افزایش فعالیت حشره‏کشی فیپرونیل روی سفیده بزرگ کلم Pieris brassicae L. (Lepidoptera: Pieridae) با استفاده از محرک تغذیه‏ای و عصاره گیاهی در شرایط آزمایشگاهی

The large white cabbage butterfly (Pieris brassicae L.) is one of the main limiting factors of cruciferous crops in world, causing severe damage to the crop by larval feeding on leaves. In case of serious infestation, the entire parts of plants are eaten up. Generally, farmers are dependent on synthetic pesticides to suppress P. brassicae infestations in Brassicaceae plants. But the adverse effect of chemicals on the environment demand a suitable alternative method of crop insect pest management that should be ecofriendly and safe for non-target organisms. Plant extracts provide a safe and viable alternative to synthetic pesticides. Also, many different studies have proven that the addition of feeding stimulants increase the toxicity of various insecticides. In this research synergistic/antagonistic interaction of fipronil and methanolic plant extract of Alhagi maurorum Medik. were evaluated against egg, first, second and third instar larvae of P. brassicae in laboratory conditions. Cabbage seed oil was also used as feeding stimulant. Leaf dipping method was used for experiments. Trials were conducted in three replications based on completely randomized design. 5% methanolic extract from A. maurorum was obtained by using soxhelet extractor. Mortality was assayed after 24 h. Cold pressing method was used to extract cabbage seed oil (as feeding stimulant). In order to determine combination effect of feeding stimulant and fipronil, the main concentrations of insecticide in estimating of the LC50 value of first instar larvae were combined with 1 and 5 % oil concentrations. The LC50 values of fipronil for P. brassicae egg, first, second and third instar larvae were estimated 4330, 540, 854 and 1110 mg/l, respectively. Results revealed that plant extract of A. maurorum has no lethal effect on eggs and mortality rate of different larval stages increased with increasing methanolic extract concentrations. Sub-lethal concentration (LC25) of methanolic extract was combined with LC25 of fipronil to investigate whether there was a synergistic or antagonistic interaction between plant extract with insecticide. Obtained results possessed synergistic effect. In bioassay, the addition of feeding stimulant improved the efficacy of the fipronil. The concentrations of fipronil required for 50 % mortality of first larvae, were reduced from 540 mg/l to 450, 377 mg/l, respectively, when the feeding stimulant was added in concentrations of 1 and 5 %. According to results of this research, combination of methanolic extract of A. maurorum and cabbage seed oil with fipronil can be useful for control of P. brassicae and as a part of an integrated pest management (IPM) strategy combined with other reduced risk control techniques. Further studies are necessary to test the efficiency of feeding stimulant (obtained from cabbage seed oil) in increasing insecticidal effects.