Aedes Aegypti Size, Reserves, Survival, And Flight Potential

7/28/2019 Aedes Aegypti Size, Reserves, Survival, And Flight Potential

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June, 2001 Journal of Vector Ecology 21

Aedes aegypti: size, reserves, survival, and flight potential

Hans Briegel*, Irne Knsel, and Susanne E. Timmermann

Institute of Zoology, University of Zrich, CH-8057 Zrich, Switzerland

* Corresponding author

Received 1 May 2000; Accepted 31 August 2000

ABSTRACT: FemaleAedes aegypti of small and large body sizes were fed ad libitum from eclosion with eight

different concentrations of sucrose from 0.1% to 50%; females were also starved with access to water. For each

experiment we determined the survivorship of such populations. The 90%, 50%, 10%, and maximal survivorships

followed linear regressions with the logarithm of the sucrose concentration. For each condition we measured

the extent of synthesis of glycogen and lipid reserves. There was a critical sucrose concentration of 0.5% for

both size classes: lower concentrations were of no nutritive effect, and all higher concentrations extended

survivorship and allowed reserve synthesis. With respect to the teneral value, and normalized for body size, the

maximal amounts of glycogen increased 2-3-fold within one week, whereas lipogenesis increased 3-5-fold

requiring two weeks. Solid sugar cubes could also be utilized as long as drinking water was available, but synthesis

of additional reserves failed. Flight mill experiments revealed the temporal flight pattern, its maturation after

eclosion, and the maximal flight performances. Flights shorter than 1000 m per female per night were considered

as low activities, whereas flights longer than 1000 m represented strong vigorous flights. Maximal distances

were from 11-18 km/female/night. Periods of continuous flights lasted between 2-9 hr per female (mean 2.2 hr).

Maximal flight performances were gradually reached within the first and third day of eclosion. Mean caloric

energy consumption during flight was 33% to 44% of the pre-flight glycogen, accompanied by lipid reductions

of 9%. Evidently, feeding on carbohydrates allows extended flight activities of this species and is essential for

survival in the absence of blood meals.Journal of Vector Ecology 26(1): 21-31.

Keyword Index: Aedes aegypti, reserves, body size, survival, flight potential

INTRODUCTION

In most mosquitoes, females require additional

protein after eclosion to initiate vitellogenesis. For

Aedes aegypti, the metabolic relationships between

blood meal utilization and fecundity have been

quantitatively determined, in relation to size and source

of the blood meal, age and size of the female, and in

comparison to Anopheles (Briegel 1990a, b). Van

Handel (1965) has characterized obesity for the

mosquitoAe. sollicitans and conspicuous lipogenesis

was also found in several other species, especially in

Ae. aegypti (Briegel 1990a, Timmermann and Briegel

1999, Briegel and Timmermann forAe. albopictus, in

prep).

Mosquitoes are not ready for reproduction

immediately after eclosion. Males require one day for

the rotation of their terminalia, and females develop

their host-seeking behavior within one to two days

(Klowden 1990; Briegel unpublished data). Depending

on the availability of a host, females might need to wait

a few more days for their first blood meal. In general,

seeking carbohydrate sources, i.e. feeding on sugar

solutions, is a common behavior for most of them and

for both sexes (Foster 1995). Feeding on sugarsolutions extends their survival time (Briegel and

Kaiser 1973, Nayar and Sauerman 1971, Foster 1995),

and improves their reserve conditions, mainly in lipids

(Van Handel 1965; Nayar and Sauerman 1971, 1974;

Briegel 1990a). So far, only Ae. aegypti was reported

to largely abstain from sugar feeding in favor of blood

meals (Scott et al. 1997, Costero et al. 1998). In nature,

nectar is assumed to be the prevalent source of sugars

but probably all sorts of sugars in different

concentrations are available (Foster 1995). Van Handel

et al. (1972) demonstrated the prevalence of sucrose,

besides fructose and glucose, and many other sugars in

minor quantities for over 40 different nectar samples

and fruit juices. The availability of sugar solutions is

not confined to nectar, but a wide variety of

carbohydrates may be accessible, with honeydew

probably the most important (Foster 1995). Ae.

