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 Asian Journal of Biotechnology and Genetic Engineering

2(3): 1-18, 2019; Article no.AJBGE.53356

Natural Pesticides (Biopesticides) and Uses in Pest

Management- A Critical Review
Oguh C. E.1*, Okpaka C. O.2, Ubani C. S.1, Okekeaji U.3, Joseph P. S.4
and Amadi E. U.1
1
Department of Biochemistry, University of Nigeria, Nsukka, Enugu State, Nigeria.
2
Department of Experimental Pharmacology and Toxicology, University of Port Harcourt, Choba,
River State, Nigeria.
3
Department of Pharmaceutical Microbiology and Biotechnology, University of Nigeria, Nsukka,
Enugu State, Nigeria.
4
Department of Biochemistry, Ibrahim Badamasi Babangida University, Lapai, Niger State, Nigeria.

Authors’ contributions

This work was carried out in collaboration among all authors. Author OCE designed the study,
performed the statistical analysis and wrote the protocol. Author OCO wrote the first draft of the
manuscript. Authors UCS and OU managed the analyses of the study. Authors JPS and AEU
managed the literature searches. All authors read and approved the final manuscript.

Article Information

Editor(s):
(1) Dr. Fatima Lizeth Gandarilla-Pacheco, Faculty of Biological Sciences (FCB), Universidad Autonoma de Nuevo Leon,
Mexico.
Reviewers:
(1) Isabel Bertolaccini, National University of the Littoral (Universidad Nacional del Litoral), Argentina.
(2) Bonaventure January, Mwalimu Julius K. Nyerere University of Agriculture and Technology, Tanzania.
Complete Peer review History: http://www.sdiarticle4.com/review-history/53356

Received 15 October 2019

Accepted 19 December 2019
Review Article
Published 25 December 2019

ABSTRACT

This paper focuses on new types of biopesticides, examine the specificity to harmful pests, and the
selectivity to beneficial animals. Many of the modern pesticides used today, persist in soil for years
and compound the store of toxins in the soil, air and water. The toxic build-up of these chemicals has
been shown to cause damage in animals, plants, human health and are not easily degradable in the
environment. Study has shown that some plants contain components that are toxic to insects and
pest called biopesticides or natural pesticides. Natural pesticides are pesticides made by organisms
usually for their own defense, or are derived from a natural source such as plant, animal, bacteria,
and certain mineral, use to control pest naturally with less effect or no effect. Examples of these
natural pesticides are Rotenone (Derris sp.), carboxin, fluroacetate, nicotine, neem (Azadiracta
_____________________________________________________________________________________________________

*Corresponding author: E-mail: collinsoguh@gmail.com;

 Oguh et al.; AJBGE, 2(3): 1-18, 2019; Article no.AJBGE.53356

indica), microbial pesticide Bacillus thuringiensis, and pyrethrins. Natural pesticides usually target
specific sites in the insect such as nervous system, resulting in knock-down, lack of coordination,
paralysis and death. Rotenone inhibits the transfer of electron from NADH to ubiquinone, it disrupts
energy metabolism by inhibition of the electron transport system (ETS) and blockage of ATP
synthesis in the mitochondria. Nicotine inhibits and compete with neurotransmitter by binding to
acetylcholine receptors at the nerve synapses and causing uncontrolled nerve discharge.
Fluoroacetate and carboxin inhibits the citric acid cycle by binding to aconitase and succinate
dehydrogenase respectively. Pyrethrin exerts their toxic effect by disrupting the sodium and
potassium ion exchange process, which interrupt the normal transmission of nerve impulses. Most
botanical pesticides shows their effect through contact, respiratory, or stomach poisons to the target
organism. Botanical pesticides are generally highly bio-degradable, and they become inactive within
hours or a few days and can easily be broken down by stomach acids in mammals, so toxicity to
humans and animals is very low to non-target organisms and are ecofriendly. Since they are also
very effective, natural pesticides should be the first choice for pest management, which in turn
reduces the bioavailability of metal and noxious effect in the environment. This review explains the
major natural pesticides, mechanism, mode of action and origin.

Keywords: Biopesticides; low-risk pesticide; mechanisms; pest management; selectivity.

ABBREVIATIONS pesticides [2]. The common natural pesticides

use are Neem, Bacillus thuringiensis (Bt),
ETS : Electron Transport System; Nicotine, Rotenone, Pyrethrins, Sabadilla,
ATP : Adenosine triphosphate; Fluoroacetate, carboxin, and Ryania.
Bt : Bacillus thuringiensis;
IRM : Intergrated resistance management; Plants and some microorganism produce many
IPM : Integrated Pest management; natural chemicals that they use for their own
DDT : Dichloro-diphenyl-trichloroethane; defense against insects and disease organisms.
PBO : Piperonyl butpxide. Natural pesticides for plants also are considered
to be those chemical made from natural
1. INTRODUCTION ingredients. People believe that natural
pesticides are always safe and more eco-friendly
During the past three decades, efforts have been than man-made or synthetic pesticides and while
made to reduce the exposure and human risk of this is mostly true but it is not always so for
pesticides, especially insecticides. There is great example, nicotine as a natural pesticide in
demand for selective and safe insecticides that tobacco leaves, and the highly addictive
spare natural enemies and non-target organisms. component of cigarette smoke, but it is much
Some conventional pesticides have been more toxic than most modern synthetic or man-
replaced by newer bio-rational (Biopesticides) or made pesticides. While some natural pesticides
"low risk" pesticides. Natural pesticides are are also toxic many are actually much safe and
pesticides that are made by other organisms more eco-friendly than synthetic pesticides.
usually for their own defense, or are derived from Since natural pesticides are also very effective, it
a natural source such as plant, animal, bacteria, should be the first choice for most home and
and certain mineral [1]. About 80% of pesticides farm pest control needs [3]. Chemicals assault or
applied enters various environmental resources enters the body at almost every hour of the day.
as a result of run-off, exposing animals, and They may come through air, food, products use
farmers as well as consumers of the agricultural on the body, and in drinking water. Toxic buildup
produce to severe health problem. Natural of these chemicals has been shown to cause
pesticides or “reduced risk” pesticides are natural several damage in the body and minimize health.
compounds that effectively control insect pests, Many modern pesticides (synthetic) used persist
with low toxicity to nontarget organisms such as in soil for years and compound the store of toxins
humans, animals and natural enemies and the such as heavy metals in the soil, air and water
environment. Most of natural pesticides break [4,1].
down very quickly in sunlight so they should be
stored in darkness for effectiveness. Both highly Natural pesticides are not products of chemical
alkaline and highly acid conditions speed up engineering and are return to the environment
degradation or break down these type of with less impact and reduced danger. Pesticides

