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4 Morphology of Various Instars of Both Sexes of the Mealybug

4 Morphology of Various Instars of Both Sexes of the Mealybug

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M. Mani and C. Shivaraju



12



both dorsum and venter, but more in the former.

Their approximate numbers are dorsal abdominal

segments IX, 4; VIII, 4; VII, 8; VI, 6; V,5; IV, 7;

III, 6; II, 6, metathorax, 10; mesothorax, II; prothorax, 14; head, 10; and ventral abdominal segments IX, 0; 2 in each of the segments VIII, VII,

VI, V, IV and III; II, 4; metathorax, 5; mesothorax, 4; prothorax, 2; head, 4. The first instar

nymph differs from other nymphal instars with

the absence of tubular ducts.



2.4.2



Second-Instar Female Nymph



Body is oval with anterior end slightly broader

and rounded; anal lobes are prominent, on an

average 620 μ long and 360 μ wide (Fig. 2.2).

Four pairs of cerarii with two conical setae on the

abdominal segments VI–IX are present. The cerarian setae of the other abdominal segments are

elongated and slender. Usually, two ducts of oral

rim type and three trilocular disc pores in each

cerarian zone of segments IX and VIII and two

disc pores in the ceracian zone of all other

abdominal segments are present. Head: Six

jointed antennae, average measurements in μ are

I, 35; II, 23; III, 33; IV, 21; V, 21; VI, 62. Eye

about 21 μ in diameter at the base and 9 μ high.

Beak is conical, on an average 83 μ long and 52 μ

wide at the base. Thorax: Average measurements

of posterior leg in μ are trochanter, 42 × 24;

femur, 85 × 35; tibia, 70 × 23; tarsus, 70 × l8;

claw, 21; tarsal digitule, 34; claw digitule, 19.

Anterior spiracle is about 29 μ long and 10 μ

wide at atrium; posterior one is about 32 μ long

and 10 μ at atrium. Abdomen: Anal ring 41 μ in

diameter; anal ring setae 64 μ long on an average.

Apical setae 173 μ long on an average. A moderately sclerotised bar is present in each anal lobe.

Circulus is present. Dermal structures: Anterior

pair of ostioles with two trilocular disc pores and

one seta on each lip; posterior ones each with

three pores and one seta on the upper lip and two

pores on the lower lip. Trilocular disc pores are

present on both dorsum and venter. Dorsal pores

measure 4.0–4.4 μ and ventral ones 3.2–3.6 μ

wide. Their approximate numbers are dorsal

abdominal segments IX, 6; VIII, 9; VII, 15; VI,

II; V, 12: IV, 12; III, 10; II, 10; metathorax, 20;



Fig. 2.2 Second-instar female nymph of M. hirsutus.

CIR circulus, ORD oral rim duct



mesothorax, 35; prothorax, 40; head, 20; and

ventral abdominal segments IX, 4; VIII, 2; VII,

4; VI, 6; V, 4; IV, 6; Ill, 4; II, 5; metathorax, 9;

mesothorax, 14; prothorax, 15; head, 5. Tubular

ducts of oral rim type about 8 μ long and 5 μ wide

are present on dorsum. Their numbers are abdominal segments IX, 2; VIII, 2; VII, 0; VI, 3; V, 4:

IV, 4; III, 5; II, 4; metathorax, 6; mesothorax, 7;

prothorax, 10; head, 3. Only one duct is present

in the venter of abdominal segment VIII.



2.4.3



Third-Instar Female Nymph



Body is oval with anterior end slightly broader

and rounded; anal lobes are prominent, on an

average 1.095 mm long and 0.678 mm wide. Five

pairs of cerarii are present on the last five abdominal segments, usually with two conical setae in

each. Anal lobe cerarii each with three trilocular

disc pores and one oral rim duct and the remaining each cerarius with two disc pores and one

oral rim duct are present. Head: Seven jointed

antennae, average measurements in μ are I, 45; II,

39; III, 31; IV, 26; V, 27; VI, 30; VII, 74. Eye is

about 25 μ in diameter at the base and 15 μ high.

