Functional Response of Adult Male and Female Hippodamia variegata Goeze (Col.: Coccinellidae) to Different Densities of Aphis fabae Scopoli

Coccinellids play a major role in aphid control. Hippodamia variegata Goeze is an aphidophagous predator of worldwide distribution that could be found in different parts of Iran. One of the criteria for evaluating the efficiency of a predator is its response to change in prey population density (functional response). The functional responses of males and females of Hippodamia variegata were studied at different densities of Aphis fabae under laboratory conditions (23±1?C, 70±10% RH, and 16:8 L:D photoperiodism). Experiments were carried out using the aphids of the same age on bean leaf disks in Petri dishes and in 15-20 replications. After 24 hours, the number of hunted preys was recorded. The results revealed that both male and female H. variegata exhibited a type II functional response to different densities of black bean aphid (2, 4, 8, 16, 32, 45, and 60 for male and 2, 4, 8, 16, 40, 60, 80, and 100 for female adults). Rogers’ random predator equation was employed in estimation process of searching efficiency (a) and handling time (Th). The mentioned parameters were estimated to be 0.1589 and 1.1945 h for male and 0.0926, 0.4098 h for females, respectively. Use of an equation with indicator variable revealed that there is a significant difference between handling times of females vs. males. Based upon handling times, females vs. males could hunt 58.6 and 20.1 aphids per day, respectively, indicating that the hunting power of females is more than twice as much as males.