Host stage preference and temperature-dependent functional response of Diaeretiella rapae (Hymenoptera: Braconidae) on Schizaphis graminum (Hemiptera: Aphididae)

The aim of this study was to investigate the host stage preference and functional response of Diaeretiella rapae (Hymenoptera: Braconidae) reared on Schizaphis graminum (Hemiptera: Aphididae). Firstly, host stage preference was determined under choice and no-choice tests. The parasitoid showed a preference for second instar nymphs of S. graminum in both choice and no-choice tests. Secondly, functional response was evaluated at five constant temperatures (10, 15, 20, 25, and 30 °C) and six host densities of second instar nymphs of S. graminum (2, 4, 8, 16, 32, and 64) during a 24 h period. The experiments were conducted at constant environmental conditions (25 ± 1ºC, 70 ± 5% RH and 16:8 h L:D photoperiod). Based on the logistic regression model, D. rapae exhibited a type II functional response at all five tested temperatures. The handling time was lowest at 30 °C (0.0263 h) and highest at 10 °C (2.5255 h). The searching efficiency of D. rapae varied at different temperatures. At 20 °C, the searching efficiency of the parasitoid was determined to be 0.0617 h −1 , which was significantly higher than other temperatures. The current results indicate that D. rapae can be used as a biological control agent of S. graminum at temperatures ranging between 20 and 25 °C, but additional data need to be collected in field and semi-field conditions.