Insecticidal activity influence of destruxins on the pathogenicity of Paecilomyces java']javanicus against Spodoptera litura

The bioactivities of destruxins (dtx), depsipeptides isolated from Metarhizium anisopliae, against Spodoptera litura were tested in laboratory. For contacting toxicities, dtx-E was more effective than dtx-A and dtx-B. The LC(50)s values of dtx-A, B and E were 197.98, 292.00 and 113.99 mg/l at 48 h after treatment, while the LT(50)s were 42.65, 59.45 and 23.68 h at 300 mg/l. In the experiment of antifeedant activity, dtx-A, dtx-B and dtx-E at five concentrations (200, 100, 50, 25 and 12.5 mg/l) were bioassayed. Destruxins in a dose-dependent manner gave an apparent antifeedant activity. Generally, dtx-A, over dtx-B and dtx-E had the significant (P < 0.05) larger choice and no-choice antifeedant indexes (CAIs and NCAIs). At the concentration of 200 mg/l, the CAIs or NCAIs of dtx-A, dtx-B and dtx-E were 96.78, 84.93 and 85.90 or 89.75, 62.42 and 72.28 respectively. Furthermore, the synergistic activity of crude destruxin (CD) for pathogenicity of Paecilomyces javanicus strain Pj01 was detected. The LC(50)s values of single Pj01 and the mixtures of Pj01 plus CD at 100 or 200 mg/l (Pj01-CD100 or Pj01-CD200) were respectively 474.63 x 10(5), and 197.45 x 10(5) or 113.11 x 10(5) spores/ml at the fifth day after treated. Meanwhile, Pj01, Pj01-CD100 and Pj01-CD200 gave the LT(50)s values of 6.99 day, 5.49 day and 4.21 day at 100 x 10(5) spores/ml. Clearly, dtx decreased the values of LC50 and LT50 of the strain Pj01.