Fungal community ecology of Lycorma delicatula in Pennsylvania, and the social-ecology of biological invasion risk
Open Access
- Author:
- Taleb, Mariam
- Graduate Program:
- Entomology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 17, 2022
- Committee Members:
- Edwin Rajotte, Co-Chair & Dissertation Advisor
Leif Jensen, Outside Unit & Field Member
Julie Urban, Co-Chair & Dissertation Advisor
Tanya Renner, Major Field Member
Gary Felton, Program Head/Chair - Keywords:
- invasion ecology
environmental sociology
spotted lanternfly
mycology
unequal exchange
biological invasion
agroecology - Abstract:
- The incidence of biological invasions is and has been rising with no evidence of a coming plateau (Seebens et al., 2017). While the direct impacts of biological invasions are reason enough for concern, the interactions of biological invasions with some of the most critical global ecological and social concerns we face today—anthropogenic climate change, biodiversity loss, and global food security—make the issue all the more urgent. The metrics by which we define and measure the incidence and impacts of invasive organisms are under debate in the literature, but it is widely agreed that once established in a new range, introduced species, through trophic interactions, competition and hybridization are economically and ecologically costly. Mitigating the impacts of the growing incidence of invasive organisms requires development of avenues of inquiry into the determinants of success and modes of impact for any one invasion, and for the global rise in invasions. Moreover, these new modes of inquiry demand interdisciplinarity in theoretical and empiric studies. Spotted lanternfly or Lycorma delicatula (Hemiptera: Auchenorrhyncha) is an invasive pest of over 70 woody-stemmed plant species, especially grapes and timber trees, first detected in southeastern Pennsylvania in 2014 (Barringer et al. 2015). L. delicatula is a large-bodied, voracious phloem-feeder and its feeding damage can cause loss of vigor, wilting, and reduced overwintering success. In addition, it deposits sugary waste, or honeydew, on the surfaces of host plants of L. delicatula as well as surrounding vegetation, which facilitates the growth of sooty mold. Sooty molds, a polyphyletic group of fungi, colonize honeydew deposits and form thick black mycelial mats on substrates (Hughes & Seifert 2012). Sooty molds are not direct plant pathogens, but they can stress host plants by reducing their photosynthetic capacity by covering leaves, increasing heat stress, and preventing normal transpiration (Chomnunti et al. 2014). Here, I use emergent methods in mycology to describe the effect of L. delicatula on plant surface fungal communities, and to examine the component fungal taxa of sooty molds found in association with L. delicatula. In Chapter 2, I used DNA amplicon sequencing to describe the fungal community structure on adaxial leaf surfaces of Ailanthus altissima trees (Tree-of-Heaven) exposed to L. delicatula honeydew over one season’s feeding. I found that fungal communities became richer and more similar to one another as they were exposed to honeydew. While it is expected for any deciduous leaf microbial community to become richer over time, it is uncommon for those communities to become more similar, indicating an effect of the honeydew or L. delicatula as opposed to just an effect of time. I also found evidence that a species of Trichomerium fungus was associated with sooty mold development on all sampled plants. In Chapter 3, I used methods similar to those in Chapter 2 to examine fungal community structures on leaf surfaces of wild and cultivated grapes, Vitis riparia and Vitis vinifera. I found that fungal community composition differed between the two Vitis species. Diversity slightly decreased with exposure to L. delicatula in both Vitis species, but I did not find evidence of communities becoming more similar to one another, either within or between plant species. I also found two fungal genera which were associated with sooty mold, Trichomerium, which was significantly more abundant in V. riparia, and Cladosporium, which was nominally more abundant in V. vinifera, though not significantly. Trichomerium was far more abundant across the breadth of samples than Cladosporium, indicating that while multiple taxa may be found in sooty mold facilitated by L. delicatula, Trichomerium may have a stronger association with the insect pest. In Chapter 4, I sought to expand on findings from Chapters 2 and 3 by complementing molecular data with morphological data examining the ultrastructure of field-collected sooty mold-infested leaf samples from plants actively fed upon by L. delicatula. While sooty mold colonies on collected leaves were morphologically mixed, I found characters from an apparent morpho-species of Trichomerium on every collected sample. The Trichomerium morphospecies was abundant on most samples, but more dominant within admixtures of sooty mold on samples with less severe sooty mold, and samples from wild-type plant species. Most sooty mold characters other than those of the Trichomerium morphospecies resembled those of species in the order Capnodiales but appeared to represent multiple families and genera within it. These findings validated my hypothesis that from Chapters 2 and 3 that while sooty mold communities in association with L. delicatula may be mixed, there is an apparent Trichomerium sp. which, based on the literature, is uncommon in similar studies in this region, yet commonly found when L. delicatula is present and feeding. A better understanding of the microbial ecology of L. delicatula may inform future efforts to develop monitoring and management tools for L. delicatula and its associated sooty mold. Biological invasion is definitionally a human-mediated phenomenon—it is the role of economic and social behavior of humans instigating biological invasion which sets it apart from other forms of range expansion. However, the process of biological invasion and the factors which govern its success or failure and its ecological and economic impacts have not been addressed in socio-economic terms in the literature. Meeting the challenge of the growing incidence of bioinvasions demands that socio-economic factors in biological invasion be defined and examined. In Chapter 5, I conducted an integrative review of literature regarding ecologically unequal exchange theory, a sociological theory which posits that countries with economic and political power have undue access to natural resources, and literature regarding biological invasion. From the findings of the literature review, I proposed a conceptual model which argues that due to political and economic inequality, at every stage of biological invasion, the risk of incidence and impact unequally falls on the least developed countries, whose capacity to prevent, manage, and mitigate biological invasions is limited by the same political and economic inequality.