Beak is conical, on an average 98 μ long and 52 μ

wide at the base. Thorax: Average measurements



2



Morphology



13



of posterior leg in μ are trochanter, 66 × 34;

femur, 127 × 53; tibia, 121 × 30; tarsus, 87 × 26;

claw, 27; tarsal digitule, 36; claw digitule, 24.

Anterior spiracle is about 34 μ long and 13 μ

wide at atrium; posterior one is 36 μ long and 13

μ wide. Abdomen: Anal lobes are prominent; anal

ring on an average is 60 μ in diameter; anal ring

setae are 84 μ long; apical setae is 209 μ long on

an average. Anal lobe bar is moderately sclerotised. Dermal structures: Ostioles can be found

with a few trilocular disc pores. Anterior pair

with three pores and one seta on each lip; posterior ones with three to four pores and zero to one

seta on each lip. Dorsal setae are of two sizes,

longer and stout, and shorter and thin. Ventral

body setae are longer and flagellate. Circulus is

about 33 μ long. Trilocular disc pores, 3.2–3.6 μ,

are present on both the surfaces of the body but

more on dorsum. Their approximate numbers are

dorsal abdominal segments IX, 14; VIII, 15; VII,

32; VI, 19; V, 18; IV, 19; III, 30; II, 30; metatho-



rax, 23; mesothorax, 36; prothorax, 42; head, 20;

and ventral abdominal segments IX, 4; VIII, 11;

VII, 12; VI, 13; V, 10; IV, 10; III, 12; II, 12; metathorax, 15; mesothorax, 28; prothorax, 24; head,

13. Tubular ducts of oral rim type are present

mostly on dorsum and a few on venter. Ducts on

dorsum are 9 μ long and 6 μ wide. Ventral ducts

are about 3/4 wide of those in dorsum. Their

approximate numbers are dorsal abdominal segments IX, 6; VIII, 11; VII, 4; VI, 10; V, 11; IV, 14;

III, 14; II, 14; metathorax, 21; mesothorax, 27;

prothorax, 19; head, 7; and ventral abdominal segments IX, 0; VIII, 2; VII, 2; VI, 2; V, 2; IV, 2; III,

3; II, 3; metathorax, 2; mesothorax, 6; prothorax,

6; head, 4. Tubular ducts are of oral collar type,

3.5–4.0 μ long and 1.5 μ wide, mostly distributed

in the marginal and submarginal areas of venter,

rarely found on dorsum. Their approximate numbers in venter are abdominal segments IX, 0; VIII,

2; VII, 4; VI, 5; V, 4; IV, 4; III, 4; II, 7; metathorax,

10; mesothorax, 8; prothorax, 4; head, 4.



Third-instar female nymph of M. hirsutus (Green).

OCD oral collar duct, ORD oral rim duct

(Courtesy: Ghose SK)



Adult female of M. hirsutus. MLDP multilocular disc

pore, VUL vulva



M. Mani and C. Shivaraju



14



2.4.4



Adult Female



Body is ovoid, slightly broader and rounded at

the anterior end, on an average 1.7 mm long and

1.1 mm wide, attaining larger size (3.2 mm × l.7

mm) with maturity. Anal lobes are prominent,

particularly in young adults. Six pairs of cerarii

in the abdominal segments IV–IX, usually with

two cerarian setae are present; occasionally a

third one is present in the cerarii of segments VIII

and IX. Segment IV has generally only one cerarian and one stout and longer setae on one side,

the other cerarius has two normal cerarian setae.

Cerarii are without auxiliary setae except the anal

lobe pair. Each cerarius of segment IX has 5–6

trilobular disc pores and three oral rim ducts.

