Chemical variability and insect repellent effects of lemon catnip essential oil and related phytochemicals against Cimex lectularius L

Plants are sources of natural products that reflect the ecological interactions that shaped their secondary metabolism. Among those, phytochemicals with insect repellent activity have shown potential to be part of integrated pest management programs. In this study, we performed an initial screening of the repellent activities of five commercially available essential oils, as well as the essential oil of lemon catnip (Nepeta cataria var. citriodora Dumoulin ex Lej.) and related natural products against the common bed bug (Cimex lectularius L.). Additionally, we studied the effects of two different growing locations (Upper Deerfield and Pittstown, state of New Jersey, United States) on the chemical composition of three lemon catnip lines (commercial lemon catnips Richters and Jelitto, and lemon-scented catnip line CN5). The chemical composition of the essential oils was determined by gas chromatography-mass spectrometry (GC-MS) and the repellent activity was assessed by the petri dish method. Cinnamon bark, clove buds, citronella and geranium essential oils were as effective as N,N-diethyl-meta-toluamide (DEET), the gold standard of insect repellents, against bed bugs after one hour of exposure in vitro. The essential oil of lemon catnip and its major compounds citronellol and geraniol were also as repellent as DEET using the same test. Citral shows promising short-term repellency but is inferior to geraniol and citronellol for extended duration of repellency. As for the chemical variability of lemon catnip lines in different growing locations, CN5 line was not significantly affected by the different locations, while both commercial lines Richters and Jelitto had significantly higher proportions of geraniol when grown in Upper Deerfield. Richters lemon catnip produced more nepetalactone in its essential oil when cultivated in Pittstown. This study is the first report of the activity of lemon catnip essential oil as an insect repellent and emphasized the importance of ecological conditions for the production of natural products for pest control applications.