CHARACTERIZATION AND IDENTIFICATION OF HOST PLANT DRIVEN PLASTICITY OF THE CABBAGE LOOPER (TRICHOPLUSIA NI) SALIVA
Open Access
- Author:
- Rivera Vega, Loren Jackeline
- Graduate Program:
- Entomology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 01, 2017
- Committee Members:
- Gary Felton, Dissertation Advisor/Co-Advisor
Gary Felton, Committee Chair/Co-Chair
Edwin George Rajotte, Committee Member
Christina M Grozinger, Committee Member
Dawn S Luthe, Outside Member
James Homer Tumlinson III, Committee Member - Keywords:
- entomology
chemical ecology
phenotypic plasticity
transcriptome
proteome
cabbage looper
caterpillar saliva
plant-insect interactions
host plant - Abstract:
- Plant-insect dynamics are a complex network of chemical interactions. How insects are able to adapt to their host plants and how plants can resist or tolerate insects are questions of much importance for evolutionary biology, ecology, physiology, insect behavior, agriculture, food security, and science in general. For example, plants are capable of inducing defenses against insects after detecting insect specific cues. Insects on the other hand might suppress these defenses by releasing molecules present in secretions like saliva. Currently, there is limited information on the saliva composition of chewing insect herbivores and how it might affect plant defenses. The main objectives of this study were to 1. Characterize the saliva of the generalist insect pest, the cabbage looper (Trichoplusia ni) and 2. Identify the changes in the composition of insect saliva driven by two of its host plants - cabbage and tomato as compared to artificial diet. These objectives were approached using both transcriptomic (RNAseq) and proteomic techniques (iTraq). A transcriptome of 14,037 genes and a proteome of 434 proteins were established. Feeding on different host plant diets resulted in substantial remodeling of the gland transcriptomes and proteomes, with 4,501 transcripts and 63 proteins significantly differentially expressed across the three treatment groups. Gene expression profiles were most similar between cabbage and artificial diet, which corresponded to the two diets on which larvae perform best. Within these libraries, several interesting enzymes were identified that may play an important role in the cabbage looper’s ability to establish on different hosts. Some of these enzymes that were further analyzed are a catalase and three potential myrosinases. Catalase activity was confirmed in the labial glands of the cabbage looper. It was also determined that catalase plays a role in detoxification by reducing the activity of peroxidases as well as herbivore offense by suppressing the induction of trypsin protease inhibitor in tomato. The myrosinase genes identified were differentially expressed in several tissues of the cabbage looper and under different diets. iii iv However, they appear to be broad-spectrum glucosidases rather than specific myrosinases. Finally, as part of the INTAD dual degree, the alternative use of water containing methyl isothiocyanate - a defensive secondary compound in the famine shrub Hanza (Boscia senegalensis), was investigated. Hanza waste water has a significant effect on seed germination of several plants and could potentially be used for weed management in small farms of West Africa. This is an example of the study of plant defensive compounds for the use in applied research. This dissertation provides information about caterpillar saliva, which can be used for future functional and ecological studies. Also, it enriches our knowledge about a usually neglected secretion from chewing insects.