Head: Antennae appear to be nine jointed

because of a pseudo-articulation in the terminal

joint. Average measurements in μ are I, 54; II, 54;

III, 52; IV, 34; V, 41; VI, 40; VII, 39; VIII,

37 + 56. Eye is about 32 μ wide at the base and 22

μ high. Beak is conical, on an average 141 μ long

and 86 μ wide at the base.

Thorax: Average measurements of posterior

leg in μ are trochanter, 97 × 36; femur, 217 × 68;

tibia, 227 × 32; tarsus, 100 × 27; claw, 33; tarsal

digitule, 49; claw digitule, 31. Tarsal digitule, of

the anterior legs are unequal, one is about 49 μ,

whereas the other is about 42 μ. Anterior spiracle

is about 51 μ long and 26 wide at atrium, and

posterior one 55 μ long and 29 μ wide.

Abdomen: Anal ring on an average is 72 μ in

diameter; anal ring setae is 154 μ long; anal lobe

bar is moderately sclerotised; apical setae are 251

μ on an average. Dermal structures: Anterior pair

of ostioles with nine to ten trilocular disc pores

and one to three setae on each lip are present;

posterior one with 9–12 pores and 1–4 setae on

each lip. Body setae are of two sizes on both dorsal and ventral surfaces, the ventral ones being

generally longer. Circulus is about 77 μ long.

Trilocular disc pores are more numerous and

larger on dorsum, about 4 μ, whereas those on

venter measure about 3 μ. These pores are much

more numerous (above 20 %) in the adult than in

the third-instar females. Tubular ducts are of two

types: oral rim ducts and oral collar ducts, the



former being predominant in the dorsum and the

latter in the venter. Oral rim ducts of dorsum are

larger than those of venter and more or less

arranged in transverse rows, about 9.5 μ long and

4–5 μ in diameter at the opening. Their approximate numbers are abdominal segments IX, 12;

VIII, 20; VII, 10; VI, 22; V, 32; VI, 35; III, 34;

I1, 36; metathorax, 54; mesothorax, 62; prothorax, 42; head, 18. A few rim ducts of venter are

found in the marginal and submarginal regions of

the body. Their numbers are abdominal segments

IX, 2; VIII, 4; VII, 3; VI, 5; V, 5; IV, 7; III, 7; II,

6; rnetathorax, 4; mesothorax, 7; prothorax, 8;

head, 4. Oral collar ducts of venter are variable in

size, 2.4–2.8 μ in diameter at opening and on an

average 10.5 μ long. The ducts of the dorsum are

generally smaller. These ducts are much more

numerous (six to seven times) in the adult than in

the third nymphal female. Multilocular disc

pores, 5 μ in diameter, are restricted to the submarginal and median regions of venter, mainly in

the abdominal segments VI–IX.



2.4.5



Second-Instar Male Nymph



Body is oval with anterior end slightly broader

and rounded; anal lobes are prominent. Average

body size in the early stage is 625 μ long and 390

μ wide. It increases greatly and attains 970 × 438 μ

at the end of the feeding period. Normally, one

pair of cerarii present are in the abdominal segment IX; generally each with two and rarely stout

conical setae, one auxiliary seta, one microduct of

oral collar type and one trilocular disc pore.

Segment VIII is occasionally with one or two cerarian setae in each. The cerarian setae of other

segments are slender and elongated. Generally,

two disc pores and one collar duct are present in

each cerarian zone of other segments. Head: Six

jointed antennae, but the joints cannot be recognised as and when the antennae of third-instar

male nymphs develop inside this instar. Average

measurements of the segments in μ are I, 32; 11,

27; III, 34; IV, 20; V, 22; VI, 62. Eye is about 22 μ

in diameter at the base and 10 μ high. Beak is

conical, on an average 94 μ long and 57 μ wide at



2



Morphology



15



the base. Thorax: Average measurements of posterior leg in μ are trochanter, 46 × 26; femur,

98 × 38; tibia, 84 × 20; tarsus, 74 × 18; claw, 21;

tarsal digitule, 34; claw digitule, 20. Anterior spiracle is about 29 μ long and 8 μ wide at atrium;

posterior one about 31 μ long and 9 μ at atrium.

