Table Of ContentPROC. ENTOMOL. SOC. WASH.
93(3), 1991, pp. 592-612
THE EGGS OF AEDESFUNEREUS, AEDESNOTOSCRIPTUS AND
AEDESALTERNANS (DIPTERA: CULICIDAE)
J. R. LiNLEY, M. J. Geary, and R. C. Russell
(JRL) Florida Medical Entomology Laboratory, IFAS, University ofFlorida, 200 9th
Street S.E., Vero Beach, Florida 32962; (MJG, RCR) Medical Entomology Unit, Uni-
versity ofSydney, at Westmead Hospital, Westmead, N.S.W. 2145, Australia.
—
Abstract. Sc3.rm\ng electron micrographs are used to provide descriptions ofthe eggs
oiAedes {Verrallina)funereus, Ae. (Finlaya) notoscriptus andAe. {Mucidus) alternans. In
the egg o{Ae.funereus the outer chorionic cells ofthe ventral (upper) and dorsal (lower)
surfacesdiffermarkedlyin structure, buttheegg'smostdistinctfeaturesareitspronounced
narrowness relative to length, and the unusually large micropylardisk. Ventral and dorsal
surfaces also differ very substantially in Ae. notoscriptus, the dorsal surface being partic-
ularly interesting as its structure probably represents an early stage in the development
oflong, dorsal surface filaments as seen in other species ofthe subgenus Finlaya. TheAe.
alternans egg is wide in relation to length and its entire surface is much more uniform.
Some data are presented on the variation found between 5 individual eggs from each
species.
Key Words: Insecta, eggs, mosquito, fine structure
The three Aedes species whose eggs are trations limited to outline drawings, was
described inthispaperareall from theAus- given by Colledge (1904) and was used by
tralasian Region. As such, their taxonomy, Mattingly (1970) in his comparison ofeggs
distribution,biologyandimportanceaspests ofseveral species ofthe subgenus Mucidus.
and/or disease vectors have all been com- The egg shell and its resistance to drying
prehensively treated elsewhere {Ae. {Ver- were studied by Pillai (1962), but details of
rallina)funereus(Theobald), Leeetal. 1987, the fine structure have never been present-
p. 276; Ae. {Finlaya) notoscriptus (Skuse), ed.
Lee et al. 1982, p. 196; Ae. {Mucidus) al- In this paperwedescribetheeggsofthese
ternans(Westwood), Lee et al. 1984, p. 73). three species with the aid ofscanning elec-
No previous description ofthe egg o{Ae. tron micrographs. Sincenumerouseggswere
funereus has been given. Graham (1929) available, opportunityalsowastakentolook
provided the first observations on the egg at intraspecific structural variation in the
oiAe. notoscriptusat the stereomicroscopic outer chorionic cells by examining 5 indi-
level, and Pillai (1962) investigated the vidual eggs of each species and recording
structureoftheeggshellandtheegg'sability selected measurements. The 5 eggs in each
to resist desiccation. The egg ofthis impor- case were not certainly from different fe-
tant species has never been completely de- males, but to optimize the probability that
scribed, however, and not at all at the elec- they were, eggs were taken from different
tronmicroscopiclevel.Averyearlyaccount egg papers where possible, or from widely
ofthe egg ofAe. alternans, but with illus- separated positions on the same paper.
)
VOLUME NUMBER 593
93. 3
Materials and Methods the GT2 method (Sokal and Rohlf 1981),
in some cases after transformation to nor-
Eggs were obtained from females collect- malize the distributions (see later). The dis-
ed in the field and induced to oviposit on tributions oflarge tubercle numbers in Ae.
wet filter paper in the laboratory. Each pa- funereusandAe. alternans (Fig. 3) were not
perbearingeggswasfoldedtolinetheinside assumed to be normal and the Kruskal-
(eggs on inner surface) of a small plastic Wallis method was used to test for differ-
petri dish and the paper moistened before ences between eggs. Meansgiven in the text
mailingtoVeroBeach.Onarrival,eggswere are with attached standard errors and were
mounted for microscopy either by cutting calculated from an equal number of mea-
out small pieces ofpaperwith attachedeggs surements from each ofthe 5 eggs ofeach
andstickingthesetodouble-sidedstickytape species.
