BIOCHEMICAL PESTICIDES

Presented by-MD.MASUD RANAJahangirnagar university

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BIOCHEMICAL PESTICIDES

 Naturally occuring pesticides. Control pests by nontoxic mechanisms. Biochemical pesticides include substances, such as-

Insect sex pheromones, that interfere with mating

various scented plant extracts that attract insect pests to traps.

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BIOLOGICAL CONTROL THROUGH INTERACTION

Controlling pests relies on following interaction:• Predation• Parasitism or• Ammensalism.

Parasitism:

Bacteria used for biological control infect insect via their digestive tract.

For example, Bacillus thuringiensis, with at least four sub-species used to control: Lepidopteran (moth,butterfly) Dipteran (true flies).

Insecticidal toxin of Bacillus thuringiensis

• B. thuringiensis is a gram positive soil bacterium that produces a toxin or crystal protein (Bt toxin or Cry) that kills certain insects

• The Bt toxin or Cry is produced when the bacteria sporulates and is present in the parasporal crystal.

mode of action• The Cry protein is made as an inactive protoxin

• Conversion of the protoxin into the active toxin requires the combination of a slightly alkaline pH (7.5-8) and the action of a specific protease found in the insect gut.

• The active toxin binds to protein receptors on the insect gut epithelial cell membrane.

• The toxin forms an ion channel between the cell cytoplasm and the external environment, leading to loss of cellular ATP and insect death.

Genetically Modified Organisms

FUNGUS

Fungi that cause disease in insects are known as entomo pathogenic fungi.

Examples of entomo pathogenic fungi:– Beauveria bassiana works against white flies, aphids.–Metarhizium spp. Against beetles, spider mites or

other pests.– Trichoderma spp. are used to manage some soil

borne plant pathogens.

MODE OF ACTION OF FUNGI

• Invade insects by penetrating their cuticle or skin.

• Rapidly multiplies throughout the body.• Death is caused by tissue destruction or by

toxin production.• Emerges from insects body by producing

spores.• Can spread infection by-Wind, Rain, and

Contact with other insects.

VIRUS • Baculoviruses are pathogens that attack insects

and arthropods.

• Insects infected by consuming plant material with viral particles.

• Viral infection begins in the insects digestive system but spread throughout the body.

• Virus killed insects break open and spill virus particles into the environment.

VIRAL ACTION

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Predation: Protozoa : protozoa must be applied before outbreaks

of disease to effect proper control.

Example : Nosema, Vairimorpha used for controlling insects (grasshoppers, mosquitoes etc).

Nematodes: Romanomermis are used to control insects.

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Ammensalism:

Streptomyces spp. that have ammensal effects and are useful in agricultural pest control.

– Produce Antibiotics such as streptomycin that are

effective against bacterial pathogens and

– Other substances such as bilanafos that are active

against weeds.

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HOW TO APPLY ?

Biopesticides are typically microbial biological pest control

agents that are applied in a manner similar to chemical

pesticides. Such as-

Soil applied biopesticides: are appliede to the soil.

Contact biopesticides: Generally control pests as a

result of direct contact.

Preplant herbicides: are applied to the soil before

seeding.

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Selective biopesticides: only control certain pests

Non-selective biopesticides: control wide range of

pests.

Foliar biopesticides: applied to plant leaves, stems

and branches.

Postmergent herbicides: apllied after the crop or

weed has emerged.

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ADVANTAGES

• Do not leave harmful residues.

• Substantially reduced impact on non-target

species

• Can be cheaper than chemical pesticides when

locally produced.

• Can be more effective than chemical pesticides

in the long-term.

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DISADVANTAGES High specificity, which will require an exact

identification of the pest/pathogen .

May require multiple pesticides to be used.

Often slow speed of action.

Often variable efficacy due to the influences of various

biotic and abiotic factors.

Living organisms increase their resistance to biological,

chemical, physical or any other form of control.