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  • REVIEW OF LITERATURE

    15

    REVIEW OF LITERATURE

    The Heteroptera is a numerically large and highly diverse group of insects.

    About 42,300 species belonging to 89 families from this suborder have been described

    many of which are pests of economically important food plants (Henry, 2009).

    Heteroptera comprises eight major infra-orders namely Coleorrhyncha,

    Enlcocephalomorpha, Dipsocoromorpha, Leptopodomorpha, Gerromorpha, Nepomorpha,

    Cimicomorpha and Pentatomomorpha. Within Cimicomorpha, Reduviidae and Miridae

    are the major families. Reduviidae is one of the largest families of terrestrial Heteroptera,

    globally comprising 6601 species and subspecies in 961 genera and 25 subfamilies

    (Maldonado, 1990). These insects are abundant, occur worldwide and are voracious

    predators, thus are named assassin bugs (Ambrose, 1999; Schaefer and Panizzi, 2000).

    Assassin bugs may not be useful as predators of specific pests as they are polyphagous

    but they are valuable predators in situations where a variety of insect pests occur. They

    kill more prey than they need to satiate themselves by their behavior of indiscriminate

    killing. Their importance as predators and their conservation augmention for utilization in

    biocontrol programmes has been discussed by Ambrose (1987, 1999).

    (A) Chromosome complement and meiosis :

    (a) Heteroptera:

    The pioneer contribution towards the cytological aspects of this suborder was made

    by Henking (1891) which was followed by very elaborate cytological investigations by

    Montgomery (1898), McClung (1901) and Wilson (1909 a, b & c). The chromosomes of

    Heteroptera are holocentric and the occurrence of the diffuse centromere was proposed

    and evidenced in a series of publications by Schrader (1935, 1940 a & b, 1947). Schrader

  • REVIEW OF LITERATURE

    16

    (1935) observed chromosomes of Protenor belfragei (Alydidae) to be without a discrete

    localized centromere. Rather spindle fibers were found to be attached all over the surface

    of the chromosome. Further, he observed that the chromosomes showed no bending at

    anaphase-I and two halves remained parallel to one another as they passed on to two

    poles. The hypothesis of diffuse kinetochore was extended to the entire group of

    Heteroptera by Schrader (1940 a & b, 1947). He elucidated the importance of diffuse

    centromere in the evolution of this group. He interpreted that the fragments formed as a

    result of accidental breakage of chromosome with diffuse kinetochore remained

    functional and behaved normally at mitosis and passed through several generations

    thereby changing the fundamental number of a species. Based on chromosome behavior

    during mitosis as well as meiosis, Troedsson (1944), too, claimed that the heteropteran

    chromosomes were holocentric. Hughes-Schrader (1948) examined the behavior of

    heteropteran chromosomes during mitosis and recorded that:

    1. Each chromosome orientated with its long axis at right angle to the polar axis at

    mitotic metaphase.

    2. No primary constriction appeared during mitosis.

    3. Terminalisation of chiasmata was completed by late diakinesis.

    4. Chromosomal fibers were organized along the entire length of each chromatid so

    that mitotic chromatids separate by parallel disjunction.

    These features were further supported by Heizer (1950, 1951), Halkka (1956) and

    Lewis and Scudder (1957). Additionally, holocentricity was demonstrated experimentally

    in the Heteroptera by Hughes-Schrader and Ris (1941) and Ris (1942) also. However,

    Mendes (1949), Parshad (1957 a, b, c & d) and Rao (1958) suggested the heteropteran

  • REVIEW OF LITERATURE

    17

    chromosomes to be monocentric because of the presence of a presumed primary

    constriction at mitotic metaphase. This claim was strongly criticized by Hughes-Schrader

    and Schrader (1961). Piza (1958), on the other hand, suggested that the heteropteran

    chromosome was dicentric. Most of the authors, however, supported the opinion of

    holocentric nature of chromosomes (Manna, 1951; Banerjee, 1959; Wolfe and John,

    1965; Ueshima, 1966, 1979; Ueshima and Ashlock, 1980). La chance et al. (1970) further

    elaborated that even in holocentric chromosomes, some fragments particularly small

    ones, may be eliminated or delayed in the anaphase separation. At the ultrastuctural level,

    Buck (1967) while working on Rhodnius prolixus, observed an extensive layer of

    material all over the mitotic chromosome to which spindle fibers were attached. Meiotic

    chromosomes, on the other hand, did not show this structure. Comings and Okada (1972)

    carried out investigations on formation of kinetochore plates in Heteroptera with a diffuse

    kinetochore during mitosis and meiosis, and discussed their suppression during

    terminalization of chiasmata. They observed a centromere plate extending for upto 75%

    of the length of the mitotic chromosome in Oncopeltus fasciatus but centromeric plate

    was absent in meiotic chromosomes. It was interesting that repeat DNA sequences were

    short and scattered over the chromosome. On the other hand, in organisms with

    monocentric chromosomes, repeated DNA sequences are in high concentration near the

    centromere (Lagowsky et al., 1973). Ruthman and Permantier (1973) found the

    centromere to cover only 4.2% of the entire chromosome in Dysdercus intermedius.