already attached to stubs, or by lifting in- IntheterminologywehavefollowedHar-
dividual eggs on a very fine artist's brush bach and Knight (1980), except for "outer
and laying them on sticky tape in the re- chorioniccell field"(Linley 1989), and"mi-
quiredposition. Eggsweredriedcompletely cropylar dome," defined as a dome-shaped
overcalciumchloridefor0.5 h, then sputter area with distinct margin surrounding the
coated with gold. Microscopy was done in micropyle and within the micropylar disk.
a Hitachi S-510 scanning electron micro-
scope. Results
In the study of intraspecific structural
Aedes {Verrallind)funereus
variation, thearea selected forexamination
(Figs. 1,2,6,7, 15)
was the chorion on the ventral surface, in
the middle of the egg. Particular care was Size:dimensionsasinTable 1. Color:dull
taken to obtain micrographs of an exactly black. Overall appearance: cigar-shaped and
equivalentareaineachofthe 5 eggsselected long in relation to width (Fig. 1, Table 1).
foreach species. Micrographsat 1000x and Dorsal (lower) side flatter, ventral (upper)
1500X were taken, the one at lower mag- sidemorecurved(Fig. 2a). Taperedanterior
nificationtoincludemorechorioniccellsfor end somewhat conical, widest at about an-
counting numbers oftubercles and measur- terior0.25, then slightly tapered posteriorly
ingcelldimensions,theotherathighermag- until posterior 0.25, then markedly so (Fig.
nification for measuring tubercles. Of the 1). Posterior end rather sharply pointed in
twocelldimensions, lengthwasthedistance someeggs, less so in others. Micropylarcol-
between the two most widely separated cell lar indistinct. Outer chorionic cells regular
comers aligned approximately longitudi- in appearance, most with single, large cen-
nally(anterior/posterior)withrespecttothe tral tubercle and several small peripheral
egg (see Fig. 15). Width was taken at the ones (Fig. 1
widest point circumferentially with respect Chorion, ventral (upper) surface: outer
totheegg(whetherornotexactlycoincident chorionic cells mostly hexagonal, occasion-
with two cell comers). Tubercle diameters ally pentagonal, rarely quadrilateral, out-
were measured at the base at the widest lines variable (Figs. 2d, 15). Cell length
point, except for the large tubercles in Ae. (mean 25.3 ± 0.4 )um, n = 50) greater than
notoscriptus, wheretheupperportionofeach width (mean 15.0 ± 0.3 )um, n = 50), cell
tubercle was measured as it was often dis- fields about 2.7 ^lm less in each dimension.
tinctly narrower than the base (see Fig. 9c, Most cells with single large tubercle, some
e, 15) and easily distinguishable. Tests for with2orrarely3 (Figs. 3, 15),meantubercle
differences between eggs with respect to diameter 5.97 ± 0.14 Aim (n = 50), range
means of all measurements were done by 2.9-7.6nm. Stmcturally,eachtuberclemade
594 PROCEEDINGS OFTHE ENTOMOLOGICALSOCIETY OFWASHINGTON
Up ofa base with shallow peripheral exca-
vations, walls smoothand vertical ornearly
so (Fig. 2d, e, 0^ capped by dome-shaped
upper portion covered with close-packed
more or less round nodules (Fig. 2e, f). Sur-
roundingcells field smooth, with slight stri-
ations appearing only at high magnification
(Fig. 2e, f)- Small tubercles confined to pe-
riphery ofcell field, adjacent to outer cho-
rionic reticulum (Figs. 2d, 15), mean num-
ber per cell 18.1 ± 0.4 (n = 50), range 10-
24, diameter 0.6-3.3 nm, size distribution
skewed(Fig.4). Regressionofsmalltubercle
diameteron numberhighly significant {P <
0.005),diametersmallerasnumberincreas-
es (Fig. 5). Small tubercle shape highly ir-
regular, each tapering upward from smooth
base to a narrower top; tops tending to be
smooth, but progressively larger ones with
increasingly numerous small nodules (Fig.
