ارزیابی آزمایشگاهی اثر ترکیبی عصاره گیاهی و محرک تغذیه‏ای با حشره‏کش تیامتوکسام روی سنین مختلف لاروی سفیده بزرگ کلم Pieris brassicae L. (Lepidoptera: Pieridae)

Pieris brassicae (L.) is a destructive pest of cruciferous vegetables worldwide. The larvae eat all the parts of the plant like leaves, branches and pods and create serious damage economically. Hence they make insecticidal application mandatory for the cultivation of cruciferous plants. Protective actions using different chemicals result in undesirable side effects to human health, as the crucifer crops are used as fresh vegetables in human diet. Also, this pest has developed resistance against some pesticides. Thus, there is a requirement to search safer eco-friendly alternatives in view of the pressing need to protect the environment and natural enemies. In this research synergistic/antagonistic interaction of thiamethoxam (Memory®) and methanolic plant extract of Alhagi maurorum Medik. were evaluated against different larval stages of P. brassicae in laboratory conditions. Cabbage seed oil was also used as feeding stimulant. A. maurorum aerial parts were collected, dried in the shade, and ground into powder form. The methanolic extraction of plant material was done using a Soxhlet apparatus. Cold pressing method was used to extract cabbage seed oil. Experiments were performed according to leaf-dipping method. Mortality of larvae were assayed after 48 h. Probit analysis was carried out to estimate toxicity values (e.g., LC25, LC50). In order to determine combination effect of feeding stimulant and thiamethoxam, the main concentrations of insecticide in estimating of the LC50 value of first instar larvae were combined with 1% and 5 % oil concentrations. Paired mixtures of plant extract with insecticide were freshly prepared at concentration levels of their respective LC25 values. The LC50 values of thiamethoxam and plant extract for P. brassicae first, second and third instar larvae were estimated (67, 339), (107, 796) and (187, 1239) mg/l, respectively after 48 h. Combination-based bioassays discovered the accomplished synergism of A. maurorum plant extract together with thiamethoxam. Observed mortality resulting from their combined effect for P. brassicae first, second and third instar larvae were estimated 73.33, 78.33, 83.33 %, respectively. The concentrations of thiamethoxam required for 50 % mortality of first larvae, were reduced from 67 to 50 and 33, respectively, when the feeding stimulant was added in concentrations of 1 and 5 %. In other words, more larvae fed on insecticide- treated plant disks when the cabbage seed oil was present for every evaluated concentration of thiamethoxam. In conclusion, we think that cabbage seed oil and A. maurorum plant extract are promising insecticide enhancer against the P. brassicae as a part of an integrated pest management (IPM) strategy. This hypothesis needs further experiments.