Week 3: fighting thrips

Most people have never encountered a thrip and for that they should be grateful.  Thrips have haunted my nightmares all summer.  They may sound like an amusing animal from a Roald Dahl novel, but truly they are vicious monsters.  While the adults may only be 1-2 millimeters long, thrips pack tremendous plant destroying power into their tiny exoskeletons.  Thrips are tiny insects that literally suck the life out of plants.  As the guardian of greenhouse bay 1, they are my arch nemesis.  Thrips roam the leaves of milkweed plants in swarms, sucking the contents out of cells.  They leave pale spots in their wake where chloroplasts have been evacuated from the leaves.  A proper infestation of thrips can kill all the leaves on a milkweed plant and leave only a sad looking stem that will then die back to the roots.  One method of thrip control is to wash the plants with insecticidal soap.  You can maybe imagine that bathing an entire greenhouse bay of potted plants is a tremendous undertaking.  The next method of control is to go stem by stem and try to crush all of the adult thrips on the leaves.  Basically petting every leaf in a bay of milkweed takes hours.

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Week 2: learning R

To improve my data analysis skills, I have been trying to teach myself how to code in R.  This is my first foray into coding so the going has been rough.  Part of the challenge is that I have no idea what is or isn’t possible to do while coding in R.  I started out by watching some videos on the basics of R coding language.  Honestly, the videos weren’t very helpful.  They went very in depth on the theory of everything and what R was doing behind the scenes.  I spent a long time watching one video explaining logical vectors.  Eventually I gave up on the watching videos method of learning and turned to old fashioned googling all of my problems.

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Week 1: reading papers

My summer research started out with reading a ton of papers on all aspects of the monarch butterfly life cycle.  I thought I knew most of it pretty well after researching the monarch and milkweed interaction for three years, but there is always more to learn.  The idea behind my project is that there was a change in the monarch butterflies’ diet over the past century as prairie was replaced by farmland and eastern forests were cleared.  I hypothesize that they are now less chemically defended because their main food plant is Asclepias syriaca which contains low levels of weakly emetic cardenolides.  This may have led to an increase in mortality during their overwintering period due to greater numbers being eaten by birds.  In the process of writing a grant proposal to fund this project, I have read about 30 papers on monarchs and milkweed.

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Analysis of Long-term Trends in Monarch Chemical Defenses

Common milkweed, Asclepias syriaca, produces steroid compounds called cardenolides to deter herbivores.  Cardenolides interfere with the function of the sodium potassium pump in cells and can disrupt heart rhythm.  In addition to this, they have an unpleasant, bitter taste.  Monarch butterfly caterpillars exclusively eat milkweed species.  They are able to do this by sequestering the cardenolides they consume.  The cardenolides stored by the monarch provide it with chemical defenses as both a caterpillar and an adult.  Monarch butterfly populations have been declining due to a multitude of causes.  One threat to monarch populations is predation by birds as they overwinter in Mexico.  Cardenolides have been shown to deter birds from eating monarchs.  Asclepias species have been declining in abundance as well, but  A. syriaca has adapted to modern land use practices better than other, more toxic species.  We predict that as the relative abundance of different Asclepias species has changed, a greater proportion of monarch caterpillars has fed on A. syriaca.  A. syriaca produces much lower levels of cardenolides than some other milkweed species.  The amount of cardenolides stored by monarchs is related to the amount of cardenolides in their diets overall.  Monarchs that fed on less toxic milkweed plants as caterpillars will be less chemically defended as adults.  This project will assess whether monarch butterflies have become less toxic over the past century as their diet has shifted towards weakly toxic A. syriaca and away from other, more toxic, milkweed species.  I will use High Performance Liquid Chromatography to analyze the cardenolide levels of monarch butterfly samples from the midwestern breeding population.  I will aim to use 100 butterfly samples that were collected between 1900 and today.  I will also assess A. syriaca samples from the same geographical range and time period to control for a change in cardenolide production by A. syriaca.

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