Identification and investigation on the insecticidal activity of Streptomyces lateritius CSF09, an endophyte strain from Eleusine indica (L.) Gaertn

To discover insecticidal ingredients from natural products, Streptomyces lateritius CSF09, an endophyte strain was isolated from Eleusine indica (L.) Gaertn. The bioactive compound was isolated from the fermentation broth by techniques of macroporous resin extraction and silica gel column chromatography, and its chemical structure was identified by MS and NMR. The obtained compound was subjected to evaluate its insecticidal activity against the 3rd larvae of Mythimna separate and adults of Musca domestica. The results indicated that the insecticidal ingredient produced by the strain was 4-methoxysalicylaldehyde with the yield of approximately 13 mg/L. 4-Methoxysalicylaldehyde showed contact toxicity against both M. separate and M. domestica. The LD50 value of M. domestica was 1.51 μg/fly. 4-Methoxysalicylaldehyde showed weak toxicity against M. separate, and the mortality rate was only 36.6% after the treatment of 10 μg/larvae. The outstanding characteristic of the insecticidal activity of 4-methoxysalicylaldehyde was quick-acting with the KT50 in most treatments less than 5 min. This investigation suggested that 4-methoxysalicylaldehyde has the potential to be developed as a health insecticide.