Microbial insecticides

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

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

Microbially produced toxic substance
Organism

TYPES

BACTERIAL
ACTINOMYCETES
VIRAL
FUNGAL
PROTOZOAN
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

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

VARIOUS STRAINS OF B. thuringiensis

MODE OF ACTION

THREE STAGE PROCESS

STAGE1
STAGE2

STAGE3

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.

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.

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®,

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

2. MILBEMECTIN

S. hygroscopicum var aureolacromosus

Have 2 group- A3, A4
GABA abonists
milbeknock

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

VIRAL PESTICIDES

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

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

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

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).