| An abbreviation for Bacillus thuringiensis is Bt, protein crystals will form in one side or both sides of cell when forming spore. This protein, known as insecticidal crystal protein, ICPs or delta-endotoxin. While ICPs has the advanced characteristics of high insecticidal efficiency, broad-spectrum and harmless to humans and animals, Bt has been used in a wide range of pest control.In this study, Monochamus alternatus was reared artificially whole year long. Indoor bioassays of 17 Bacillus thuringiensis against Monochamus alternatus and Bursaphelenchus xylophilus were implemented. Studies on parasporal crystal protein of toxic strain and biological characteristics of strains were carried out. The study results were as follows:(1)Stable experimental population had been successfully set up by artificial feeding and artificial indoor feeding whole year long was finally realized. It showed that this artificial diet was suitable for Monochamus alternatus larvae. Biological indexes of Monochamus alternatus were clear under the artificial feeding conditions.(2)Through the virulence selection among 17 Bt against Monochamus alternatus, we found that the mixtures of spores and parasporal crystals of 2 strains (RBT-200701,RBT-200702) exhibited a good poisonous activity against Monochamus alternatus, the corrected mortality of 2～3 instars Monochamus alternatus larvae were both more than 70%; and the survived larvae could not eat , moult and grow normally. A further study showed that there was certain positive correlation between the corrected mortality and the concentration of the mixtures of spores and parasporal crystals. When the determined concentration range was from 2000μg·g-1 to 125μg·g-1; the determined time range was from 0d to 20d, the insecticidal effect increased as extension of time.(3)The mixtures of spores and parasporal crystals of 2 strains (RBT-200701,RBT-200702) induced antifeedant effect, further affected the growth and development of larvae, which will avoid damaging through feedant. SDS-PAGE protein analysis showed that the spectrums of two crystal proteins were the same, two clear bands are appeared, molecular weight of which were about 65KD, 140KD respectively.(4)The characteristics of vegetative cell, spore and colony of RBT-200701 and RBT-200702 were almost the same, the main difference between them was that the average length of vegetative cell of RBT-200702 was 10μm more than RBT-200701's, parasporal crystal of RBT-200702 was less and mainly rectangle, while RBT-200701 almost dissociative and rhomboid.(5)The optical fermentation condition of RBT-200701 and RBT-200702 was that temperate was 30℃, pH was 7.2, vibrating speed was 200r·min-1, cultivation time was 36h.(6)Bioassay result of 17 Bt against Bursaphelenchus xylophilus showed that B. thuringiensis strain RBT-200701and 020 had apparent virulence effect on B. xylophilus, corrected mortality were more than 70% and 80% respectively. The corrected mortality of both strains were linearly relative to the concentrations. The semi-lethal concentration (LC50) and 95% concentration (LC95) of strain 020 at 24h and 48h were 183.20μg·mL-1 and 80.13μg·mL-1 respectively. Semi-lethal and 95℅ concentration of RBT-200701 at 24h and 48h were 368.00μg·mL-1 and 82.73μg·mL-1 respectively. According to SDS-PAGE analysis, strain 020 and strain RBT-200701 had different spectrum, 020 had a clear band where molecular weight was about 90KD, RBT-200701 had two clear bands where molecular weights were about 65KD and 140KD respectively.
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