Identification and Pathogenicity of a New Entomopathogenic Fungus, Mucor hiemalis (Mucorales: Mucorales), on the Root Maggot, Bradysia odoriphaga (Diptera: Sciaridae)

Abstract

Bradysia odoriphaga Yang and Zhang (Diptera: Sciaridae), the Chinese chive root maggot, is a destructive pest of Allium vegetables and flowers that causes severe losses in northern China. Novel biological control technologies are needed for controlling this pest. We identified a new entomopathogenic fungus isolated from infected B. odoriphaga larvae and evaluated the susceptibility of the biological stages of B. odoriphaga and the effects of temperature on fungus growth and pathogenicity. Based on morphological characteristics and molecular phylogeny, the fungus was identified as Mucor hiemalis BO-1 (Mucorales: Mucorales). This fungus had the strongest virulence to B. odoriphaga larvae followed by eggs and pupae, while B. odoriphaga adults were not susceptible. A temperature range of 18-28°C was optimum for the growth and sporulation of M. hiemalis BO-1 and virulence to B. odoriphaga larvae. At 3 and 5 d after inoculation with 105 spores/ml at 23°C, the survival rates were 24.8% and 4.8% (2nd instar larvae), respectively, and 49.6% and 12.8% (4th instar larvae), respectively. The potted plant trials confirmed that M. hiemalis BO-1 exerted excellent control efficiency against B. odoriphaga larvae, and the control exceeded 80% within 5 d when the spore concentration applied exceeded 107 spores/ml. In conclusion, these findings supported the hypotheses that this fungus could serve as an effective control agent against B. odoriphaga larvae and is worth being further tested to determine its full potential as a biocontrol agent.

Keywords: Bradysia odoriphaga; biocontrol agent; control efficiency; entomopathogenic fungi; pathogenicity bioassay.

Graphical abstract

Fig. 1.

Macroscopic morphological characteristics of Mucor hiemalis BO-1. A (a) white and slightly transparent aerial hyphae on potato dextrose agar (PDA) medium; B (b) small black sporangium; (c) vertical and uniramous sporangiophore; C (d) smooth, aseptate and polynuclear hyphae; (e) branched hyphae; D (f) broken sporangium releasing sporangiospores.

Fig. 2.

Neighbor-joining tree based on the analysis of partial ITS sequences of Mucor hiemalis BO-1 and other Mucor species. A, The electrophoretic band of Mucor hiemalis BO-1 partial ITS sequence. B, neighbor-joining tree.

Fig. 3.

Pathogenesis of B. odoriphaga larvae infected by Mucor hiemalis BO-1. A 24 hr after inoculation; (a) green food particles were present in larval guts; B 48 hr after inoculation; (b) few food particles were present in larval guts; (c) the body gradually became transparent and bright; C 72 hr after inoculation; (d) yellow, turbid and supple larval body; D 120 hr after inoculation; (e) numerous white aerial hyphae grew from the dead larval body; (f) black sporangia at the top of the mycelium.

Fig. 4.

Pathogenic effects of Mucor hiemalis BO-1 on different stages of Bradysia odoriphaga. Data in the figure are the mean ± SE. Different letters over the same column indicate significant differences between different spore concentration treatments at the P < 0.05 level as indicated by one-way ANOVA.

Fig. 5.

Effects of temperature on mycelial growth (A) and conidiation (B) of Mucor hiemalis BO-1. Data in the figure is the mean ± SE. Different letters over the same column from the top indicate significant differences between different temperature treatments at the P < 0.05 level as indicated by one-way ANOVA.

Fig. 6.

Effects of environmental temperatures on the pathogenicity of Mucor hiemalis BO-1 to Bradysia odoriphaga 2nd (A) and 4th (B) instar larvae. Data in the table are the mean ± SE. Different letters over the same column from the top indicate significant differences between different temperature treatments at the P < 0.05 level as indicated by one-way ANOVA.

Fig. 7.

Control efficacy of Mucor hiemalis BO-1 against Bradysia odoriphaga 2nd and 4th instar larvae. Data in the table are the mean ± SE. Different letters over the same column from the top indicate significant differences between different treatments at the P < 0.05 level as indicated by one-way ANOVA.