Culex
mosquito oviposition is mediated by
chemical and physical cues that are
associated with typical oviposition
sites such as ponds and other bodies
of stagnant water that contain
decomposing plant debris. We have
identified a number of volatile
chemical cues that influence
mosquito oviposition from aqueous
infusions of decaying plant
materials mimicking natural
oviposition waters. Compounds were
identified both by traditional
bioassay-driven fractionation of
solvent extracts of infusions, and
by collection of headspace
volatiles, followed by analysis by
coupled gas chromatography-electroantennogram
detection. Behaviorally and
physiologically active compounds
included indole and 3-methylindole,
phenols, aldehydes, and sulfur
compounds. We also investigated the
development of bioassays to
determine which steps in the
oviposition sequence (attraction or
oviposition stimulation) were
influenced by various chemical cues.
Several general conclusions could be
drawn from experiments with Culex
quinquefasciatus and Cx. tarsalis.
First, concentration was critically
important; compounds which were
attractive or stimulatory at parts
per billion levels in water became
repellent at higher concentrations,
particularly to Cx. tarsalis.
Second, oviposition stimulation
(treatment vs. control frequently >
10:1) appeared to be more strongly
mediated by chemical cues than
attraction (treatment vs. control,
~3:1). Third, blends of compounds
were more biologically active than
individual compounds, with the
increase in activity being
approximately additive rather than
synergistic. Fourth, correct
formulation of blends was important
because the release rates of
compounds from aqueous solutions was
dependent on their hydrophobicity
and hydrogen bonding abilities.
Thus, if the relative proportions of
compounds in the headspace volatiles
from infusions were used to
formulate synthetic blends,
hydrophobic compounds were
overrepresented, and hydrophilic
compounds were underrepresented.
Once blends had been adjusted to
compensate for these effects, the
corrected blends were more
biologically active than the
unadjusted blends. Overall,
considerable progress has been made
in identification of compounds that
mediate Culex mosquito oviposition,
but even the best synthetic blends
are not yet as active as crude
infusions of decaying plant
material, indicating that further
compounds remain to be discovered.
Index terms: Culex tarsalis,
Culex quinquesfasciatus, oviposition
stimulant, oviposition attractant
Copyright:
The copyrights of this original
work belong to the authors (see
right-most box in title table).
This abstract appeared in
Session 4 – CHEMICAL AND
PHYSIOLOGICAL ECOLOGY Symposium
and Poster Session, ABSTRACT
BOOK I – XXI-International
Congress of Entomology, Brazil,
August 20-26, 2000.