Experimenting with aphids at Bobcat Ranch

Will Wetzel and I made a quick day trip to Bobcat Ranch to try setting up a new experiment with aphids. The question behind this experiment is: “Does prior herbivory by aphids influence the larval success of monarchs?”. The aphids that attack milkweed around here are Oleander aphids, and they tend to hit the milkweeds hard early in the season. I’m particularly interested to know if the early season presence of aphids influences the seasonal fitness landscape for monarchs. In other words, if a milkweed is hit hard by aphids early in the season, would a monarch do better to oviposit on it later? There have also been some previous greenhouse studies of aphid effects on milkweeds that show a disproportionate reduction in root biomass in particular, so I’m also wondering if aphid attach in year 1 will have negative effects on monarchs in year 2. To answer these questions experimentally, we’d need to be able to move aphids around, so that we can randomly assign some plants to be aphid present, while others are maintained as aphids absent.

Our first attempt at this will be to simply take aphids from other plants, and transfer them on a small cutting. Hopefully, the aphids will disembark, and establish on their new host plants. Stay tuned!

A few notes from the field: Many of the narrow-leaved milkweed is already thick with aphids, so we will focus on A. eriocarpa for this experiment. The A. fascicularis is also harboring an impressive number of ladybird beetles. We tried a few plants with bags:


…but got a little worried about them getting too hot in there, so we did the rest without bags. The experiment itself it set up with patches as “blocks”, which we hope will help control for both genotype and microhabitat effects. Also notable was the number of Chrysochus on several plants:


Fingers crossed for the aphid manipulation treatment!

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