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Working with weevils!

The internship has come to a close, and I’m excited to talk the rest of our research this summer. After returning from Door County, we immediately began to work on feeding studies, utilizing three different species of biocontrol weevils. The weevils were placed in artificial habitats in the lab, where they were allowed to feed on Cirsium pitcheri and other plants, while their utilization of the plants was recorded over time. In studies similar to these, we also gave the weevils a choice in host plant, to document their preferences for the various species. This information will be used to determine which species pose a threat to C. pitcheri, as well as exactly how each species is able to exploit its host plant.

       

From left to right: Larinus minutus, Larinus obtusus, Larinus planus

We used Larinus planus, which is an invasive weevil that is currently threatening multiple C. pitcheri populations, as well as Larinus minutus and Larinus obtusus, which are used to control weeds in Wisconsin but may be able to utilize Cirsium pitcheri as well. I was interested in the differences and similarities between these three species, and I decided to investigate their behavior and utilization of their enclosures for my project. I was able to observe L. minutus and L. obtusus while they were in enclosures for the feeding studies, and I set up a separate enclosure for L. planus. I watched one individual out of each group for two five-minute periods every hour, and documented each behavior type as well as the duration and frequency of behaviors. I made my observations over the course of two days, which meant that I spent a lot of time watching weevils with a stopwatch in my hand! Some examples of their behaviors included perching, feeding on flower flourets, mating behavior and crawling.

With this information I was able to make an ethogram for each species, which shows the amount of time devoted to each activity. Each ethogram was quite different from one another, but to find out the statistical significance of the observed differences, I used several tests including a principle components analysis for the behavioral data, and t tests with resampling for their activity and detectability measurements. I tried to look at each piece of the data I collected, to see what could be learned. In doing this I found that overall, the species showed significant differences from one another, including their placement within the enclosures, the activity level and behaviors between L. minutus and L. obtusus, and the detectability of L. planus when compared to L. minutus. This is especially interesting because the three species are quite similar. Larinus minutus and L. obtusus are only able to be identified to species using a microscope, since the morphological differences between them are so subtle. They are also commonly used in similar situations for biocontrol purposes, as both use the invasive Centaurea stoebe as a host plant. Nevertheless, these data show that they do have differences from one another, and when placed in identical circumstances they may not perform in the same way. If I had more time on my project, I would like to look at temporal patterns among the species. For instance, when are they most active and most sedentary, and do all species show the same patterns over the course of a day?

Looking back, I’ve had an incredible summer and I’m so grateful for this opportunity. I was able to learn so much and work with amazing mentors. I'm going to miss my time at the garden!