Abdomen: Anal ring on an average is 36 μ in

diameter; anal ring setae are 66 μ long; apical

setae are on an average 172 μ long. Anal lobe bar

is moderately sclerotised. Dermal structures:

Three trilocular disc pores and one to three setae

on both upper and lower lips of anterior pair of

ostioles and two to three pores and zero to one

seta on each lip of the posterior pair are present.

Circulus is present. Trilocular disc pores are about

3 μ and more numerous on dorsum. Their approx-



imate numbers are dorsal abdominal segments IX,

9; VIII, 9; VII, 18; VI, 13; V, 15; IV, 16; III, 22; II,

19; metathorax, 20; mesothorax, 44; prothorax,

32; head, 26; and ventral abdominal segments IX,

4; VIII, 5; VII, 10; VI, 9; V, 8; IV, 7; III, 8; II, 7;

metathorax, 11; mesothorax, 21; prothorax, 16;

head, 17. The microducts are of oral collar type,

about 7 μ long, present on both dorsum and venter. The ducts in dorsum are wider (3.2–3.6 μ)

than those in venter about 2.4 μ; their numbers are

dorsal abdominal segments IX, 2; VIII, 5; VII, 2;

VI, 2; V, 2; IV, 5; III, 3; II, 7; metathorax, 4; mesothorax, 6; prothorax, 5; head, 4; and ventral

abdominal segments IX, 0; VIII, 1; VII, 3; VI, 4;

V, 3; IV, 2; III, 2; II, 2; metathorax, 2; mesothorax,

2; prothorax, 2; head, 3.



Second-instar male nymph of M. hirsulus. OCD oral

collar duct

(Courtesy: Ghose SK)



Third-instar male nymph of M. hirsutus. ANT antenna, AS

anterior spiracle, MLDP multilocular disc pore, AO anterior ostiole, PO posterior ostiole, AT anal tube, WL

wing-bud



2.4.6



the antennae of fourth-instar male become prominent, as and when these are formed inside the

antennae of third instar. Mouthparts are absent.

Eyes are not discernible.

Thorax: Two small wing buds more or less at

right angles to the lateral margins of the mesothorax. Legs are short in comparison with body



Third-Instar Male Nymph



Body is oval, more rounded at the anterior end,

on an average 1.138 mm long and 0.504 mm

wide. Sclerotisation is in general very weak.

Head: Segmentation of antennae is obscure,

with the average length being 276 μ. The joints of



16



M. Mani and C. Shivaraju



length, with a few pointed setae. Average measurements in μ are trochanter, 52 × 32; femur,

112 × 43; segmentation of tibia, tarsus and claw is

not well differentiated, their combined length and

maximum breadth being 175 × 31. Tarsal and

claw digitules are absent. Anterior spiracle is

about 29 μ and posterior one is 29 μ long and 14

μ wide.

Abdomen: Anal ring is absent. A wellsclerotised anal tube, 23 μ long and 26 μ wide, is



present in between the abdominal segments

IX–X, but its opening on dorsum or venter is not

discernible. Near the posterior end of the abdomen, six to seven setae are arranged transversely.

Marginal and submarginal areas of segment IX

dorsally with five to six more or less transversely

arranged setae are present.

Dermal structures: Both anterior and posterior

pair of ostioles are present. Trilocular disc pores

are absent.



