Microbial insecticides

Single-cell organisms, such as bacteria, fungi and protozoa, and viruses, have been mass-produced and formulated for use as insecticides.

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INTRODUCTION

  • The insect population is the largest with more than
  • 750000 species
  • Negative effects of insects
  • Synthetic chemical insecticides provide many benefits to food production and also pose some hazards.
  • Alternative methods of insect management offer adequate levels of pest control and pose fewer hazards.

MICROBIAL INSECTICIDES

Single-cell organisms, such as bacteria, fungi and protozoa, and viruses, have been mass-produced and formulated for use as insecticides.

Microbial insecticides can be

  1. Microbially produced toxic substance
  2.  Organism

TYPES

  1. BACTERIAL
  2. ACTINOMYCETES
  3. VIRAL
  4. FUNGAL
  5. PROTOZOAN
  6. NEMATODES

BACTERIAL INSECTICIDES

  • Spore forming
  • Rod-shaped
  • Genus Bacillus.
  • Isolated from soil samples
  • Stomach poisons

TYPES

  • OBLIGATE- B. papillae, B. lentimorbus
  • FACULTATIVE- B. cereus, BT
  • POTENTIAL- P. aeruginosa

HISTORY OF BT

  • Discovered in Japan in 1901 by Ishiwata
  • Officially described by Berliner in 1915, isolated from Mediterranean flour moth in the province of Thuringia in 1911
  • US production of a subspecies thuringiensis in the late 1950s
  • Discovery of highly active subspecies kurstaki HD-1 by Dulmage, 1960s, commercial production 1970s
  • Discovery of mosquito, black fly active subspecies israelensis by Goldberg and Margalit, the 1980s
  • Discovery of beetle-active subspecies Morrison by Krieg, 1980s
  • Genetically engineered cotton, corn, potatoes ongoing

Bacillus thuringiensis Berliner

  • gram-positive, aerobic
  • parasporal body (known as the crystal) that is proteinaceous and possesses insecticidal properties.
  • The parasporal body comprises crystals and tightly packed with proteins called protoxins or endotoxins.
  • over 60,000 isolates of Bt are being maintained in

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. Three-dimensional structure of Cyt toxins from Bacillus thuringiensis displayed by Swiss PDB viewer. Cyt1Aa, PDB 3RON; Cyt2Aa, PDB 1CBY; and Cyt2Ba, PDB 2RCI.

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VARIOUS STRAINS OF B. thuringiensis

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MODE OF ACTION

THREE STAGE PROCESS

  • STAGE1
  • STAGE2
  • STAGE3

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B. thuringienis parasporal crystal composed of Cry1 protoxin protein. Conversion of the 130-kDa protoxin into an active 68-kDa toxin requires an alkaline environment (pH 7.5 to 8) and the action of a specific protease, both of which are found in the insect gut. The activated toxin binds to protein receptors on the insect gut epithelial cells.

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and the action of a specific protease, both of which are found in the insect gut. The activated toxin binds to protein receptors on the insect gut epithelial cells.

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The toxin is inserted in gut epithelial cell membranes of the insect and forms an ion channel between the cell cytoplasm and the external environment, leading to loss of cellular ATP and insect death.

APPLICATION

  • Spray when caterpillars are still small.
  • Completely cover all leaf surfaces. The insects
    must ingest the bacteria when they are feeding.
  • Spray in the evening or during cloudy (but not
    rainy) days.
  • There may be a need to reapply if it rains soon
    after application.

COMMERCIAL BT PRODUCTS

organism Product name

1.Bacillus thuringiensis

var. kurstaki

2. B.thuringiensis var.
aizawai

3. B. thuringiensis var.

israelensis (Bti)

4. Bacillus popillae and
Bacillus lentimorbus.

Dipel®, Javelin®, Thuricide®,
Worm Attack®, halt
Caterpillar Killer®,
Bactospeine®, and SOK-Bt®

Certan®

Vectobac®, Teknar®,
Bactimos®, Skeetal®, and
Mosquito Attack®.

Doom®, Japidemic®, Grub
Attack®,

5. Bacillus thurigiensis
var. san diego,

M-One®,

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GLOBAL SHARE OF BT

• USA

• INDIA

• CHINA

• ARGENTINA

• BRAZIL

• S. AFRICA

• CANADA

• PHILIPHINES

• AUSTRALIA

• URUGUAY

Plant Biotechnology Journal ª 2011 Society for Experimental Biology,  Association of Applied Biologists and Blackwell Publishing Ltd, Plant Biotechnology  Journal, 9, 283–300

ACTINOMYCETES

  • Large group of gram positive bacteria that
    grow as hyphae like fungi
  • Mortality is due to secretion of bioactive
    materials which stimulate GABA system or
    disruption of nicotinic acetylcholine recepters

HISTORY

  • In 1978, an actinomycete was isolated at the kitasato institute from a soil sample collected at kawana, japan.
  • The family of compounds were finally characterized by a team at merck in 1978.
  • In 2002, kitasato university and at the kitasato institute, proposed that streptomyces avermitilis be renamed streptomyces avermectinius.

1. AVERMECTIN

  • From Streptomyces avermectin
  • Major homologues- A1a, A2a, B1a, B2a
  • Minor homologues- A1b, A2b, B1b, B2b
  • B1b and B2b are effective- abamectin
  • GABA agonist
  • Vermac –A, albentin, verbend

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2. MILBEMECTIN

  • S. hygroscopicum var aureolacromosus
  • Have 2 group- A3, A4
  • GABA abonists
  • milbeknock

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3. SPINOSAD

  • S. spinosa
  • 2 metabolites- spinosin A(C4H65O10), spinosin D (C4H67O10)
  • Against caterpilllars and thrips
  • Acts as Ach agonist
  • Success 2.5 EC , tracer 45EC

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VIRAL PESTICIDES

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VIRAL PESTICIDES

GENERAL OVERVIEW

  • Insect-specific viruses can be highly effective natural controls of several caterpillar pests.
  • Stomach poison
  • No threat to humans or wildlife is posed by insect viruses.

BACULOVIRUSES

  • Rod shaped DNA viruses
  • Include NPV and GV
  • Pathogenic for lepidoptera(83%), hymenoptera(10%) and diptera(4%)
  • Infection is by ingestion of food

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Mode of action

  • The polyhedrin protein dissolves in the alkaline environment of the new host’s gut and the occluded virus is released.
  • This virus infects the gut epithelial cells and virus replication takes place.
  • Nonoccluded virus is then produced and budded from the infected gut cells

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GRANULOSIS VIRUS

  • Develop either in the nucleus/cytoplasm/ tracheal matrix / epithelial cells of host
  • virions are occluded singly in small inclusion bodies called capsules
  • rod shaped virion, ds DNA
  • oval occlusion bodies about 200x400nm
  • they enter through ingestion
  • fat body is the major organ invaded
  • diseased larvae – less active, flaccid, fragile, wilted prone to rupture in later stages, death in 6-20 days

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The recommended dosage is 200 ml of NPV/acre or 500 ml/ha containing 100 and 250 larval equivalent (LE) of NPV respectively as active infective material (one LE = 6 x 10^9 pobs).

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Field efficacy 70-80%

FUNGAL INSECTICIDES

 

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