The ecological roles of two entomopathogenic endophytes: Beauveria bassiana and Purpureocillium lilacinum (formerly Paecilomyces lilacinus), were investigated in both applied and basic studies utilizing cultivated cotton, Gossypium hirsutum, as a model system. Fungal endophytes are defined as microorganisms living inside plant tissues, but do not cause symptoms of disease to the host. First, we evaluated the plant performance of cotton and the negative effects, if any, on two different herbivores feeding in planta under greenhouse and field conditions. We first tested cotton aphid (Aphis gossypium Glover) in greenhouse and field experiments in 2012 and 2013 and found a reduction in aphid reproduction when feeding on plants inoculated with the target endophytes. Our research also evaluated the effects of the endophytes on both the performance of cotton and development of its chewing herbivore pest (Helicoverpa zea). The results showed an increase in dry biomass and number of reproductive tissues on plants treated with the endophytes, along with reduced longevity and slower developmental rates across multiple H. zea life history stages. One of the mechanisms suggested behind endophytic-mediated plant protection from herbivores is a systemic response in the plant induced by the presence of the fungus. Thus, the plant hormone profile of plants inoculates with target endophytes was investigated using UPLC-MS/MS analysis. Results showed a priming effect of plant defense response when the plants were inoculated with the endophytes and then challenged by an insect herbivore, A. gossypi. Lastly, a field experiment was conducted to investigate the role of host plant genotype and its local genetic environment in shaping fungal endophyte communities. The diversity of endophytes was different depending on date of sampling, plant genotype and its local environment. Overall, our research results provide support for the beneficial effects of manipulating fungal endophytes in plants as part of reliable insect pest management strategies in the near future.
