Abstract
Host stage preference, functional response and mutual interference of Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae: Aphidiinae) on Diuraphis noxia (Mordvilko) (Hemiptera: Aphididae) were investigated under defined laboratory conditions (20?1?C; 60?5% relative humidity; 16 h light/8 h dark photoperiod). Nicholson?s model and linear regression were used to determine per capita search-efficiency and the interference coefficient, respectively. There was a significant difference between the rates of parasitism on different stages of D. noxia. The highest parasitism percentage was observed on the third instar nymphs of D. noxia in both choice and no-choice preference tests. Results of logistic regression revealed a type II functional response. The estimated values of search-efficiency (a) and handling time (Th) were 0.072 h-1 and 0.723 h, respectively. The maximum attack rate was calculated to be 33.22. The per capita search-efficiency decreased from 0.011 to 0.004 (h-1) as parasitoid densities increased from 1 to 8. Therefore, different host-parasitoid ratios can affect the efficacy of D. rapae.
Highlights
The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) is regarded as an important cereal pest in many cereal-producing areas of the world, including Iran, (Liu et al, 2010) where it is widely distributed (Dolati, 2005)
There was no significant difference in the percentages of parasitism in the third and fourth instar nymphs and adults of D. noxia (Fig. 1)
We found that D. rapae prefer the third and fourth nymph instars of D. noxia in the course of two types of experiments
Summary
The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) is regarded as an important cereal pest in many cereal-producing areas of the world, including Iran, (Liu et al, 2010) where it is widely distributed (Dolati, 2005). The aphid causes direct damage by sucking the sap of plants, and indirect damage by transmitting plant viruses, thereby causing tremendous yield losses in wheat at high infestation levels (Jones et al, 1989; Kindler and Hammon, 1996; Kruger and Hewitt, 1984; Von Wechmar, 1984). Diaeretiella rapae McIntosh is the main parasitoid of D. noxia (Noma et al, 2005; Rakhshani et al, 2008; Starý, 1999) and widely distributed in different parts of Iran (Rakhshani et al, 2008; Starý et al, 2000).
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