BIOFERTILIZERS AND PEST CONTROLEFlame Institute

? Sporeine developed in Germany is first commercial bioinsecticide obtained from Bacillus thuringenesis.

? Red squill (Urginea maritima) produce a raticide harmles to other animals.

? Juvenile Hormone : spray prevents larvae to metamorphose. They die without reproduction.

? Male Sterilisation : The technique was developed by Kiplings (19955). It has been used to eradicate Screw Worm.

? Biological Control of Parthenium : Zygogramma bicolorata, a beetle, suppresses Parthenium hysterophorus effectively. It, however, also attacks sunflower, shoot and root borer insect Nupserha lenita reduces population of the weed. Marigold and Cassia tora are two plants that can displace Parthenium. The latter is also controlled by spray of Gliocladium virens and Trichoderma viride.

? Parasitoids : They are organisms which are parasite in early stages (egg and larval) but live freely later one e.g., parasitoid Wasp or Cabbage Butterfly.

Biofertilizer

The biofertilizer present in the roots of legumes is

(a) Anabaena (b) Rhizobium

The chemical fertilizer required for better rhizobial nitrogen fixation is

(a) Phosphorus (b) Potassium

A green manure is

(a) Rice (b) Sorghum

Which of the following plants are used as green manure in crop fields and in sandy soils [CBSE PMT 2003]

(a) Dicanthium annulatum and Azolla pinnata

(b) Crotalaria junecea and Alhagi camelorum

(d) Saccharum munja and Lantana camara

The nitrogen fixing symbiotic organism present in Azolla is

(a) Nostoc (b) Anabaena

VAM is

(a) Bioinsecticide (b) Bioherbicide

A nitrogen fixing bacterium that forms a loose assocation with the roots of crop plants is [Kerala PMT 2001]

(a) Azotobacter (b) Bacillus polymyxa

A legume having symbiotic association with two nitroge fixing bacteria (Rhizobium and Aerorhizobium) is

[MP PMT 1987]

(a) Crotalaria juncea (b) Sesbania aculeata

Composited manure is formed from

(a) Rotted vegetable and animal refuse’

(b) Farmyard manure and green manure

(d) Organic wastes from which biogas has been extracted

Biofertilizers include

(a) Nitrogen fixing bacteria

(b) Nitrogen fixing cyanobacteria

(d) Bacteria, cyanobactria and mycorrhizal fungi

Mycorrhiza is a symbiotic association between

[Pb. PMT 1998]

(a) Bacteria and fungi

(b) Algae and fungi

(d) Blue green algae and roots of higher plants.

Azolla enriches rice fields with nitrogen due to its association with [Wardha 2001, CET Chd.2001]

(a) Anabaena (b) Nostoc

Green manuring enhances crop yield by [RPMT 1986]

(a) 5 –10% (b) 15 –25%

The best fertilizer for paddy is [APMEE 1987]

(a) Azolla pinnata (b) Bacillus megatherium

What is required for nitrogen fixation by Rhizobium

[DPMT 1988; APMEE 1989]

(a) Potassium (b) Phosphorus

Root nodules for nitrogen fixation of a non-leguminous tree possess [BHU 1994]

(a) Frankia (b) Rhizobium

Which is correct [CBSE PMT 1994]

(a) Legumes fix nitrogen through bacteria in their leaves ‘

(b) Legumes fix nitrogen through bacteria in their roots

(d) Legumes do not fix nitrogen

VAM represents [HP PMT 1994]

(a) Saprophytic fungi (b) Symbiotic fungi

Mycorrhiza represents [CBSE PMT 1994]

(a) Antagonism (b) Endemism

Which element plays an important role in nitrogen fixation

[CBSE PMT 1995]

(a) Mn (b) Mo

Nitrogen fixation is [APMEE 1996; CPMT 1996]

(a) Nitrogen ® Ammonia (b) Nitrogen ® Nitrates

Leghaemoglobin occurs in [Bih. PMT 1996]

(a) Coralloid root (b) BGA

Azotobacter and Bacillus polymyxa are [CBSE PMT 1996]

(a) Decomposers

(b) Nonsymbiotic nitrogen fixers

(d) Pathogenic bacteria

Crop rotation is carried out for [AFMC 1996; BHU 2004]

(a) Increasing acidity of soil (b) Decreasing fertility of soil

Which disease is caused in children due to excessive use of nitrate fertilizers [MP PMT 1996]

(a) Septicemia (b) Jaundice

Which of the following is free living aerobic and nonphotosynthetic nitrogen fixing bacterium

[CBSE PMT 1997, 1998]

(a) Rhizobium (b) Nostoc

Biofertilizers include [CBSE PMT 1997, 2001]

(a) Cowdung manure and farmyard waste

(b) A quick growing crop ploughed back

(d) All the above

Yield of paddy field can be increased by application of

[MP PMT 1997; CBSE PMT 1999]

(a) Iron bacteria (b) Nostoc/Anabaena

Green manure plants belong to [CET Chd. 1997]

(a) Compositae (b) Solanaceae

Which of the following can use molecular nitrogen as nutrient [MP PMT 1998]

(a) Methanomonas (b) Mucor

Symbiotic nitrogen fixation in root nodules of some legumes is caused by [AFMC 1998]

