Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2004
Publication Date: 5/1/2005
Citation: Lee, J.H., Elliott, N.C., Kindler, D., French, B.W., Walker, C.B., Eikenbary, R.D. 2005. Natural enemy impact on the Russian wheat aphid in southeastern Colorado. Environmental Entomology. 34:115-123.
Interpretive Summary: Several species of natural enemy [predatory insects and parasitic insects (parasitoids)] were imported from overseas and released during the late 1980s and early 1990s in an attempt to establish them for biological control of an invasive and economically important pest, the Russian wheat aphid (RWA). In 1994, we evaluated the role of the imported natural enemies that had established, and also native natural enemies, in biological control of the RWA in winter wheat in southeastern Colorado. Southeastern Colorado was notable for being particularly heavily impacted by the RWA. An experimental method known as the exclusion cage method was used to evaluate the impact of the natural enemies on the RWA. A native species of lady beetle, Hippodamia convergens, and a native predaceous bug, Nabis spp., were the most abundant predators of the RWA, but they did not substantially reduce RWA numbers. The dominant parasitoid was the native species Lysiphlebus testaceipes, but parasitism rates by this species and by imported species that had established was very low. There were close associations between the abundance of predators and RWA abundance in wheat fields. We concluded that in 1994, natural enemies played a limited role in controlling RWA infestations in wheat.
Technical Abstract: The effectiveness of predators and parasitoids of the Russian wheat aphid (RWA) was experimentally evaluated using mechanical exclusion in production winter wheat, Triticum aestivum L., fields at four locations in southeastern Colorado. Three types of enclosure were used: complete exclusion enclosures, partial exclusion enclosures that permitted entry by parasitic Hymenoptera, and environmental exclusion enclosures that reduced the effects of wind and rain on RWA and trapped emigrating alate RWA so that they could not return to plants within the enclosure. RWA in non-enclosed plots were also studied. RWA density varied among treatments in the following order: complete exclusion ³ partial exclusion > environmental exclusion > non-enclosed plots. The trapping of alatae within enclosures and reduced adverse stresses such as rain and wind within enclosures were partially responsible for the greater RWA density in complete and partial exclusion enclosures compared to environmental exclusion enclosures and non-enclosed plots. The aphidophagous coccinellid, Hippodamia convergens Guèrin-Mèneville and the generalist Nabis spp. were the most abundant predators during the increasing phase of RWA population development, but they did not substantially reduce RWA numbers. H. convergens, Coccinella septempuntata L., and H. sinuata Mulsant were the most abundant predators during the declining phase of RWA population growth. The dominant parasitoid was Lysiphlebus testaceipes (Cresson), but parasitism rates were very low. Canonical correspondence analysis demonstrated close associations between the abundance of predators and RWA density, RWA density and wind during the increasing phase of RWA population development, and RWA density and rainfall late in the growing season.