EXTRA AND INTRA CELLULAR
MICRO-ORGANISMS AND THEIR ROLE IN
VAKALIYA MUSTUFA A.
M.Sc. (Agri.) Entomology
BACA, AAU, ANAND
EXTRA AND INTRA CELULLAR
THEIR ROLE IN PHYSIOLOGY
The insects are rather uniform in their nutritional requirements
(Dadd , 1985) but remarkably diverse in their diets (Slansky & Rodriguez
1987). There are insect predators, herbivores, generalist ‘scavengers’ and
an array of specialists that utilize, for example, nectar, pollen, plant sap,
fungi, fur, feathers, skin and blood. The capacity of some insects to adopt
certain nutritional lifestyles cannot be attributed to traits of the insect alone
but to an alliance between the insect and microorganisms with different
biosynthetic or degradative capabilities from the insect. The basis for this
nutritional ecology of many insects can be understood only by including
microorganisms as an integral part of the ecological and physiological
Microorganism related to insect with relation is divided into in a two
(1) Casual associations
(2) Constant associations
Micro-organisms are almost inevitably ingested during
feeding and so an intestinal flora is present in most insects.
The alimentary canal of grasshopper , for instance , is
sterile when the insects hatch from the eggs but soon acquires
a bacterial flora, which increases in number and species
In general insects with straight alimentary canals contain
fewer micro-organisms than those with complicated guts with
a range of pH ,providing a number of different niches.
These Casual Association with microorganisms are important in the
nutrition of some insects.
Scarabaeoid larvae have a fermentation chamber in the hindgut in
which decaying woods with its content of microorganisms is
The microorganisms continue to ferment the wood and without
them the larvae is unable to utilize the cellulose of the wood.
Microorganisms also assists with wax digestion in galleria
although the insect can survive without them.
In General, constant association with
microorganisms occur in insects with a restricted
diet deficient in certain essential nutrients,
suggesting that the microorganisms make good
thus microorganisms found in insects feeding on
woods, dry cereals, feather, hair and wool, in
sap feeding which at the some stage partake of
other food do not house microorganisms.
Thus symbionants are found in blood sucking bugs and
lice ,and glossina and Nycteribidae, which are viviparous,
among Diptera , but not in Fleas, blood sucking
Nematocera or Tabanidae ,since these have free living
larvae. (wigglesworth, 1952)
Microorganisms also found in cockroaches and some
ants. These are omnivorous insects and hence in this
instance the presence of microorganisms is not correlated
with a restricted diet.
TYPES OF MICRO-ORGANISMS
The most commonly occuring microorganisms in insects are
Bacteria or Bacterium like forms which are found in
Blattodea, Homoptera, Heteroptera, Anoplura,
Mallophaga, Coleoptera, Hymenoptera, and Diptera.
In additional flagellates (protozoa) are found in wood eating
cockroaches and termites, yeast in Homoptera and
Coleoptera and a Actinomycetes in Rhodnius. in many cases
precise nature of the microorganisms is unknown.
LOCATION IN THE INSECT BODY
In some insects the symbionants are free in the gut
This is the case with the flagellates which live in the
hindguts of wood eating cockroaches and termites and
with the bacteria living in the gastric caeca of the last
segment of the midgut in plant sucking Heteroptera.
In Rhodnius Actinomycetes lives in crypts between
the cells of the anterior midgut. 10
Most microorganisms are intracellular in various
parts of the body.
The cell housing symbionants are known as
mycetocytes and these my be aggregates together
to form organs known as mycetomes.
Mycetomes originates in the gut walls, as in
Anoplura and Glossina, where the mycetome is a
ring of enlarged midgut cells, or in modified
malpighian tubules, as in some Coleoptera but
frequently they are independent of the gut.
In Calandra (coleoptera) larvae the mycetome is a U-
shaped structure well supplied with tracheae lying below
the foregut, but not connected to it (musgrave, 1964).
The wood eating cockroaches have two sets of
symbionants; Intestinal-flagellates and intra-cellular
bacteriods in the fat bodies. this situation also occur in
termites Mastotermes darwiniensis, but the remaining of
the wood eating termites only retain the intestinal fauna.
THE ROLE OF MICRO-ORGANISMS IN INSECT
Digestion and nutrition
In insects the digestion of food by gut associated bacteria
has been demonstrated in crickets and cockroaches. The
protozoan population is enriched when the cockroaches are
exposed to a cellulose rich diet .