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for organic gardens must meet certain criteria set environmental factors that promote to the pests
forth by the United States Department of and their ability to thrive are ideal options [9].
Agriculture (USDA) and bear a logo stating they While the term pesticide is now often associated
are certified for use. The benefits of using with synthetic chemical compounds, it was not
organic or natural pesticides for plants are their until relatively recently that synthetic pesticides
specific target range, a slow mode of action, came into use. Naturally occurring compounds or
shorter persistence, low residue levels and safe natural extracts have been used as pesticides
use than conventional or synthetic pesticides [5]. since ancient times. The earliest pesticides were
These attributes are a win-win for consumers most likely salt, sulfurous rock, and extracts of
and the earth alike, but strict attention to time tobacco, red pepper, and the like. The
and mode of application and the precautions napoleonic army used crushed chrysanthemums
have to be strictly followed. That doesn’t mean to control lice, with limited effectiveness [10].
they are free from chemicals, just that the
chemicals are derived from botanical and mineral Natural insecticides can be chemical, mineral,
sources. They must still be used carefully, but the extract or biological. The common goal of all
chemicals break down more quickly than these is to kill, repel, or otherwise interfere with
commercial sources and are deemed less the damaging behavior of insect pests. Because
threatening [6]. this purpose corresponds with the legal definition
of a pesticide, all-natural insecticide products
The recognized categories of bio-rational must comply with federal and state regulations
pesticides may be synthetic or natural for registration, sales, transport, use, storage,
compounds of microbial, plant protectant and and disposal. Some natural insecticides are
biochemical (pheromones, hormones, natural allowed for use in certified organic systems if
growth regulators and enzymes) origins. Most additional organic federal standards are met [11].
biopesticides are nerve poisons acting at specific However, it is advisable to read the label of each
target sites in the insect's nervous system. Some product for specific application instructions. Many
pesticides act similarly to the old nerve poisons of the products described may also be used in
that result in knock-down, rapid intoxication, lack commercial crop production, but do not represent
of coordination, paralysis and death, and have the entire list available to commercial growers.
higher affinity to insect receptors than to As with any pesticide, it is important to choose a
mammalian. The other pesticides affect specific natural insecticide that fits the situation in which
systems, such as the molting processes, you will use it. These products vary in their
metamorphosis and the pest endocrinology toxicity to non-target organisms such as fish and
system. Biopesticides are third-generation bees, as well as their effectiveness at controlling
pesticides that are environmentally friendly and specific insect pests. If used improperly, organic
closely resemble or are identical to chemicals insecticides can harm people and the
produced in nature. The examples of environment, so do not make the mistake of
biopesticides are the microbial pesticide Bacillus thinking that products labelled as “natural” are
thuringiensis (Kurstaki), Most of the biopesticides non-toxic. There is a great effort to reduce the
show effectiveness against different strains of risk of human exposure to pesticides and special
resistant species, with no evidence of cross- demand for safe and more selective pesticides
resistance; hence these can play an important for natural enemies and non-target organisms.
role in integrated resistance management (IRM)
strategies [7]. 1.1 Definition of Terms

Most of the newer biopesticides are preferable to 1.1.1 Pest

the conventional pesticides because of their
specificity to target pests, effectiveness at low Pest is any harmful, destructive, or troublesome
rates, selectivity to beneficial insects and their animal, plant or microorganism.
non-persistent characteristics in the environment.
However, they are an alternative to the use of 1.1.2 Pesticides
conventional pesticides such as
organophosphates, organochlorine, Pesticides are chemical substance use to kill or
organosulphur, carbamates and pyrethroids [8]. retard the growth of pests that damage or
However, insect control using integrated pest interfere with the growth of crops, shrubs, trees,
management (IPM) means by use of several timber and other vegetation desired by humans.
techniques to reduce the favorable Practically all chemical pesticides, however, are

