Screening And Toxicity Determination Of Biocontrol Bacteria: Bacillus Thuringiensis Against Mushroom Pests: Lycoriella Sp.

Fungus gnats, Lycoriella sp. (Diptera: Sciaridae), is one of the important pests in mushroom cultivation. The feeding of sciarid fly larvae causes damage to the cultivation substrates, compost and casing. The adult can also spread fungus diseases and mites. The disadvantages of the chemical control has been increasing and physical prevention can not effectively control damage of the pest. So biological control, as a safe and effective method, is increasingly becoming the focus on preventing and controlling mushroom pests. The purpose of this study is to develop effective Bt strains to Lycoriella sp., determine its main insecticidal activity ingredients and Bt treatment effects on edible fungus hypha growth. And then to improve the scientific basis for Bt prevention mushroom pests in the future. Main results are as follows.1. BRC-LLP29 and IPS82 are effective strains after preliminary screening, the corrected mortality of larvae aged 7⁸ days of Lycoriella sp. was 87.93% and 70.21%, respectively. The concentration-mortality tests of the two strains showed BRC-LLP29 was better than IPS82, and their LC₅₀ was 1.182×10⁸ cfu/mL and 1.977×10⁸ cfu/mL, respectively.2. Low doses of crystal proteins (0.02648 mg/mL) of BRC-LLP29 has higher insecticidal activity, the corrected mortality of larvae aged 7⁸-day-old of Lycoriella sp. was 90% (24 h) and 100% (48 h); Spore crystal mixture also showed insecticidal activity, the corrected mortality is 75% (48 h) in the concentration of 26.48 mg/mL; Spores of BRC-LLP29 has no insecticidal activity. The crystal protein is the main insecticidal factor, and the LC50 of BRC-LLP29 crystal protein to larvae 7⁸-day-old of Lycoriella sp. is 0.004 mg/mL.3. BRC-LLP29 fermented fluid can inhibit edible fungi hyphae growth, with the increase of concentration, inhibitory effect increased, And inhibitory effect of BRC-LLP29 to 8 kinds of edible fungi (EC50/cfu/mL PDA) is: Lentinus edodes (1.175×10⁵) > Agaricus bisporus (4.467×10⁵) > Agrocybe chaxinggu (1.148×10⁶) > Auricularia polytricha (1.318×10⁶) > Flammulina velutipes (2.512×10⁶) > Pleurotus pulmonarius (3.802×10⁶) > Pleurotus ostreatus (9.772×10⁶) > Pleurotus eryngii (1.000×10⁷).4. Pleurotus ostreatus, Agaricus bisporus, Lentinus edodes, Pleurotus eryngii, Flammulina velutipes hyphae growth can be significantly (p<0.05) inhibited by metabolites dilutions 20 times and 40 times of BRC-LLP29 strains, Auricularia polytricha hyphae growth can be significantly (p<0.05) promoted in contrast; Agaricus bisporus be severely inhibited even by metabolites dilutions 320 times; BRC-LLP29 metabolites 320 times diluent can significantly (p<0.05) promote hyphae growth of Agrocybe chaxinggu and Pleurotus pulmonarius. Based on the above results, Lycoriella sp. can be controlled by BRC-LLP29 if a higher concentration is used in the laboratory. However, BRC-LLP29 is not as effective as chemicals, and edible fungi hyphae growth can be inhibited. Therefore, it will have great difficulty in applying Bt to control sciarid pests in mushroom cultivation.