Transcript Mansoura university Chemical control of insects For 4th year undergraduate students Chemistry/Entomology by Dr. Zeinab Shaaban Abo-Elnaga •Entomology 2008 Zoology Department, Faculty of Science [email protected] http://zaboelnaga.synthasit e.com.

Mansoura university
Chemical control of insects
For
4th year undergraduate students
Chemistry/Entomology
by
Dr. Zeinab Shaaban Abo-Elnaga
•Entomology 2008
Zoology Department, Faculty of Science
[email protected]
http://zaboelnaga.synthasit e.com
Chemical control of insects
Insecticides what dose it means?
Do you mined all the insects can considered as a
pest?
What is a pest?
Pest status depends on Population levels and Economic factors
Some pest management terms:
1.
Equilibrium position (EP)
The average density of a potential pest on a specific host (or crop).
(The “normal” population level which Varies above and below a mean level)
2.
Economic threshold (ET)
The population or damage level of a pest that serves as a warning of coming problems
(The Signal that it is time to “do something”)
3.
Economic Injury level (EIL)
The level of damage, or potential damage, that is equal to the Cost of Control
(The level of damage that justifies Control)
• Some Insects are never pests their Equilibrium position (EP) is
always below the economic
threshold (ET)
• Some Insects are occasional pests and must be controlled at ET or they
will reach EIL
• Some Insects are regular and
serious pests Equilibrium position
(EP) is always above EIL
1.
2.
3.
4.
Agriculture (crop) pests
Stored product pests
Medical pests
Veterinary pests
All of these harnful
insects should be
controlled
insect control:
refers to the regulation or management of a species defined
as a pest, usually because it is perceived to be detrimental
to a person's health, the ecology or the economy.
Mechanical
devices
• IntegratedPest Management
(IPM) is a pest control strategy
that uses an array of
complementary methods:
mechanical devices, physical
devices, genetic, biological,
legal, cultural management,
and chemical management.
Physical
devices
Genetic
IPM
biological
Cultural
management
•
Chemical
management
insecticides
What is the first word that comes to
mind when you hear the word
insecticide?
insecticides
• An insecticide is a pesticide
used against insects in all
developmental forms. They
include ovicides and larvicides
used against the eggs and
larvae of insects respectively.
• Insecticides are used in
agriculture, medicine,
industry and the household.
Chemical control of insects
insecticides
chemical
natural
Classes of the chemical insecticides
Heavy metals
Inorganic
Chemical
Synthetic
Lead, mercury,
arsenic
Miscellaneous &
Organochlorine
compounds
organic
Organophosphorus
& Carbamates
Inorganic insecticides (Lead, mercury, arsenic)
• Inorganic insecticides are manufactured with metals and include arsenates copper- and
fluorine compounds, which are now seldom used, and sulfur, which is commonly used.
•The earliest method for insect control using chemicals
• Copper aceo-arsenite Cu4(CH3COO)2(AsO2)2
• Successfully employed in the USA (1864) for the control of Colorado beetle on potatoes.
• In view of the high intrinsic mammalian toxicity of lead, preparations containing calcium
arsenates are often preferred because environmental pollution by lead presents a serious problem
• Now due to high poisonous nature of arsenites , it has been banned, but where long-term
residual insecticidal activity is needed to protect fruit trees against chewing insects; lead arsenate
is still used to limited extent.
• Inorganic compounds of arsenic, such as lead
arsenate, have long been used against insect
pests.
However, these materials
are highly toxic to non-target organisms and
persist in the environment. (Years after apple
growers stopped using lead arsenate, high
concentrations of lead can still be found in
orchard soils.)
Inorganic
insecticides
Synthetic insecticides (organic)
•
Organic insecticides are synthetic chemicals which comprise the largest numbers of pesticides available
for use today.
1. Miscellaneous Compounds:
A.Dinitrophenols :
•Dinitrophenols and their derivatives are very versatile pesticides
OH
1
NO2
2
6
3
5
4
•in tests against the eggs of the purple thorn moth, phenol and
NO2
cresols were found to be toxic, and the activity was progressively
Dinitrophenol
increased by the introduction of two nitro groups in the molecule,
but further nitration reduced activity.