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poisons and pose a long-term danger to the necessary to understand how the pests’ targeted
environment and humans through their systems normally function. It is also helpful to
persistence in nature or body tissue. Most of the understand how human systems function in order
pesticides are non-specific and may kill life forms to know similarities and differences between
that are harmless or useful [12]. Pesticides are humans and the pests we try to control. It is also
classified in three ways generally: Based on very important to understand the modes of action
chemical structures, According to their mode of of the pesticides we use is to prevent the
action and According to their mode of entry i.e. development of pesticide resistance in the target
ingestion, inhalation, contact absorption. pest(s). Using pesticides with same mode of
action contributes to this problem by killing the
1.1.3 Natural pesticides susceptible pests and leaving only those with
resistance to the entire class of pesticides that
Natural pesticides are naturally occurring work through similar mechanisms [15].
chemicals extracted from plants. Natural
pesticide products are available as an alternative 2. SCOPE OF BIOPESTICIDES
to synthetic chemical formulations but they are
not necessarily less toxic to humans. Some Efforts is been made to find biopesticides with
deadly, fast-acting toxins and potent carcinogens novel mechanism of action and have no cross-
occur naturally [13]. resistance with the old pesticides. Biopesticides
are a distinct group of pesticides which is
1.1.4 Pest management different from conventional pesticides. They are
comprised of two major categories, which are the
Pest management is a means of reducing pest biochemical pest control agents (e.g.,
numbers to an acceptable or economical pheromones, hormones, natural plant growth
threshold. While IPM is a developed method or regulators and enzymes) and the microbial pest
ways use to control pests without relying solely control agents (e.g., microorganisms). Pesticides
on pesticides. The IPM is a systematic plan to be included in these categories must be
which brings together different pest control naturally occurring, or if man synthesizes the
tactics into one program. Management does not chemical, and then it must be structurally safe
mean eradicating pest. It means finding tactics and identical to a naturally occurring chemical.
that are effective and economical, and that keep Minor differences between the stereochemical
environmental damage to a minimum level. isomer ratios (found in the naturally occurring
compound compared to the synthetic compound)
1.1.5 Selectivity will normally not rule out a chemical being
classified as a biopesticides unless an isomer is
Selectivity is the use of pesticides to kill pests but found to have significantly different toxicological
not affecting their natural enemies. Or are a type properties from those of another isomer. Thus,
of pesticide that target a specific pest species. the application of active toxic biopesticides
agents as an alternative control strategy results
1.1.6 Mode of action in an urge to look for environment-friendly,
biodegradable and easily available at affordable
The mode of action or mechanism of action of prices products for pests control.
pesticide is how the pesticide works. In other
words, it is how the specific systems in the pest 2.1 Uses of Biopesticides
are affected by the pesticide. Mode of action
refers to the specific biochemical interaction Biopesticides give better control than
through which a pesticide produces its effect on conventional pesticides such as organochlorine,
the pest. Usually, the mode of action includes the biopessticides are usually a narrow spectrum of
specific enzyme, protein, or biological step activity; are cheaper, less toxic to workers or
affected. While most other classifications are the consumers; usually true to type, safer for the
pests controlled, physical characteristics, or environment and for beneficial insects; and
chemical composition, mode of action specifically required for certified organic production
refers to which biological process the pesticide surroundings. Biopesticides may be applied
interrupts [14]. Knowing the mode of action is shortly before harvest without leaving excessive
integral for scientists to improve the quality and residues, are less persistence in the environment
sustainability of a product. To understand how and have reduced risks to non-target organisms.
pesticides work (their mode of action), it is They act very quickly in insect to stop feeding,

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 Oguh et al.; AJBGE, 2(3): 1-18, 2019; Article no.AJBGE.53356

they may not cause death for hours or days, but chrysanthemum plant and are effective on
they often cause immediate paralysis or flying insects and to flush out larvae and
cessation of pests feeding. Most biopesticides grubs. Chemicals extracted or derived from
insecticides may have low to moderate plants may be present and subsequently
mammalian toxicity. In the field, their rapid extracted from the plant material (a
degradation and action as stomach poisons constitutive chemical). It may be activated in
make them more selective in some instances for the plant as a response to insect activity
plant-feeding pest insects and less harmful to (inducible chemicals). Some are chemically
beneficial insects. Many biopesticide are not modified after extraction to enhance their
toxic to plants, however, it is always best to test a insecticidal properties.
new product on few plants first before applying
on a large scale [16,17].  Essential oil

2.2 Various Types of Natural Pesticides Some plants also produce essential oils in
specialized gland cells. Peppermint oil
The major categories of biopesticides include control of household pests such as
botanicals, microbials, essential oil and minerals cockroaches and ants. Clove oil inhibits soil-
based, many of these come from plants born fungal disease. Citrus oil control of flea,
themselves, insects, or naturally occurring aphid and mites. Lavender oil insect
minerals. Some of the more commonly used and repellent. Thyme oil, Rosemary oil and
effective natural pesticides are insect and mite Cedar oil.
growth regulators, Bacillus thuringiensis
(Kurstaki), horticultural oils, insecticidal soaps, 3. LIST OF NATURAL PESTICIDES
entomopathogenic nematodes and neem (BIOPESTICIDES)
products. The advantage of using biological
products is because they have less negative Natural pesticides are naturally occurring
impact non-target organisms, including humans chemicals extracted from plants use to kill or
[18]. retard the growth of pests that damage or
interfere with the growth of crops, shrubs, trees,
 Microbial timber and other vegetation desired by humans.
These natural pesticides include: Rotenone,
This category include Fungi, bacteria, Nicotine, Neem, Ryania, Pyrethrins, Sabadilla,
protozoans, algae, viruses, etc. which can be Fluoroacetate, Carboxin and Bacillus
used to cause disease in an insect thuringiensis.
population. Several microbial have been
genetically engineered to kill target insects 3.1 Rotenone
more rapidly. These either introduce a
disease to a certain insect population, Rotenone insecticides have been in use for
produce a toxin or limit reproduction of centuries. Products containing rotenone are
insects. Milky spore is an example of this typically prepared from plant species of the
type of natural pesticide e.g. Bacillus genus Derris plant or Lonchocarpus
thuringiensis. (Leguminosae) with the majority from Cubé resin,
a root extract of Lonchocarpus utilis and
 Mineral Lonchocarpus urucu [19]. Although rotenone is
the major constituent in Cubé resin and hence in
Mineral based controls include sulfur and rotenone products, the active ingredients
lime-sulfur. Both combination are sprayed deguelin, rotenone, and tephrosin are also
as part of the control of common insect present [20]. Rotenone based products are
pests. approved for use as organic insecticides under
many trade names and most are sold as blends
 Botanical containing both rotenone and pyrethrum extracts.
Rotenone has been in use as a fish poison for
Botanical pesticides are gotten from plants. more than 150 years [21]. It is also highly toxic to
Nicotine, Neem, Rotenone, anabasine, fish and is often used to eradicate unwanted fish
azadirachtin, ryania, essential oil, Sabadilla populations, for instance, minnows in lakes
and Pyrethrins are all derived from other before introducing trout, or to eradicate salmon in
plants. Pyrethrins for instance, is from the rivers in order to get rid of Gyrodactilus salaries,

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 Oguh et al.; AJBGE, 2(3): 1-18, 2019; Article no.AJBGE.53356

an obligate fish parasite that is a big threat to the and is often used as a fish poison (piscicide) in
salmon population [12]. water management programs.

