Researching Pelecinids – Part 2

One of the most useful resources the Triplehorn Insect Collection has to offer is its extensive HOL database, an online taxonomic initiative that documents collected specimens of various insect groups. This database already contains records for over 845 thousand Hymenoptera specimens, and it continues to grow every week through the hard work of countless contributors.

One way to contribute to HOL is to photograph and upload images of collected specimens, further enriching the available data on specific taxa. Prior to the start of my research on pelecinids, there were zero images of the genus Pelecinus available in the database. To remedy this, I had the opportunity to work with Jordan Reynolds, an undergraduate student in Art & Technology who is currently working on specimen photography for the collection. Over the last several weeks, Jordan taught me about the technologies and techniques required for taking high-quality images for the database.

My goal in photographing a selection of the collection’s Pelecinus polyturator specimens is three-fold. First, I will obtain a more in-depth understanding of the external anatomy of these intriguing insects. Second, I can compare the morphologies of males and females of different sizes and localities. Third, I will contribute previously unavailable data to the HOL database.

Photographing collection specimens is not as simple as taking a picture with a camera. Because the specimens are relatively small, and because we require intricate detail in the images, we instead use a method known as focus stacking. With this method, the camera gradually moves along a track and takes multiple images at different distances. The focused areas of each image are then “stacked” together by a computer program so that the entirety of the final image is clear. Because the P. polyturator specimens required a large depth of field, we sometimes had to photograph and stack up to 100 images to create a sufficiently focused final image.

In addition to taking individual specimen images, we also took several comparison images. These provide a quick side-by-side comparison between two different specimens. Some of the images we took compare males and females of similar localities. Other images showcase females of similar localities and their dramatic variance in size.

comparison image of P. polyturator females

Comparison image illustrating the size variation in P. polyturator females

Of course, no system is perfect, and we faced many challenges along the way. Most of the parasitic wasps that get photographed by the collection are very small in size (no more than a few millimeters long). Therefore, the collection’s microscopic camera that is traditionally used for parasitoid photography is designed to take highly detailed images of very small specimens. P. polyturator females are unusual in that they are very large parasitoids that can exceed 40 mm in length. Because of this, many of the specimens we wanted to photograph could not fit under the microscopic camera. We instead opted to use a DSLR camera, which is used for macrophotography of larger specimens such as beetles and butterflies. Using this nontraditional method of parasitoid photography, we were able to produce high-quality images of the larger specimens by exploiting various imaging techniques.

Another challenge we faced was the handling of the specimens. All mounted insects in a collection must be handled with great care because they are dry and brittle. Pelecinids must be handled with extra caution because their long, string-like antennae and fragile abdomens will break with even the slightest bump.

We ended up with many beautiful images of these wasp specimens. The complete collection of images has been uploaded to HOL and is available on the page dedicated to P. polyturator. I would like to thank Jordan for all of his help with this photography endeavor. Without the countless hours he spent performing behind-the-scenes image processing, the final images could never have turned out so well.

About the Author: Hannah McKenzie is an undergraduate entomology major at the Ohio State University. She currently works at the Triplehorn Insect Collection and is participating in undergraduate research on Pelecinus wasps.