Quantitative Structure−Activity Relationship of Botanical Sesquiterpenes: Spatial and Contact Repellency to the Yellow Fever Mosquito, Aedes aegypti

Abstract

The plant terpenoids encompass a diversity of structures and have many functional roles in nature, including protection against pest arthropods. Previous studies in this laboratory have identified naturally occurring sesquiterpenes contained in essential oils from two plants, amyris (Amyris balsamifera) and Siam-wood (Fokienia hodginsii), that are significantly repellent to a spectrum of arthropod pests. In efforts to further examine the biological activity of this class of compounds 12 of these plant-derived sesquiterpenes have been isolated, purified, and assayed for spatial and contact repellency against the yellow fever mosquito, Aedes aegypti . These data were used to develop quantitative structure-activity relationships that identified key properties of the sesquiterpene molecule, including electronic and structural parameters that were used to predict optimal repellent activity. There were notable similarities in the models developed for spatial repellency over five time points and for contact repellency. Vapor pressure was an important component of all repellency models. Initial levels of spatial repellency were also related to polarizability of the molecule and lowest unoccupied molecular orbital (LUMO) energy, whereas the equation for late spatial repellency was dependent on other electronic features, including Mulliken population and electrotopological state descriptors. The model identified for contact repellency was the best fit and most significant model in this analysis and showed a relationship with vapor pressure, Mulliken population, and total energy.

A sensitive bioassay for spider mite (Tetranychus urticae) repellency: a double bond makes a difference

“…For example 360 nmol/cm 2 was the concentration used for QSAR studies of sesquiterpenoid mosquito repellents (Paluch et al 2009). Also for QSAR studies, synthetic mosquito repellents were tested at 2.5 and 25 lmol/cm 2 (Katritzky et al 2008).…”

“…But, recently QSAR (quantitative structure activity relationships) approaches have been evaluated for discovery of new mosquito repellents, at least repellents having longer durability (Katritzky et al 2008). Also QSAR has been used to provide a better understanding between structure of natural products and their ability to repel mosquitoes (Paluch et al 2009). …”

Comparison of the Insecticidal Characteristics of Commercially Available Plant Essential Oils AgainstAedes aegyptiandAnopheles gambiae(Diptera: Culicidae)

“…Some terpenoids repel or kill various arthropod pests and have also been implicated in the attraction of pollinators and other beneficial species. For example, some extracts from amyris (Amyris balsamifera) and Siamwood (Fokienia hodginsii) have been implicated in the repellency of mosquito species, while volatiles from Brassica oleracea have been implicated in the attraction of various parasitoids that prey on caterpillars that damage the plants (Paluch et al 2009, Maia and Moore 2011, Poelman et al 2012, Harrewijn et al 1994. While the chemistry of many plant essential oils has been well documented, there is still much to learn about their respective bioactivities, particularly in regards to repellent or lethal activity against insects.…”

Elemol and amyris oil repel the ticks Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae) in laboratory bioassays

“…The concentrations at which elemol and amyris essential oil repelled I. scapularis and A. americanum in our bioassays and the concentrations which Paluch et al (2009) found repelled A. aegypti mosquitoes are low enough to indicate that elemol and amyris oil should be investigated more thoroughly for their potential as marketable repellents. …”