2d, e, 0- Groups of small tubercles often
joined bybridgesand some similarlyjoined
to large tubercles (Fig. 2d, e). Outer chori-
onic reticulum low, width 2.5-3.6 ij.m, con-
sistingofa fine reticulated mesh (Fig. 2e, f),
with central line ofbead-like prominences,
diameter 0.3 ixm, 0.7-2.6 jum apart. Retic-
ulum mesh often partially covering lower
sidesofclosely adjacent small tubercles(Fig.
2e, 0.
Chorion, lateral surface (ventral-dorsal
transition): down lateral surfacesofeggcho-
rionic cells become more irregular in form
and, unlike ventral surface, progressively
longercircumferentiallythan longitudinally
(Fig. 6a, b). Large tubercles progressively
become more numerous with nodular sur-
faces less distinct. Tubercles at first remain
more centrally positioned in cell, then dis-
place small tubercles around edges of cell
field (Fig. 6a, c, d). In lower (more dorsal)
portion oftransition (Fig. 6b), small tuber-
cles almost disappear, large tubercles be-
Fig. 1. Ae.funcreus. Entireegg,ventral(upper)view,
anteriorend at top. Scale = 100 ^m.
VOLUME 93. NUMBER 3 595
Table 1. Dimensions ofeggs ofthree species ofAedes(n = 10).
PROCEEDINGS OFTHE ENTOMOLOGICAL SOCIETY OF WASHINGTON
596
Fig. 2. Ae. funereus. (a) Whole egg, lateral view, anterior end at right; (b) anterior end and micropylar
apparatus; (c) detail, micropylar apparatus; (d) typical outerchorionic cells, ventral surface, middle ofegg; (e)
detail, single chorioniccell; (f)detail, largeand smalltuberclesand outerchorionic reticulum. Scale = 200 fim
(a), = 10Mm (b, c, d, e), = 5 ^m (0-
Fig. 3. Ae.funereus, Ae. alternans. Distributions ofnumbers oflarge tubercles.
«
VOLUME 93, NUMBER 3 597
80- Ae. funereus
60- Egg
1
40- n = 36
20-
——
-|
Ae. alternans
60-
2 40-1
40- 20 H
20-
^
80-
^^
'
60- 60-
n = 31
40- 40-
20- 20-
0-
^^T^
,
60-
0)
40-
20-
598 PROCEEDINGS OFTHE ENTOMOLOGICALSOCIETY OFWASHINGTON
Ae.funereus
21 n = 118
18
15 I!
12
9
6
3H
n-q
"h
0.30 1.10 1.90 2.70 3.50 4.30
21-1
Ae.notoscriptus
L n = 136
18
I5i
E
Z3 9
6
r^a
A m
0.30 0.74 1.18 1.62 2.06 2.50
0-
VOLUME 93, NUMBER 3 599
1.7 ± 0.1 nm, n = 20), surfaces smooth or y = 2.199-0.034X
1.80
slightly uneven (Fig. 10b). Spaces between
tubercles occupied by small, button-like tu-
bercles, and these also covering reticulum 1.66-
(width 1.6-3.3 nm), but less prominent on
lowcentralridge(Fig. 1Ob). Dorsaltypecells 0) 1.52-
typically asjust described, but occasionally o
with fewer, scatteredtubercles, vacantspac- E
es filled by very small tubercles (Fig. 10c). S 1-38H
c
Anterior end, micropyle: chorionic cells
<«
smallerapproachinganteriorend, cell fields 5a> 1.24H
become occluded, large tubercles less con-
spicuous, surfaces smoother, spokes in more
lateral cells fewer(Fig. 1 la, b). Dorsal (low- 1.1015 —1I7 19T" —21r- ~2l3 215
er)surfacetransition from micropylarcollar Number of small tubercles
to typical dorsal cell structure rapid, and as
illustrated(Fig. 1 Ic). Micropylarcollarfair- Fig. 5. Ae. funereus. Regression ofmean diameter
ly prominent, almost always continuous, ofsmalltuberclesonnumberofsmalltuberclesincell.
