Aphid Predation by Harpalus rufipes (Degeer) (Coleoptera: Carabidae) in the Laboratory and Field

Abstract

To have a deep understanding on the mechanisms of cadmium (Cd) toxicity on peanut plants is of theoretical and practical significances for the selection and utilization of Cd-resistant peanut germ plasm resources. With fourteen peanut varieties as test materials and taking the chlorophyll content of functional leaves, malondialdehyde (MDA) content and cell membrane permeability of roots and leaves, and oxidative vitality of roots at flowering stage as test physiological parameters, a sand culture experiment was conducted in an artificial climate chamber to investigate the physiological responses of different peanut varieties to six levels of Cd stress. The results showed that within the range of 0-60 mg Cd x L(-1) addition, the chlorophyll content of functional leaves and the oxidative vitality of roots decreased significantly with increasing Cd addition, while the MDA content and cell membrane permeability of leaves and roots were in adverse. The cell membrane permeability of roots and leaves was the most sensitive physiological parameter, while the chlorophyll content of functional leaves was the least sensitive one in the responses of peanut plant to Cd stress. In the linear regression equations describing the relationships between test physiological parameters and Cd concentrations in nutrient solution, the absolute value of slope (b)/intercept (a) ratio, /b/a/, could better describe the sensitivity of peanut plants to Cd stress. It was known from the integrative evaluation of /b/a/ values and the cluster analysis of sensitivity that among the fourteen peanut varieties, "Zhonghua-4", "Xiangnong-55" and "Xiangnong-3010-w" were highly sensitive to Cd stress (first grade), "Lainong-29", "Xiangnongxiaoguo-w2-7", "Fenghua-2", "Lainong-13", "Yuhua-15" and "Fenghua-3" were sensitive (second grade), "Xiangnong-312", "Qiyangxiaozi" and "Pingdu-01" were less sensitive (third grade), while "Huayu-20" and "Huayu-23" were insensitive (forth grade).