OH
CH3
•This led to the development of 4,6-dinitro-o-cresol (DNOC) or 2methyl-4,6-dinitrophenol, (R=CH3)
cresol
R
B. Organic thiocyanates:
CH3
•Isobornyl thiocyanate (Thanite) and terpene isoborneol, both are used
OH
currently as insecticides, mainly in fly sprays (specific).
•The activity is due to possessed the optimum oil/water solubility
balance for penetration of the insect cuticle
•The insecticidal properties of thiocyanates have not been fully
terpene isoborneol
exploited probably because of the dramatic successes achieved by the
organochlorine insecticides such as DDT.
CH3
•The insecticidal thiocyanates possibly merit further investigation, they
O
OC CH2SCN
are rapid-acting compounds against flying insects ,they also show
ovicidal activity against a number of insect eggs.
Thanite
Organochlorine insecticides
(DDT, Dieldrin, Lindane)
•The most important member of this group of insecticides is dichloro diphenyl tri-chloroethane
or DDT.
•The first preparation of DDT is by Zeidler (1874) but its powerful insecticidal properties were
not discovered until 1939 by Müller of the Swiss Geigy Company
•DDT was the first of a long line of insecticides
•Pure DDT can be obtained as a white powder
based on hydrocarbons with chlorine atoms
m.p. 108⁰C by recrystallization from ethanol.
replacing some of the hydrogen atoms. Its chemical
•However the increased cost involved in
name is dichloro, diphenyl, trichloroethane (see
purification is only when DDT is used for special
figure).
purposes.
•The general symptoms of DDT poisoning in
insects are violent tremors, loss of movement
followed by convulsions and death, clearly
indicating the DDT acts on the nervous system.
Advantage of
DDT
•DDT was introduced during World War II and, along with penicillin and the sulfa drugs,
during this period it has a medical history, by decreasing the rate of death from malaria,Plague
and yellow fever.
•The benefits to mankind from the use of organochlorine insecticides have been tremendous
and DDT has become the most widely used insecticide in the world, the annual production
was more than 100,000 tons in the late 1950s
•The main advantage of DDT appeared to be its stability, persistence of insecticidal action,
cheapness of manufacture, low mammalian toxicity (LD50 (oral) rats 300mg/kg).
•DDT kills a wide variety of insects , including domestic insects and mosquitoes, but it is not
very effective against mites and does not act nearly as rapidly on flying insects as pyrethrum
or thiocyanates.
Drawbacks of DDT
•DDT was formerly used to control flies in milking sheds but it was found in the milk so it is
now banned in most countries for this purpose.
•– Accumulates in food chain
•By 1950, a number of examples of DDT-resistant strains of insects and this problems
raised and become serious.
•Causes thin egg shells in birds
•
– DDT is stable and fat soluble. These properties cause it to accumulate in fat tissue. People
who were heavily exposed to DDT (during its manufacture or application) often showed
concentrations of DDT in their fat 1000 times higher than that in their blood.
•– Kills all insects, including off their natural enemies.
•– Spreads in the environment
•– Dangerous to handle
Chemical control of insects
Organophosphates
•The organophosphates, e.g., parathion (right), are related to
the nerve gases developed during World War II (by Gerhard
schrader in Germany .
•They react irreversibly with the enzyme acetylcholinesterase,
which is responsible for inactivating acetylcholine (ACh) at
neuromuscular junctions and at certain synapses in the central
and peripheral nervous systems.
•These synthetic insecticides contains phosphorus in their
molecules and act as surface active poisons
•Some other examples:
•malathion , diazinon , phosmet (Imidan®) , hlorpyrifos
(Lorsban®)
Parathion
(C10H14NO3PS)
•
Pure parathion is a pale yellow liquid with an
odor of garlic, slightly soluble in water and
rapidly hydrolysis in alkali solution
•
Its highly toxic to both insects and mammals.
•
Symptoms of parathion poisoning are headache,
nausea, and constriction of pupils.
•
Treatment or the antidote is Atropine.