outerwallsoftenrounded(Fig. 1 la,c),height
7-11 ixm, diameter 36-41 ixm, wall width
5-1 1 /um, surfaceroughandpitted(Fig. 1 Id, oniccellsappearinguniform overwholeegg
e), internaldiameter21-24^m, internalwall surface.
with shallow excavations (Fig. 1 le). Micro- Chorion, ventral, lateral and dorsal sur-
pylar disk small, boundary very clearly de- faces: all surfaces very similar. Structure
marcated (Fig 1 le), surface rough, diameter typifiedbyanddescribedforcellson ventral
7-9 Aim, micropylar orifice trilobed, diam- (more curved) surface, with comments on
eter 2.7 nm. lateral and dorsal surface differences, as fol-
Posterior end: chorionic cells become lows. Shape ofcells quite irregular, mostly
smaller approaching posterior end, small pentagonal, occasionally hexagonal or
tubercles and spokes connected to large tu- quadrilateral (Fig. 13b), length (mean 22.2
bercles fewer, cell fields increasingly oc- ±0.5 Aim, n = 50)greaterthan width (mean
cluded, totally so at extreme end (Fig. lOd, 16.3 ± 0.4 Mm, n = 50). Shape of lateral
e), large tubercles at end smooth surfaced, (Fig. 13c) and dorsal (Fig. 13d) surface cells
irregularly shaped (Fig. lOd, e). On dorsal similar, but dimensions somewhat smaller,
Oower) surface, typical dorsal type cells especiallyondorsal surface. Cell fieldsabout
present almost to extreme end ofegg (Fig. 2.0ixvci smallerineachdimension. Twolarge
lOf). tubercles mostfrequentlypresent, butnum-
bers variable between eggs (Fig. 3). Tuber-
Aedes (Mucidus) alternans cles in larger ventral cells in some instances
(Figs. 12-14, 15) more centrally placed, but in others more
Size:dimensionsasinTable 1. Color:dull towards edges ofcell field (Fig. 13b, f); tu-
black. Overall appearance: rhomboidal in berclesalwaystendingtobecentrallyplaced
ventral (Fig. 12) or dorsal view, widestjust in smallerlateral (Fig. 13c, g) and especially
anterior to 0.5 of length, width, relatively dorsal (Fig. 13d, h) cells. Mean diameter of
great with respectto length. Shape in lateral large tubercles 5.64 ±0.12 ^m (n = 50),
view similar, but curvature ofventral sur- range 3.2-7.6 nva. Each tubercle construct-
face greater than dorsal (Fig. 13a). Micro- edofan irregularlypolygonalbase,each side
pylar collar distinct (Fig. 12), outer chori- shallowlyindented (Fig. 13g, i), with smooth
Fig. 6. Ae.funereus. (a) Upper(more ventral) portion ofventral-dorsal transition, middle ofegg; (b) lower
(dorsal) portion ofventral-dorsal transition; (c) outerchorioniccell detail, ventral-lateral portion oftransition;
(d)celldetail,lateralportionoftransition;(e)celldetail, lateral-dorsalportionoftransition;(f)celldetail,dorsal
(lower) surface. Scale = 20Mm (a, b), = 5 Mm (c. d, e, 0-
VOLUME 93, NUMBER 3 601
Fig. 7. Ae. funereus. (a)Anteriorend, ventralsurface;(b)anteriorend,outerchorioniccelldetail;(c)anterior
end, dorsal surface; (d) posterior end, ventral view; (e) posterior end, outer chorionic cell detail; (f) posterior
end, dorsal surface. Scale = 20 ^m.
