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Project description

Evaluation of Interactions among Russian Wheat Aphid, an Effective Parasite, and Plant Resistance. (96FE046)
Program UC IPM competitive research grants program
Principal
investigator 		D. Gonzalez, Entomology, UC Riverside
Host/habitat Small Grains
Pest Russian Wheat Aphid Diuraphis noxia
Discipline Entomology
Beneficial
organism 		Aphelinus albipodus
Review
panel 		Applied Field Ecology
 Start year (duration)  1996 (Three Years)
Objectives Assess impact of Aphelinus albipodus, an effective introduced parasite, on Russian wheat aphid (RWA) in combination with tworesistant cultivars displaying different resistance mechanisms.

Assess impact of extant (naturally occurring) parasites (especially D.rapae) and predators against RWA on resistant plants with open (uncurled)leaves.

Implement releases of A. albipodus against RWA on the most promising plant resistant cultivar.

End-year
progress 		The two resistant wheat varieties tested in our trials the past three years were included in L. Jackson's 1998 University of California Cooperative Extension regional cereal evaluation trials in the intermountain valleys of northeastern California, in collaboration with us in Lassen, Modoc, and Siskiyou Counties. Aphid numbers and survival were relatively low compared with previous years because of unusually extensive rains in May and June. Test plants were seeded with approximately 5000 Russian wheat aphid (RWA) per each 2000 parasites released over a period of six consecutive weeks (May - June). On plants with strong antibiosis few RWA survived and those aphids and the few parasitized RWA were notably smaller than aphids on the control, susceptible barley plants. Numbers of RWA were highest on barley plants and fewer on plants with RWA-tolerant properties. Highest numbers of parasitized RWA were from tolerant plants. Significantly fewer parasitized RWA were recovered from barley despite greater numbers of RWA available on barley. These results support data from two previous years and our contention that biological control can be enhanced significantly by combining it with appropriate host plant resistance. In our trials strong antibiosis does not support or encourage biological control agents, whereas milder antibiosis combined with tolerance did result in significant increase in numbers of biological control agents.

In yield results from three different valleys in northern California, the tolerant variety produced significantly highest yields compared with thirty other entries, including yields from the variety with strong antibiosis and the control barley variety.

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