microbe mediated insect resistance is a major concern in agriculture due to the enhanced application of pesticides and rapid development of insect resistance

2. Introduction
• Bacteria and insects have had the opportunity to evolve
together in both mutualistic and
• parasitic relationships for some 250 million years.
• Symbiotic relationships are an important motor for
organisms diversification and evolution.
• The relationships insects have established with some
endosymbiotic microorganisms (that is, those inhabiting
the inner of their bodies) have provided them of a lot of
surprising physiological and ecological adaptations.

3. Types of
endosymbiosis in
insects
• Endosymbiotic
microorganisms
can be found
inside the gut,
in the spaces
between cells
and inside
cells.

4. • It is considered that at least 70% of insects has endosymbiotic
microorganisms inside its cells.
• There exist two types of intracellular endosymbionts
• 1) Mycetocyte symbionts or Blochmann bodies (Produce
essential aminoacids Eg: Buchnera aphidicola in aphids
produce Glutamine and Vitamin B2 (Riboflavin)
• 2) Guest endosymbionts (affect the sex ratio of insects Eg:
Wolbachia pipentis kills the male insects, induce
parthenogenesis in males, feminization or cytoplasm
incompatability)

5. How they acquire endosymbionts?
1. Horizontal transmissoin
2. Vertical transmission
3. Environmental acquisition

6. 1. Horizontal transmission
• Unlike other endosymbionts, gut
microbes are horizontally transmitted
between insects; that is, insects
don’t inherit gut microbes from
their parents, but they should
acquire them throughout their
lives.
• In termites, acquisition of gut
microbes takes place through a
process called trophallaxis: the
workers, which are the only able to
feed by themselves, digest the food
and transmit the resulting product
mixed with gut microorganisms to
the rest of the colony members
through their mouthparts. Moreover,
microorganisms are removed
during molting processes, so
termites (and other insects
performing trophollaxis) can
acquire them again through
trophollaxis.

7. 2. Vertical transmission
• Unlike gut microbes and endoparasites, extracellular and
intracellular endosymbionts are vertically transmitted
generation after generation; that is, the insect inherits
them from its parent
Figure: Brown winged
green colored stinkbug
Plautia stali (Left) and
its mid gut symbiotic
organ (Right) with blue
green color
Transmitts microbes
vertically

8. 3. Environmental Acquisition

9. The value of the relationship between
insects and their endosymbionts
• The major cause for insects evolutive and
adaptive success is their potential to establish
beneficial relationships with other life beings
and, especially, with those microorganisms
inhabiting their insides: the endosymbionts.

10. Roles of endosymbiont’s in insects
Degradation of pesticdes
Change of sex, parthenogensis
Change plant host physiology to benefit
insect host
Expanding host Range
Help in insect survival
Eg: production of defence
compounds
Nutrition to insect Eg: Aphids
Degradation of
complex materials
inside gut

11. a) Aphid and endosymbiont Buchnera interaction
(Mutualistic)
Mutualistic bacterium Buchnera, have a great role in
supplying
1) Essential amino acids that plant saps lack (Except
Tryptophan) (Douglas, A.E, 1993)
2) Nitrogen recycling inside gut (it is not quantitatively
important to the nutrition of aphid species) and
3) Lipid and sterol nutrition of aphids (Douglas, 1998)
4) Vitamin provision (Vitamin C and B) (Dadd, 1967)

12. • Located in a specialized eukaryotic cells known as Bacteriocytes
• Bacteriocytes: 60-80 in each aphid (Douglas, A.E and Dixon,
A.F.G, 1987) and they are polyploid
• Bacteriocytes are surrounded by a host membrane called
symbiosome
• The bacteriocytes are assembled in a bilobed organ like structure
called bacteriome
• The bacteria are transmitted vertically via the aphid ovary, and
the association is obligate for both partners: bacteria-free aphids
grow poorly and produce few or no offspring, and Buchnera are
both unknown apart from aphids and apparently unculturable
(Douglas, 1998)
• Bacteria free aphids are called as aposymbiotic aphids, these can
be created by treating insect with chlortetracycline's or
Rifampicin (Griffiths, G.W and Beck, S.D, 1974)

13. Other roles of Buchnera
• Buchnera have been implicated in resistance of
aphids to insecticides (Von Amiressami and Petzold
H, 1976)
• Buchnera helps the aphids to secrete more honey dew
and it is related to age. Ants collect the honeydew as
a supply of carbohydrates and in return may defend
the homopterans from natural enemies (Nixon 1951;
Way, 1954; Banks, 1962; Addicot, 1979; Volki, 1992)

14. Wolbachia-Insect sex ratio
• Wolbachia are well known as bacterial symbionts of
Arthropods, where they are reproductive parasites,
but have also been described from nematode hosts,
where the symbiotic interaction has features of
mutualism
• In some insects, Wolbachia destroys males of its
host species
• Wolbachia can turn males into females by
interfering with the male hormone
• If a male and female are uninfected with the
Wolbachia, they produce offspring normally. If only
the males are infected, the insects fail to reproduce
• If one or both insects of a mating pair are infected,
only the females reproduce and transmit Wolbachia
in the cytoplasm of their eggs
• Offspring produced without fertilization are
obviously developed into females. The result is the
bacteria are transmitted to the next generation. This
type of reproduction is called as parthenogenesis

15. • Wolbachia pipientis is a widespread intracellular
bacterial symbiont of arthropods and is common in
insects
• To enhance its transmission, W. pipientis has evolved
a large scale of host manipulations: Parthenogenesis
induction, Feminization, and Male killing
• Wolbachia are alphaproteobacteria that live
intracellularly in a range of animal hosts

16. • Killing the bacteria with tetracycline affects
nematode growth, molting, fecundity, and lifespan
• In arthropods, in most cases, tetracycline treatment
yields cured, healthy hosts
• W. pipientis show high affinity towards microtubules
associated with the early divisions in eggs. Such
inherited microorganisms are thought to have been
major factors in the evolution of sex determination,
and speciation

17. W. pipientis isolates are also of interest as vectors for
the
a) Modification of wild insect populations,
b) In the improvement of parasitoid wasps in biological
pest control, and
c) As a new method for interfering with diseases caused
by filarial nematodes

18. Herbivore oral secretions and
microorganisms
• Herbivorous insects typically produce oral
secretions that interact with food plants, either
stimulating or suppressing plant defense
responses. Microorganisms in the gut lumen
potentially can produce compounds or enzymes
that mediate these responses.
• For example, feeding by caterpillars of
Spodoptera exigua (beet armyworm) results in
the release of N-acyl-amino acids that potentially
function in emulsifying food for digestion but
that also trigger plants to produce volatiles that in
turn attract natural enemies (Alborn et al., 1997).
• Microbacterium arborescens isolated from
beet armyworm foreguts was found to
produce an N-acyl amino acid hydrolase that
breaks down these defense elicitors
potentially affecting nutrient availability by
releasing amino acids and also potentially
impacting plant defense responses
Beet armyworm

19. • In 2017, researchers discovered that
the oriental fruit fly (Bactrocera
dorsalis) had developed resistance to
the insecticide trichlorphon thanks to
a species of symbiotic bacteria,
Citrobacter freundii, in its gut that
helps the fly degrade the chemical
Bactrocera dorsalis