The biochemistry and biological roles of the epicuticular lipid layer of the mosquito Aedes aegypti (Diptera: Culicidae).
The biochemical characterisation of the hydrocarbon fraction of the cuticular
lipids of the vector mosquito, Aedes aegypti, was carried out using a variety
of chemical methods, optimised for this application. Forty-four of the
seventy-eight compounds detected by gas chromatography were identified,
mainly using mass spectrometry. Several of the other compounds were
partially characterised. The changes in composition of the cuticular
hydrocarbon profiles in response to various biological factors such as age,
gender, mating status and body part were studied using gas chromatography.
Two models for age grading mosquitoes were proposed. Trends exhibited by
the major hydrocarbons in response to increasing age and increased length of
time in contact with the opposite sex were highlighted and body parts
exhibiting gender-specific, concentrated areas of particular hydrocarbon
compounds were identified. From the results, possible candidates for close
range/contact pheromones and mating stimulants expressed in females were
proposed. These compounds were examined for their effects on male mating
behaviour using a bioassay procedure, testing both individual specimens, and
paIrs of speCImens from different experimental groups ( choice tests).
Monomethylhentriacontane and (to a lesser extent) monomethylnonacosane
appeared to act as a mating stimulant though when present in higher
localised concentrations, the males were deterred from approaching the
source. It was postulated that swarming activity, resulting in a raised
monomethylhentriacontane concentration in the surrounding air, was an
important factor in stimulating males to mate. The straight chain
hydrocarbons, n-heptacosane, n-pentacosane, n-tricosane and n-nonacosane
were attractive to the males and may have action as close range chemical
stimuli or contact pheromones. The very high localised concentration of nheptacosane
on the abdomen of the female only, made this compound a
likely candidate for a contact pheromone. Courtship and mating behaviour
was observed using video filming and the feasibility of the theory that
cuticular hydrocarbons may be active in modifying this behaviour was
discussed in relation to these observations.