Fourth-instar male nymph of M. hirsutus. WP wing pad



Adult male of M. hirsutus. CS coronal suture, DS

Digitiform seta, QDP quadrilocular disc pore, PS penial

sheath, PW part of wing, PSG penta locular stellate gland,

DE dorsal eye, LE lateral eye, VE ventral eye



2



Morphology



Multilocular disc pores: It is 5 μ in diameter,

found on both dorsum and venter. Their numbers

are dorsal abdominal segments IX, 1; VIII, 4;

VII, 11; VI, 3; V, 4; IV, 4; III, 9; II, 4; metathorax,

2; mesothorax, 6; prothorax, 13; head, 8; and

ventral abdominal segments IX, 0; VIII, 2; VII, 3;

VI, 3; V, 3; IV, 4; III, 2; II, 2; metathorax, 8;

mesothorax, 7; prothorax, 6; head 0. Microducts

are of oral collar type, about μ long, present on

both dorsum and venter. Ducts of dorsum are

about 3.2 μ wide, whereas those of venter are

about 2.4 μ. Their numbers are dorsal abdominal

segments IX, 0; VIII, 7; VII, 5; VI, 10; V, 10; IV,

14; III, 19; II, 19; metathorax, 14; mesothorax, 4;

prothorax, 16; head, 4; and ventral abdominal

segments IX, 0; VI, 3; VII, 4; VI, 7; V, 5; IV, 5;

III, 8; II, 4; metathorax, 5; mesothorax, 2; prothorax, 6: head, 3.



2.4.7



Fourth-Instar Male Nymph



Anterior end of the body is round, narrowing

gradually on the posterior end, on an average

1.061 mm long and 0.340 mm wide. Head, thorax

and abdomen are more differentiated than the

previous instar; sclerotisation is weak. Head: Ten

jointed antennae, average measurements in μ are

I, 34; II, 46; III, 34; IV, 24; V, 27; VI, 29; VII, 32;

VIII, 37; IX, 34; X, 74; second segment is the

broadest. Mouthparts are absent. Eyes are not

discernible. Thorax: Average measurements of

hind leg in μ are trochanter; 60 × 29; femur,

128 × 44; tibia, 142 × 28; tarsus, 101 × 25; claw,

16; tarsal and claw digitules are absent. Anterior

spiracle is about 26 μ long and 13 μ wide at

atrium; posterior one is about 31 μ long and 16 μ

at atrium. Wing pads are obliquely attached to

the mesothorax. Abdomen: In segment X, six to

seven setae are transversely arranged on dorsum.

Two marginal setae are on dorsum on each side

of segment IX, the longest one about 63 μ, and

two corresponding ones on venter about 17 μ.

Anal tube, apparently without an external opening, is present in between segments IX and X, 22

μ long and 26 μ wide. Penial sheath of adult male

is visible as and when it is formed inside this

stage.



17



Dermal structures: Both anterior and posterior

pairs of ostioles are present, with two multilocular disc pores and one seta on each lip of posterior

pair. Multilocular disc pores, 5 μ in diameter, are

present on both dorsum and venter. Their numbers are dorsal abdominal segments IX, 0; VIII,

3; VII, 9; VI, 3; V, 4; IV, 4; III, 4; II, 4; metathorax, 5; mesothorax, 3; prothorax, 12; head, 0; and

ventral abdominal segments, IX, 0; VIII, 2; VII,

2; VI, 2; V, 2; IV, 3; III, 2; II, 4; metathorax, 5;

mesothorax, 5; prothorax, 4; head, 0. Microducts

are of oral collar type, about 7 μ long, present on

both dorsum and venter. The ducts of dorsum are

much wider (about 3.2 μ) than those of venter

(1.8–2.4 μ) arranged more or less in transverse

rows. Their approximate numbers are dorsal

abdominal segments IX, 0; VIII, 13; VII, 10; VI,

13; V, 13; IV, 17; III, 17; II, 11; metathorax, 8;

mesothorax, 4; prothorax, 30; head, 4; and ventral abdominal segments IX, 0; VIII, 4; VII, 8; VI,

8; V, 8; IV, 12; III, 0–1; II, 0; metathorax, 0;

mesothorax, 0; prothorax, 10; head, 0.