taeniorhynchus is quite tolerant in accepting most

sugars, while Ae. aegypti was reported to be more

selective (Nayar and Sauerman 1971). Observations of

mosquitoes feeding on flowers are relatively rare,


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22 Journal of Vector Ecology June, 2001

despite great efforts by several entomologists in the

field (McCrae et al. 1969, McCrae 1989, Haeger 1960).

Flight potential is an important consequence of the

status of reserves, particularly for Ae. aegypti and its

epidemiological potential (Reiter, personal

communication). The first movements in their imaginallife take place before any food sources are encountered,

and therefore, the energy requirements have to be met

by the reserves they carry over from the larval/pupal

period, i.e. the teneral reserves. Subsequently,

carbohydrate sources need to be found and tapped for

as long as no blood donors are available.

This study aims at a complete, systematic and

quantitative laboratory investigation of the sucrose

feeding and its metabolic consequences. While Nayar

and Sauerman (1974) studied the regulation of daily

intake and its inverse correlation with concentrations,

we exclusively followed the effects of increasing

concentrations on survival and the absolute synthesisof reserves. Newly eclosed females were provided with

sucrose solutions of gradually increasing

concentrations from zero up to 50% ad libitum. The

survivorships were recorded, live and dead females

sampled from these experiments, analyzed for reserves

and then compared with the conditions at eclosion. In

view of the quantitative analyses, we then addressed the

flight performance ofAe. aegypti and its quantitative

relationships to the glycogen and lipid reserves present

at selected times of life. For that purpose we have

utilized a computerized flight mill similar to Rowley

et al. (1968) or Nayar and Sauerman (1973) and

recorded distances flown by individual mosquitoes, and

simultaneously recorded the temporal flight pattern.

We did not attempt to imitate field conditions, but

rather aimed at a more complete analysis of the

physiological interactions between the metabolic

background and the maximal flight potential for the

yellow fever mosquito, Ae. aegypti. In addition, these

data form the background for results on reproductive

cycles, which will be reported elsewhere (Briegel et

al., in preparation).

MATERIALS AND METHODS

Aedes aegypt i (L.) strain UGAL, was used

exclusively for this investigation. Larvae were reared

under optimal conditions, i.e. 200 larvae per pan, fed

TetraMin with our standard regime, or under moderate

crowding conditions, i.e. 400 larvae per pan, fed 1 spoon

of standard diet on alternate days, as described in detail

by Timmermann and Briegel (1993). The former

colonies produced large imagines, the latter small ones.

Wing length and its cubic value were used to record

body size (Briegel 1990a). All colonies were kept at

27C, the imagines at a relative humidity of 852%,

and with long-day conditions (14 hr photophase) with

dim light periods of 45 min to simulate sunset and

sunrise. All experimental cohorts (50 each) were kept

in 8 l cages and provided with two cotton wicks thatwere soaked with the sucrose solutions to be offered

ad libitum: 0.1%, 0.5%, 1%, 2%, 5%, 10%, 20%, and

50%, or water. Survival was recorded by daily counts

and removal of dead insects, which were fixed for

analyses. At the same time, in parallel cages of identical

treatment, live females were sampled (5-10 per day)

and fixed as well, to trace their changes in reserves.

For tissue fixation, each female was put into a reacting

tube (14x100 mm), together with 100 l ethanol 100%,

and heated for 10 min at 90C. These samples were

stored at room temperature until analysis, but no longer

than two weeks.