Similarly, it has been established that gut bacteria are
responsible for the nitrogen metabolism of insect host and
these microbes fix atmospheric nitrogen in fruit flies and
These results amply support the view that bacteria associate
with insects in providing essential nutrients, as against
bacterial pathogens which depend on the insect/animal for
its nutrient supply(R.Rajgopal, 2009).
Insects belonging to the order Hemiptera like
aphids, white fly, mealy bug, plant hoppers feed
exclusively on the plant sap a freely available
sugar rich diet.
Since plant sap is very poor in nitrogen and amino
acids, these insects have developed obligate
symbiosis with bacteria like Buchenra (aphid) or
Portiera (white fly), where in the bacteria supply
all the essential amino acids required by the insect.
While the insect accommodate these bacteria in
specialized structures in their gut - mycetomes /
IMMUNITY AND PROTECTION
Gut is a very dynamic environment, providing
plenty of opportunity for the bacteria to flourish,
thus resulting in extreme competition among
bacteria to utilize the nutrients and survive within
Many of the gut commensal bacteria have evolved
to inhabit this environmental niche and thus are
able to colonize the gut.
In doing so, they provide effective protection
against invasion by pathogenic microbes a process
called colonization resistance (CR).
Axenic (germ-free) locusts were found to be extremely
susceptible to infection by entomopathogenic fungus –
Beauvaria and Metarhizium.
Certain phenolic components having antifungal activity
were absent in germfree locust and introduction of one
of the gut bacteria – Pantoea agglomerans resulted in
the appearance of a part of the phenolic repository.
A similar effect on CR against Serratia marsceans was
also observed Similarly, axenic silkworm (Bombyx
mori) larvae were found to be more susceptible to
Serratia piscatorum and baculo virus
Some microorganisms associated with insects have been
implicated in altering the population ecology of their hosts.
The most studied of these are the Wolbachia, a common and
widespread group of bacteria found in insect reproductive
These bacteria are protect against cytoplasmically inherited
rickettsia that cause a number of reproductive alterations in
their host, including cytoplasmic incompatibility between
strains, parthenogenesis induction (Werren, 1997).
Wolbachia have additionally been shown to increase fecundity
of insects (Vavre et al. 1999), and the nature of their effects
vary with strain, arthropod species, and host genetic system
(Johanowicz and Hoy 1998). 17
OTHER ROLE OF BACTERIA
Other role of gut microorganisms are potential in the
detoxification of food. Certain sources of nutrients
are available only if toxins can be neutralized, and
hydrolysis of some molecules.
Such as some plant cell wall components can both
detoxify them and make them available as sources of
Many insects specialize on toxic plants or overcome
chemicals used for insect control, and gut bacteria
might serve as a portal for acquiring capabilities to
digest and detoxify local food sources.
Termites are consuming dead plants at any level of
decomposition. They also play a vital role in the ecosystem by
recycling waste material such as dead wood, faeces and
Many species eat cellulose, having a specialised midgut that
breaks down the fibre.
Termites having primarily symbiotic protozoa (metamonads)
and other microbes. in their guts to digest the cellulose for
them, allowing them to absorb the end products for their own
Gut protozoa, such as Trichonympha, in turn, rely on
symbiotic bacteria embedded on their surfaces to produce
some of the necessary digestive enzymes. 19
3. YEAST AND ACTINOMYCETES
The yeast of Stegobium (Coleoptera) provide B-Vitamins
and sterols , which may be secreted into the guts, or
release by the digestion of the microorganisms.
The symbionants of Bllatella provide certain amino acids
and possibly a tripeptide as well as B-vitamins .blood is
normally sterile and contains some of the B-vitamins in
smaller amounts. than are required by insects.
In Rhodnius Actinomycetes lives in crypts between the
cells of the anterior midgut, which are associated with
bacteria in symbionants and help in the synthesis of some
nutrients in guts.
There is some evidence that the microorganisms,
particularly those in Homoptera and Heteroptera ,are
concerned with nitrogen metabolism (Toth, 1952).
This may result from the fixation of free nitrogen or by the
breakdown of the insects metabolic waste products ,urea
,uric acids. into nitrogenous compounds that can be used.
Although it seems certain that the organism can perform
these functions in vitro ,there is no proof that they do so
when inside the host insects.
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