The Insecticidal Activity Of Flaveria Bidentis Extracts And α-Terthienyl To Helicoverpa Armigera (Hübner)

Flaveria bidentis was an invasive plant, which invaded northern China in recent years. It had spread to Hebei, Tianjin, Henan and Shandong, etc. provinces, and damaged the ecological environment and biodiversity in intrusion areas. With the loss of herbivorous insects, F. bidentis might distribute more resource for growth and reproduc tion in intrusion areas. Meanwhile, it had special biological characteristics and allelopathy, which affected the soil environment and inhibited local plants growth. These changes promoted the local ecological environment developed towards the direction of further invasion. Secondary metabolites in F. bidentis played an important role in invasion and defense. The isolated secondary metabolites had antioxidant, antithrombotic, bactericidal and herbicidal activity. In present, researches mainly focused on the threat of invasion and its biological characteristics, but studies on the toxicity of the secondary metabolites in F. bidentis were few yet.The biological activity of F. bidentis extracts and the mode action of α-terthienyl to cotton worm(Helicoverpa armigera(Hübner)) were studied. The secondary metabolites in F. bidentis were extracted by the immersion method. Three organic solvents, 95% ethanol, ethyl acetate and petroleum, were used to extract the secondary metabolites in powder and fresh samples of F. bidentis. Dip method, disc leaf dipped method and diet-corporated were used to determined the activity of antifeedant activity, contact-toxicity and the effect of solutions on cotton worm’s growth and development, respectively. Three digestive enzymes in cotton worm’s gut, amylase, lipase and total protease were tested by Iodine- starch colorimetry, Assay and Lowry colorimetric assay, respectively.1. The six extracts of F. bidentis showed different antifeedant activities in experiments. The antifeedant activities of the ethanol and ethyl extracts in powder and the ethyl extract in fresh samples of F. bidentis were 50.49%、32.06% and 41.63% at 24 h, 29.67%, 14.58% and 15.15% at 48 h respectively, which were higher than others extracts.2. Three extracts, the ethanol and ethyl extract in powder and the ethyl extract in fresh samples of F. bidentis, inhibited growth and development of cotton worm. The weight growth inhibition rates of 180, 36 and 7.2 mg ? mL-1(W / V) of the ethanol extract of F. bidentis powder with 3 d treatment were 51.44%, 41.80% and 35.15%, respectively. The larval emergence rate, 43.70%, 45.79% and 50.09%, and adult emergence rate, 47.24%, 56.95% and 70.89% were inhibited by the extracts, respectively. The three digestive enzymes activities in larvae guts treated with 180 mg ? mL-1 extract for 3 d were reduced. Activities of amylase, lipase and total protease were 0.52, 0.54 and 0.66 times of control. The ethyl extract of F. bidentis powder showed the same activity with the ethanol extract, and the weight growth inhibition rates treated with 180, 36 and 7.2 mg ? mL-1 were 51.44%, 41.80% and 35.15%, respectively. The larval emergence rates of three concentrations were 47.22%, 57.25% and 76.50%, the adult emergence rates, 46.67%, 67.29% and 77.78%, which were lower than control. Three digestive enzymes in cotton worm larvae guts were reduced by 180 mg·mL-1extracts, which were 0.57, 0.61 and 0.65 times of control. Compared with the other two extracts, the ethyl extract of fresh samples had poor inhibition on the growth and development of cotton worm. The weight inhibition rates of cotton worm w ere 35.36%, 30.45% and 26.65% after treat with 500, 100 and 20 mg·mL-1 extracts for 3 d. The larval emergence rate, 74.44%, 91.11% and 96.67%, and adult emergence rate, 74.70%, 73.35% and 74.69%, respectively, that had no significant difference with control. After fed with the 500 mg·mL-1extract for 3 d, the activities of amylase, lipase and total protease were 0.68, 0.87 and 0.90 times of control, that showed a poor inhibition on the enzymes.3. According to results on the active mode of α-terthienyl, α-terthienyl had antifeedant activity and inhibited the growth and development of the cotton worm. At the 10-1000 mg·L-1, α- terthienyl had significant antifeedant activity on 3 instars larvae. With the concentrations of α-terthienyl increasing, feeding area decreased in treatment while antifeedant rate increased. The concentrations for median antifeedant effects concentration(AFC 50) in choice and no-choice were 11.52 mg·L-1 and 12.26 mg·L-1 at 24 h, respectively. Meanwhile, α-terthienyl had inhibition effect on the growth and development of larvae and pupae. The weight inhibition rates was 72.14%, 63.07% and 52.35% after treated with 1000, 100, 10 mg·L-1 for 1 d. 1000 and 100 mg ? L-1 solutions prelonged larval development duration at 1.37 d and 1.51 d, and mitigated pupa weight for 53.07 g and 47.41 g compared with the control. The pupation rates were 53.35% and 67.70%, and emergence rate s were 70.67% and 69.95%, respectively. Both of them were significantly different from control. After 1 d and 3 d treatment, α-terthienyl had little influence on the amylase and total proteases activity in guts of larvae. It reduced lipase activity, and the lipase activity treated for 1 d was 0.52 times of the control.In summary, the extracts of F. bidentis inhibit feeding of cotton worm; reduce the weight gain and the activities of three digestive enzymes; decrease the emergence rate and pupation rate. The secondary metabolite in F. bidentis, α-terthienyl, has antifeedant activities on larvae feeding; inhibites larvae weight gain; prolongs larval duration and reduces the emergence rate and pupation rate.