Biology of Chauliognathus spp. (Hentz) (Coleoptera: Cantharidae) in Virginia agroecosystems

Chauliognathus pensylvanicus (De Geer) and C. marginatus (Fabr.) are two of the most common species of cantharid beetles observed in agroecosystems in Virginia. Despite their widespread abundance and early recognition and description in the 1700s, little is known about their phenology and ecological role in agricultural systems. Immatures have been recorded feeding upon soft-bodied insects such as lepidopteran larvae, and adults frequently visit flowering plants, where they eat nectar and/or pollen. Beyond those observations, relatively little is known about these species, which are conspicuous elements on and around farms, though there is considerable potential for their use as pollinators and predators in a biological pest control context. I employed a phenological study to determine the period of C. marginatus activity in Southwestern Virginia, and found adults active on a variety of flowers from mid-May to late July. On these flowers, they spent a large percentage of their day mating or feeding, with significant differences in the percentage of beetles participating in behaviors based on time of day and beetle sex, but not based on month. The majority of C. marginatus observations occurred on narrowleaf mountain mint (Pycnanthemum tenuifolium Schrad.), poison hemlock (Conium maculatum L.), and wild bergamot (Monarda fistulosa L.). I also used a community science-based approach to evaluate the usage of host plants and flower colors by C. marginatus and C. pensylvanicus. Chauliognathus marginatus utilized white flowers more than expected based on their potential availability, while C. pensylvanicus utilized yellow flowers over all other flower colors and more than expected based on their potential availability. Communities of flowers available to and observed with C. marginatus and C. pensylvanicus differed significantly at the family and genus levels. Laboratory bioassays supported these conclusions regarding C. pensylvanicus color preference, but not C. marginatus color preference. Lastly, because of their susceptibility to nontarget chemical exposure in agroecosystems, I tested the efficacy of both organic and conventional vegetable insecticides against C. marginatus adults. The highest mortality was seen in the acetamiprid, flupyridifurone, sulfoxaflor, and imidacloprid treatments, which reached 97-100% mortality at two days after treatment. High mortality (60-97% two days after treatment) was also seen in the organic treatments containing azadirachtins, pyrethrins, and Chromobacterium subtsugae strain PRAA4-1T. Mortality in the Burkholderia spp. strain A396 and spinosad treatments was not significantly different from that of the controls, however, control mortality was relatively high in both assays.