Research

One explanation for why invasive species are so problematic in their introduced ranges is that they have "escaped" their co-evolved natural enemies, and thus experience a "release" from the pathogens, parasitoids, and predators they normally encounter in native habitats. Release from these top-down pressures allows introduced species to grow their populations rapidly, leading to ecological and economic damage. Classical biological control seeks to re-establish co-evolved relationships between specialist natural enemies and invasive species across their introduced range. Inherent to the success of biological control programs is the ability of biological control agents to find, accept, and kill their targets. 

Our research group is currently studying how parasitoid physiology may alter response to cues associated with the presence of hosts, and how environmental variation may impact the likelihood of parasitoid establishment and the rate of population growth. Led by Masters Student Vanshika Jindal,  we are addressing these questions in laboratory bioassays with Spathius agrili, and Spathius galinae, two classical biological control agents of the destructive emerald ash borer.

Representative publications: Johnson et al. 2014

Global change is an umbrella term that describes how human activities are altering managed and unmanaged ecosystems throughout the world. As globalization continues to accelerate, trade partnerships have expanded moving goods and raw materials from geographically disconnected regions at increasingly fast rates. Wood and wood products are critical to global trade, as pallets, crates, dunnage are constructed from this renewable material. 

Longhorned beetles (Coleoptera: Cerambycidae) are a highly diverse (~35,000 species), cosmopolitan group of insects that are found on all continents except for Antarctica. Because many species of longhorned beetles spend one or more years developing as larvae inside their woody hosts, this group is readily moved inside wood or wood products globally. The use of long-range volatile pheromones is critical for mate-location by longhorned beetles. Identification of these compounds has not only facilitated the development of traps to monitor for native and non-native species, but also led to the finding that many species of longhorned beetles produce identical blends of pheromones, or share some compounds between pheromone blends. The production of identical pheromones by different species, known also as semiochemical parsimony, has facilitated the rapid collection of many species of longhorned beetles and the subsequent identification of their pheromones.

Our research group has a number of ongoing projects that take advantage of semiochemical parsimony to improve our understanding and management of longhorned beetles. Led by PI Johnson and Research Associate Elise Grossman, and in collaboration with Synergy Semiochemical, we are using single and multi-component lures to assess the abundance, diversity, and phenology of longhorned beetles and their associates, as well as their response to different types of traps in subtropical Louisiana. Additionally, Masters Student Chiranjivi Sharma is currently leading a study investigating how host impacts the development and adult reproductive ecology of two species abundant, polyphagous longhorned beetles, Neoclytus acuminatus and Xylotrechus colonus.

Representative publications: Diesel et al. 2017, Hanks et al. 2019, Johnson et al. 2021

After their introduction, invasive species cause direct and indirect impacts to the function and structure of ecosystems they invade. To best understand the impact of the invasive emerald ash borer (Buprestidae: Agrilus planipennis) on forest ecosystems in subtropical Louisiana, Masters Student Andrew Sanford has been leading a field study generating baseline data on arthropods associated with green (Fraxinus pennsylvanica), pumpkin (Fraxinus profunda), and Carolina ash (Fraxinus caroliniana). Outcomes from our work will contribute to our fundamental understanding of ecological interactions within bottomland hardwood ecosystems, generate valuable information on the abundance and diversity of arthropods associated with ash prior to the emerald ash borer invasion in southeastern Louisiana, and lastly provide valuable specimens for future study by scientists collaborating with the Louisiana State Arthropod Museum, the region's premier collection of arthropods for biodiversity and museum studies.

One result of global change is increased frequency and severity of drought and other environmental stressors. Many woodboring insects rely on environmental stressors to weaken their hosts prior to colonization. The flatheaded hackberry borer (Buprestidae: Agrilus macer) is a secondary pest that can only colonize its woody host plants when they are stressed. Led by Research Associate Elise Grossman, we have undertaken studies to evaluate the impact of bottom-up (e.g.., host species, size, and age) and top-down factors (i.e., parasitoids and predators) on oviposition behaviors and success. Outcomes from our study will improve our understanding of how and when secondary pest outbreaks may occur, and contribute important natural history to our understanding of ecologically and economically important genus Agrilus. This project is the first of an developing collaboration with Jian Duan (USDA-ARS), Claire Rutledge (Connecticut Agricultural Station), Toby Petrice (USDA Forest Service Northern Research Station), Kamal Gandhi (University of Georgia), and other colleagues to survey ovipositional behaviors of native Agrilus and their egg parasitoids in North America.

Relevant publication: Duan et al. 2024.

The geographic mosaic of coevolution predicts that ecological interactions vary in number, strength, and outcome across the heterogeneous landscape. The phytochemical landscape hypothesis posits that bottom-up effects resulting from variation in soil chemistry and subsequently plant chemistry explain the differences observed across the geographic mosaic. How chemistry shifts ecological interactions across space and time is a central focus of our research in the forest entomology group at LSU. We have a number of completed, developing, and ongoing projects that fall within this broad category of research questions. 

Building off of former Statistical Consultant Chris Kuetsinya's analysis that soil type impacts the outcome of management of the southern pine beetle in the southeastern United States, Undergraduate Researcher Daniel Debutts received an LSU College of Agriculture grant to study how soil types identified in Kuetsinya's analysis impacts the development of functional traits and volatile production in loblolly (Pinus taeda) and longleaf (Pinus palustris) under drought and non-drought conditions.

Additionally, we have a number of developing projects related to vegetational complexity within ash (Fraxinus) and how this impacts the success of the invasive emerald ash borer (Agrilus planipennis) and its classical biological control agents.