Honors College Theses

Publication Date

2025

Major

Biology (B.S.B.)

Release Option

Open Access

Faculty Mentor

Dr. Scott Harrison

Abstract

Bacterial endosymbionts can influence host physiology and ecology, shaping processes such as species introductions. Wolbachia pipientis, a maternally inherited intracellular bacteria common in arthropods, alters host biology through cytoplasmic incompatibility, parthenogenesis induction, increased fertility, nutritional enhancement, and pathogen resistance. The kudzu bug (Megacopta cribraria), a legume-feeding insect native to Asia, was introduced to northern Georgia in 2009 and has since spread across 15 southeastern U.S. states. This species harbors two major bacterial endosymbionts: Candidatus Ishikawaella capsulata and Wolbachia pipientis. While the relationship with Candidatus is well studied, less is known about Wolbachia. This study used multilocus sequence typing (MLST) to characterize Wolbachia in kudzu bugs collected during early invasion (2013) and in current populations (2024). The following questions were asked: (1) Has Wolbachia infection frequency changed over time in introduced populations? and (2) Is there genetic variation in Wolbachia between native and introduced populations, or between different U.S. collection years? Results show 100% infection across all introduced populations, with little temporal change between 2013 and 2024. Genetic comparisons revealed sequence divergence from 5% between native and introduced samples and between Chinese populations. These findings support a single introduction and a stable association between kudzu bugs and Wolbachia, offering insight into the role of endosymbionts in the establishment and spread of invasive insects.

Thesis Summary

This thesis examines the invasion of the kudzu bug (Megacopta cribraria) in the southeastern U.S., with a focus on its association with the endosymbiont Wolbachia pipientis. Using mitochondrial COI and Wolbachia MLST gene data, I compared introduced U.S. populations (2013, 2024) to native populations from Kunming and Shanghai, China. U.S. bugs showed no genetic variation and carried a single haplotype for both genes, supporting a single introduction event and rapid expansion. In contrast, Chinese samples, especially from Kunming, showed significant genetic divergence, suggesting multiple species or lineages in the native range.

All sampled bugs were infected with Wolbachia, indicating a stable, maternally inherited symbiosis that may contribute to invasion success. Genetic similarities between U.S. bugs and those near Shanghai—but overall distinctiveness from both Chinese groups—support a likely Japanese origin, consistent with earlier studies. The congruence of COI and MLST data points to co-inheritance and a lack of recombination or multiple introductions.

These findings highlight the potential role of microbial symbionts in invasive species success. While Wolbachia’s functional effects in kudzu bugs remain unclear, its high prevalence suggests it may enhance reproduction or survival. Future studies should explore this further and assess whether Wolbachia influences host plant use, particularly in relation to soybean feeding in the U.S.

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Available for download on Thursday, April 15, 2027

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