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r,ffi}SURFACE ARCHITECTURE OF EGG OF A PYRGOMORPHIDGRASSHOPPER, POEKILOCERUS PICTUS FABRICIUS

SOMENATH DEY* AND M. RAZIUDDINP.C. Department of Zoology,Vinoba Bhave University, Hazaribag - 825 301, Jharkhand* Depaftment of Zoology, Krishnagar Covernment College,

Krishnagar, Nadia - 741"101, West Bengal

E-mai I : [email protected]. i n

KEYWORDSPoekilocerus pictusEgg

Chorion, AeropyleMicropyle, SEM

Received on:19.06.2008Accepted on :

21.06.2008

*Corresponding

author

numberof workers in different insects using biochemical,genetic and ultrastructural methods (Mazur et al., 1982;Margaritis, 1985; Mindrinos et al., 1986; Mazzini and

Caino, 1988; Caino and Mazzini, 1989, 1990). However,SEM studies of chorion perhaps mainly relate only to a

" few orders viz., Diptera and Lepidoptera ( Buning,1994).

The present paper deals with the surface structure of egg

of an orthopteran insect, P. pictus as revealed under

scanni ng electron m icroscope.

MATER=ilHXSl

Live Poekilocerus pict.us were collected from wild fieldsof both Jharkhand and West Bengal states and reared in

insect rearing cage at P.C. Department of Zoology, VinobaBhave University, Hazaribag. Selected gravid females

which were trying to deposit eggs were dissected in

Orthopteran saline ( Clayton et al., 1958) under a

stereoscopic binocular microscope and eggs wereobtained.

For SEM studies, the eggs of mature female P. pictus werefixed in 2.5 % gluteraldehyde prepared in 0.1 M phosphate

buffer at pH 7.4 at 4oC tor 2.5 hours followed by twowashing in phosphate buffer. Then the eggs weredehydrated in ascending grades of alcohol, i.e. 30%, 50%,

INT

Poekiloceruspictus (painted or Aak grasshopper) commonthroughout the planes of lndia (Raziuddin and Anwar,1997) is primarily a defoliator of madar or akand or Aak

plants ( Calotropis procera). Besides C. procera, it feeds

upon a number of alternative host plants, many of whichare of economic value ( Raziuddin et al., 199'l). This

grasshopper is a prolific breeder and the females lay large

n um ber of el on gated, sa usage.shaped eggs, each contai n i ng

a little amount of cytoplasm and relatively large amountof yolk.

lnsect eggs are covered externally by a complex multilayer

egg shell consisting basically of outer chorion and inner

vitelline membrane formed by the follicle cells while the

eggs are inside the ovariole. Surface of the chorion isprovided with fine pores, the aeropyles for adequate oxygen

supply and micropyles for entry of sperms ( Buning, 1994;

Chapman, 2000). Chorion ultrastructure has been used

for phylogenetic reasons within many insect orders (Kafatos

etal.,1977;fuegier and Kafatos, 1985; Margaritis, .l985;

Kambysellis, 1993; Mazzini et a/., 1993).

Chorion architecture of different insect species is not related

to each other and hence a variety of ways of choriogenesis

are expected. Formation of chorion has been studied by a

SOMENATH DEY AND M. RAZIUDDIN

and 70o/, ,90% and absolute alcohol at 4oC for two hoursin each grade (two changes of one hour duration).ln absolute alcohol specimens were dehydrated at 4oC forone hour and at room temperature for another one hour.Eggs were then immersed in a mixture of alcohol andacetone of different grades (3:.1, 2:1, 1 :1,1 :2). Two changesof one hour duration were given in each grade at roomtemperature. Then dehydrated in acetone for one hour andfinally in anhydrous acetone at room temperature andproceeded for critical point drying (CpD) to get rid ofremaining water. After CpD, the eggs were pasted oncarbon tape. The tape was placed over the grid and thenplaced inside the sputter for gold coating 6O minutes).Th is was then viewed under scanning electron microscope(jEoL JSM 6700 F).

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The mature eggof Poekilocerus pictusis elongated, sausage_shaped, yellowish structure measuring 8.0 x-l .0 x 1.0 mm.

