Effect of Clove Oil on the Bean Beetle Callosobruchus maculatus and Its Gut Microbiome Público

Abstract

Bean beetles (Callosobruchus maculatus) are one of the pests that attack bean crops. Due to the drawbacks of traditional insecticides, alternatives are being explored for pest control. Plant essential oils have shown promising results in protecting stored bean crops against bean beetles, and among them, clove (Syzygium aromaticum) essential oil is easy to access and has exhibited insecticidal properties. It is also known that clove oil can act as an antimicrobial, and insects rely on their microbiome to detoxify compounds harmful to them. As a result, it is possible that the bean beetle microbiome changes in response to clove oil exposure. Previous studies have not examined the possibility of bean beetles developing resistance to clove oil and the role that the beetle gut microbiome might play in the process. To explore these questions, a multi-generation study was conducted. Bean beetles were reared under no, low, or high clove oil treatments for four generations. The results suggested that only high clove oil exposure significantly decreased bean beetle populations, but the effect did not last throughout the study. Analysis of bacteria cultured from beetles showed that clove oil could affect the beetle’s microbial community, but next-generation sequencing data from the last generation of beetles showed no difference in the microbial community between the three treatments. In addition, the dominant bacteria strains showed no difference in resistance to clove oil. However, due to the temperature variation during the beetle rearing and the limited span of the experiment, further investigation is necessary to confirm these findings. 

Table of Contents

Introduction                                                                                                                                   1

Materials and Methods                                                                                                                  5

Bean Beetle Selection Lines                                                                                              5

Bean Beetle Cohort Life History Traits                                                                            6

Figure 1                                                                                                                  7

           Culturing Bean Beetle Microbiome                                                                                  7

Identification of Cultured Microbes                                                                                  8

           Figure 2                                                                                                                  8

           Disc Diffusion Assays                                                                                                       9

Whole-Community Microbiome Sequencing                                                                 10

Results                                                                                                                                         12

           Bean Beetle Cohort Life History Traits                                                                          12

Number of Successful Emergences                                                                     12

           Table 1                                                                                                     12

           Figure 3a – b                                                                                             13

Time to Emergence                                                                                             13

           Table 2                                                                                                     14

           Figure 4a – b                                                                                             14

Cultured Bean Beetle Microbiome                                                                                   15

Colony Counts                                                                                                     15

           Figure 5a – d                                                                                             16

Colony Diversity                                                                                                  18

           Table 3                                                                                                     19

           Table 4                                                                                                     19

           Figure 6                                                                                                    19

           Figure 7a – b                                                                                             20

Disc Diffusion Assays                                                                                         20

           Figure 8a – b                                                                                             21

Whole-Community Microbiome Sequencing                                                                 21

           Figure 9a – b                                                                                                                 22

           Figure 10a – f                                                                                                       22

           Table 5                                                                                                                25

           Figure 11a – d                                                                                                       26

           Figure 12a – b                                                                                                       28

           Figure 13a – d                                                                                                       29

Discussion                                                                                                                                    30

Literature Cited                                                                                                                           38

About this Honors Thesis

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School	Emory College
Department	Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Biology, Microbiology
Palavra-chave	bean beetles
Committee Chair / Thesis Advisor	Christopher Beck, Emory University
Committee Members	Nic Vega, Emory University David Barba, Emory University

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