Analysis and optimization of a synthetic milkweed floral attractant for mosquitoes.

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)-ß-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.

Phytochemicals as population sampling lures.

Most mosquito species have 2 hosts: vertebrate animals and vascular plants. The kairomones of vertebrates have been employed extensively as attractants in traps that are used for surveillance, either to assess adult density of mosquito populations or to detect pathogen activity. They also have been employed in basic field studies of mosquito physiology, behavior, and ecology. The semiochemicals that mosquitoes use to find plant hosts for their sugar, by contrast, have not been utilized at all. Currently we are characterizing attractive blends of volatile compounds produced by plant species visited by Aedes vexans, Culex pipiens, and Anopheles gambiae. These blends may be effective in attracting a unique subset of a mosquito population when deployed in surveillance traps. The principal advantages of phytochemical attractants are that they lure a) both sexes, b) all ages, including those that are newly emerged, c) females in all gonotrophic states, and d) both nondiapausing and reproductively diapausing females. Potential challenges to their successful use are the abundance of competing volatiles, narrow plant-host specificity, and a weaker behavioral response to phytochemical cues.

Effect of discriminative plant-sugar feeding on the survival and fecundity of Anopheles gambiae.

BACKGROUND: A previous study showed for Anopheles gambiae s.s. a gradation of feeding preference on common plant species growing in a malaria holoendemic area in western Kenya. The present follow-up study determines whether there is a relationship between the mosquito's preferences and its survival and fecundity. METHODS: Groups of mosquitoes were separately given ad libitum opportunity to feed on five of the more preferred plant species (Hamelia patens, Parthenium hysterophorus, Ricinus communis, Senna didymobotrya, and Tecoma stans) and one of the less preferred species (Lantana camara). The mosquitoes were monitored daily for survival. Sugar solution (glucose 6%) and water were used as controls. In addition, the fecundity of mosquitoes on each plant after (i) only one blood meal (number of eggs oviposited), and (ii) after three consecutive blood meals (proportion of females ovipositing, number of eggs oviposited and hatchability of eggs), was determined. The composition and concentration of sugar in the fed-on parts of each plant species were determined using gas chromatography. Using SAS statistical package, tests for significant difference of the fitness values between mosquitoes exposed to different plant species were conducted. RESULTS AND CONCLUSION: Anopheles gambiae that had fed on four of the five more preferred plant species (T. stans, S. didymobotrya, R. communis and H. patens, but not P. hysterophorus) lived longer and laid more eggs after one blood meal, when compared with An. gambiae that had fed on the least preferred plant species L. camara. When given three consecutive blood-meals, the percentage of females that oviposited, but not the number of eggs laid, was significantly higher for mosquitoes that had previously fed on the four more preferred plant species. Total sugar concentration in the preferred plant parts was significantly correlated with survival and with the proportion of females that laid eggs. This effect was associated mainly with three sugar types, namely glucose, fructose, and gulose. Except for P. hysterophorus, the results suggest that feeding by mosquitoes on preferred plant species under natural conditions results in higher fitness-related benefits, and that the sugar content in preferred plant parts is largely responsible for these effects.