Wading for Bugs: Exploring Streams with the Experts

20. In Defense of Whirligig Beetles

117 20 In Defense of Whirligig Beetles Fred Benfield When I began graduate study, I was interested in developmental biology and planned to pursue a PhD in botany at Virginia Tech (then known as Virginia Polytechnic Institute). I had been teaching at a junior college in Georgia for a couple of years and needed a job before starting my program in the fall. As luck would have it, I was offered a summer job by Dr. Stuart Neff at VPI, who was working on a National Science Foundation grant with Dr. Jim Wheeler, a natural products chemist from Howard University. Neff’s two students, George Simmons and Bruce Wallace, were collecting and culturing several species of pest insects (tent caterpillars, face flies, and corn earworms) from which they hoped to extract and identify sex attractants or other 118 Bugs and Beetles on Their Best Behavior pheromones. Because Simmons was busy working on his PhD research in limnology and Wallace was trying to complete his dissertation on wetland flies by summer’s end, I took over the collection and culturing duties of the project. Toward the end of summer, we began working with defensive secretions of a group of snail-eating beetles of the family Carabidae (ground beetles). These beetles have mandibles adapted to feeding on snails, and they normally hunt at night. So we wandered around the mountains of Virginia, West Virginia, and North Carolina in the middle of the night looking for these unusual beasts. When caught, the beetles could be induced to squirt their defense secretions into a vial containing an organic solvent. Wheeler had a mobile laboratory outfitted with analytical instruments where his students began preliminary chemical analyses of the secretions. But after a time we found that field collection of the secretions failed to yield sufficient material for the definitive analyses. So I became a “beetle keeper” in order to collect the secretions from “kept” beetles over time. I began hunting snails to feed the beetle colony, which I kept going while I “milked” the beetles for their defensive chemicals. When the secretions were collected, I packed them in dry ice and mailedthemtoWheelerforanalyses.Throughouttheensuingfall, I continued working with the colony, restarting it the following spring, summer, and fall. After spending my first summer at VPI hanging out with Simmons and Wallace, occasionally helping them with their research and, in the following year, going into the field to collect with Neff, I gladly chucked the idea of studying developmental biology and decided that aquatic biology would be my career path. Stuart Neff was an entomologist specializing in aquatic groups; by the time I joined his lab, his interests had turned towards In Defense of Whirligig Beetles 119 a group of aquatic beetles that had long been connected to a familiar odor: the scent of apples. Among aquatic beetles, the Gyrinidae (apple-bug or whirligig beetles) are probably the most visible because they swim on the surface of lakes and streams. During the previous winter, I thought I had settled on midges for my doctoral dissertation; however, as I started learning more about gyrinids, my fascination grew and I changed directions, working full time on gyrinid secretions and attendant behaviors. There are four genera in the family Gyrinidae, and the genera Dineutus (forty-one species) and Gyrinus (fourteen) make up the bulk of the North American species. Individuals of Dineutus emit a sweet-smelling odor reminiscent of apples when disturbed. Gyrinus, on the other hand, emits a pungent sulfurous odor when disturbed. Because gyrinids live on the water surface of ponds, lakes, and streams, they are highly exposed to potential predators from above and below. Yet they are frequently found in groups ranging from a few individuals to massive, singlespecies colonies numbering in the thousands. Because we were interested in defensive secretions, we tried to identify the chemical nature and function of the secretions Dineutus discolor produced. We knew the secretions were produced in a pair of pygidial glands that open in the membrane of the last abdominal segment. At first, we tried a chemist’s approach—-to extract the secretion from large numbers of individuals in a solvent. Later, we changed the strategy to “milking” the secretion from individual beetles—a biologist’s approach that proved to be a more efficient method of collection. The secretion was identified as a mixture of C14 compounds including a novel one, which the chemist named gyrinidone. As the...