Alfalfa Aphids From Pixel to Picture: Deciphering Symbiotic and Predatory Interactions Across Scales

Alfalfa is the cornerstone of Nevadan agriculture. Together with alfalfa aphids, these organisms exemplify the complex ecology of herbivory. This dissertation explores multiple dimensions of this ecology: the landscape context of aphid predation and biocontrol, interactions between the microbial symbionts of alfalfa and aphids, and the factors influencing the occurrence of aphids' secondary bacterial endosymbionts. Chapter 1 focuses on pest control of alfalfa aphids using natural predation. In this study, we applied remote sensing and distance-weighted spatial analysis to determine the sizes, types, and arrangements of habitats that were most beneficial to predators. We paired this study with exclosures to estimate the true effects of predators on aphid population control. We found that coccinellid beetles, which are key aphid predators, were associated with weedy cover in and around alfalfa fields. Our results suggest that weedy areas may provide an undervalued ecosystem service to alfalfa farmers. Chapter 2 explores the potential interactions between the legume-rhizobia and aphid- Buchnera mutualisms. Both rhizobia and Buchnera transform nitrogen into forms that can be assimilated by their hosts and modulate the expression of host plant defense. Yet, the potential nutrient- or plant defense-mediated effects of rhizobia on Buchnera have never been examined. The experiments described in chapter 2 show that nutrient-mediated processes can affect Buchnera , and pave the way for future experiments that directly address rhizobia's nutrition-mediated effects. Aphids also form facultative symbiotic associations with several other types of bacteria, and these symbioses are the subject of chapter 3. In this chapter, we examined the factors that shape the occurrence of facultative symbionts across a broad range of alfalfa habitats. We leveraged a survey of alfalfa traits and arthropod occurrence that spanned 56 sites and seven states across the western US. In a subset of these sites, we sequenced DNA from aphid extractions to identify secondary symbionts and model their occurrence. Importantly, we identified intraspecific host plant variation as a key predictor of symbiont occurrence-a factor that has been largely overlooked in previous work. In summary, this dissertation extends our knowledge of alfalfa and alfalfa aphids in several directions, including aphid biocontrol, interactions between alfalfa and aphid mutualisms, and the distribution of aphid facultative symbionts. It combines experiments and observational studies, extends across spatial scales, and embraces a wide range of techniques to explore the unique ecology of these organisms.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctorate Degree

Grantor

University of Nevada, Reno

Year dc:date.issued

2024

Author dc:creator

• Call, Anson C.

Advisor dc:contributor.advisor

• Pringle, Elizabeth

Committee members dc:contributor.committeemember

• Forister, Matthew
• Ramirez-Reyes, Carlos
• Sullivan, Benjamin
• Solomon, Juan

• Aphid
• Aphid Secondary Endosymbionts
• Buchnera
• Endosymbiont
• Integrated Pest Management
• Rhizobia

Repository record dc:identifier.uri

https://scholarwolf.unr.edu/handle/11714/10944

OAI identifier oai:identifier

oai:scholarwolf.unr.edu:11714/10944