The flight mills were round containers (15x6 cmfor diameter and height). At the tips of two thin arms of

5 cm length, a human hair of 1-2 cm was fixed at which

the mosquito was glued with a minimal drop of wax

applied to its anterior portion of the mesothoracic

tergite. The correct flight position of the mosquito was

crucial for optimal performance. The revolutions of the

drum were recorded by a photocell and fed into the

computer. A program was designed to count and store

these revolutions per selected time interval, 30 sec in

our experiments. The program then converted these

revolutions into absolute distances flown per time

interval, which also were summed up to total distances

in meters. In our experience, flight durations of more

than 18 hr were extremely rare with Ae. aegypti and

therefore, this was the arbitrary cut-off point of daily

data collections. All flight trials were run at a room

temperature of 20-22C and overnight to minimize

disturbances by lab personnel. In preliminary tests we

found no dependence of the flight activities from

lighting regimes in this species.

The printout of the computer protocols provided

all single spikes of flight activities for the entire test

period on absolute time axes, revealing the temporal

pattern of flight activities. Spontaneous interruptions

or resumptions were visible (exemplified in Figure 3).Movements of less than 1m/min were neglected as

noise or background activities. Based on their total

flight distances, we defined weak fliers with total

distances below 1000 m, and strong fliers exceeding

1000 m per female per night. Females were considered

exhausted when they did not move any more on the flight

mill, but were still alive; dead females were discarded.

A total of 294 females was available for analysis.

The analyses for glycogen and lipid were carried


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Figure 1. Effect of female body size (large versus small) and sugar diet (0.5% versus 5% ad lib.) on the

content of glycogen and lipid ofAe. aegypti. Caloric data are related to the teneral conditions, i.e.

at eclosion. The absolute calories were converted to SSCC-values and its teneral amount defined as

1.0, marked as a dashed horizontal line in each diagram. The shadowed band represents the respective

m.i.a., i.e. the death line. As a further means of comparison, the actual survivorship data of these

four cohorts have been plotted. Open circles are values for dead females, and filled circles for live

controls.


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Figure 2. The 50% survival times (solid lines) ofAedes aegypti fed water (shadowed area) or increasing

concentrations of sucrose ad lib. plotted against the logarithmic value of sucrose concentration

for females of different body sizes (solid lines). Large females had wing lengths always higher

than 3.1 mm, and all small females had wing lengths below 2.8 mm, both groups representing

extremes of the possible sizes. For comparison, the 90% (lower), 10% (upper), and maximal survival

time regressions have been added (dashed lines). All survival times follow linear regressions

(formulas in Table 1).

out by the procedures of Van Handel and Day (1988),

which allowed us to quantify both components within

the same samples. In certain experiments we also

measured the content of total sugar with glucose as a

standard. The glycogen and lipid data were expressed

in calories per single female. These caloric values were

then normalized for size and presented as SSCC-values

(size-specific caloric contents; see Timmermann and

Briegel 1993). Furthermore, the SSCC-values of small

and large teneral females were arbitrarily set as 1.0 in

all diagrams, and all SSCC-values converted accordingly.

Data for survivorship were plotted as survival

curves, and the 90%, 50%, 10% and maximal survivaltimes were determined graphically from these plots.

These four survival points from all the diets were then

related to the logarithm of sucrose concentrations by

plotting against the log value of the sugar concentration;

all showed significant linear regressions. All means are

accompanied by standard errors (S.E.) and sample sizes

(N).

RESULTS

Survival times

Survivorship curves usually follow an inverse

sigmoidal pattern, revealing the maximal survival time

for each feeding regime (Figure 1). By graphic

interpolation we determined the 90%, 50%, 10%, and

maximal survival times. When plotting these selected

time points against the increasing dietary sucrose

concentrations in a semilogarithmic diagram, they

showed linear regressions (Figure 2). Females of the

two extreme size classes were analyzed. Females

provided with water to prevent desiccation showed theeffect of starvation. Their body size clearly affected

survival, which was 4.0 1.0 d (N=9) for small females

with a mean body size of14.102.08 mm3 (N=112,

range 9.26-20.80),and 9.82.1 d (N=9) for large

females with a size of 41.443.20 mm3 (N=48, range

32.77-48.69), a significant difference in survival time

(t=3.69, p


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Table 1. Regression formulas (Y=a+bX) for the various survival times (Y, days) of small and large

females with access to water only (starvation), or increasing sucrose concentrations (X,

logarithmic value; N=7 for each). Values for starving females and for females offered 0.1%

sucrose are excluded from the regressions. See also Fig. 1.