•
Important for controlling the agriculture pests.
Mode of action of organophosphorus insecticides
•
It was inhibits the action of several enzymes, Specially against the
acetylcholinestrase enzyme
•
This controls the hydrolysis of the acetylcholine , generated at nerve junctions,
into choline
•
In the absence of effective acetylcholinesterase, the liberated acetylcholine
accumulates and prevents the smooth transmission of nerveous impulses across the
synaptic gap at nerve junctions
•
This causes loss of muscular coordination, convulsions, and ultimately death .
•
This enzyme is an essential component of the nervous systems of both insects and
mammals so, the basic mechanism of toxic action is the same.
Mechanism of toxic action of Organophosphorus
O
(CH3)3 N+- CH2-CH2-O
C
H
CH3
:O:
(a) acetylcholinestterase
H2O:
(CH3)3N+-CH2-CH2
OH
C
O
Fast reaction with water
(b)
H
O
+
regenerated enzyme
(CH3) NCH2 CH2 0H + CH3 CO2H
CH3
•a): depicts the formation of the initial enzyme-substrate
complex by the orientation of the active centers of
acetylcholinesterase to the substrate (acetylcholine).
 Acetylcholine is extremely toxic to mammals and to
certain insects.
•b): shows formation of the acetylated enzyme, which is
subsequently rapidly hydrolysed to choline and acetic
acid leaving the enzyme with both active sites intact,
so permitting it to repeat the enzymic hydrolytic process
on further substrate molecules .
 The early organophosphorus insecticides like parathion, schradan, and
tetraethylpyrophosphate (TEPP) were highly active compounds but were also
extremely toxic to mammals. They the most dangerous to be used in agriculture
They have caused several human fatalities and any birds or small mammals
covered by the spray are killed . However, they are comparatively rapidly
biodegradable to non-toxic, water-soluble compounds which are quickly
excreted by animals. Consequently, unlike the Organochlorine insecticides .
Chemical control of insects
Carbamates
 the
successful
development
of
organophosphorus
insecticides stimulated examination of other compounds
known to possess anticholinesterase activity.
NH2
 Carbamates, or urethanes, are a group of organic
compounds sharing a common functional group with the
HO
O
general structure -NH(CO)O-. Carbamates are esters of
carbamic acid, NH2COOH, an unstable compound. Since
carbamic acid contains a nitrogen attached to a carboxyl
group, it is also an amide.
Carbamic acid
A group of insecticides also contains the carbamate functional group, for
example, Aldicarb, Carbofuran, Furadan, Fenoxycarb, Carbaryl, Sevin,
Ethienocarb, and 2-(1-Methylpropyl) phenyl N-methylcarbamate.
These insecticides can cause cholinesterase inhibition poisoning by reversibly
inactivating the enzyme acetylcholinesterase. The organophosphate pesticides
also inhibit this enzyme, though irreversibly, and cause a more severe form of
cholinergic poisoning.
In addition, some carbamates are used in human pharmacotherapy,
for example, the cholinesterase inhibitors neostigmine and rivastigmine,
whose
chemical
physostigmine.
structure
is
based
on
the
natural
alkaloid
•The alkaloid Carbamates being quite strong bases are ionized in
aqueous solution and therefore have very low lipid solubility.
•They are unable to penetrate the ion-impermeable sheath
surrounding the insect nervous system. Therefore, efforts
were made to synthesize compounds of molecules was
attached to a less basic, more lipophilic moiety, since such
compounds should show greater insecticidal activity.
 Isolan
 (1-isopropyl-3-methylpyrazolyl-5-dimethyl-carbamate),
this water soluble compound was a most effective aphicide
CH3
4
3
O
5
N
2
N 1
OCN(CH3)2
and against houseflies, but showed a very high mammalian
toxicity (LD50 (oral) to rats ≈12 mg/kg) so, the compound was
not extensively developed.
CH(CH3)2
ISOLAN
 Sevin or Carbaryl
O
 phenol carbamates are especially useful in insecticides
OCNHCH3
 is a contact insecticide with slight systemic properties
and a broad spectrum of activity-effective against many
insect pests of fruit, vegetables, and cotton .
 used also for control of earthworms and other insect in
turf.
