3. Introduction
• Bacteria and insects have evolved together- mutualistic &
parasitically for some 250 million years.
• Symbiotic relationships are an important motor for
organisms diversification and evolution.
• The relationships have provided with lot of surprising
physiological and ecological adaptations.
5. What are endosymbionts ???
The term symbiosis refers to a permanent association
between two or more distinct individuals, called
symbionts, at least during a part of their life cycle.
The organisms which live inside the cell of the other
are called endosymbionts.
Symbiotic relationship can exist at various levels:
between prokaryotes and eukaryotes, between
unicellular and multicellular organisms etc.
6. The symbiotic associations can be grouped as
Mutualism
Commensalism
Parasitism
with respect to the effect of that symbiont on the
host.
7. Roles of endosymbiont’s in insects
Degradation
of pesticdes
Change plant host
physiology to benefit
insect host
Expanding host Range
Help in insect survival
Eg: production of defence
compounds
Degradation of
complex materials
inside gut
Nutrition to insect Eg: Aphids
Change of sex,
parthenogensis
8. Insect endosymbionts….
Insects have intra and extra-cellular relationships with
virus, bacteria, yeasts and reckettsia.
Intracellular endosymbionts are found in Anoplura,
Mallophaga, Isoptera, Orthoptera, Homoptera, Coleoptera,
Diptera and Hymenoptera.
They provide their hosts with specific nutritional
compounds that are important for their survival and
development.
Others can cause severe effects on various biological
functions of their insect partner (Feldhaar and Gross, 2009).
9. Buchnera aphidicola endosymbiotic bacteria of the pea
aphid, Acyrthosiphon pisum, synthesize essential amino
acids that the aphids cannot receive from the plant sap.
10. Wigglesworthia glossinidia endosymbionts of tsetse flies
(Glossina morsitans) produce essential vitamins that are
not present in the vertebrate blood meal (Aksoy and Rio,
2005)
11. In rice weevil Sitophilus oryzae , elimination of
endosymbionts Wolbachia impairs many physiological
traits including flight.
12. They are co-evolved…..
Insects have co-evolved with their primary
endosymbionts for several million years; therefore
their relationship is obligate.
This means that insects lacking their bacteria are
unable to grow and reproduce while the symbiotic
bacteria are not viable in the absence of their host
(Kikuchi, 2009).
14. 1. Horizontal transmission
• Unlike other endosymbionts, gut
microbes are horizontally
transmitted between insects
• Insects don’t inherit gut microbes
from their parents, but they should
acquire them throughout their
lives.
• Eg: termites -trophallaxis:
Microorganisms are removed
during molting processes
Can acquire them again through
trophollaxis.
15. 2. Vertical transmission
microbes and endoparasites, extracellular and• Unlike gut
intracellular endosymbionts are vertically transmitted
generation after generation; that is, the insect inherits
them from its parent
Brown winged stinkbug
Plautia stali
17. Where do they exist ????
A. Primary endosymbionts
are mainly found in bacteriocytes, which are
specialized cells that provide nutrients to the bacteria
and they are contained within the bacteriome.
18. A. Secondary endosymbionts
can be transmitted horizontally, vertically or via the
environment. These are commensal bacteria that have
evolved symbiotic relationships with their hosts more
recently and can be found in the haemocoel.
For example, Sodalis glossinidius
bacteria are secondary symbionts
the tsetse fly, which are maternally
transmitted to the progeny and can be
found inter- and intra-cellularly in
various tissues of the fly.
Sodalis was the first insect endosymbiont that was reported
to be successfully isolated and cultured in vitro.
19. In diptera endosymbionts are found in testes, ovaries,
pole cells, nurse cells and gut wall cells.
Different types of endosymbionts are presents in
different parts of insects like gut, malpighian tubules,
fat body, gonads etc.
20. The most commonly found facultative endosymbiotic
bacteria in insects are Wolbachia and Spiroplasma.
Wolbachia is a group of
maternally transmitted,
intracellular alpha-proteobacteria.
Infect a wide range of insects
as well as filarial nematodes.
First discovered in 1924 in
insects; largely unknown until the 1990s (Evade
detection).