survival a b r2 t starving sugar-fed

time females 0.1%

SMALL 90 % 10.54 12.98 0.932 8.29 a 1.3 1.5

50 % 17.16 18.32 0.913 7.23 a 2.0 2.0

10 % 22.11 22.15 0.878 5.98 b 2.5 3.5

maximal 25.15 29.41 0.824 4.84 b 4.0 4.0

LARGE 90 % 12.99 10.32 0.806 4.56 b 5.7 3.8

50 % 21.58 21.13 0.909 7.06 a 7.1 7.4

10 % 27.06 30.57 0.912 7.19 a 8.4 10.0

maximal 32.94 35.50 0.893 6.46 b 9.8 10.5

ap


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Table 2. Reserve synthesis by femaleAe. aegypti when fed increasing concentrations of sucrose. The table

shows the days at which maximal many-folds of the teneral SSCC-value occur (average values).

Data from females fed less than 1% sucrose are omitted because none allowed additional synthesis

of glycogen nor lipids. A dash indicates that these values consistently fell below the teneral SSCC-

value.

SMALL FEMALES LARGE FEMALES

GLYCOGEN LIPIDS GLYCOGEN LIPIDS

day x-fold day x-fold day x-fold day x-fold

SF 1% 1-3 1.1 3 1.4 3 1.9 - -

SF 2% 2-14 2.6 2-4 2.3 1-3 2.1 - -

SF 5% 1-10 2.3 2-6 2.2 1-5 3.2 2-8 1.2

SF 10% 1-8 2.8 2-10 4.1 1-4 3.6 1-12 2.8

SF 20% * >2.0 * >4.0 * >2.0 * >2.0

SF 50% * >2.0 * >3.0 * >2.0 * >2.0

* sporadic measurements throughout the complete life-span

Table 3. Frequency distribution of flight performances of femaleAe. aegypti (recorded during single

nights). Five flight ranges are arbitrarily defined. WF for water-fed, SF for sugar-fed, BF for

blood-fed.

TOTAL FLIGHT PERFORMANCE (km/female) POOR

CONDITIONS FLIGHTS 10 * FLIERS **

teneral: 2-8 h 8 7 1 9

WF 1-5 d 31 20 10 1 17

SF 1d-8w 101 8 34 36 20 3 24

SF 1-3d; mini *** 7 6 1 15

BF 1-2d; before ovipos. 25 13 10 1 1 9

BF 3-5d; after ovipos. 34 14 12 7 1 12

* The absolute maximal distances observed were 10.9, 13.4, 14.7, 17.2, and 18.8 km per female per night.

** shown for comparison

*** small-sized females

Table 4. Mobilization of teneral glycogen or lipid of females that died in the feeding experiments. The table

indicates the day at which 50% of the teneral reserves (in SSCC-units) have been mobilized, and at

which they fell to the minimal irreducible level, i.e. the death line. For comparison, the 50% survival

times (ST) are also given.

SMALL FEMALES LARGE FEMALES

GLYCOGEN LIPIDS GLYCOGEN LIPIDS

ST 50% death 50% death ST 50% death 50% deathWF 2 1.5 3 30

SF 5% 32 *16 >10 *19 >20 43 *30 >30 *30 >30

SF 10% 35 *>40 >30 >40 >40 49.5 *>50 *>50

SF 50% 51 never never 59 never never

* These cohorts first had synthesized amounts higher than teneral values (see Table 3)


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Figure 3. Examples of temporal flight patterns of three selected individual females ofAe. aegypti of increasing

age at the time when the flight trial started. The computer printouts indicate the individual flight

performance (m/min) for each female, recorded during 16 h on the flight mill. At this point females

were alive but did not move any more. The corresponding total flight distance (km) is at the upper

right corner. Single, isolated spikes mark bursts of trivial flights, therefore black segments represent

non-stop vigorous flight periods of approximately 2.5 and 9 h in these examples.

