http://www.nature.com/articles/srep12690
- Scientific Reports 5, Article number: 12690 (2015)
- doi:10.1038/srep12690
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- Published online:
Abstract
Synergistic
interactions between constituents of essential oils have been reported
for several areas of research. In the present study, mechanisms that
could explain the synergistic action of the two major insecticidal
constituents of rosemary oil, 1,8-cineole and camphor against the
cabbage looper, Trichoplusia ni were investigated. 1,8-Cineole
was more toxic than camphor when applied topically to larvae, and when
coadministered in their ratio naturally occurring in rosemary oil, the
binary mixture was synergistic. However, when injected directly into
larvae, camphor was more toxic than 1,8-cineole. GC-MS analyses showed
that penetration of topically-applied camphor was significantly enhanced
when it was mixed with 1,8-cineole in the natural ratio. A bioassay
combining injection and topical application methods confirmed the
increased penetration of both compounds when mixed, showing the same
bioactivity as seen for higher amounts applied individually. Lowered
surface tension as well as increased solubility of camphor by
1,8-cineole, along with the interaction between 1,8-cineole and the
lipid layer of the insect’s cuticle may explain the enhanced penetration
of camphor. Because of the similarities in biological function of
animal and microbial membranes, our finding has potential for
application in other fields of study.