|Elliott, Norman - Norm|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2005
Publication Date: 4/11/2005
Citation: Brewer, M.J., Noma, T., Elliott, N.C. 2005. Hymenopteran parasitoids and dipteran predators of the invasive aphid Diuraphis noxia after enemy introductions: Temporal variation and implication for future aphid invasions. Biological Control 33:315-323. Interpretive Summary: More than a decade after the first detection of the Russian wheat aphid (RWA) and first release of RWA enemies we studied the natural enemies of the RWA in the field. The species of natural enemy and their abundance had changed a great deal over the 10+ years. The RWA enemies detected were primarily endemic or long-time residents derived from previous introductions. They had adapted over the 10+ years to exploit the RWA as prey by increasing in abundance in wheat fields. The best evidence of biological control of the RWA was field observations of parasitoids in the rare instance of the RWA exceeding economic thresholds. The practical significance of this study is that it may not be necessary to explore in foreign lands for parasitoids the next time an exotic aphid invades and establishes in cereal fields in North America because the community of natural enemies already existing may adapt over time to provide a degree of biological control of the aphid. Under those circumstances more emphasis on finding ways to conserve and enhance the natural enemies to increase their importance biological control may be more effective and economical.
Technical Abstract: Shifts in prevalence and abundance of hymenopteran parasitoids and dipteran predators, D. noxia, and other aphids were measured in the west-central Great Plains of North America, April--September, in 2001 and 2002, corresponding to over a decade after first detection of D. noxia and first release of D. noxia enemies. Significant temporal shifts in enemy species prevalence and diversity were detected in this study and more broadly during an 11 year time span. At any given time, some species were relatively common. One parasitoid had been predominant throughout (Aphelinus albipodus), two had shifted in dominance (Lysiphlebus testaceipes and Diaeretiella rapae), three parasitoids had been detected infrequently (Aphidius avenaphis, Aphidius matricariae, and Aphelinus asychis), one parasitoid was detected in the 1990s but not during 2001 and 2002 (Aphelinus varipes), two predatory flies occurred at occasional significant levels (Leucopis gaimarii and Eupeodes volucris), and two parasitoids may have been minor members of the fauna (Aphidius ervi and Praon yakimanum). Aphid populations detected were usually very low or not detected, precluding estimation of percent parasitism. The best evidence of D. noxia suppression were field observations of parasitoids in the rare instance of D. noxia exceeding economic thresholds, which complemented past replicated field studies using high aphid densities. The D. noxia enemies detected were primarily endemic or long-time residents derived from previous introductions. This enemy community may provide flexibility in responding to a future aphid invasion, allowing more strategic use of conservation biological control and other pest management approaches and selected release of classical biological control agents.