Carbaryl
Chemical control of insects
Resistance of insects
towards synthetic
insecticides
 Defined as the ability of a
given strain of insects to tolerate
doses of an insecticide which
would kill the majority of a
normal
population
insect species.
of
some
 Some of the best documented cases of insect resistance have been observed
with DDT and other persistent organochlorine , and organophosphorus
insecticides.
By 1946 some strains of DDT-resistant houseflies had been discovered and in
1950, 5 to 11 species had aquired tolerance to one or more insecticides. In 1969
there were 102 resistant insect species: 55 to DDT, 84 to dieldrin and 17 to
organophosphorus compounds.
 By 1974, over 250 species had become resistant to one or more insecticides.
 the inheritance of specific resistance is generally comparatively simple and often
monofactorial, although the influence of the principle gene may sometimes be
modified by 2ry genes.
Do you mined one insect can
show multiple resistance?
 Really, when different
resistance mechanisms exist
in a given insect, it is said to
show multiple resistance.
 This can be induced when
the insect population has
been exposed to different
insecticides.
How does the Resistance occurred?
 The various physiological resistance mechanisms are very important; in DDTresistant strains, tolerance is due to an abnormally high concentration of the
enzyme DDT-dehydrochlorinase which converts DDT to the non-insecticidal DDE
(DDT-dehydro-dichloro-etylene).
 Mechanisms associated with resistance to organophosphorus compounds are
more complex.
 They may be deactivated by enzymes-phosphatases, and carboxyesterases.
 So, the toxicity of the given compound depends on the balance of activeating
and deactivating enzymes within the insect.
 With malathion, for instance, the low mammalian toxicity is ascribed to
the higher carboxyesterase activity in mammals in comparison with the low
activity of this enzyme in susceptable insects .
 insects exhibiting resistance to malathion generally show no cross-
resistance to other insecticides, suggesting that tolerance depends on high
carboxyesterase activity.
 The resistance to organophosphates shown by several strains of
houseflies and blowflies is associated with exceptionally low levels of
aliesterase activity which is controlled by a single gene, whereas normally
houseflies have large quantities of an aliesterase.
Chemical control of insects
Natural
insecticidesd
Botanical
Hormones
&
Pheromones
Botanical insecticides

Plants combat insect attack by developing a number of
protective mechanisms, such as repellency, and insecticidal
action.
 Thus a large number of different plant species contain
natural insecticidal materials.

Natural insecticides, such as nicotine and pyrethrum,
are made by plants as defenses against insects. Nicotine
based insecticides have been barred in the U.S. since 2001 to
prevent residues from contaminating foods.

Chemicals extracted or derived from plants,
 Limited numbers of extractable chemicals have
performed well enough to have been made commercially
available
List of plant derived materials as insecticides
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Caffeine
Derris (rotenone)
Anabasine
Anethole (mosquito larvae)[3]
Annonin
Asimina (Pawpaw tree seeds) for lice
Azadirachtin
Carapa
Cinnamon leaf oil (very effective for killing mosquito larvae)[3]
Cinnamaldehyde (very effective for killing mosquito larvae)[4]
Cinnamyl acetate (kills mosquito larvae)[3]
Deguelin
Derris
Desmodium caudatum (leaves and roots)
Eugenol (mosquito larvae)[3]
Linalool
Myristicin
Neem (Azadirachtin)
Nicotiana rustica (Nicotine)
Peganum harmala, seeds (smoke from), root
Oregano oil kills beetles Rhizoppertha dominica[5] (bug found in stored cereal)
Polyketide
Pyrethrum
Quassia (South American plant genus)
Tetranortriterpenoid
Thymol (controls varroa mites in bee colonies)[6]
Nicotine
Extract and isolated from tobacco
plant
 water extract of the tobacco
plant were being used to kill
sucking insects on garden plants.
Nicotine the active compound
which is an alkaloid.
Extracted from the leaves and
roots of the plants by treatment
with aqueous alkali, followed by
steam distillation.
