First report of entomopathogenic nematode Steinernema affine (Nematoda: Steinernematidae) in Syria and its virulence against Galleria mellonella L. (Lepidoptera: Pyralidae)

Abstract

Background: Entomopathogenic nematodes (EPNs) have a great potential as a biocontrol agent for a wide range of insect pests. EPNs have attracted much interest around the world to study their distribution, virulence, and usage in the IPM programs. This research was conducted to identify the steinernematids M.22 and M.313, which were isolated during the survey of EPNs in different agricultural and ecological systems, in the Syrian coastal region between 2017 and 2020. Additionally, to evaluate the virulence of these isolates against the last instar larvae of the greater wax moth, Galleria mellonella (Linnaeus 1758) (Lepidoptera: Pyralidae), three bioassays were carried out at 18 °C. The exposure time assay was performed by applying different times (15, 30, 45, and 60 min) using a specified concentration (400 IJs/Larva). The concentration–response and one-on-one assays were conducted by using different concentrations of the infective juveniles (IJs) (5, 15, 25, and 40 IJs/L) and an individual juvenile, respectively, for 72 h of exposure. LC50 and LT50 values were calculated. Results: The steinernematids M.22 and M.313 were isolated from 2 of 821 soil samples (0.24%). The positive isolates were identified as Steinernema affine (Bovien, 1937), based on morphological, morphometric, and molecular characterization. Steinernema affine was recovered in the walnut orchard and grassland in AL-Kadmous area of Tartus governorate, Syria. The soil type was silty loamy and silty, PH was slightly acidic, and organic matter content was 6 and 4.1%. In the exposure time assay, the mortality ratio increased gradually by increasing time, M.22 and M.313 achieved the highest mortality ratios at 60 min, which were 90.16 and 91.49%, respectively. In the concentration–response assay, complete mortality was achieved at the concentration of 40 IJs/L for both isolates. Low mortality ratios were observed in the assay of one-on-one, 20 and 23.6%, respectively. The LC50 and LT50 values were calculated and resulted in (11.7 IJs/L, 33.47 min) and (11.5 IJs/L, 32.43 min), respectively. Nonsignificant difference between both isolates was recorded. Conclusions: The results showed that the isolates were identical and identified as Steinernema affine. This is the first report of S. affine in Syria. It could be an effective biological control agent.