Plant Stress Insect Interactions PDF Download

Drought and herbivory are two stresses that threaten productivity and survival of plants. While plant responses to either drought or herbivory are well studied, the responses of plants to concurrent drought and herbivory are unclear. This dissertation investigates the impact of water availability on plant-insect interactions using chemical ecology, plant physiology, molecular biology, and ecology approaches. We discovered that drought stress enhances plant resistance against insect herbivores and reduces plant tolerance against defoliation. In addition to its negative impact on plant tolerance, drought stress also reduces the number of insect natural enemies and other arthropods on plants. The reduction in arthropod number was found to benefit certain insect herbivores by reducing negative species interactions such as competition and predation. We hypothesized that the reduction in arthropod number on drought-stressed plants are partly associated with changes in plant volatile emission and found that the detrimental effects of drought on natural enemy attraction was associated with changes in herbivore-induced plant volatile (HIPV) emissions. Using current knowledge on ecology of drought-plant-insect interactions, we discussed the implications of water availability on plant anti-herbivore defenses and the integration of water and pest management in crop production around the world. Furthermore, we discover the ability of insect herbivores to induce drought-like response for their own benefit. We identify a hydrogen peroxide-producing salivary protein (glucose oxidase, GOX) in caterpillar Helicoverpa zea that triggers stomatal closure in plants. Stomatal closures were further linked to inhibition of important defense related HIPVs, such as (Z)-3-hexenyl acetate and (Z)-3-hexenol, which is similar to HIPV changes caused by drought. The findings discover an herbivore adaptation that utilize drought-like responses of plants for their own benefits and show the links between stomatal behavior and HIPV emission. This is the first study that utilizes CRISPR-Cas9 mutagenesis to study salivary protein function of insect herbivores and showed that organisms other than microbes can modulate behavior of stomata. As changes in water availability and pest continue to threaten plants in both natural and agricultural systems under climate changes, this dissertation contributes to a better understanding of the impacts of drought stress on plant-insect interactions from molecular, organismal, to populational levels. Additionally, we highlight the ability of insect herbivores to induce drought-like responses of plants, such as stomatal closure, for their own benefit, which is a novel strategy that have not been reported to date. We further demonstrate that stomata are important parts of plant responses to herbivores, in addition to its roles in responses to abiotic stresses and pathogen attack. However, significant knowledge gap exists in stomatal functions in plant-insect interactions, we are certain that the findings in this dissertation will incite further research and lead to a better understanding of stomatal functions in plant responses to their environment.