Rotenone are derived from the roots of over 68 Compound that disrupts energy metabolism has
plant species and is very toxic to fish, pigs, and been identified from both natural and synthetic
cool blooded animals. It is used to control leaf- sources. Complex I is inhibited by rotenone
eating caterpillars and beetles. Direct contact which is derived from cube or derris root.
may cause skin and mucous membranes Disruption of energy metabolism occurs in the
irritation. Rotenone is one of several mitochondria and usually takes the form of either
isoflavonoids produced in the roots. Extraction of an inhibition of the ETS, blockage of ATP
the root with organic solvents yields resins synthesis. The ETS (complexes i-iv are
containing as much as 45% total rotenoids; macromolecular complexes that use high energy
studies indicate that the major constituents are electrons to pump out hydrogen into the
rotenone (44%), and deguelin (22%) [22]. intermembrane space and to store this energy as
Rotenone is commonly sold as dust containing 1 a proton gradient, which is harnessed to
to 6% active ingredients for home and garden synthesize ATP. Inhibition of ETS blocks
use, but liquid formulations used in organic indirectly the production of ATP and cause a
agriculture can contain as much as 9% rotenone decrease in oxygen consumption by the
and 16% total rotenoids. mitochondria. Rotenone inhibit complex I in the
ETS and blockage at this site can reduce energy
Rotenone is a mitochondrial poison, which blocks production and induce whole animal toxicity. The
the electron transport chain and prevents energy disruption energy metabolism and the
production. As a pesticide, it is considered a subsequent loss of ATP results in a slowly
stomach poison because it must be ingested to developing toxicity, and the effects of all these
be effective. Pure rotenone is comparable to compounds include inactivity, paralysis, and
Dichloro-diphenyl-trichloroethane (DDT) and death [25] shown in Fig. 1.
other synthetic pesticides in terms of its acute
toxicity to mammals (rat oral LD50 is 132 mg 3.2 Nicotine
kg−1), although it is much less toxic at the levels
Nicotine is an alkaloid obtained from the foliage
seen in formulated products. Safety of rotenone
of tobacco plants (Nicotiana tabacum) and
has recently been called into question because
related species, has a long history as an
of: Controversial reports that acute exposure in
insecticide. Nicotine (Fig. 2) and two closely
rats produces brain lesions consistent with those
related alkaloids, nornicotine and anabasine, are
observed in humans and animals with
synaptic poisons that mimic the neurotransmitter
Parkinson’s disease [23]. And the persistence of
acetylcholine. As such, they cause symptoms of
rotenone on food crops after treatment. A study
poisoning similar to those seen with
of rotenone residues on olives conducted in Italy
organophosphate and carbamate insecticides
determined that the half-life of rotenone is 4
[13]. Owing to the extreme toxicity of pure
days, and at harvest residue levels were above
nicotine to mammals (rat oral LD50 is 50 mg
the tolerance limit [24]. Moreover, residues were
kg−1) and its rapid dermal absorption in humans,
concentrated in oil obtained from the olives. As
nicotine has seen declining use, primarily as a
an Agricultural pesticide, use of rotenone is
fumigant in greenhouses against soft-bodied
limited to organic food production.
pests. However, there remains some interest in
preparing stable nicotine fatty acid soaps,
3.1.1 Rotenone mode of action presumably with reduced bioavailability and
toxicity to humans [26]. Nicotine is a Pale yellow
Rotenone is an important insecticide extracted
to dark brown liquid which is highly toxic to
from various leguminous plants. It inhibits the
warm-blooded animals. Nicotine is a fast-acting
transfer of electrons from nicotine amide-adenine
contact killer for soft bodies but does not kill most
(NADH) to ubiquinone. Rotenone is a powerful
chewing insects. Nicotine is highly lipophilic and
inhibitor of cellular respiration, the process that
can pass through dermal tissues as well as the
converts nutrient compounds into energy at the
blood brain barrier.
cellular level (Fig. 1). In insects rotenone exerts
its toxic effects primarily on nerve and muscle 3.2.1 Nicotine mode of action
cells, causing rapid cessation of feeding. Death
occurs several hours to a few days after In both insects and mammals, nicotine is an
exposure. Rotenone is extremely toxic to fish, extremely fast-acting nerve toxin. It competes

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 Oguh et al.; AJBGE, 2(3): 1-18, 2019; Article no.AJBGE.53356

with acetylcholine, the major neurotransmitter, 13 mg kg−1), but commercial preparations

by bonding to acetylcholine receptors at nerve typically contain less than 1% active ingredient,
synapses and causing uncontrolled nerve providing a margin of safety. These alkaloids are
firing. This disruption of normal nerve impulse remarkably similar to that of the pyrethrins,
activity results in rapid failure of those despite their lack of structural similarity. Sabadilla
body systems that depend on nervous input for is used primarily by organic growers; in California
proper functioning. In insects, the action of about 100 kg is used annually, primarily on citrus
nicotine is fairly selective, and only certain crops and avocado [19].
types of insects are affected [27] shown in
Fig. 2. 3.3.1 Sabadilla mode of action

3.3 Sabadilla In insects, sabadilla’s toxic alkaloids affect nerve

cell membrane action, causing loss of nerve cell
Sabadilla is a botanical pesticide obtained from membrane action, causing loss of nerve function,
the seeds of the South American lily paralysis and death. Sabadilla kills insects of
Schoenocaulon officinale. In purity, the active some species immediately, while others may
principles, celandine-type alkaloids, are survive in a state of paralysis for several days
extremely toxic to mammals (rat oral LD50 is ca. before dying.

