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Environmental parameters related to winter mortality of the Russian wheat aphid (Homoptera: Aphididae): basis for predicting mortality

Armstrong, J.S., Peairs, F.B.
Journal of economic entomology 1996 v.89 no.5 pp. 1281-1287
Diuraphis noxia, Triticum aestivum, overwintering, mortality, population density, soil temperature, soil water, snow, solar radiation, regression analysis, models, prediction, Colorado
Relationships between winter environment and mortality of the Russian wheat aphids Diuraphis noxia (Mordvilko), infesting winter wheat, Triticum aestivum (L.), were investigated. Russian wheat aphid densities from 0.3 m drill row of 'TAM 107' (dependent variable) accumulated subzero temperatures, soil moisture, snow amounts, snow cover duration, and solar radiation (independent variables) were measured in 2 differing winter environments in 1989, 1990, and 1991. Multiple regression analysis for best-fit relationships indicated that Russian wheat aphid winter mortality was highly correlated with the accumulation of freeze-hours <0 degrees C. A 2nd relationship was established by regressing aphid densities against the accumulation of freeze-degrees <0 degrees C. The hour accumulation resulted in stronger relationships with declining aphid densities compared with degree accumulations, especially in 1991-1992 when there was 87 d of snow cover. Freeze degrees accumulate faster the greater the soil surface temperature drops below 0 degrees C, but are limited under insulating snow. Average daily snow cover was the 2nd most important independent variable in relation to aphid decline when the duration (>40 d) and depths (> 1 cm) were dominant winter factors. Neither soil moisture nor solar radiation were statistically significant components in our models. Complete Russian wheat aphid mortality occurred within 3,000 freeze-hours or -12,000 freeze-degrees when data for all 3 yr were included. The 2 climatic events that resulted in 100% mortality were a sudden drop (-29.6 degrees) in soil surface temperature and an extended (>40 d) period of snow cover.