Adult males are only of macropterous form,

on an average 1.055 mm long, including the projected penial sheath, and 0.310 mm wide. Head:

Ten jointed antennae, average measurements in μ

are I, 39; II, 66; III, 79; IV, 69; V, 66; VI, 63; VII,

67; VIII, 67; IX, 58; X, 71. The antennae are

clothed mainly with digtiform setae, up to about

39 μ; a few thicker specialised digtiform setae are

present on the last three apical segments, the longest ones being 39, 49 and 49 μ on segments VIII,

IX and X, respectively. Coronal suture is well

developed. Dorsomedian sclerite is weakly

sclerotised. Three pairs of eyes are present: dorsal, ventral and lateral. The average diameter of

the dorsal and ventral pairs is 30 and 34 μ, respectively. Lateral pair is 25 μ in diameter at the base

and 18 μ high on an average. Mouthparts are

absent. Thorax: One pair of wings, on an average

0.92 mm long and 0 .42 mm wide; each wing has

four to five sensory setae near the basal region;

average measurements of the posterior leg in μ

are trochanter, 62 × 26; femur, 216 × 39; tibia,

283 × 23; tarsus, 99 × 19; claw, 34; tarsal digitule

is very slender, 34. As in antennae, legs are

clothed with both digitiform and slender-pointed

setae, their maximum length being 31 and 21 μ,



M. Mani and C. Shivaraju



18



respectively. The inner distal end of tibia has

three spines. Tarsus has three to four spines at the

inner distal end. Anterior and posterior spiracles

are about 21 μ wide at atrium, their lengths being

23 and 26 μ. Abdomen: Penial sheath is about 179

μ long and 70 μ at the widest portion and 6.5 μ at

the projected tip, which is rounded. It has two

distinct median lobes, each more or less triangular in shape. Dermal structures: Only posterior

pair of ostioles is present. Quadrilocular disc

pores, 4.8–5.6 μ in diameter, are present on both

dorsum and venter; numbers on dorsum are

abdominal segments IX, 0; VIII, 4; VII, 2; VI, 2;

V, 3; IV, 2; III, 2; II, 11; metathorax, 0; mesothorax, 0; prothorax, 8–16; head, 4; and ventral

abdominal segments IX, 0; VIII, 3; VII, 3; VI, 3;

V, 3; IV, 3; III, 0; II, 2; metathorax, 2; mesothorax, 4–8; prothorax, 4–8; head, 0. Two dorsal

clusters of stellate or tail-forming pentalocular



disc pores are present on each side of the

abdominal segment IX. In the centre of each cluster, there are eight to ten disc pores of smaller

dimension (about 4 μ in diameter) and three long

setae, two of which on an average are 260 μ long.

Around the central zone 38–44 disc pores, 5 μ in

diameter, are present.



References

Ghose SK (1971) Morphology of various instars of both

sexes of the mealy-bug, Maconellicoccus hirsutus

(Green) (Pseudococcidae: Hemiptera). Indian J Agric

Sci 41(7):602–611

McKenzie HL (1967) Morphology and classification.

Mealybugs of California, University of California

Press, Berkeley, pp 36–40

Williams DJ (2004) Mealybugs of southern Asia. The

Natural History Museum, Southdene Sdn. Bhd., Kaula

Lumpur, Malaysia, pp 18–21



3



Cytogenetics

Ramakrishna Sompalaym, Kokilamani A.

