkweed.  After twenty-four hours, we take off the cages and allow the beetles to run free.  In addition, nectar samples were taken before and after to see if cardenolides increase in nectar pre- and post-herbivory.  The day after the cages are taken down, we made two observations per block, one in the morning and one in the afternoon.  One of the plants are observed in person, and two were observed by video.  After that, we photographed each leaf

We managed to complete 34 blocks, which involved 102 plants, 204 observations, and 2,500 photographs of leaves.  After we finished with the blocks, we left Blandy farm to come back to campus.  For the remainder of our time, myself and the other technician will be processing the Mt. Vesuvius of data that we need to process.  Hopefully, we will be able to get everything done we need to.  It will definitely be a race to the finish.

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