| dc.description.abstract | Aphids are among the most damaging pests of cereal crops. Because aphid control is largely chemical, little attention has been given to ecological complexities that promote aphids’ success. How aphids interact with antagonists (natural enemies) and potential mutualists (ants) is important because these interactions can impact the feasibility of biological pest control. One recent and invasive pest of grain sorghum, Sorghum bicolor, is the sorghum aphid, Melanaphis sorghi (SA). Understanding this pest’s ecology in the grain sorghum agroecosystem is critical to developing SA control strategies. Consequently, this dissertation studied SA interactions with a common parasitoid (Aphelinus nigritus) and a potential ant mutualist (the red imported fire ant Solenopsis invicta (RIFA)) to assess the practicality of SA biocontrol. Since parasitoids often use aphid honeydew as a sugar resource, SA honeydew was first assessed as a potential attractant to A. nigritus. As SA feeds on grain sorghum and the nearby overwintering host Johnson grass, Sorghum halepense, A. nigritus preference for SA honeydew produced on either host plant was also assessed. Ultimately, A. nigritus was attracted to SA honeydew and preferred honeydew produced on Johnson grass, which could support the augmentation of this parasitoid in Johnson grass to suppress SAs before grain sorghum is planted. Second, a potential for SA to exhibit fecundity compensation (i.e., a rapid increase in reproduction in response to natural enemies) was explored to determine whether SAs could defend themselves by increasing their fecundity after experiencing wounding akin to parasitoid oviposition. Fecundity compensation was observed in daughters of aphid mothers parasitized by A. nigritus, which may question the use of certain parasitoids in SA biocontrol programs. Third, the effects of RIFAs on SA population growth were assessed over two field seasons. It was determined that RIFA increases SA populations, but only when initial aphid densities are low. This result provides baseline data on potential mutualistic interactions between two invasive species, SA and RIFA, allowing future monitoring of its evolution. As a relatively new invader, the 2013 arrival of SA grants a unique opportunity to explore aphid ecological adaptations to new environments, an often-overlooked factor that may inform future biocontrol. | en |
