Sterols are amphipathic lipids based on the steroid ring structure but with a polar hydroxyl (OH group) on one of the 6-membered rings. They are also known as steroid alcohols, ex. cholesterol. They are generated in living systems from acetyl-coA by the HMG-CoA reductase pathway.

1. NEW ASPECTS OF STEROLS IN
PLANT INSECT INTERACTION
Submitted By:-
Hemlata
Ph.D scholar
Deptt. of Entomology

2. What are Sterols???
 Sterols are amphipathic lipids based on the steroid ring
structure but with a polar hydroxyl (OH group) on one of
the 6-membered rings.
 They are also known as steroid alcohols, ex. cholesterol.
 They are generated in living systems from acetyl-coA by the
HMG-CoA reductase pathway.

3. STEROLS
 Sterols can occur in plants in the 'free' state, because the
sterol hydroxyl group is not linked to any other moiety.
 They are usually present also as conjugates with the
hydroxyl group covalently bound.
 Example -sterol esters, acyl steryl glycosides and steryl
glycosides.

4. STEROLS
• Cholesterol occurs as a component of plant membranes and
as part of the surface lipids of leaves which is the major
sterol. Sterols of plants are called phytosterols (Nes & Mc
kean ,1977). The most important phytosterols include:
 Campesterol
 Sitosterol
 Stigmasterol

5. • The most common sterols present in the plant and animals is
Cholesterol.
• Cholesterol is the most abundant sterol recovered from most
insects which feeding on plants ( Behmer and Nes,2003)
• Most insects have an absolute requirement for cholesterol as
the precursor for ecdysteroid synthesis (Grieneisen,1994).
CHOLESTEROL

7. • Campesterol is the precursor of 70 polyhydroxy steroids
that occur in small amounts which act as growth hormones.
• They are collectively named brassinosteroids, including
brassinolide were first detected in Brassica sp.
• They have crucial importance -
 Plant growth processes -cell elongation, division,
differentiation, immunity. (Mandava,1988)
CAMPESTEROL

8. Development of reproductive organs (regulation of
innumerable genes).
They are also signalling molecules in stress
responses against bacterial pathogens.

9. • β-sitosterol and stigmasterol have a major role in
maintaining the structure and function of cell membranes.
(Schaller,2004)
• Stigmasterol and cholesterol regulate the activity of the
Na+/K+-ATPase in plant cells, probably in a manner
analogous to that of cholesterol in animal cells.
• Stigmasterol may be required specifically for cell
differentiation and proliferation.
β-sitosterol and Stigmasterol

10. FUNCTIONS OF STEROLS
Sterols serve three critical functions in insects:
 As structural components in the phospholipid bilayer of the
membranes of cells and organelles.( Behmer & Nes,2003)
 As a precursors for many hormones (e.g. 20-OH ecdysone).
(Gilbert & Warren, 2005 )
 As a molecule that regulates organismal growth and
patterning via the Hedgehog (Hh) signaling
pathway.(Cooper et.al,2003)

11. PLANT-INSECT INTERACTION
• Insects lack the capacity to synthesise steroid. (Behmer &
Nes, 2003; Grieneisen, 1994)
• They depend on exogenous sources of sterols (Clark and
Bloch, 1959).
• Sterols are required as membrane components.
• Insects generally acquire sterols from two main sources:
parental loading during oogenesis and food.

12. PLANT-INSECT INTERACTION
• In most insects, 20-hydroxyecdysone (20E) is the major
moulting hormone & cholesterol is the required precursor.
 The plant-feeding heteropterans, leaf-cutting ants, and
honeybees, use the ecdysteroid makisterone as their
moulting hormone. (Lafont et.al ,2005)
 These insects have lost the ability to dealkylate phytosterols.

13. Metabolic pathways by which plant sterols are changed to cholesterol and the molting hormones in
phytophagous insects

14.  They directly convert-
Campesterol into Makisterone A (which has a methyl at
the C24 position)
Sitosterol into Makisterone C (which has an ethyl at the
C24 position).

