| dc.description.abstract | This dissertation analyzed plant-associated fungal effects on two insect pests of cotton (Gossypium hirsutum), the boll weevil (Anthonomus grandis grandis) and cotton aphid (Aphis gossypii), as well as on the predatory convergent lady beetle (Hippodamia convergens). In chapter 2, I tested whether cotton plants grown from seeds treated with plant-associated fungi affect boll weevil behavior, fecundity, and development. In chapter 3, the direct pathogenicity of different plant-associated fungal isolates towards cotton aphids was tested. In chapter 4, I tested whether olfactory cues from cotton plants seed-treated with plant-associated fungi and infested with cotton aphids affect convergent lady beetle behavior.
Boll weevil behavior towards fungal-treated cotton squares was strain-specific, in some cases making them avoid squares from fungal-treated cotton plants. Regarding boll weevil fecundity, fewer larvae hatched, and fewer adults emerged from fungal-treated plants. In addition, developmental time to the adult stage was prolonged in fungal-treated plants. These results indicate the potential for fungal cotton treatments as a new tool for boll weevil management that can repel adults, reducing offspring numbers and affecting their performance. Consequently, fungal treatments could negatively affect the population size of subsequent generations in the field.
Spore suspensions of four plant-associated fungal strains originally isolated as endophytes from cotton were shown to be entomopathogenic to cotton aphids and lowered survival to levels comparable to the commercially-available entomopathogen, Beauveria bassiana, in all the treatments tested. Mycosis was confirmed from the cadavers, establishing the complete infection cycle for all tested isolates. These results highlight the potential to develop these fungi as novel bioinsecticides.
Lastly, cotton aphids infesting fungal seed-treated plants were used in olfactory assays to assess predatory convergent lady beetle behavioral responses. Minor strain-specific responses were found, with one isolate having mild negative effects on convergent lady beetle host selection behavior while another had no effect. This evidence suggests that lady beetle behavioral responses to plants might vary according to fungal treatment but would not strongly impact their use as part of an insect pest management strategy. | |