Figure 4. Flight performance (km total distances and h duration) of femaleAe. aegypti of increasing age (1-

7 d, 3-6 weeks), with permanent access to 10% sucrose before flight, and for 1-5 d after blood

meal (= 4-9 d of absolute age); oviposition (inverted triangle) between day 2 and 3. Only strong and

vigorous fliers are considered. The black areas of each bar denote the sum of continuous flight

episodes (mean S.E., N=8-14 for each bar).


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glycogen. With respect to lipid synthesis however, large

females required 5% or higher concentrations to

synthesize additional reserves, whereas small females

were capable of lipogenesis with 1% sucrose solutions.

When the sucrose ingested was above 10%, in all

females the maximal glycogen synthesis was 2-3-foldthe teneral value, and the maximal lipid values were 4-

5-fold the teneral SSCC in small females, but 3-4-fold

the teneral values in large females (Table 2). Even

among all dead females fed 10-50% sucrose, lipid was

always above teneral SSCC-values. From this we

concluded that death may be caused by glycogen

depletion, but not by exhausted lipids.

To test whether female Ae. aegypti were able to

ingest carbohydrate from solid sources as reported by

Eliason (1963), we had a population of large females

set up with wicks of drinking water and with a sugar

cube on the bottom of a dry cage. The 50% survival

time was 58 d, i.e. about 50 d longer than with wateralone. But their glycogen never exceeded teneral levels,

and lipid levels fell below the teneral value, thus

resembling the situation with a 1-2 % sugar diet.

Flight performance ofAe. aegypti

With respect to total distances flown by 294 single

females, two groups could be clearly distinguished:

weak fliers, all below 1000 meters per night (N=89),

and strong fliers (N=205), all above 1000 meters/

female/night. To provide a reasonable estimate of the

actual or maximal flight potential ofAe. aegypti, we

focused on the strong fliers only, as defined by their

distances and flight kinetics. In Figure 3 three typical

flight patterns are presented, comparing the flight

activities between newly eclosed, teneral females and

females with permanent access to sucrose before the

start of the flight trials. At 2-8 h only trivial flights

prevailed that represent small hops, probably away from

the water surface to avoid predators such as spiders.

The capability for appreciable flight developed already

within the first day of imaginal life. We extended the

studies with sugar-fed females for up to 56 d (8 weeks)

after eclosion, i.e. beyond the 50% survival-time of

such a female population. The flight performances of

the strong fliers are summarized in Figure 4; blood-fedfemales are also included. The bars represent mean

flight distances (km) or duration (h), where the non-

stop flight segments are in black (Figure 4). With

permanent access to sucrose, maximal flight potentials

persist throughout the entire life span (Figure 4). In

Table 3 the numerical distributions of females are

broken down to five selected flight ranges. Females

deprived of sucrose and given only water died after 5

days and their flight potential remained extremely low,

two thirds flying less than 1000 m. The flight potential

clearly developed only when sucrose was available. The

long-lasting flights are composed of continuous flight

segments of an average of 2.2 0.6 hr (N=17). The

pauses usually varied between fractions of a minute and

fractions of an hour, possibly representing periods ofmetabolite mobilization. There were similar

distributions ofthe frequencies of flight performances

whether previously fed sugar or blood (Table 3). It is

noteworthy that the small females even with access to

sucrose ad lib. flew as poorly as water-fed or teneral

sisters of larger size.