Lingarajaiah, Raju G. Narayanappa, Jayaprakash,

and Venkatachalaiah Govindaiah



3.1



Introduction



The coccoids which include mealybugs are a relatively small group of highly specialized hemipteran insects. They are parasitic on plants and

quite sedentary in behavior (Miller and Kosztarab

1979; Gullan and Kosztarab 1997; Mani 1989;

Kondo et al. 2008). The chromosome system of

coccoids is of special interest because it is characterized by chromosomal heterochromatization

or elimination of the paternal endowment of

chromosomes during early embryogeny of the

male in the majority of scale insects. The first

cytological insight into the nature of this remarkable system came from the pioneering cytology

described by Schrader (1921, 1923a). Subsequent

studies by Hughes-Schrader (1948) have provided insightful thoughts into the explanation of

the genetic and evolutionary implications of

“paternal heterochromatization” that could serve

as an intermediate stage between regular diploidy

and true male-haploidy.



R. Sompalaym (*) • K.A. Lingarajaiah

Department of Zoology, Bangalore University,

Bengaluru 560 056, India

e-mail: srkbuz@ymail.com

R.G. Narayanappa

Department of Biotechnology, KSOU,

Mukthagangotri, Mysore 570 006, India



Schrader’s interpretation was later confirmed

experimentally with a mealybug, for example,

Pseudococcus obscurus and/or Planococcus citri

by Brown and his associates (Brown 1958, 1959,

1963, 1964, 1965, 1969; Brown and Nelson-Rees

1961; Chandra 1962, 1963a, b; Brown and Nur

1964; Baer 1965; Nur 1963, 1966a, b, 1967;

Brown and Weigmann 1969). Earlier cytological

scrutiny had been reviewed by White (1973) and

certain aspects of coccoid chromosome systems

especially their possible role in the involvement

in the chromosome imprinting processes, have

been aptly dealt with by Brown (1977) and

Brown and Chandra (1977), about certain unusual

features by Nur (1980, 1990), and about recent

achievements made with respect to biochemicalbased cytology by Prantera and Bongiorni (2012).

Enormous and extensive cytological and genetic

studies of mealybugs belonging to worldwide fauna

are available (Little 1957; Carter 1962). However,

the efforts on the systematic and cytogenetic aspects

of Indian coccoids are very limited. There have



Jayaprakash

Department of Zoology, Bangalore University,

Bengaluru 560 056, India

Centre for Applied Genetics, Bangalore University,

Bengaluru 560 056, India

V. Govindaiah

Centre for Applied Genetics, Bangalore University,

Bengaluru 560 056, India



© Springer India 2016

M. Mani, C. Shivaraju (eds.), Mealybugs and their Management in Agricultural

and Horticultural crops, DOI 10.1007/978-81-322-2677-2_3



19



R. Sompalaym et al.



20



been sporadic reports that provide incomplete and

contradictory information pertaining to Indian

fauna for their chromosome systems (Tulsyan

1963; Dikshith 1964, 1966; Chauhan 1970, 1977).



3.2



Mealybug Chromosomes



All coccoids possess holocentric chromosomes,

that is, diffuse centromeres (Hughes-Schrader

and Ris 1941). Inverse meiosis is a second ancestral condition manifested in coccoids that is also

shared with the other closely allied aphids (Ris

1942; Hughes-Schrader 1944, 1948).

Although the cell cycle sequence is different

from that of typical meiosis, results are the same;

each of the four chromatids of meiotic bivalents

reaches one of the four nuclei produced by meiosis. Coccoids are also manifested by those systems

in which at least some of the females are produced

parthenogenetically, in addition to the usual bisexual mode of reproduction. They are considered to

have unique chromosome systems and they offer

enormous potential in our understanding of problems such as chromosome imprinting and differential regulation of homologous chromosome sets

(Chandra 1971; Chandra and Brown 1973).

Chandra (1971) suggested for the first time that

there are some similarities and also contrasts

between mammalian X-chromosome inactivation

and the inactivation of paternal chromosomes in

mealybugs. These include genomic imprinting,

facultative heterochromatization, and differential

regulation of homologous chromosomes.

