Insecticidal activity and HPLC correlation of thuringiensin from fermentation and two-phase aqueous separation processes
1997
Hsu, T.H. | Tzeng, Y.M. | Wu, M.M.
Thuringiensin produced by Bacillus thuringiensis subsp. darmstadiensis was further subjected to a two-phase aqueous separation system. A modified HPLC method and a test for quantitative pathogenicity using the house fly Musca domestica were used for analysis of thuringiensin. Within a realistic range of dosages, more effect was observed in the pupal stage than in the larval stage. The percentage effective control rate (ECR) was calculated by (100 - percentage emergence); malformed and non-reproductive adults were considered as emerged. Pupal mortality, pupal weight, and ECR after feeding the three-day-old larvae were the measured response criteria for bioassay. The EC50 of thuringiensin for pupae mortality was 1.64 micrograms ml-1 diet, and 0.83 micrograms ml-1 for mortality of adults. Insecticidal activity of the broth increased with fermentation time-course from 9th to 21st hour. The bioassay curve constructed with three-hour sampling interval during the fermentation course had good correlation to thuringiensin content as determined by the HPLC method. In the two-phase aqueous separation system, a maximum of 96.7% ECR was achieved with the bottom salt layer, compared to a value of 46.7% with the upper PEG layer. These results suggest that thuringiensin, prepared through a fermentation and recovery process, is suitable for pest control.
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