Billbug (Sphenophorus spp.) chemical ecology and seasonal biology in Indiana turfgrass
Billbugs (Coleoptera: Curculionoidea: Sphenophorus) are serious pests of managed turfgrass across North America. Damage symptoms are most visible during stressful periods of the growing season and are commonly confused with disease, drought, or nutrient deficiency. Billbugs are frequently a perennial problem and when misdiagnosed, damage often results in seriously degraded stands of turfgrass that are easily encroached by weeds. Presently, management of billbugs relies heavily on chemical insecticides. Even then, the nationwide assemblage of multiple sympatric billbug species and the cryptic nature of the damaging larval stage makes management of these insects challenging. A better understanding of billbug biology and behavior could improve the efficacy of insecticide inputs and provide a basis for the development of alternative, non-pesticide management techniques that are aligned with integrated pest management (IPM). This thesis focused on characterizing the billbug species composition in Indiana and clarifying the seasonal phenology of one particularly problematic species, S. venatus. To accomplish this, I examined the utility of molecular techniques to identify the otherwise cryptic larval stage of several sympatric, turf-inhabiting billbug species. I also explored the potential for S. venatus to use two forms of chemoreception: recognition of volatile organic compounds and cuticular wax components.^ Weekly monitoring of pitfall traps revealed four sympatric billbug species in Indiana: S. venatus, S. parvulus, S. minimus, and S. inaequalis. Further investigation on the seasonal biology of S. venatus revealed two overlapping cohorts in Indiana and molecular confirmation of overwintering S. venatus larvae through examination of three genetic loci (CO1, 18S, and ITS2). In y-tube olfactometer bioassays, S. venatus males were attracted to the combination of conspecifics and host-plants as well as host-plants alone. S. venatus females were attracted to the combination of male conspecifics and host plant material and male conspecifics alone. These findings suggest S. venatus males are predominantly influenced by host-plant volatiles while females likely respond to a male-produced volatile pheromone. Coupled gas chromatography-mass spectrometry (GC-MS) analysis of S. venatus and S. parvulus whole-body cuticular extracts revealed a series of aliphatic hydrocarbons with qualitative and quantitative interspecific differences, as well as intraspecific quantitative differences between males and females. These differences in cuticular hydrocarbon profiles could serve as critical mate-recognition cues among sympatric Sphenophorus species, a hypothesis that remains to be tested.^ By clarifying the seasonal phenology of S. venatus, results provide a foundation for improved insecticide selection and application timing in the Midwestern U.S. for this pest. Furthermore, findings demonstrate that a DNA-based larval identification tool could be useful for clarifying the seasonal phenology of sympatric billbug species with morphologically indistinguishable larval stages. Findings also support the idea that volatile and contact semiochemicals could potentially be used for the development of improved billbug monitoring techniques and sustainable mating disruption strategies.^
Douglas S. Richmond, Purdue University.