    White (1973) elaborated that the ability of spindle fibres to attach large part of the

    chromosome during cell division becomes the basis for the principle of Karyotypic

  • REVIEW OF LITERATURE

    18

    Orthoselection. The aberrations induced by radiations and chemicals help to understand

    various aspects of the chromosomes, its organization, rearrangements and evolution.

    The behavior of holokinetic chromosomes during the course of mitosis and meiosis

    has been studied by Darlington and Upcott (1938) by taking the measurements of packing

    and contraction in the chromosomes. Darlington (1939) further discussed the genetic and

    mechanical properties of sex chromosomes during division in Heteroptera. The details of

    kinetic activities of autosomes and sex chromosomes during meiosis have been discussed

    by Hughes-Schrader and Schrader (1956, 1957, 1961), Gonzalez-Garcia et al. (1996) and

    Perez et al. (1997, 2000).

    Any scientific study of an organism needs its prior identification, naming and

    classification. Taxonomists use various morphological characters to bring different

    members of a group of plants and animals under a systematic list showing their natural

    phylogenetic relationships. With the growing knowledge of nuclear structures, the

    cytologists believe that chromosomal attributes are also morphological and can be

    substantially utilized for the purpose of taxonomy in addition to general morphological

    features. In Heteroptera, karyotype is prone to evolutionary changes either by fusions or

    fragmentations of chromosomes which lead to decrease or increase in the chromosome

    number in different species. Every fusion and fragmentation appears first in a

    polymorphic state prior to its fixation in the karyotype. The importance of heteropteran

    material for cytological studies from evolutionary point of view was recognized in the

    beginning of twentieth century by Montgomery (1901a & b, 1904, 1906), Wilson (1905a,

    b & c, 1906, 1907a, b & c, 1909a & b, 1910, 1911, 1912, 1913, 1932) and Browne (1916)

    who carried out cytological investigations along with morphological characters of

  • REVIEW OF LITERATURE

    19

    Heteroptera. Payne (1909, 1910, 1912), Chickering (1927a & b, 1932, 1933) and

    Nishimura (1927) stressed upon the importance of chromosome studies of different

    families of Heteroptera with respect to their karyotypic evolution. This practice is

    becoming more and more obvious in modern systematics. Cytologists are interested in

    collecting the cytological data of more and more species of Heteroptera. At international

    level, karyological studies on Heteroptera have been done by Foot and Strobell (1907,

    1912, 1914), Schrader (1932, 1935, 1939, 1940a & b, 1941a & b, 1945a & b, 1946a & b,

    1947, 1960a & b), Toshioka (1933, 1934, 1935, 1936, 1937), Geitler (1937, 1938, 1939a

    & b), Pfaler-Collander (1937, 1941), Freeman (1940), Mc Clung (1940), Hughes-

    Schrader (1931, 1940, 1942, 1948, 1955), Schrader and Hughes-Schrader (1956, 1958),

    Ekblom (1941), Troedsson (1944), Yosida (1944, 1946, 1947, 1950, 1956), Xavier

    (1945), White (1948), Heizer (1950), Lewis and Scudder (1957), Leston (1957, 1958),

    Ueshima (1963, 1966, 1979), Mikolajski (1964, 1965, 1967a & b, 1968, 1970,1971),

    Takenouchi and Muramoto (1964, 1967, 1968, 1969, 1970a & b, 1971a & b, 1972a & b,

    1973), Muramoto (1973a, b, c & d, 1974, 1975a, b & c, 1976, 1977, 1978a & b, 1979,

    1981, 1982, 1985), Akingohungbe (1974), Kuznetsova and Petropavlovskaya (1976) and

    Reddi and Chari (1976, 1978).

    Extensive cytological studies have been carried out on Heteroptera by Ueshima

    and Ashlock (1980), Sands (1982a & b), Nuamah (1982), Newman and Cheng (1983),

    Nokkala and Nokkala (1983, 1984, 1997, 1999, 2004), Papeschi and Bidau (1985),

    Nokkala (1985, 1986). Papeschi (1988, 1991, 1992, 1994, 1995, 1996), Papeschi and

    Mola