اثرات کشندگی سه حشره‌کش روی شته کاهو، Nasonovia ribisnigri (Mosely) در شرایط آزمایشگاهی

The currant lettuce aphid, Nasonovia ribisnigri (Mosely) (Hemiptera: Aphididae) is considered the key pest in the important areas of cultivation of lettuce such as Khuzestan and Tehran provinces. Considering the importance of application of new and safer insecticides in the integrated management of pests, in the present study, the lethal effects of three insecticides including imidacloprid (Imidaria® 35SC), pymetrozine (Pymetrozine Aria® 25WP), and flonicamid (Teppeki® 50WG) was investigated against the second and fourth instars of lettuce aphid. Aphids were collected from lettuce (Lactuca sativa L.) fields around Dezful and were reared on lettuce (Romaine cultivar) in a growth chamber (temperature 20 ± 1°C, relative humidity 60 ± 5%, and photoperiod 16:8 (dark: light)). The toxicity of the three insecticides was evaluated by leaf dipping method. A total of five concentrations were used along with one control for each insecticide bioassay. For each concentration, five repetitions and 20 aphids were considered in each repetition. The experiments were repeated three times. Due to the difference in the effect time of the pesticides, the number of deaths caused by the application of pymetrozine and flonicamid insecticides was counted after 72 hours and for imidacloprid after 24 hours. Probit analysis was used to calculate LC50 (with 95% confidence limits). The LC50 values of imidacloprid, pymetrozine and flonicamid insecticides against the second instar nymphs were 0.273, 80.33 and 32.51, and against the fourth instar 1.02, 650.91 and 69.21, respectively (mg a.i/L for all). Based on the results, imidacloprid was the most toxic compound on second and fourth-instar nymphs, followed by flonicamid insecticide. The lethality of all insecticides on second-instar nymphs was significantly higher than fourth-instar nymphs (P < 0.05).