Spatial and Temporal Dynamics of Aphids (Hemiptera: Aphididae) in the Columbia Basin and Northeastern Oregon.

Aphid species, such as the potato aphid, Macrosiphum euphorbiae Thomas, and the green peach aphid, Myzus persicae Sulzer, are routinely considered the most important pests of potatoes. Potato aphid, green peach aphid, and more recently, other aphids such as the bird cherry-oat aphid Rhopalosiphum padi L. have been identified as vectors of multiple plant pathogenic viruses in potatoes. Since 2006, an area-wide trapping network consisting of ∼60 sites was developed through collaboration between researchers, extension faculty, and stakeholders, to monitor aphid populations in the Columbia Basin of Oregon (Umatilla and Morrow counties) and in northeastern Oregon (Union and Baker counties). Over a 9-yr period (2006 to 2014), aphid specimens were collected weekly using yellow bucket traps and specimens were then identified and counted to determine population levels during the growing season (May-September). Thus, aphid population data were compiled and subjected to spatial and temporal distribution analysis. Weather data, obtained from an established network of weather stations located in the monitoring areas, were used in a nonparametric multiplicative regression analysis to determine which abiotic variables may impact aphid populations. Weather conditions were characterized using confidence intervals (CIs) established based on weather data from 1999 to 2005 for each environmental variable. Aphid populations were found to have a heterogeneous distribution in most years; a few sites had high aphid populations while low numbers were observed at most sites; aphids were also found to correlate with several abiotic variables, namely, elevation, previous season temperature, and previous season dew point.

Categorization of Putative Factors Against Rhopalosiphum padi (L.) (Heteroptera: Aphididae).

The bird cherry-oat aphid, Rhopalosiphum padi (L.) (Heteroptera: Aphididae), causes heavy losses to wheat crops worldwide by direct damage and virus transmission. This study was conducted to identify putative resistance mechanisms in four wheat varieties (Bobtail, Ladd, Stephens, and Skiles) and one advanced line (YS434)where R. padi was subjected to choice and no-choice tests. Antixenosis, antibiosis and tolerance studies were conducted in controlled environmental conditions at temperature of 20±5°C, 50­65% RH, and a photoperiod of 14:10 (L:D) h. Based on the antixenosis test, the variety Skiles was found susceptible to R. padi, while the line YS434 showed a significant level of resistance; the varieties Bobtail, Ladd, and Stephens showed intermediate response. In the antibiosis experiment, R. padi produced less progeny on the variety Skiles as compared with other varieties, but the developmental time for nymphs was also significantly shorter on Skiles and recorded higher intrinsic rate of natural increase (r(m)) values as compared with the varieties YS434, Bobtail, and Ladd. In the tolerance tests, the variety Ladd showed significantly lower tolerance index value than YS434, followed by Skiles, Bobtail, and Stephens. The plant resistance index value was greater for the variety Ladd, followed by Stephens, YS434, and Bobtail. In conclusion, this study provides baseline information that will contribute to the identification of putative resistance factors for a future breeding program against this aphid.