21. Scientific classification
Domain: Bacteria
Phylum: Proteobacteria
Class: Alphaproteobacteria
Subclass: Rickettsidae
Order: Rickettsiales
Family: Rickettsiaceae
Genus: Wolbachia
Species
i. Wolbachia melophagi (Noller, 1917) Philip,1956
ii. Wolbachia persica Suitor and Weiss, 1961
iii. Wolbachia pipientis Hertig, 1936
22. It is one of the world's most common parasitic microbes
and the most common reproductive parasite in
the biosphere.
Its interactions with its hosts are often complex, and in
some cases have evolved to be mutualistic rather
than parasitic.
Some host species cannot reproduce, or even survive,
without Wolbachia infection.
Studies have concluded that >16%of neotropical insect
species carry Wolbachia and 25 to 70 % of all insect
species are estimated to be potential hosts.
23. Diversity
Infects over 1 million
species of insects and
other invertebrates!
Google images
Google images
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25. Wolbachia are found in the reproductive tissues of
their hosts, exerts a population control and hence
i. A force in speciaton in insects
ii. Possibility for the evolution of insects
Insect eggs containing Wolbachia Wolbachia infested insect ovaries
26. Mechanisms involved
These symbionts are able to manipulate the reproductive
properties of their insect hosts by inducing
i. Cytoplasmic incompatibility
ii. Parthenogenesis
iii. Feminization
iv. Male-killing
28. If both males and females insects are infected then progeny
will be infected,
If female is infected and male is not infected. The progeny
will all be infected.
If the females is not infected and male is infected there will
not be any progeny.
29. II. Thelytoky - Parthenogenesis
In Trichogramma wasps.
Haplodiploid condition with males haploid and
females diploid.
Virgin females produce diploid females without
fertilization.
The hapoid (n) is converted into dipoid (2n).
This occurs early in the first mitotic division.
30. III. Feminization
In isopods.
Suppression of androgenic
glands.
Cause males to become
functional females.
31. IV. Male killing mechanism
Studied in two species of insects.
Adalia bipunctata Acraea encedon
32. In Adalia bipunctata and Acraea encedon the
pressence of Wolbachia halves the hatch size and
changes female/male ratio.
Treatement with antibiotics like rifampin and
sulphamethoxazole hatch size returns to normal and
with the normal sex ratio.
The conditions can be artificially induced by injection
of macerated infected insect into pupae of uninfected.
33. Why male killing ???
Reduces competition for food.
Reduces cannibalism in siblings.
Improve female fitness for breeding-selective
advantage.
Insures propagation of Wolbachia endosymbionts to
future generations.
34. Wolbachia – Evidence for specificity
of infection
PCR for 16sRNA from infected lines.
Product is purified and ligated
into pGEM vector.
39/42 positive for Wolbachia
not other bacteria
Transformants are recognised by blue
colour on agar plate
35. Mutualistic bacterium Buchnera, have a great role in
supplying,
• Essential amino acids that plant saps lack (Except
Tryptophan)
• Nitrogen recycling inside gut (Douglas, 1993)
• Lipid and sterol nutrition of aphids (Douglas, 1998)
• Vitamin provision (Vitamin C and B) (Dadd et al., 1967)
• Resistance of aphids to insecticides (Amiressami and
Petzold, 1976)
36. Herbivore oral secretions andmicroorganisms
• Herbivorous insects typically produce oral
secretions that interact with food plants -
stimulating or suppressing plant defense
responses.
• Microorganisms in the gut lumen potentially can
produce compounds or enzymes that mediate
these responses.
• Eg: Spodoptera exigua (beet armyworm):
release of N-acyl-amino acids
• Emulsifying food for
• Trigger plants to produce volatiles that in
turn attract natural enemies
• Microbacterium arborescens isolated from
beet armyworm foreguts - produce an N-acyl
amino acid hydrolase ,
• Breaks down these defense elicitors affecting
nutrient availability by releasing amino acids
• Impacting plant defense responses
Beet armyworm
(Alborn et al., 1997)
37. In 2017, researchers discovered that the
oriental fruit fly (Bactrocera dorsalis)
had developed resistance to the
insecticide trichlorphon - a species of
symbiotic bacteria, Citrobacter
freundii, in its gut that helps the fly
degrade the chemical
Bactrocera dorsalis
38. Conclusions
Further study of this endosymbionts will enhance our
understanding of,
Evolutionary entomology
Nematode symbiont coeveolution
Other biological systems
Targeting them for biocontrol
Disease eradication by endosymbionts will have huge
economic and medical benefits.
