Bae, Michael (2022-08). Novel Nanocomposite Biopesticides with Azadirachtin to Protect Tomato Plants against Fall Armyworms. Doctoral Dissertation.
Thesis
Nano-biopesticides have received attention for protecting the plants against the pests, and sustaining the soil environment. For integrated pest management, the introduction of current nano-biotechnology is essential for higher efficacy, biocompatibility, enhanced photostability, and controlled release of pesticides. Moreover, composing the pesticides with naturally derived compounds such as essential oils and plant extracts is recommended owing to the concerns that synthetic and petroleum-based materials can persist in the soil to harm the environment and the quality of the crops. In this dissertation, the preparation of two novel nanocomposite biopesticides encapsulating the neem seed extract and its characterization, efficacy against the insects and its corresponding mechanism studies, and systemic delivery of the nanoformulations into the tomato plants are reported. The whey protein and glycine were selected as a matrix for the composite preparation, at the same time working as an emulsifier when dissolved in water. Owing to the encapsulation via self-assembly mechanism under mechanical energy generated from the ultrasonic application for the emulsification step, the particles have shown highly monodispersed size characteristics and zeta potential. The photodegradation was slower compared to the bulk neem seed extracts for both nanocomposite biopesticides, and the release kinetics have shown the unique dispersion characteristics of each formulation, and it corresponded with the mortality response characteristics against the fall armyworm (S. frugiperda) in this study. Through scanning electron microscope, two main possible uptake pathways of nanoparticles into the insects were reported, and the confocal microscope has verified that the head part via mouth pathway has more accumulations of fluorescence embedded nanoparticles compared to the abdominal part via spiracles and others. The wetting and adhesion behavior of the nanoformulations were investigated through static contact angle of different concentrations deposited on the leaflet surfaces. Due to the highly hydrophilic characteristics with lower static angles by elevating the concentration, it is expected that the nanoparticles are coated to the leaflet surface after the sprayed water evaporates. The contact assay and the leaf feeding assay of nanoformulations against the fall armyworm have given the idea of delivering the biopesticides to the insects either by spraying directly to the insects or coating the plant surfaces. To further sustain the protection of the plants, the systemic delivery of nanoformulations was conducted by tagging the fluorescence dye in the formulations. The optical microscopy has verified the possible uptake pathway starting from the root in hydroponics, and the xylem bundles were shown as the main pathway from the root to the midrib of the leaflet to deliver the red dye with water. The confocal microscopy has shown the accumulation of nanoparticles in the same location as a red dye, which optical microscopy has confirmed. Due to the size differences, glycine formulation with a size below 50 nm has shown much more uptakes compared to the whey protein formulation with a size distribution of 100-1000 nm. Also, by elevating the concentration, the uptake amount has increased for both formulations, and especially the accumulation of glycine formulation with higher concentration has reached up to the leaflet surfaces, indicating that nanopesticides can intercellularly translocate if the size is small enough to pass through the apoplastic and symplastic pathway.