3
4
4'
5
3'
5'
2
N
1
2'
N1
Nicotine
CH3
 Nicotine may applied as a dust
Nicotine functions as a non-persistent contact insecticide against aphids,
capsids, leaf miner, codling moth, and thrips on a wide variety of crops.
 With high mammalian toxicity (LD50 (oral) ≈ 50 mg/kg).
 With lack of effectiveness in cold weather.
 Nicotine kills vertebrates because it mimics acetylcholine by combining
with the acetylcholine receptor at the neuromuscular junction causing
twitching, convulsions, and finally death.
 some researches improved that, a similar mode of action accounts where
nicotine blocks synapses associated with motor nerves.
Chemical control of insects
Rotenoids
These are a group of insecticidal compounds occurring in the roots of Derris
elliptica and a species of Lonchocarpus.
 Derris has been used as an insecticide for a long time, and recommended for
controling the caterpillars.
Derris dust is manufactured by grinding up the roots and mixing the powder
with a clay diluent.
Alternatively the rotenoids can be extracted from the powder roots with organic
solvents, by crystallization from ether or carbon tetrachloride gave rotenone
A white crystalline, lavorotatory solid.
 Rotenoids are toxic to fish and
CH3
H2C
many insects, but are almost harmless
C
to most warm-blooded animals.
20
21
14
18
19O
 recently it used in horticulture
13
O
9
8
O
17
16
15
12
11
against aphids, caterpillars, sawflies,
10
wasps, wasps raspberry beetles, and
6
7
red spider.
1
5
O
 it
2
4
3
OCH3
was
extremely
safe
garden
insecticide because it is degraded by
light and air and does not leave
Rotenoids
OCH3
residues (LD50 (oral) to rats ≈ 135mg/kg).
Rotenoids biochemical mode of insecticidal action
The toxic action involves the inhibition of mitochondrial electron
transport, and in isolated mitochondria, rotenone inhibits oxidation linked
to NADH2, although at low concentrations succinate oxidation was not
affected.
 The inhibition of the electron transport chain appears to arise from the
binding of rotenone to a component of the chain, but NADH2
dehydrogenase is not inhibited.
The poisoning symptoms characterized by reduction of 02 consumption,
depressed respiration and heartbeat, and eventual paralysis.
Chemical control of insects
Pyrethroids
 Pyrethrum is a contact insecticide obtained from flower
heads of Chrysanthemum cinerariaefolium and used as
insecticide since ancient time.
 Pyrethrum owes its importance to the outstanding rapid
knockdown action (a few seconds) on flying insects
combined with a very low mammalian toxicity due to its
ready metabolism to non-toxic products.
 Not persistent, leaves no toxic residues and not tend to
induce the development of resistant insect populations.
 Pyrethrum used to control pests in the
stored food and against household and
idustrial pests.
 Pyrethrum
aerosol
sprays
are
excellent home insecticides because of
their safety and rapid action.
 However the major disadvantage of
pyrethrum, especially against agricultural
pests lies in its lack of persistence due to
its instability in the presence of air and
light.
 Pyrethrum obtained from the dried chrysanthemum flowers by extraction
with kerosene or ethylene dichloride and the then concentrated by vacuum
distillation.
 It contains four main insecticidal components which are collectively termed
pyrethrins
R
C
CH
H
H3C
H
CH3
H
H3C
Compound
R'
Pyrethrin 1 -CH=CH2
Pyrethrin 11 -CH=CH2
Cinerin 1
-CH3
Cinerin 11 -CH3
OC
O
CH3
CH2
R
-CH3
-CO2CH3
-CH3
-CO2CH3
O
CH=CH
R'
Synthetic Pyrethroids
• Alterations in the acid components yield a reduced degradation rate
compared to natural pyrethrins
• Often with additional modification to enhance synergistic action
•Several have been used in forestry, seed orchard or nursery work
– Permethrin
– Cypermethrin
– Esfenvalerate
– Lamda cyhalothrin
Chemical control of insects
More recent botanicals
(and similar ingredients)
and their origins
 Linalool and d-limonene
– citrus oil derivatives
 Neem
–
Azadirachta
spp. and Melia spp.
