Acta Entomologica Sinica ›› 2019, Vol. 62 ›› Issue (5): 602-614.doi: 10.16380/j.kcxb.2019.05.009

• RESEARCH PAPERS • Previous Articles     Next Articles

Bioefficacy of the combined application of entomopathogenic nematode Heterorhabditis beicherriana strain LF and Bacillus thuringiensis strain HBF-18 against Holotrichia oblita (Coleoptera: Scarabaeidae) larvae

LI Er-Tao1, CAO Ya-Zhong1, ZHANG Shuai1, LI Ke-Bin1, LI Jian-Yi1, WANG Qing-Lei2, LIU Chun-Qin2, YIN Jiao1, *   

  1.  (1. State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China; 2. Cangzhou Academy of Agriculture and Forestry Sciences, Cangzhou, Hebei 061001, China)
  • Online:2019-05-20 Published:2019-05-16

Abstract: 【Aim】 This study aims to assess the possible synergistic effect of combined application of the entomopathogenic nematode Heterorhabditis beicherriana strain LF (LF) and Bacillus thuringiensis strain HBF-18 (Bt HBF-18) based on their pathogenicity to Holotrichia oblita larvae, so as to develop a new alternative method for white grub control. 【Methods】 The pathogenicity of LF at different doses to the 7-10-day-old larvae of H. oblita were investigated at different temperatures and soil moistures in the laboratory. The effects of Bt HBF-18 on the survival of LF, and the bioefficacy of the combined application of nematodes and Bt against the 7-10-day-old larvae of H. oblita were also investigated in the laboratory. At the same time, the bioefficacy of the combined application of LF and Bt HBF-18 against the 7-10-day-old larvae of H. oblita was investigated with outdoor pot experiments. 【Results】 The results showed that the larval mortality of H. oblita increased with the increase of the application dosage of LF and the treatment duration, with the larval mortality rate reaching 100% at 7 d after treatment with LF at the dosage of 800 IJs/100 μL and above. Moreover, 25℃ temperature and 14%-20% soil moisture were proved to be the ideal conditions for the best infection efficiency of LF, and too low or too high humidity significantly affected its infection efficiency. Laboratory bioassays showed that the LC50 of Bt HBF-18 against H. oblita larvae after treatment for 9 d was 1.44×108 CFU/g soil, and at this concentration Bt HBF-18 showed little effect on the survival of LF. In addition, both the indoor bioassay and outdoor pot experiment revealed that the combined application of LF and Bt HBF-18 could significantly improve their bioefficacy against H. oblita larvae, showing additive or synergistic effect. Indoor bioassay showed that the larval mortality rates in the treatment with LC50Bt+200 IJs/100 μL LF for 3 d were increased by about 43.07% and 36.05%, respectively, as compared with that in LF or Bt HBF-18 applied alone, indicating that the combined application of LF and Bt HBF-18 has significant synergistic effect against H. oblita larvae. Treatments with 1/2 LC50Bt+1 000 IJs/mL LF, LC50Bt+1 000 IJs/mL LF and 1/2 LC50Bt+1 500 IJs/mL LF in the outdoor pot experiment showed synergistic effect against H. oblita larvae, and 1/2 LC50Bt+1 500 IJs/mL LF showed the best effect, with the mortality of H. oblita larvae increased by about 38.89% and 80.55%, respectively, as compared with that in LF or Bt HBF-18 applied alone. 【Conclusion】 Overall, the interaction between the entomopathogenic nematode LF and Bt HBF-18 against the larvae of H. oblita is either additive or synergistic.

Key words: Entomopathogenic nematode; Heterorhabditis beicherriana strain LF, Bacillus thuringiensis strain HBF-18, Holotrichia oblita, synergistic effect