Walnut aphid (Chromaphis juglandicola) population growth tied to foliar nitrogen in walnuts

Biological control of walnut aphid (Chromaphis juglandicola) and aphid population growth tied to foliar nitrogen in walnuts: The intensification of farming practices, mainly the increased use of fertilizers and pesticides, has led to significant water and air pollution, human health risks, and environmental costs. There is an important tradeoff between increasing agricultural yield and preserving the health and safety of human populations and natural environments. Nitrogen rich fertilizer is at the center of this tradeoff because it boosts crop yields yet causes substantial pollution. Understanding the effects of nitrogen management with regard to pests and their natural enemies is essential for reducing agricultural pollution. Nitrogen management affects the nutritional quality of leaves, which in turn can significantly impact the populations and population growth rates of herbivores. Because nitrogen is often limiting for insects, the nitrogen content may play an important role in insect population dynamics. Managing nitrogen to maximize yield may prompt an increase or decrease in herbivorous pest population growth rates. Moreover, plant nutrients affect multiple trophic levels through trophic cascades and direct transfer. Understanding the effects of nitrogen management in an agricultural setting on pests and their natural enemies is important for understanding and improving biological control. The relationship between fertilizer management practices, foliar nutrient status, and biological control is unstudied. Organic and convention farms manage nitrogen in different ways, which may impact biological control. In a comparative study using field surveys, the impact of pre-existing levels of foliar nitrogen and phosphorus on an insect pest and its natural enemies was examined for organic and conventional walnut orchards. Twelve orchards were surveyed 4 times of the course of the 2012 growing season. Pre-existing nutrient levels did have an impact on the total number of aphids and their natural enemies as well as on the natural enemy to prey ratio. Interestingly, farm management type (organic or conventional) was not a significant factor in determining pre-existing nutrient levels or the natural enemy to prey ratio.