Fig. 1. Mode of action of rotenone in energy metabolism

Fig. 2. Mechanism of nicotine in the nerve synapse

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3.4 Ryania Pyrethrins are insecticidal chemicals extracted

from the dried pyrethrum flower. The flower
Ryania Botanical insecticides are made from heads are processed into a powder to make a
grounded stem of Ryana speciosa. Is highly toxic dust. This dust can be used directly or infused
to the fruit moths, and citrus thrips. Another into water to make a spray. Most of the world’s
botanical in declining use is ryania, obtained by pyrethrum crop is grown in Kenya. The term
grinding the wood of the Caribbean shrub Ryania “pyrethrum” is the name for the crude flower dust
speciosa (Flacourtiaceae). The powdered wood itself, and the term “pyrethrins” refers to the six
contains < 1 % ryanodine, an alkaloid that related insecticidal compounds that occur
interferes with calcium release in muscle tissue naturally in the crude material, the pyrethrum
(National Research Council). It is used to a flowers. The flowers are ground to a powder and
limited extent by organic apple growers for then extracted with hexane or a similar nonpolar
control of the codling moth, Cydia pomonella. solvent; removal of the solvent yields an orange-
More information on sabadilla and ryania can be colored liquid that contains the active principles.
found in the two reviews [19]. These are three esters of chrysanthemic acid
and three esters of pyrethric acid. Among the six
3.4.1 Ryania mode of action esters, those incorporating the alcohol
pyrethrolone, namely pyrethrins I and II, are the
Ryania is a slow-acting stomach poison. most abundant and account for most of the
Although it does not produce rapid knockdown pesticidal activity. Technical grade pyrethrum,
paralysis, it does cause insects to stop feeding the resin used in formulating commercial
soon after ingesting it. Little has been published pesticides, typically contains from 20 to 25%
concerning its exact mode of action in insect pyrethrins [19].
systems. Ryania is effectively synergized
piperonyl butoxide (PBO) and is reported to be The insecticidal action of the pyrethrins is
most effective in hot weather [28]. characterized by a rapid knockdown effect,
particularly in flying insects, and hyperactivity
3.5 Pyrethrum and convulsions in most insects. These
symptoms are a result of the neurotoxic action of
Pyrethrum, also known as pyrethrins, is extracted the pyrethrins, which block voltage-gated sodium
from the seed of Chrysanthemum cineraria channels in nerve axons. As such, the
folium and has been used as an insecticide for mechanism of action of pyrethrins is qualitatively
over 100 years. Today these plants are grown similar to that of DDT and many synthetic
primarily in Kenya. Pyrethrum is effective against organochlorine pesticides. In purity, pyrethrins
a wide range of soft-bodied garden pests such as are moderately toxic to mammals (rat oral acute
scales, whitefly, mealybugs, and thrips, but will LD50 values range from 350 to 500 mg kg−1),
not control mites. Pyrethrins are neurotoxins that but technical grade pyrethrum is considerably
attack an insect’s nervous system and cause less toxic (ca. 1,500 mg kg−1) [30]. Pyrethrins
repeated and extended nerve firings. They may are especially labile in the presence of the UV
also have a repellant effect. Pyrethrins are easily component of sunlight, a fact that has greatly
broken down by stomach acids in mammals, so limited their use outdoors. A recent study
toxicity to humans and pets is very low. However, indicated that the half-lives of pyrethrins on field-
toxicity can occur when significantly more grown tomato and bell pepper fruits were 2 h or
product is applied than specified on the label. Do less [31]. This problem created the impetus for
not spray pyrethrins around ponds or other the development of synthetic derivatives
bodies of water, as they can kill fish. Pyrethrum (“pyrethroids”) that are more stable in sunlight.
is a broad-spectrum insecticide that is toxic to
beneficial insects. Pyrethrum can paralyze The modern pyrethroids, developed in the 1970s
susceptible insects upon exposure, but also and 1980s, have been highly successful and
degrades in sunlight within hours Pyrethrum is a represent one of the rare examples of synthetic
daisy-like Chrysanthemum. In the tropics, pesticide chemistry based on a natural product
pyrethrum is grown in mountain areas because it model. However, note that the modern
needs cool temperatures to develop its flowers pyrethroids bear little structural resemblance to
[29]. Pyrethrins is Very toxic to cool blooded the natural pyrethrins, and their molecular
animals, some peoples and cats. Very effective mechanism of action differs as well. Pyrethrum
on most insects. It rapidly breaks down in use data from California [32] in 2003 clearly
sunlight, air and water. demonstrate the dominance of this material

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 Oguh et al.; AJBGE, 2(3): 1-18, 2019; Article no.AJBGE.53356