15. • Aphids generally convert sitosterol to
cholesterol at a rate of 40%. (Campbell et.al
1983)
 The aphid M. persicae has extremely low
survival rates and reproductive output on
tobacco plants containing phloem-mobile
ketonesteroids.
 The ketonesteroids may interfere with
cholesterol uptake from the insect gut lumen.
 They may become inserted into cell
membranes and disrupt membrane function.
(Nes et.al.1997)
APHIDS

16. • The phloem sap of fava bean (Vicia faba) plants utilized by the
pea aphid Acyrthosiphon pisum contains three sterols,
cholesterol, stigmasterol and sitosterol. (Bouvaine et.al,2012 )
 Larval growth rate and aphid lifespan did not vary significantly
across the diets.
 Their is a shortfall in dietary sterol over at least one generation.
 The reproductive output was depressed lifetime in aphids on
diets containing stigmasterol or no sterol, relative to diets
supplemented with cholesterol or sitosterol.

17. • The seven spotted lady beetle (Coccinella
septempunctata) grew and developed
normally on an all-prey diet. (Ugine et al.
2019)
 It may suffered a complete loss of fitness
(spermatogenic failure).
 They feeding exclusively on pea aphids,
which have very low tissue sterol content.
 There fitness was restored by feeding on
plants or eating phytosterols or
cholesterol.
SEVEN SPOTTED LADY BEETLE

18. SILKWORM
• The silkworm Bombyx mori, a phytophagous
insect, feeds on mulberry leaves or can be
fed an artificial diet.
• The diet of the silkworm typically lacks Chl,
but contains phytosterols. (Nagata &
Nagasawa,2011)
• Once phytosterols reach the midgut, they are
absorbed in the epithelial cells and converted
into desmosterol through several enzymatic
reaction steps;

19.  Chl is finally obtained via the conversion of
desmosterol by 3β-hydroxysteroid-Δ24
reductase . (Svoboda, 1999)
• From the midgut cell to the hemolymph,
 Chl is transferred to a major insect
lipoprotein, lipophorin (Lp), which has
high- and low-density lipoproteins. (Chino
& Downer,1982)
 Chl, Lp transports other lipids, fatty acids,
diglyceride, and a small amount of
phytosterols .(Miura & Shimizu,1988)

20.  As major dietary sterols, phytosterols (β-
sitosterol, campesterol, stigmasterol) are
detected from Lp in the silkworm.
• Insect tissues incorporate sterols from Lp
and maintain sterol homeostasis, the
disruption of which causes severe
damage.
• Brain and prothoracic glands are known to
be Chl-rich tissues.
• Disruption of sterol homeostasis in these
tissues causes their malfunctioning, and
subsequent fatality (Behmer,2017).

21. HONEY BEE
• Drosophila pachea, a specialist on the
senita cactus (Lophocereus schottii).
(Lang et.al. 2012)
• This food resource is rich in
lathosterol.
• It serves as the precursor for the
ecdysteroid that drives moulting in
D. Pachea.
• D. pachea’s close relative Drosophila
melanogaster, which uses cholesterol.

22. • The first molt of Drosophila neonates
reared on diets that lack dietary
sterols. (Voght et.al. 2007)
• There is a insufficient cholesterol
ingestion during larval stages
• They affect oogenesis and lead to
reduced fecundity. (Behmer
&Grebenok , 1998)

23. • Sitosterol supported the growth of the
locusts as well as did cholesterol.
• The [4-14C]cholest-4-en-3-one and [4-
14C]cholesta-4,6-dien-3-one were given
to insects in mixture of [1α,2α-
3H]cholesterol.
• These putative precursors were increase in
ecdysteroid titre in fifth instar and
maturing adult female S. gregaria. (Dinan
and Rees, 1981).
LOCUSTS

24. CONCLUSION
•Sterols are precursors of many hormones.
•To develop agro-economically transgenic plants that contain sterol
profiles that used to manage insect herbivore pests.
•By knowing sterol nutritional requirements and constraints as a novel
and potentially powerful approach to manage insect pests in agricultural
systems.

25. THANK YOU