Discussion:-

The culture of L.
migratoria was maintained in the laboratory as per the techniques suggested
by Hunter Johns (1961) with several researcher report modifications in the
cages in order to suit the climatic condition of central India. Using the
modified techniques a large of individuals of different stages could be
produced for experimental purposes. Source of food for the growing individuals
was the commonly occurring grass and Jowar plants in the tropical environment.

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To ensure the population built up, the locust must
aggregate, mate and oviposition in such a way that gregarious integrity of the
locust population is ensured. This has been achieved through synchronization of
mature of adults and oviposition at common egg laying site (Popov, 1958; Stower
et al., 1958; Noris, 1964 and
Amersinge, 1978).

Convenient insect pest control
strategy involves application of large spectrum chemical insecticides, which
are produce harmful effect. Further, growing public disquiet about the
environmental and human risk associated with chemical pesticides, emergence of
pesticide resistant insect populations as well as rising prices of new chemical
pesticides have stimulated the search for new eco-friendly vector control tools
(Mittal, 2003).

The use of biopesticides based on microorganisms has
been effective mainly against Lepidoptran pests. King and Taylor (1936)
identified a pathogen M. locustae
which had some limitations to use against L.
migratoria as suggested by Mc Laughlin (1971), as a result various other
protozoan drew attention among which the most important was Nosema locustae canning, a pathogen reported
from L. m. migratorides. Due to high
temperature in the ecosystems where usually locusts invasion occurs, survival
of N. locustae is medium. However,
it’s biocontrol potential against rangeland grasshopper has been well
documented (Henry, 1981; Heny et al.,
1985; Johnson and Andrews, 1987). Since M.
locustae can thrive at high temperature and reported to have only one
target organ i.e., malpigian tubules, the work on M. locustae got attention and compared to N. locustae better results in the laboratory conditions were
obtained (Raina et al., 1992)

The results obtained in the present study indicate
that M. locustae can achieve nearly
40-50% mortality target if used at fourth instar stage causing delayed
development, reduced body weight, reduced fecundity and hatching due to M. locustae infection its protozoan
biocontrol agent. Its pathological effects were also evidenced in the midgut,
fat body tissues and other organs which have also been reported earlier
(Jackson et al., 1968). Cross
infection of M. locustae in S. gregaria caused 80 % infection in the
laboratory (Raina et al., 1992).
Lumen of malphigian tubules of the host insect is completely filled with the M. locustae affecting the execration and
leading to the deterioration of cells and the tissues as evidenced in the present
study. Similar observation were made earlier by Evans and Elias (1970). The
colony of L. migratoria got infected
due to contamination of M. locustae
as reported by Proux, (1991). He further reported that no infection in other
tissues was observed however; in the present study we found the disruption of
even midgut epithelial layer of M.
locustae. The external signs of infection could also be seen in the
abdominal segments.

The pathogenic effect of M. locustae may be severe in combinations of N. locustae as both pathogens were able to wipe able to wipe out
the entire laboratory colony of L.
migratoria (Raina, 1987). Results of the present study the use of M. locustae together with other
potential biocontrol agent might be able to control the locust and grasshopper
population below the economic injury level.

A bacterium B.
thuringiensis is considered as biocontrol agent and is used against, the
pest insects of Lepidoptera, Diptera, Coleoptera and Orthoptera. Dhillon and
Charley (1986) reported 39 isolates of B.
thuringiensis isolated from locust and grasshopper collected from the field
and laboratory reared individuals. B.
thuringiensis has already been reported to be effective against
Mediterrenean locust, D. maroccanus
(Quesada-Moraga et al., 2001).

Earlier reported that bacterium evidenced the
presence of bacteria in the eggs of L.
migratoria reared in the laboratory condition. Two bacteria were isolated
belonging to Bacillus group. This is
the occurrence of bacteria in the egg of L.
migratoria suggesting their transmission via ovary.

The nymphs of L.
migratoria inoculated with the isolated B.
thuringiensis caused infection in the midgut and epithelial layer. The
similar pathogenic effects were also demonstrated in other chrysomelids when
infected with B. thuringiensis var. tenebrionis (Krieg et al., 1983). Histopathological effects of B. thuringiensis in midgut of D.
maroccanus, with loss of epithelial cells of the gut have been reported
(Quesada-Moraga et al., 2001)

Earlier reported that,
B. thuringiensis infection at nymphs
stage delayed the adult maturity and increase development duration and embryo
incubation period. The nymphs that consumed less spread more bacterial
infection to the gut and other tissues. In many individuals this infection led
to death of the insect due to 

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