Abstract
A new strain QHLA of Lecanicillium uredinophilum was isolated from a Chinese caterpillar fungus complex and its optimum growth temperature and fermentation conditions were studied. Its insecticidal activity was tested against larvae of seven different insect pests, including Henosepilachna vigintioctopunctata, Spodoptera exigua, Plutella xylostella, Spodoptera frugiperda, Sitobion avenae, Hyalopterus perikonus, and Aphis citricola. The optimum growth temperature was 21-24 °C. The highest spore production of the strain QHLA was 4.08 × 10(6) spore/mL on solid medium with a nitrogen source of NH(4)Cl. However, the highest mycelial growth rate of the strain QHLA was on solid medium with a nitrogen source from yeast extract (4.63 ± 0.03 mm/d). When the liquid medium contained peptone, yeast extract, and glucose, the water content of the mycelia was the lowest, while the spore production was the highest until day 12. When the liquid medium contained glucose, tussah pupa powder, KH(2)PO(4), and MgSO(4), the mycelia production was highest until day 8. The bioassay for insecticidal activity indicated that the LC(50) values of QHLA were 6.32 × 10(3) spore/mL and 6.35 × 10(3) spore/mL against Sitobion avenae and Aphis citricola, respectively, while the LC(90) values of the strain QHLA against Aphis citricola and Sitobion avenae were 2.11 × 10(7) spore/mL and 2.36 × 10(8) spore/mL, respectively. Our results demonstrated that the strain QHLA was a high virulence pathogenic fungus against insect pests, with the potential to be developed as a microbial pesticide.