Insecticidal activity of rhamnolipid isolated from pseudomonas sp. EP-3 against green peach aphid (Myzus persicae).

Microorganisms capable of growth on oils are potential sources of biopesticides, as they produce complex molecules such as biosurfactants and lipopeptides. These molecules have antimicrobial activity against plant pathogens, but few data are available on their insecticidal activity. The present study describes the insecticidal activity of a rhamnolipid isolated from diesel oil-degrading Pseudomonas sp. EP-3 (EP-3). The treatment of cell-free supernatants of EP-3 grown on glucose-mineral medium for 96 h led to > 80% mortality of aphids (Myzus persicae) within 24 h. Bioassay-guided chromatography coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MADLDI-TOF MS) and (¹H, ¹³C) nuclear magnetic resonance (NMR) analyses was employed to isolate and identify the EP-3 insecticidal metabolites. Dirhamnolipid, with molecular formulas of C₃₂H₅₈O₁₃ and C₃₄H₆₂O₁₃, was identified as a main metabolite exhibiting insecticidal activity against aphids. Dirhamnolipid showed a dose-dependent mortality against aphids, producing about 50% mortality at 40 μg/mL and 100% mortality at 100 μg/mL. Microscopy analyses of aphids treated with dirhamnolipid revealed that dirhamnolipid caused insect death by affecting cuticle membranes. This is the first report of rhamnolipid as an insecticidal metabolite against M. persicae. Rhamnolipid shows potential for use as a pesticide to control agricultural pests.