CHEMICAL ECOLOGY, MICROBIAL DYNAMICS, AND FOREST HEALTH: INVESTIGATING INTERACTIONS AMONG NON-NATIVE SCOLYTINE BEETLES, FUNGI, AND NEMATODES IN BLACK WALNUT ECOSYSTEMS

In this era of changing global climate and globalization, the intricate relationships between non-native organisms and their impacts on forest health are of paramount concern. Bark and ambrosia beetles are diverse groups of insects that are among the most intercepted insects at international ports of entry. Once established, these insects can vector pathogens and disrupt functional forest dynamics. Bark and ambrosia beetles are known to attack various tree species, including black walnut (Juglans nigra), a valuable timer and nut-producing tree native to Eastern North America. Non-native woodboring beetles provide unique opportunities for ecological studies and pest management. This research investigates the chemical ecology and microbial dynamics in black walnut ecosystems to fill critical knowledge gaps and address the pressing issues surrounding forest health and sustainable management.

In Chapter 1, I review the current literature describing the use of semiochemicals in bark and ambrosia beetle management, non-native scolytines as vectors of phytopathogens, and the use of nematodes as natural antagonists of fungal pathogens in trees.

In Chapter 2, I aim to identify attractant and repellent semiochemicals for the ambrosia beetle Anisandrus maiche, which is a first step in developing effective management strategies for this species. I found that conophthorin and verbenone are strong repellents and that this beetle is attracted to ethanol in a dose-dependent manner.

In Chapter 3, I tested the hypothesis that Anisandrus maiche will be influenced by volatiles of its nutritional fungal symbiont, Ambrosiella cleistominuta, and that these compounds may synergize with ethanol. I identified seven unique compounds from the fungus and two fungal alcohols in the field. I found isobutyl alcohol to repel A. maiche while isoamyl alcohol has seasonal effects on A. maiche capture when paired with ethanol.

In Chapter 4, I aimed to characterize the assemblage of microorganisms residing on two non-native ambrosia beetles across diverse forest types. I tested the hypothesis that forest stand diversity and management regimes would affect the assemblage of microorganisms of ambrosia beetles. I found forest type influences the abundance of fungi and bacteria on A. maiche and Xylosandrus crassiusculus and that both beetle species transport genera of pathogenic fungi.

In Chapter 5, I test the hypothesis that inoculation with Geosmithia morbida alters the volatile profile of black walnut. I found one isolate of G. morbida induced changes in the volatile profile of black walnut bark and identified the compounds that changed relative to the control trees.

In Chapter 6, I tested the hypothesis that free-living fungivorous nematodes can modulate Thousand Cankers Disease severity. I found two genera of nematodes Panagrolaimus and Aphelenchoides to orient towards agents of the TCD system in Y-tube bioassays. Aphelenchoides sp. that were exposed to G. morbida grown on agar media augmented with black walnut bark extract significantly reduced G. morbida cankers in black walnut seedlings. This research has important implications for the management of TCD.

In Chapter 7, I summarize results from each of research chapter and discuss future research needs and directions to continue development of the knowledge surrounding chemical ecology and microbial dynamics of non-native scolytine beetles.