Dept. of Soil Science and Agricultural Chemistry
• Microbes & microbial products used as
• Less harmfull, fewer environmental effects.
• Microbial insecticides are biological
preparations that are often delivered in ways
similar to conventional chemical insecticides.
About 90 species of bacteria pathogenic to insect
Bacillus thuringiensis – first discovered in 1902-
japanese bacteriologists, Ishiwata from infected silk
worms stands out prominent.
B. thuringiensis (‘Bt’) is a spore forming gram positive
crystalliferous soil bacterium.
Produces a toxin or crystal protein (Bt toxin or Cry) that
kills certain insects
Commercially produced worldwide using fermentation
The commercial Bt products are produced as dust,
wettable powder and emulsifiable concentrates.
The toxin genes have also been genetically engineered
into several crop plants.
The Bt toxin or Cry is produced when the bacteria
sporulates and is present in the parasporal crystal
Several different strains and subspecies of B.
thuringiensis exist and produce different toxins that kill
Used as alternative to DDT and organophosphates since
Bt toxin is used as specific insecticides under trade
names such as Dipel and Thuricide
TARGET INSECTS FOR BT TOXIN
Cry toxins have specific activities against insect species of the orders
Lepidoptera (moths and butterflies), Diptera (flies and mosquitoes), Coleoptera
(beetles), Hymenoptera (wasps, bees, ants and sawflies) and nematodes.
SOME PROPERTIES OF THE INSECTICIDAL TOXINS
FROM VARIOUS STRAINS OF B. THURINGIENSIS
Strain/subsp. Protein size Target Insects Cry #
berliner 130-140 kDa Lepidoptera CryI
kurstaki KTP, HD1 130-140 kDa Lepidoptera CryI
entomocidus 6.01 130-140 kDa Lepidoptera CryI
aizawai 7.29 130-140 kDa Lepidoptera CryI
aizawai IC 1 135 kDa Lepidoptera, Diptera CryII
kurstaki HD-1 71 kDa Lepidoptera, Diptera CryII
tenebrionis (sd) 66-73 kDa Coleoptera CryIII
morrisoni PG14 125-145 kDa Diptera CryIV
israelensis 68 kDa Diptera CryIV
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.
MODE OF ACTION
Was initially believed to kill larvae by septicaemia
It is now well established that delta-endotoxin alone is
responsible for the death of most susceptible
After ingestion by larvae, the crystal protein broken by
midgut juice proteases, under high pH > 9 conditions,
into smaller toxic peptic molecules, the delta-endotoxin.
The latter causes mouth and gut paralysis within ½ hour
of eating a larger doses, thus preventing further feeding
within hours, the epithelium of the midgut is destroyed
and gut contents invade the body cavity, rapidly causing
ORGANISM TRADE NAME TARGET PEST
Bacillus popilliae - Japanese beetle
var.kurstaki plus beta-
Javelin Armyworm & other
B. Thuringiensis var.
Agree Wax moth
Novodor Colorado potato
VectoBac Mosquitoes, black flies
Spicturin Larvae and moths and
More than 750 species known to infect insects.
Mostly causing disease to insects.
Some attack insects through cuticle.
Spore attached to cuticle- germinates & penetrates
into body wall.
Spreads – colonize the hemocoel & sometimes
Toxins – rapid death or death delayed until nutrients
depleted or organs destroyed.
It is known as 'white – halo' fungus because of the
white mycelial growth on the edges of infected
It can be multiplied on medium based on locally
available grains and tubers.
It is formulated as wettable powder.
It is effective against coffee green bug and certain
o Deuteromycotina fungus, naturally occurring in soil throughout
o Mass produced on locally available grains and other solid
o Formulated as wettable powder, water dispersible granule, and oil
based emulsifiable suspension.
o Useful against Coffee berry borer, Diamond backmoth, Thrips,
Grasshoppers, White flies, Aphid, Codling moth etc.
o Birds: Oral LD50: (5 days) quail >2,000 mg/kg daily (by gavage).
Metarrhizium anisopliae is a widely distributed soil inhabiting
The spore of M. anisopliae can be formulated as dust and
It is used to control termites, mosquitoes, leaf hopper,
Nomuraea rileyi is of cosmopolitan occurrence and
pathogenic to a number of economically important
It is formulated as wettable powder.
The fungus could be multiplied on polished rice grains
and crushed sorghum.
ORGANISM TRADE NAME TARGET PEST
mites, scales, etc
Taenure® Thrips and beetle
Tick-Ex® Grubs and ticks
PFR-97® Whiteflies, aphids
Other genera- Nomuraea, Entomophthora and
Zoophthora. – affects insects.
Baculoviruses are rod-shaped, double stranded DNA viruses
that can infect and kill a large number of different invertebrate
Immature (larval) forms of moth species are the most common
hosts, but these viruses have also been found infecting sawflies,
mosquitoes, and shrimp.
Baculoviruses have limited host ranges and generally do not
allow for insect resistance to develop
Slow killing of target insects occurs
In order to speed killing (enhance effectiveness), several genes
can be expressed in the baculovirus including diuretic hormone,
juvenile hormone esterase, Bt toxin, scorpion toxin, mite toxin,
wasp toxin, and a neurotoxin.
Larvae infected with GV and NPV usually die within
5-12 days after infection.
These viruses are produced on the host insects and
are formulated both as liquid and dust formulation.
NPV viruses develop in the host cell nucleus where one
or several virus rods occur singly or in groups encased in
The envelops are occuled in many-sided crystals called
After ingesting the polyhedra, larvae show no outward
symptoms for 4 days to 3 weeks.
At this time, the larval skin darkens & larvae climb to the
highest point on their host plant, where they die.
Dead, blackened larvae may be found hanging from
the tops of plants.
The integuments of these dead larvae rupture, and
millions of polyhedra are released into the
Such diseases collectively – caterpillar wilt.
Seven virus registered with EPA.
NPV microbials – celery looper, gypsy moth,
douglas fir tussock moth, corn earworm & beetle
Two GV microbials – codling moth & Indian meal
NPV -250 – 500 ml/ ha 2 - 3 time at 10 days
Being obligate, virus has
to be produced only in
Thus, for the production
of HaNPV, either rear H.
armigera on large scale
or collect the larvae from
field and use them for
Collect the 250 larvae (6-
7 day old) of H. armigera
Production of HaNPV
Larvae are singly placed in
plastic tubes containing food
contaminated with NPV.
After 7-8 days collect larvae
showing the symptoms of
NPV infection before they
liquefied, in air tight
Keep this container for 8-10
days to decompose the
larvae, so that polyhedra
released from infected tissue.
Homogenize the decomposed suspension of diseased larvae
using a homogenizer.
Dilute the homogenized content with small amount of water
and filter through two layers of muslin cloth.
Little water is sprinkled 2-3 times over the remnants to
extract residual polyhedra.
For crude preparation the filtrate is diluted with water
to make solution of 250 ml.
This is known as 250 LE (LE-larval equivalent) HaNPV
HaNPV in stoppered bottle, and store in cool and
Some of them parasitize and kill insects.
Formulated as baits.
When bait ingested- protozoa spores – active- grow
and replicate in the insect’s digestive system- kills.
Effective – insects in immature stage.