among botanicals: Pyrethrum accounted for 74% paralysis, these insects may recover rather than
of all botanicals used that year, but only 27% of die. To prevent insects from metabolizing
that amount was used in agriculture (ca. 800 kg). pyrethrins and recovering from poisoning, most
Major uses of pyrethrum in California are for products containing pyrethrins also contain the
structural pest control, in public health, and for synergist, piperonyl butoxide (PBO) [33].
treatment of animal premises. Pyrethrum is the
predominant botanical in use, perhaps 3.6 Neem Products (Azadirachtin)
accounting for 80 % of the global botanical
insecticide market [19]. The organic solvent Neem is derived from the neem tree (Azadiracta
extract of the flowers was tenned pyrethrum, and indica) of arid tropical regions, contains several
it possessed many favorable properties. Its insecticidal compounds. Neem (Azadirachta
safety for mammals and rapid photodegradation indica) belonging to the Meliaceae family has
led to many situations that required low emerged as a highly potent biopesticide. The
mammalian toxicity and no residue problems main active ingredients is azadiractin, which both
(dairies, vegetables). This combination of deters and kills many species of caterpillars,
desirable characteristics fueled numerous thrips and whitefly. Both seeds and leaves can
attempts to develop synthetic analogues that be used to prepare the neem solution. Neem
would be more widely available and perhaps seeds contain a higher amount of neem oil. The
more potent; the synthetic pyrethroids will be leaves of neem are available all year compared
presented in the second-generation products of to the seed. A neem solution loses its
the botanical pesticides. effectiveness within about 8 hours after
preparation, and when exposed to direct sunlight.
Pyrethrins break down very quickly in sunlight so It is most effective to apply neem in the evening,
they should be stored in darkness. Both highly directly after preparation, under humid conditions
alkaline and highly acid conditions speed up or when the plants and insects are damp. High
degradation so pyrethrins should not be mixed neem concentration can cause burning of plant
with lime or soap solutions. Liquid formulations leaves. Also, natural enemies can be affected by
are stable in storage but powders may lose up to neem applications [34].
20 percent of their effectiveness in one year. To
Seeds from neem tree comprises 40% of oil with
get adequate management of some pests,
azadirachtin as the major active ingredient
repeated applications are needed. Pyrethrum
responsible for the insecticidal activity of neem
products frequently contain a low hazard
[35]. Neem oil contains more than a dozen
activator or synergist such as piperonyl butoxide
azadirachtin analogs, but the major contributor to
or piperonyl cyclonene that substantially
the insecticidal activity is azadirachtin. Further,
increases the effectiveness of the pyrethrum and
the seed cake obtained during the processing of
reduces its cost. Depending on the way these
neem oil is a vital natural fertilizer used in
synergists have been manufactured, some
common agricultural practices. Neem leaves
pyrethrum products containing synergists may be
have been employed for centuries against the
allowed for use in organic agriculture.
stored grain pests due to its repellent properties.
3.5.1 Pyrethrin mode of action Collectively, all parts of neem plant are known to
exhibit by-products that inherently impart an
Pyrethrins cause immediate paralysis to most internal chemical defense making neem free
insects. Low doses do not kill but have a from the pest attack, which can also be exploited
knockdown effect stronger does kill. Pyrethrins to develop an efficient pest control strategy.
are not poisonous for humans and warm-blooded Further, the functional ingredients of neem,
animals. However, human allergic reactions are exhibit, therapeutic significance as neem oil,
common. It can cause rash, and breathing the bark, leaves and their purified biochemicals are
dust can cause headaches and sickness. documented to have anticancer [36] and
Pyrethrins exert their toxic effects by disrupting antimicrobial [37] properties. Neem leaf extract
the sodium and potassium ion exchange process possesses anti-inflammatory properties [38],
in insect nerve fibers and interrupting the normal while the neem oil acts as an antifertility agent
transmission of nerve impulses. Pyrethrins [39]. This unique attribute of neem makes it an
insecticides are extremely fast-acting and cause ideal bio-pesticide agent, as it does not cause
an immediate “knockdown” paralysis in insects. non-specific toxicity to mammals.
Despite their rapid toxic action, however, many
insects are able to metabolize (break down) Neem oil, obtained by cold-pressing seeds, can
pyrethrins quickly. After a brief period of be effective against soft-bodied insects and mites

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but is also useful in the management of Nonetheless, several azadirachtin based

phytopathogens. Apart from the physical effects pesticides are sold in the United States and at
of neem oil on pests and fungi, disulfides in the least two such products in the European Union.
oil likely contribute to the bioactivity of this In California, azadirachtin-based insecticides
material [4,40]. More highly valued than neem oil constituted about one third of the botanicals used
are medium- polarity extracts of the seed residue in agriculture in 2003 (ca. 600 kg). In practice,
after removal of the oil, as these extracts contain reliable efficacy is linked to the physiological
the complex triterpene azadirachtin. Neem seeds action of azadirachtin as an insect growth
actually contain more than a dozen azadirachtin regulator; the antifeedant effect, which is
analogues, but the major form is azadirachtin spectacular in the desert locust, is highly variable
and the remaining minor analogues likely among pest species, and even those species
contribute little to overall efficacy of the extract. initially deterred are often capable of rapid
Seed extracts include considerable quantities of desensitization to azadirachtin (Bomford and
other triterpenoids, notably salannin, nimbin, and Isman 1996). What is clear is that azadirachtin is
derivatives thereof. The role of these other considered nontoxic to mammals (rat oral acute
natural substances has been controversial, but LD50 is > 5,000 mg kg−1), fish [45], and
most evidence points to azadirachtin as the most pollinators [46]. The influence of azadirachtin on
important active principle. Neem seeds typically natural enemies is highly variable. Like the
contain 0.2–0.6% azadirachtin by weight, so pyrethrins, azadirachtin is rapidly degraded by
solvent partitions or other chemical processes sunlight. For example, on olives growing in Italy,
are required to concentrate this active ingredient azadirachtin has a half-life of approximately 20 h
to level 10–50% seen in the technical [47]. Azadirachtin has systemic effect in certain
grade material used to produce their products crop plants, greatly enhancing its efficacy and
[41]. field persistence [34]. On the other hand, [48]
mentioned further that NeemAzal-T/S had
Azadirachtin has two profound effects on insects. reduced the parasitism rates, to 40, 55.4, 77.8
At the physiological level, azadirachtin blocks the and 81.3% (at 2, 1, 0.5, 0.25% cons.),
synthesis and release of molting hormones respectively, compared to 93.3% on control
(ecdysteroids) from the prothoracic gland, plants.
leading to incomplete ecdysis in immature
insects [11]. In adult female insects, a similar The seed has the highest content of azadirachtin
mechanism of action leads to sterility. In addition, of all plant parts, and most products are based
azadirachtin is a potent antifeedant to many on oil extractions from the seed kernel.
insects. The discovery of neem by western Comparatively lower bioactivity occurs in leaves
science is attributed to Schmutterer [42], who owing to lower concentrations of the bioactive
observed that swarming desert locusts in Sudan compounds. However, many African farmers use
defoliated almost all local flora except for some the leaves in the preparation of crude pest
introduced neem trees. control products, despite low efficacy as the
leaves are easier to use: also, in some cooler
Indeed, azadirachtin was first isolated based on climates neem trees do not flower so do not
its exceptional antifeedant activity in the desert produce seed. Clearly practices need modifying
locust, and this substance remains the most and end-users need information to ensure time
potent locust antifeedant discovered to date. and resources are not wasted using ineffective
Unlike pyrethrins, azadirachtin has defied total materials. Neem seed oil has been formulated
synthesis to this point. In USA, Neem rapidly into hundreds of different products such as
became the modern paradigm for the soaps, medicines and pesticides. A number of
development of botanical pesticides. Enthusiasm Neem pesticidal products are being produced
for neem was fostered by several international and traded internationally, especially from China
conferences in the 1980s and 1990s, and several and India, whereas in Africa neem has enjoyed
volumes dedicated to neem and neem far less success [49].
insecticides have been published [43,34].
Unfortunately, neem’s commercial success has Neem insecticides are effective against many
fallen well short of the initial hype fueled by the caterpillars, flies, whitefly, and scales, and are
explosive scientific literature surrounding it. In somewhat effective against aphids. Neem may
part this is due to the relatively high cost of the not show signs of efficacy for 3–8 days, and it
refined product [44] and the relatively slow action can degrade within 3–5 days. Multiple
on pest insects. applications are generally needed to obtain good