Figure 1: Scanning electron micrograph of anterior hatfmature egg of Poekilocerus picfus showing warts

oJFigure 3: Scanning electron mirr6,ure r: )cannrng electron micrograph of enlarged eggsurface of P. pictus showing the imbiicate arrangements ofsurface warts

Figure 2a: Scanningelectron micrograph ofenlarged posterior poteof mature egg of p.pictus. Note that thesculpture.less area bearsthe micropyles (mic)arranged in a ring

Figure 2: Scanning electron micrograph of posterior half ofmature egg of Poekilocerus pictus. Note the ibsence of wartsnear the pole

Figure 4: Scanning electron micrograph of the surface of p.pictus e-gg. Note the presence of poies (aeropyles) on theegg surface

SURFACE ARCHITECTURE OF EGG

/

Figure 5: Magnified SEM photomicrograph of the egg surfaceol P. piaus showing the aeropyles.Note the hallow aroundeach aeropyle

It contains a little amount of cytoplasm and large amountof yolk. lt is covered externally by the egg shell consistingof outer chorion and inner vitelline membrane. Thechorion, is a product of follicular cells of the oocyte. Theouter surface of chorion is beautifully sculpturedthroughout the egg surface except just below the micropylarregion. This rim of sculpture-less area at the posterior endof the egg, has a width of 1 50 lo 175 mp (Figs. 1 , 2 and3). Except this sculpture-less region the entire surface ofegg bears "boomerang- shaped" warts arrangedlongitudinally in clear cut imbricate fash ion. Each row ofwarts runs obliquely over the sufface. Unlike some insects(Chapman, 2000) in Poekilocerus pictus egg chorion noline of weakness (hatching line) has been observed. ln the

Figure 7: Scanning electron micrograph of an aeropyle (aer)ol P. pictus egg (ultra magnified). Note the hexagonal areason the rim of chorion and aeropylar complex consisting of23 sub-units

sculpture-less region of the egg about 38 m icropyles arepresent near the posterior pole (Fig 2A). These are arrangedin ring- like manner (Figs. 2 and 24). Each micropyle is asmall slit- like opening measuring 37.5 mp x 3.5 mtrr insize. These m icropyles allow entry of sperm into the egg.The chorion surface bears a large number of rounded(occasional ly el I iptical) open i ngs of various di mensions,ranging from 50 lo 270 nm in diameter (Figs. 4 and 5).These openings are the aeropyles which permit the freemovement of respiratory gases. 25 m/./ square area of eggsurface has been found to have 65 to 73 aeropyles. Underhigh magnification (x 100000) each aeropyle appears tobe a simple opening surrounded by 23 comparatively moreelectron transparent hexagonal units. This 23 number is

fairly conserved in each opening (Figs. 6 and 7).

ln all insect orders follicle cells synthesize the shell(vitelline mpmbrane and the chorion) of the egg. The outersurface of chorion is often sculptured with hexagonal unitsreflecting the impressions of underlying follicle cells(Buning, 1994; Chapman 2000). ln P. pictus also thesurface of chorion bears hexagonal impressions. The gross

architecture of follicle cells changes during different phases

of egg development viz., previtellogenic, vitellogenic andchoriogenic growth phases. Such changes in the shape offollicle cells are accompanied by changes in thecytoskeleton (Cutzeit, 1 990).

The exochorion of insect egg is provided with two kindsof openings viz., the aeropyles and the micropyles whichserve the respiratory function and insemination of eggrespectively. Since the insect eggs are deposited in differentmedia, the distribution of aeropyles vary, e.g. silkworm

Figure 6: The egg surface of P.

show the aeropyles surroundedtransparent sub-units

pictus, ultra magnified toby comperatively electron

SOMENATH DEY AND M. RAZIUDDIN

egg have aeropyles on the whole surface of egg andDrosophila egg have specialized respiratory appendagesat its anterior pole ( Margaritis, '1985; Buning, 1994;Chapman, 2000). ln P. pictus egg aeropyles are notuniformly distributed and unlike Antheraea pernyi(Margaritis, '1985) and some other insects these lackcrowns and appear as simple openings, each surrounded

by almostfixed number (23) of hexagonal units with less

electron opacity in comparison to the surrounding areas

and hence, forms a hallow around the aeropyle(Fig. 5)'

Another interesting observation in P. pictus egg is theconspicuous absence of surface warts near the posteriorpole of the egg, the significance of which is not yet clear.Obviously this demonstrates a different mode of formationof chorion in this region. Possibly in this region thearchitecture of follicle cells is different from other regionsof the bgg.

ln P. pictus egg there are about 3B micropylar openingsarranged in a ring just below the wart-less area near theposterior pole. The number of micropyles in P. pictusthus conform to the number described for other acridids (

Chapman,2000).

Authors are thankful to the Director, lndian Associationfor the Cultivation of Science, Jadavpur, Kolkata forproviding facilities of SEM. One of the authors (SD) is

thankf ul to Dr.P. K. Das, Pri ncipal, Krish nagar Government

College, Nadia (W.8.) for his interest in the work.

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