Temperature-Dependent Functional Response of Diaeretiella rapae (Hymenoptera: Braconidae), a Parasitoid of Diuraphis noxia (Hemiptera: Aphididae)

Abstract

The effects of host density and temperature on the functional response of Diaeretiella rapae (M’Intosh) parasitizing Diuraphis noxia (Mordvilko) were evaluated at six constant temperatures (10, 15, 20, 25, 30 and 32.5°C) and six host densities (2, 4, 8, 16, 32, and 64 numbers). A type II functional response was obtained at all temperatures tested. The maximum parasitism rate was observed in density of 64 hosts, ranged from 3.00±0.67 at 10°C to 24.20±0.94 at 25°C. The searching efficiency (a) was highest at 15°C and then decreased linearly as the temperature increased to 32.5°C. The searching efficiency ranged from 0.080±0.008 h-1 at 15°C to 0.032±0.017 h at 10°C. The estimated value of handling time (Th) decreased linearly with increasing temperature from 10 to 25°C. The maximum rate of parasitization was observed at 15, 20 and 25°C (32.94, 32.22 and 36.51 nymphs/24 h, respectively). The results suggest that D. rapae has potential as a biocontrol agent of D. noxia and warrants further evaluation in the field conditions.