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management of the targeted pests. Neem is ingesting the food (due to secondary hormonal or
regarded as nontoxic to vertebrate animals and physiological effects of the deterrent substance).
has been shown to minimally affect many As a growth regulator, neem is thought to disrupt
beneficial insects such as bees, spiders, and normal development interfering with chitin
ladybugs. Well known as a potent insect synthesis. Susceptibility to the various effects of
antifeedant, azadiractin. A appears to work by neem differs by species.
blocking the synthesis and release of molting
hormones (ecdysteroids) from the prothoracic 3.6.2 Neem seed kernel extract: The recipe
gland. Many neem/azadirachtin based products
are approved for use as organic insecticides. An Pound 30 g neem kernels (the seed of which the
added advantage of neem oil-based products is seed coat has been removed) and mix it in 1 litre
their ability to control fungal infections as well as of water. Leave that overnight. The next morning,
a wide variety of both insect and mite pathogens filter the solution through a fine cloth and use it
[50]. immediately for spraying. It should not be further
diluted.
The seeds from the Indian neem tree,
Azadirachta indica, are the source of two types of 3.7 Bacillus thuringiensis (B.t.)
neem-derived botanical insecticides; neem oil
and medium polarity extracts. Neem seeds This is probably the most common microbial
contain more numerous azadirachtin analogues, ‘active ingredient’. This organism is incorporated
but the major form is azadirachtin A (Fig. 3) and into several products, most of which are used to
the remaining minor analogues likely contribute control caterpillar pests. Specific strains of B.T.
little to overall efficacy of the extracts [19]. have been selected for their ability to control
mosquitos, black flies and other organisms. For
example, B. t. strains ‘kurstaki’, ‘berliner’ and
‘aizawai’ are used for controlling larvae of many
Lepidoptera pests, while B.T. ‘tenebrionis’ is
used against larvae of Colorado potato beetle,
and B.T. ‘israelensis’ is used to control mosquito
larvae. Be sure that the product chosen is
labelled to control the pest the growers are
targeting. Additionally, while some crops have
been modified to express the insecticidal protein
produced by B. thuringiensis these genetically
altered plants are not considered.

3.8 Fluoroacetate

Fluoroacetate is produced by many plants in

Fig. 3. Schematic representation of the agro- Australia and South Africa and has an important
medicinal tree [51] function as a natural pesticide for the plants. It is
highly toxic to rodents and other mammals. In
3.6.1 Azadirachtin mode of action certain parts of Australia, where such plants are
abundant, opossums have become resistant to
Neem products are complex mixtures of fluoroacetic acid.
biologically active materials, and they are difficult
to pinpoint the exact modes of action of various 3.8.1 Mode of action of fluoroacetate
extracts or preparations. In insects, neem is most
active as a feeding deterrent, but in various The mode of action of fluoroacetate is well
forms it also serves as a repellent, growth understood: it is converted to fluoroacetyl-CoA,
regulator, oviposition (egg deposition) which is thereafter converted to fluorocitric acid.
suppressant, sterilant, or toxin. As a repellent, This structure analogue to citric acid inhibits the
neem prevents insects from initiating feeding. As enzyme that converts citric acid to cis-aconitic
a feeding deterrent, it causes insects to stop acid, and the energy production in the citric acid
feeding. As a feeding, either immediately after stops. Citric acid, which accumulates, sequesters
the first “taste” (due to the presence of deterrent calcium. Α-Ketoglutaric acid and therefore
taste factors), or at some point soon after glutamic acid are depleted. These changes are,

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 Oguh et al.; AJBGE, 2(3): 1-18, 2019;; Article no.AJBGE.53356
no.

of course, detrimental to the organism. The fungicides are active only as a coating on the
nervous system is sensitive to these changes surface of the plants and do not fight back
because glutamic acid is an important transmitter growing mycelia inside the plant tissue.
substance in the so-called called glutaminergic
synapses, and calcium is a very important 3.9.1 Carboxin mode of action
mediator of the impulses.
lses. Furthermore, the halt
of aerobic energy production is very harmful. Carboxin inhibit the dehydrogenation of succinic
acid to fumaric acid, an important step in the
3.9 Carboxin tricarboxylic acid cycle.
e. The toxicity to animals
and plants is low in spite of this very fundamental
Carboxin is a systemic pesticide is taken up by mode of action. The fungicides in this group are
the organism it protects and may kill sucking anilides of unsaturated or aromatic carboxylic
aphids or the growing fungal hyphae. The older acids.

Fig. 4. Steps in preparation of neem seed solution

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no.

Fig. 5. Names, structure and leaves of biopesticides

4. GENERAL MODE OF ACTION OF persist in the environment, much safer to handle

NATURAL PESTICIDES and apply when compared to most chemical
pesticides,
esticides, and tend to preserve beneficial
Mode of action is the sum of anatomical, organisms. The most of the bio bio-rational
physiological and biochemical interactions and insecticides have diverse modes of action, show
responses that result in p toxic action of a effectiveness against different strains of resistant
chemical, as well as the physical (location) and species, with no evidence of crosscross-resistance,
molecular (degradation) fate of the chemical in has assisted in managing resistance to insect
the organism. These compounds nds have achieved pests and they can play an important role in IRM
several currently desired goals of pest managers strategies. Most bio-rational
rational pesticides are nerve
and the greater public demands. These are very poisons acting at specific target sites in the
selective, targeting just the pest, usually do not insect's nervous system. Some insecticides act

