Functional Responses of Nephus arcuatus Kapur (Coleoptera: Coccinellidae), the Most Important Predator of Spherical Mealybug Nipaecoccus viridis (Newstead)

Abstract

Nephus arcuatus Kapur is an important predator of Nipaecoccus viridis (Newstead), in citrus orchards of southwestern Iran. This study examined the feeding efficiency of all stages of N. arcuatus at different densities of N. viridis eggs by estimating their functional responses. First and 2nd instar larvae as well as adult males exhibited a type II functional response. Attack rate and handling time were estimated to be 0.2749 h-1 and 5.4252 h, respectively, for 1st instars, 0.5142 h-1 and 1.1995 h for 2nd instars, and 0.4726 h-1 and 0.7765 h for adult males. In contrast, 3rd and 4th instar larvae and adult females of N. arcuatus exhibited a type III functional response. Constant b and handling time were estimated to be 0.0142 and 0.4064 h for 3rd instars, respectively, 0.00660 and 0.1492 h for 4th instars, and 0.00859 and 0.2850 h for adult females. The functional response of these six developmental stages differed in handling time. Based on maximum predation rate, 4th instar larvae were the most predatory (160.9 eggs/d) followed by adult females (84.2 eggs/d). These findings suggest that N. arcuatus is a promising biocontrol agent of N. viridis eggs especially for 4th instar larvae and adult females.