Plant Damage and Yield Response to the Russian Wheat Aphid (Homoptera: Aphididae) on Susceptible and Resistant Winter Wheats in Colorado

Abstract

Plant damage and yield response to the Russian wheat aphid, Diuraphis noxia (Mordvilko), were evaluated on a susceptible (TAM 107) and a resistant (RWA E1) winter wheat, Triticum aestivum L., in three Colorado locations in the 1993 and 1994 crop years. Russian wheat aphid was more abundant on TAM 107 than on RWA E1. Russian wheat aphid days per tiller were greater at the higher infestation levels. Yield losses as a result of Russian wheat aphid infestation occurred most of the time with TAM 107 but rarely with RWA E1. Seed densities were reduced at higher infestation levels in TAM 107 at two locations. Russian wheat aphids per tiller had a negative relationship to yield in TAM 107 but not in RWA E1. In TAM 107 yield decreased as aphid densities increased, but yield remained constant regardless of initial aphid abundance on RWA E1 in all environments. Seed densities were reduced at higher infestation levels in TAM 107 at two locations. The resistance conferred by the Dn4 gene seems to be an effective management approach across a range of field conditions.

Influence of Three Resistance Sources in Winter Wheat Derived from TAM 107 on Yield Response to Russian Wheat Aphid

“…Seed for the 0ϫ infestation plots was treated with imidacloprid (5.2 ml of Gaucho 480 per kg of seed) (Gustafson, Plano, TX). The 1ϫ and 10ϫ plots were artiÞcially infested with Russian wheat aphid provisionally designated as Biotype 1 in a manner similar to that described by Randolph et al (2003). Two 1-m rows in the center of each of the 1ϫ and 10ϫ plots were infested with Russian wheat aphids at rates of 46 and 460 on 24 March 1998 and 62 and 588 on 25 February 1999 in Fort Collins; 60 and 120 on 9 April 1998, and 138 and 702 on 2, 7, and 20 April 1999 in Akron; and 30 and 300 on 5 March 1999 in Lamar, respectively.…”

“…There was no additional insecticide treatment in Akron. Aphid and yield data were collected as described by Randolph et al (2003). Climate data were obtained from the Colorado Climate Center (http:// climate.atmos.colostate.edu/).…”

Insect economic levels in relation to crop production

“…The time in a plant's growth cycle when injury occurs has an obvious influence on the plant's response to the injury (Randolph et al 2003). Generally, seedling plants are most susceptible to injury, whereas young, but not seedling, plants are better able to tolerate or compensate injury.…”

“…It is important to emphasise that the nature of the injury is fundamental to a plant's response to different intensities of that injury (Randolph et al 2003).…”

“…Therefore, these two responses are usually unimportant with respect to EILs and, consequently, are often unrecognised or neglected. However, aphid damage usually is described solely by the desensitisation portion of the damage curve ( Figure 1(b)) (Randolph et al 2003). An important distinction must be emphasised between desensitisation and what has been called competition or interference between insects (Fenemore 1982).…”