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 Oguh et al.; AJBGE, 2(3): 1-18, 2019; Article no.AJBGE.53356

similarly to the old nerve poisons that result from chemical, and then it must be structurally
knocking-down, rapid intoxication, lack of identical to a naturally occurring chemical. Minor
coordination, paralysis and death, and have differences between the stereochemical isomer
higher affinity to insect receptors than to ratios (found in the naturally occurring compound
mammalian. The other insecticides affect specific compared to the synthetic compound) will
systems, such as the molting processes, normally not rule out a chemical being classified
metamorphosis and the insect endocrinology as a bio-rational unless an isomer is found to
system. All the bio-rational or low-risk have significantly different toxicological
insecticides have relatively low detrimental effect properties from those of another isomer. Thus,
on the environment and its inhabitants, and have application of active toxic bio-rational agents as
little or no adverse consequence for non-target an alternative control strategy results in an urge
organisms, thus rendering them among important to look for environment-friendly, biodegradable
components in IPM program [12]. and easily available at affordable prices products
for pest’s control.
4.1 Scope of Biopesticides
4.2 Regulations of Bio-rational Pesticides
Efforts have been made to find bio-rational
insecticides with novel modes of action and have The philosophy and approach to the regulations
no cross-resistance with the old insecticides. of bio-rational pesticides shall require registrants
Biopesticides are a distinct group, inherently to obtain clearance from the expert's committee
different from conventional pesticides. They are prior to the registration of the products. In
comprised of two major categories, the regulating bio-rational pesticides, it shall be
biochemical pest control agents (e.g., recognized that these kinds of pesticides are
pheromones, hormones, natural plant growth inherently different from conventional pesticides
regulators and enzymes) and the microbial pest and will take due consideration that many
control agents (e.g., microorganisms). Pesticides classes of biopesticide control agents might pose
to be included in these categories must be lower potential risks than conventional pesticides.
naturally occurring, or if man synthesizes the The most important inherent difference

Fig. 6. Mode of action of natural pesticides

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 Oguh et al.; AJBGE, 2(3): 1-18, 2019; Article no.AJBGE.53356

between biopesticides and conventional 6. There are no legal registrations

pesticides are target species specificity, generally establishing their use.
non-toxic mode of action and natural occurrence 7. Not all recommendations followed by
of the bio-rational agents. These factors provide growers have been scientifically verified.
the basis for the expectation that many classes 8. Short residual activity (some users
of bio-rational pest control agents pose a lower consider this to be an advantage), maybe
potential hazard than conventional pesticides more expensive than older conventional
and support the approach to testing needed for pesticides, and somewhat less pest-
the registration of manufacturing product. Thus, specific, especially when compared to
the Environmental Protection Act in various newer synthetic pesticides.
states has framed a number of rules and
regulations to check the application of chemical 4.5 Pest Management
control agents in nature [52].
Pest management is a way to keep pests below
4.3 Advantages of Natural Pesticides the levels where they can cause economic
damage. Management does not mean
1. Plants producing the above-mentioned eradicating pests. It means finding tactics that
compounds are known by the farmer are effective and economical, and that keep
because most of the time they grow in the environmental damage to a minimum. The IPM is
same general area. the managing of crops using many tactics to
2. Eco-friendly safer for user/applicator, and keep pest levels below an economic threshold.
very effective when used correctly. The IPM has been developing as a way to
3. Often these plants also have other uses control pests without relying solely on pesticide.
like household insect repellents or are Integrated pest management is a systematic plan
plants with medicinal applications. which brings together different pest-control
4. The rapid degradation of the active product tactics into one program. It reduces the emphasis
may be convenient as it reduces the risk of on pesticides by including cultural, biological,
residues on food. genetic, physical, regulatory, and mechanical
5. Some of these products may be used controls. To carry out an IPM program, you need
shortly before harvesting. to scout and monitor your fields, recognize
6. Many of these products act very quickly abnormal conditions and identify their causes,
inhibiting insect feeding even though long understand the different control methods
term they do (will?) not cause insect death. available, and determine the economic costs and
7. Since most of these products have a benefits. A good IPM program requires planning,
stomach action and are rapidly monitory and evaluation. Pest management are
decomposed they may be more selective very site-specific. Pest management is based on
to insect pests and less aggressive with the identification of pests, accurate measurement
natural enemies. of pest populations, assessment of damage
8. Most of these compounds are not levels, and knowledge of available pest
phytotoxic. management strategies or tactics that enable the
9. Resistance to these compounds is not specialist to make intelligent decisions about
developed as quickly as with synthetic control. The IPM offers the possibility of
pesticides. improving the effectiveness of pest control
programs while reducing some of the negative
4.4 Disadvantages of Natural Pesticides effects. Many successful IPM programs have
reduced pesticide use and increased protection
1. Most of these products are not truly of the environment.
pesticides since many are merely insect
deterrents and their effect is slow. 5. CONCLUSION
2. They are rapidly degraded by UV light so
that their residual action is short. Soil pollution, Air pollution has occurred from the
3. Not all plant pesticides are less toxic to use of synthetic pesticides and it takes years and
other animals than synthetic ones. sometimes decades for some of these chemicals
4. They are not necessarily available season to break down. These pesticides are also harmful
long. to the animal, microorganisms, plants as well as
5. Most of them have no established residue human health. Luckily there are many Natural
tolerances. pesticides (Biopesticides) that are also effective

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 Oguh et al.; AJBGE, 2(3): 1-18, 2019; Article no.AJBGE.53356

in pest control. People need to break the habit of 8. Horowitz AR, Peter CE, Isaac I. Bio-
using harmful pesticides and switch to rational pest control – An overview.
biopesticides which break down quickly in Springer Science and Business Media;
sunlight and in the soil. The faster a chemical 2009.
breaks down, the sooner the soil can return to a 9. Muhammad S. Usage of bio-rational
healthy state. Most biopesticides are also safe to pesticides with novel modes of action,
use around people and pets. They can easily be mechanism and application in crop
washed from fruits and vegetables making them protection. International Journal of
healthier for us and our family to eat. Materials Chemistry and Physics.
2015;1(2):156–162.
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Authors have declared that no competing Council: National Academy Press; 1993.
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