The average speed of flight for all females was 0.64

km/hr; for poor fliers it was only 0.47 km/hr, and for

the vigorous, continuous flyers average speed was 1.00

km/hr with individual maxima of 1.2 km/hr.

The previous data suggest that females require

feeding on carbohydrates shortly after eclosion. We

investigated the feeding history and its effects on theflight dynamics depending on caloric conditions. The

caloric content of carbohydrates and lipids before and

after flight were measured and compared with sisters

that were kept motionless in a reacting tube for the

duration of the flight trials. The glucose data of pre-

flight females largely represent the crop content. Based

on the glucose determinations, large females had

ingested volumes in the range of 0.6-1.1 l whereas

their small-sized sisters contained only half of those

volumes, 0.3-0.5 l. But when their glucose content

was normalized for body size, the ranges were similar:

0.009-0.015 cal/mm3 in smaller and 0.008-0.012 cal/

mm3 in larger females. In sugar-fed females the glucose

and glycogen contents steadily rose during the first 3-

5 days post eclosion to absolute levels of 0.3-0.5 cal

each per female (N=34).

Measurements of females flown to exhaustion, and

subtraction of their mean values from unflown sisters,

revealed the actual utilization of reserves for the flight

activity recorded on the mill. Among 129 females with

access to sugar before flight, reduction of glucose was

3319% (N=11) of pre-flight content; for glycogen

these values were 4422% (N=11), and their pre-flight

lipid was reduced during flight by 95% (N=11) or by

44%(N=5) in 83 blood-fed females. These figuresare means with considerable variability, despite the

same body sizes and identical treatments of all females

before the flight trials. The five females with maximal

flights over 10 km showed the following distributions.

When sugar-fed before flight (1 day to 4 weeks) they

consumed more of their reserves: 16-33% of glucose,

up to 86% of their glycogen, and 13% of their lipid for

flights between 11 and 15 km, although in an

inconsistent pattern. Among the 83 blood-fed females


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two maximal fliers with 17 and 19 km/night respectively,

consumed an average of 24% of their pre-flight glucose,

and 11% of their glycogen, while their lipid

consumption appeared very erratic (1-30%).

DISCUSSION

In the absence of blood meals, survival of

mosquitoes strongly depends upon feeding on

carbohydrates. The teneral reserves per se, a product

of larval biosynthesis (Timmermann and Briegel 1999)

guarantee a limited flight potential and survival time of

only a few days, maintained by mobilization of most

glycogen and lipid reserves present. Survival times are

a very sensitive indicator for the effects of almost any

physiological parameter. With access to high sugar

concentrations maximal survival times were 69-90 d

for large and 55-75 d for small females. The body size

at eclosion and its reserve status form the baseline forfurther comparisons. There is a limit of caloric contents

of lipid, glycogen and protein, the minimal irreducible

amounts (m.i.a.), that form the border line between life

and death. This level is dependent on body size too,

which explains the 4 d survival of small versus 9-10

days of large females. Consequently, in mosquitoes the

trait of frequent and constant seeking for and feeding

on carbohydrates has evolved, as shown many times by

field investigations or as routinely experienced in

laboratory colonizations (Foster 1995). Because

survival times are linearly correlated with the logarithm

of the dietary sugar concentrations, Figure 1 allows the

estimation of the 50%, 90%, or 10% survival times of

small and large females Ae . aegypt i for any

concentration. We have to point out however, that

different principles may prevail in females offered

blood meals, as suggested by Scott et al. (1997) and

Costero et al. (1998).

