Stage-Specific functional response of Nephus arcuatus to Nipaecoccus viridis

Background and objectives Understanding the functional response of a predator to its prey and its parameters including attack rate and handling time, are one of the basic methods in applied biological control for evaluation of the efficiency of a predator. Nephus arcuatus is one of the most important biological control agents of Nipaecoccus viridis. Material and Methods In this study, a laboratory study has been conducted to evaluate the stage-specific functional response of larval stages and adult females and males of N. arcuatus to varying densities of N. viridis 2nd instar nymph. Experimental conditions were based on optimal temperature for N. arcuatus activities, 30±1ºC, 65±5% RH, and 14L:10D photoperiod. Results and Discussion The shape of functional response curve and the functional response parameters were determined respectively by logistic regression and nonlinear least square regression. The 1st instar, 2nd instar larvae, adult males as well as adult females exhibited a type II functional response. Attack rate (a) and handling time (Th) were estimated to be 0.1139 h-1 and 11.4117 h for the 1st instar, 0.3237 h-1 and 4.7013 h for 2nd instar larvae, 0.2233h-1 and 1.4711 h for adult males, and 0.2836h-1 and 1.0198 h for adult females, respectively. In contrast, the 3rd instar and 4th instar larvae of N. arcuatus exhibited a type III functional response. Constant b and handling time were estimated to be 0.0195 and 1.7396 h for the 3rd instar, and 0.00774 and 0.4912 h for 4th instar larvae, respectively. Our results indicated that estimated attack rates did not change significantly between different stages of N. arcuatus with similar functional response curve. In contrast, the handling times of N. arcuatus to its prey increased as the larval age of this predator increased, also females had longer handling time than adult males. Based on the maximum predation rate (T/Th), the 4th instar larva was the most voracious stage (48.56 prey/d) followed by the adult female (23.53 pey/d) and male (16.32 egg/d) N. arcuatus. These findings suggest that the voracity of all stages of N. arcuatus toward N. viridis hold good promises for a use of especially simultaneously 4th instar larvae, and adult males and females of N. arcuatus in a biological control program against N. viridis in orchards and on ornamental plants.