Consumption patterns of the multicolored Asian ladybird Harmonia axyridis on the broad bean aphid Aphis craccivora

The multicolored Asian ladybird Harmonia axyridis Pallas is often used as a biological control agent against Aphis craccivora Koch, a key pest aphid of broad bean. Understanding consumption characteristics of biological control agents is critical for developing effective biological control programs. Here, under laboratory conditions we studied consumption patterns of H. axyridis on A. craccivora including functional response and intraspecific competition. All larvae (1st-, 2nd-, 3rd-, 4th-instar) and adults (male and female) of H. axyridis exhibited a Type II functional response to A. craccivora. We found H. axyridis females were superior to individuals of other developmental stages, based on three key parameters in functional response model, i.e. attack rate (a = 90.0%), handling time (T_h = 2.7 min), and consumption threshold (N_max = 526.7 individuals). Results from our analysis of intraspecific competition showed that when attacking A. craccivora, 4th-instar larvae of H. axyridis suffered from the greatest intraspecific competition (coefficient of mutual interference, m = 0.48). Our results show that 4th-instar larvae and adults of H. axyridis are most effective in controlling A. craccivora, and proper density of H. axyridis released will reduce intraspecific competition. This analysis reveals both prey-predator and predator-predator interactions, and highlights the value of biological control in reducing pesticide use and protecting ecological environments.