Functional response of Prospaltella berlesei Howard (Hym.: Aphelinidae) on varying densities of different instars of white peach scale, Pseudaulacaspis pentagona Targioni (Hem.: Diaspididae)

Functional response determines the effect of natural enemy on host's population and its ability to suppress its population. Functional response of Prospaltella berlesei Howard on different densities of white peach scale, Pseudaulacaspis pentagona Targioni was studied at (25±1.C, 70±10% RH, 16:8h. L: D photoperiod). Different densities (5, 10, 20, 40, 60, 80 and 100) of first, second and third instar nymphs of P. pentagona were provided to female P. berlesei (2 day-old) as host with ten replicates in 24 hours. Functional response of P. berlesei on different densities of first instar nymphs exhibited type ΙΙI, whereas parasitoid response on second and third instars showed type ΙΙ. Parameter b and the handling time (Th) for first instar were estimated 0.002 ± 0.001 h-1 and 2.941±0.358h, respectively. Searching efficiency (a) and (Th) for second instar were 0.028 ± 0.005 h-1 and 0.617± 0.106 h, and for third instar were 0.025 ± 0.007 h-1 and 0.881 ± 0.179 h. Comparing functional response parameters for second and third instars with an equation with indicator variables showed no significant differences between parameters. Maximum attack rate (T/Th) for first, second and third instars of white peach scale were estimated 8.16, 38.9 and 27.24 hosts/day, respectively. Therefore, second instar nymphs of white peach scale are considered as the most suitable host stage for rearing of P. berlesei.