 Garlic oils
 Hot pepper oils
Azadirachta windbreak.
(E. Fernandez, http://www.css.cornell.edu/
ecf3/Web/new/AF/arid.html)
Modes of action, toxicity, and uses
Citrus
derivatives
Nerve cell
stimulants
Low
On pets, indoor
plants
Neem
Multiple actions,
ecdysone agonist
Very Low
(medicinal uses)
Many crop pests
Many labeled
uses, limited
positive data on
effectiveness
Garlic oil
?
Low
Hot pepper
extracts
?
Low
Chemical control of insects
Insect growth regulators
 Because they are enclosed in an exoskeleton, insects must "shed their skins", or molt, to
grow larger. The molting process in immatures and the transformation from larva to pupa to
adult is regulated by hormones.
 One is ecdysone (molting hormone) secreted by the prothoracic gland; it stimulates
shedding of the cuticle.
 Another is juvenile hormone (JH). JH is secreted from the corpora allata; it suppresses
adult characteristics. As growth during each stage triggers secretion of ecdysone, if juvenile
hormone is present, the cuticle is shed and replaced, and the insect reaches its next juvenile
stage.
 As the immature insect grows and eventually discontinues production of juvenile hormone,
secretion of ecdysone in the absence of JH triggers pupation and subsequent development of
adult form.
 Synthetic hormones that mimic JH and ecdysone have been developed for use as
insecticides that disrupt insect development and cause death.
Insect growth
regulators
 The insect cuticle is comprised in part
of chitin (N-acetyl-D-glucosamine), a
complex polymer that gives strength
and
flexibility
to
the
insect
as
chitin
exoskeleton.
 Compounds
identified
inhibitors also are considered to be
insect growth regulators and have been
developed as insecticides.
Insect growth regulators
 Compounds
that
interfere
with the function of juvenile
hormone
 Compounds
that
interfere
with the function of ecdysone
(molting hormone)
 Compounds
that
with chitin formation
interfere
Insect Growth Regulators (IGRs)
 These insecticides alter the growth and
development of insects.
 Act as Juvenile Hormone (JH) mimics
 Insect cannot molt into an adult
 Act as Chitin Synthesis Inhibitors
– Insect cannot produce the new exoskeleton
 Act on all insects, non-selective
Juvenile hormone
mimics
•
•
•
•
methoprene
hydroprene
kinoprene
pyriproxyfen
Pyriproxyfen
 Against an eclectic range of flies (including mosquitoes
and midges), beetles, scales, and whiteflies. Trade names
include Esteem, Knack, and Nemesis.
Chemical control of insects
Pheromones for direct control
 Removal trapping
 Mating disruption by imitating the sex
pheromone
 Very species specific
 Routinely used for monitoring
 Various mechanisms for release
 – (puffers, bands, microcapsule spray)
– Sustained release dispensers, sprayable
formulations, aerosol “puffers”
Course evaluation
 Please consider the following in your comments about the course.
Would you prefer weekly quizzes rather than the “practice quizzes?
Are the listed objectives helpful?
Are the study questions helpful?
Is the list of terms helpful? The glossary?
Are the video clips helpful or distracting?
What can I do to improve attendance?
Would you recommend the course to a friend? An enemy?
Did the course meet your needs?
Were the exams representative of material presented in the course?
Would you prefer to have a text book if available at reasonable cost?
Please list any suggestions for improving the course?
References
 Text book of “pesticides: Preparation and mode of action”. John Wiley and Sons, (1978), New
York. Brisbane. Toronto.
 Text book of “Fundamentals of applied entomology”. 3rd edition, by Robert E. Pfadt.
Macmillan publishing Co.,INC. New York, 1971.
See:
http://home.comcast.net/~john.kimball1/BiologyPages/I/InsectHormones.html
http://en.wikipedia.org/wiki/Pest_control
http://en.wikipedia.org/wiki/Pesticide
http://www.ulib.org.cn:8080/wiki/index.php/Chemical_Control_Of_Insects