Subsequently, Brown and Chandra (1977) have

drawn attention to emphasize that coccoids are at

the pinnacle of an evolutionary pyramid of cytogenetic variants and complexity. In order to understand these variations in chromosome mechanics,

it becomes essential briefly to review pseudococcid chromosomes.



3.3



Chromosome Numbers

and Chromosome Forms



Coccoid chromosomes lack specified centromeric regions. It appears obvious to point out that

chromosome fragments perpetuate themselves



during successive divisions. In the absence of

kinetochore-based cell divisions that prevail in

coccoid chromosome systems, and also, in order

to accommodate the occurrence of karyotypic

changes, Brown (1961) assays chromosome fracture and fusions in the place of the prevalent

nature of chromosomal rearrangements. It was

also envisaged that simple breakage can determine increase or decrease in chromosome numbers unless a breakage–fusion–bridge cycle

intervenes to eliminate the breakage points.

Species relationships can be explained by citing chromosome variability occurring with

respect to either chromosome numbers or morphology. Brown (1961) insists upon spontaneous

occurrence of chromosome breakage resulting in

abundant availability of ruptured chromosomes

for increase in the diploid numbers either by

chance or incurred by selection. There are an

abundant number of cases dealing with karyotypic changes incurring based on chromosome

fragmentation in mealybug genomes (Nur et al.

1987; Cook 2000).

Changes in chromosome numbers with respect

to pseudococcid species have been reported to be

in the range of 8 to 64 and that ranges within coccoids are rather small compared to other insect

groups (Hughes-Schrader 1948; Nur et al. 1987).

Until now, 115 cytogenetically studied species of

mealybugs belonging to 44 genera have been

made known (Gavrilov 2007; Gavrilov and

Trapeznikova 2007, 2010). Eventhough, the diploid number of chromosomes ranges from 8 to 64,

the modal number seem to fall on 10 (Plate 3.6

Fig. 4, 6, 8). Few mealybugs showed intrageneric

variation in their chromosome numbers; for example, in genera such as Antonina (2n = 12, 16,

24 + Bs), Nesopedronia (2n = 18, 14, 10) and

Trionymus (2n = 16, 10, 8), such instances can be

cited as useful in taxonomic and phylogenetic considerations of the genus. Accessory chromosomal

elements (B-chromosomes) were found in several

species of mealybugs (Nur et al. 1987; Gavrilov

2004). But, the detailed investigation of

B-chromosomes has been done only in

Pseudococcus viburni (Signoret; Nur 1962a,

1966a, b). The majority of pseudococcids possess

2n = 10 (Nur et al. 1987; Moharana 1990; Nur

1990; Gavrilov and Trapeznikova 2007, 2010).



3



Cytogenetics



Excepting Planococcus citri and a few other species, the number of species studied based on

employing recently evolved cytogenetic techniques is very low. One of the reasons cited was

the difficulties incurred in procuring enough cells

for the preparation of chromosomes and of understanding of chromosome basics for detailed cytological analyses. For cytological investigations of

Indian mealybug taxa, Parida and Moharana

(1982) and Moharana (1990) attempted to enumerate chromosome numbers based on conventional cytological techniques and they were also

able to present preliminary assessments of karyomorphological features for more than 20 different



Plate 3.1 Planococcus citri



21



species. Based upon female pachytene chromomeric sequences, Raju (1994) made an initial

attempt to describe karyotype and comparison of

three species of the Indian genus Planococcus

(viz. P. citri, P. lilacinus and P. pacificus) essentially based on differential banding patterns, but

was unable to identify individualistic karyotypes

because of lack of discriminating cytogenetic features (Plates 1–5). Gavrilov (2004a, 2007) and

Gavrilov and Trapeznikova (2007, 2010) have

made elaborate studies resulting in the elucidation

of the karyotype for more than 25 species of

Russian mealybugs based on squashing techniques

for chromosomal preparations. Nur et al. (1987)



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4 Morphology of Various Instars of Both Sexes of the Mealybug

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