By offering females increasing concentrations of

sucrose, two questions were addressed: how much of a

caloric input is required to prevent exhaustion of the

reserves, and how efficient is the synthesis of additional

reserves? A threshold level of 0.5% sucrose was found

for this species. When more than 1% sucrose solutions

were available, females of all body sizes increased theirteneral glycogen 2-3 times. However, lipogenesis

occurred differently. Small females could increase their

teneral lipid level up to 5 times already with 1% sucrose,

while in large females over 5% was required to produce

3-4 times the teneral lipid. Van Handel (1965) coined

the term the obese mosquito for the salt marsh

mosquito Ae. sollicitans. When fed 13 cal of sugar,

both teneral lipid and glycogen increased by a factor of

roughly 2.5. Therefore, obesity is even more

pronounced inAe. aegypti than inAe. sollicitans. With

sucrose diets higher than 10% however, in all females

the lipid content never fell below their teneral value,

they even died when considerable amounts of lipids

were still present. Obviously, as long as carbohydrates

are available in unlimited amounts, death is not a matterof exhausted lipid reserves, but it was consistently

accompanied by glycogen depletion. Lipid depletion

to its minimal irreducible amount is only possible with

complete starvation, i.e. with access to water only

(Briegel 1990a). High sugar concentrations could also

be a disadvantage; despite high caloric values, the

viscosity could cause artefactual mortality in laboratory

populations through glued extremities. Of course,

physiological parameters other than glycogen contents

definitely affect longevity, as revealed by glycogen

contents far below teneral values in females still alive.

Our experiment with solid sucrose cubes

demonstrates that in nature any carbohydrate source isaccessible as a nutritive substrate, independent of its

concentration, as long as drinking water is also available.

This result confirms the observations of Eliason (1963)

and the stipulation by Foster (1995) that extra-floral

nectars or honey-dew can be approached and utilized

by mosquitoes but may not be detected in the field. This

might explain why entomologists have observed so few

mosquitoes on flowers (McCrae et al. 1969; McCrae

1989, and personal communication). Honeydew most

likely is a major source of sugar, a feeding substrate

that can easily be visited at night without an

entomologists recognition.

Our results on flight performance are in line with

conclusions reached by Rowley and Graham (1968).

The maximal distances flown by single females are

similar, except that in our studies the effect of age was

less pronounced; even 4 weeks old females flew as far

and as long as 2 week old females. Obviously, flight-

mill studies are a reliable and potential means to assess

maximal flight abilities of mosquitoes. The diminished

flight potential, as observed by several investigators

(Rowley and Graham, 1968; Johnson and Rowley 1972;

Nayar and Van Handel 1971) relates to the diminution

of glycogen synthesis from sugar feeding. As lipids do

not contribute to flight energy (Clements 1955; Nayarand Van Handel 1971), the extent and the synthetic

potential of glycogen reserves (Table 2) is of crucial

significance for extended flight performances ofAe.

aegypti. It should be emphasized that this approach did

not claim to show flight performances encountered in

the field; we rather wanted to demonstrate the absolute

flight potential of these females. For that purpose forced

flight conditions are appropriate.

The question of the significance of sugar feeding,


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raised by Foster (1995) in his broad review, has been

convincingly answered. We have established that

feeding on carbohydrates in whatever form or

concentration can be a relevant behavior to maintain a

reserve status and finally the flight potential. Our

findings do not rule out the usual situations with Ae.aegypti living in extremely domestic environments,

as reported by Scott et al. (1997) and Costero et al.

(1998), but the blood meal story was not the central

issue of this study. In conclusion, all these parameters

undoubtedly increase its vector potential, of course, in

combination with its haematophagy that has been

thoroughly quantified previously (Briegel 1990a).

Acknowledgments

We thank Mr. H.J. Baumann for the skillful

development of the software program for our flight mill

and its computer. Mrs. I. Flckiger was responsible forthe colonization of the mosquitoes, and Mrs. R. Haigis

contributed with her reliable biochemical analyses. The

financial support by the Swiss National Science

Foundation to HB is greatly acknowledged. We also

appreciate substantial suggestions by one of the

reviewers.

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Eliason, D.A. 1963. Feeding adult mosquitoes on solid

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Haeger, J.S. 1960. Behavior preceding migration in the

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Aedes Aegypti Size, Reserves, Survival, And Flight Potential

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