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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.