فریبا سهرابی

The cotton mealybug, Phenacoccus solenopsis,is one of the potential pests with a widespread distribution that makesserious damages to ornamental and field crops. One of the most important parasitoids of cotton mealybug is Aenasius bambawalei (Hymenoptera: Encyrtidae). In this study, sublethal effects of two current insecticides, chlorpyrifos (1 ppm) and spirotetramat (7.5 ppm), were investigated on the biology and functional responses of A. bambawaleito different densities (2, 4, 6, 8, 16, 32) of third instar nymphs of mealybug under laboratory condotions. The results showed that there were no significant differences in total preoviposition periods (TPOP) of the wasp among different treatments. The intrinsic rates of increase (rm) of the wasp were calculated to be 0.16, 0.12, and 0.13 in control, chlorpyrifos and spirotetramat, respectively. This parameter decreased in both insecticidal treatments and its decline was significant in chlorpyrifos in comparison with control. Females and males’ longevities were also significantly decreased in chlorpyrifos and spirotetramat treatments compared with control. The net reproductive rate (R0) in Chlorpyrifos and Spirotetramat treatments were calculated to be 12.2 and 16.9 (female/ female) which were significantly less than control (34.92 female/female). Average generation times (T) decreased in chlorpyrifos (20.40 days) and spirotetramat (21.13 days) and significant difference was seen between chlorpyrifos and control (22.05 days) treatments. The most decrease of life expectancy (ex)was seen in the initial stages of the wasp development in chlorpyrifos treatment. The results of functional responses experiments showed type II response in control, chlorpyrifos, and spirotetramattreatments. The number of parasitized nymphs increased with increasing the host density, but the ratio of parasitized host to initial density decreased with increasing density. Searching efficiencies (a) of the parasitoid wasp were calculated to be 0.260