Analysis and Optimization of a Synthetic Milkweed Floral Attractant for Mosquitoes

Abstract

A pentane extract of flowers of common milkweed, Asclepias syriaca (Asclepiadaceae), elicited significant orientation from both male and female Culex pipiens in a dual-port flight olfactometer. Analysis of the extract by gas chromatography–mass spectrometry revealed six major constituents in order of relative abundance: benzaldehyde, (E)-β-ocimene, phenylacetaldehyde, benzyl alcohol, nonanal, and (E)-2-nonenal. Although not all were collected from the headspace profile of live flowers, a synthetic blend of these six compounds, when presented to mosquitoes in the same levels and proportions that occur in the extract, elicited a response comparable to the extract. Subtractive behavioral bioassays demonstrated that a three-component blend consisting of benzaldehyde, phenylacetaldehyde, and (E)-2-nonenal was as attractive as the full blend. These findings suggest the potential use of synthetic floral-odor blends for monitoring or control of both male and female disease-vectoring mosquitoes.

Volatile phytochemicals as mosquito semiochemicals

“…Laboratory assays have further shown that floral and vegetative scents play a vital role in the attraction of Ae. aegypti to Asclepias syriaca (Vargo and Foster, 1982), Culex pipiens pipiens to L. vulgare , A. millefolium , Asclepias syriaca , and Solidago canadensis (Mauer and Rowley, 1999; Otienoburu et al, 2012), and An. gambiae to Parthenium hysterophorus , Ricinus communis and Bidens pilosa (Nyasembe et al, 2012).…”

“…Solvent extraction has been widely used to collect plant volatiles for elucidation of their potential attractiveness to various mosquito species, with a single solvent (Otienoburu et al, 2012) or a series of solvents (Vargo and Foster, 1982; Jepson and Healy, 1988) used to extract floral compounds of different plant species. Solvent extraction is advantageous in that it is possible to get the full volatile organic profile of the plant by varying the type of solvent used.…”

“…Another method that has been employed collecting volatiles from mosquito host plants is the static headspace volatile collection techniques (Otienoburu et al, 2012). In their study, Otienoburu et al (2012) placed Asclepias syriaca florets in a glass vial and collected the volatiles on solid phase micro-extraction (SPME) fibre with no circulation of air.…”

“…In their study, Otienoburu et al (2012) placed Asclepias syriaca florets in a glass vial and collected the volatiles on solid phase micro-extraction (SPME) fibre with no circulation of air. Various SPME fibres that adsorb volatile organic compounds of varying polarity and molecular weights are available and have been reviewed in Tholl et al (2006).…”

Nectar protein content and attractiveness to Aedes aegypti and Culex pipiens in plants with nectar/insect associations

“…A. curassavica was another plant species selected based on published indications of attractiveness to mosquitoes. It is related to A. syriaca, which possesses floral scents attractive to mosquitoes (Foster, 2008;Otienoburu et al, 2012) and is commonly associated with mosquitoes in the field (W.A. Foster, personal communication).…”