(a) Nitrosomonas (b) Rhizobium

If wheat field is inoculated with Rhizobium [Pb. PMT 1998]

(a) Soil will become nitrogen rich

(b) No effect on soil nitrogen

(d) Soil will become rich in calcium

Which one is a nonsymbiotic nitrogen fixer [Pb. PMT 1998]

(a) Rhizobium (b) Oscillatoria

Farmers have reported 50% higher yield of rice by using biofertilizer [CBSE PMT 1998]

(a) Azolla pinnata

(b) Legume-Rhizobium symbiosis

(d) Mycorrhiza

Aquatic fern which is an excellent biofertilizer

[CBSE PMT 1999, 2000,01]

(a) Salvinia (b) Azolla

Which is correct about nitrogen fixation by legumes. They fix nitrogen through [AFMC 1999]

(a) Specialised bacteria in their roots

(b) Specialised bacteria in their leaves

(d) The statement is wrong

Rhizosphere is the region where [AMU 1987; CPMT 1992]

(a) Rhizobium forms root nodules

(b) Algae and root make contact

(d) Bacterial and root nearly make contact

Biofertilizers [BVP 2000]

(a) Kill pests (b) Prevent pest growth

VAM is important for [Kerala PMT 2000]

(a) Breaking of dormancy (b) Phosphate nutrition

(e) Decrease in yield

Leghaemoglobin takes part in [Kerala PMT 2000]

(a) Energy release

(b) Stimulating growth of Rhizobium

(d) Protecting nitrogenase

(e) Supply of oxygen

Most famous nitrogen fixing bacterium/biofertilizer is

[Kerala PMT 2000; JIPMER 2000]

(a) Nitrobacter (b) Nitrosomonas

Azolla possesses symbiotic association with [Wardha 2001]

(a) Anabaena (b) Nostoc

Which one is a biofertilizer [BVP 2001]

(a) VAM (b) Sporeine

Azolla is used as biofertilizer as it has [DPMT 2001]

(a) Rhizobium (b) Cyanobacteria

Cow dung is appropriately used as [DPMT 2001]

(a) Manure (b) Fuel

Red pigment (Leghaemoglobin) having affinity for oxygen is present in the roots of [CBSE PMT 2001]

(a) Mustard (b) Soybean

Some blue green algae can be used as biofertilizer as they are [KCET 2002]

(a) Photosynthetic (b) Surrounded by mucilage

Organic forming is the technique of raising crops through use of [AMU 2003]

(a) Manures (b) Resistant varieties

Organic forming does not include [Wardha 2003]

(a) Green manures

(b) Chemical fertilizer

(d) Compost and farmyard manures

Mycorrhiza is helpful in [CPMT 2003]

(a) Synthesis of food

(b) Getting nutrients from soil

Increase the fertility of soil

Agricultural chemicals include [Pb. PMT 2000]

(a) Pesticides

(b) Fertilizers

(d) All of these

Pest control

Biopesticides include

(a) Bioherbicides

(b) Bioinsecticides

(d) Bioherbicides, bioinsecticides and biofertilizers

Transgenic crop developed to tolerate herbicides is

(a) Sunflower (b) Tomato

A transgenic crop that is resistant to hornworm larvae is

(a) Sunflower (b) Tomato

The first bioherbicide developed in 1981 was based on

(a) Phytophthora palmivora (b) Phytophthora infestans

‘Devine’ and ‘Collego’ are two agricultural substances that are used as

(a) Biofertilizers (b) Natural insecticides

Pheromones are chemicals that are used in animals for

(a) Sex attractants (b) Sending alarm signals

Rotenone is a [CBSE PMT 1995]

(a) Natural herbicide (b) Bioherbicide

A natural insecticide obtained from plants is

(a) Azadirachtin

(b) Rotenone

(d) All the above

Cochineal insect has been used in checking the wild growth of

[CBSE PMT 1996]

(a) Opuntia (b) Eichhornia

Pheromone traps have

(a) Sterile males (b) Male pheromones

In confusion technique, the pheromone coated paper strips are thrown over an area in order to

(a) Attract insects and kill them

(b) Repel insects from an area

(d) Confuse females so that they are unable to locate males

Juvenile hormone causes

(a) Early sexual maturity

(b) Late sexual maturity

(d) Development of giant larva without ability to undergo maturation

Pyrethrin is a common ingredient of

(a) Mosquito coils (b) Fly sprays

Thurioside is

(a) Insecticide (b) Fungicide

Antifeedant property occurs in

(a) Nicotine (b) Azadirachtin

Confusion technique uses [DPMT 2001]

(a) Juvenile hormone

(b) Ecdysone

(d) A combination of hormones

Which one is an effective plant insecticide [Bihar PMT 1987]

(a) Pyrethrin (b) Cinerin

Pyrethrin is extracted from

[RPMT 1989; CPMT 1999, 2004;
BHU 2000, 02; AFMC 2002]

(a) Azadirachta indica

(b) Helianthus annus

(d) Chrysanthemum cinerarifolium

The earliest pesticide was [MP PMT 1990]

(a) Margosa (b) Pyrethrum

First bioinsecticide developed on commercial scale was

[Bihar PMT 1988]

(a) Quinine (b) DDT

Biological control of pests is [CBSE PMT 1994; CPMT 2000]

(a) Polluting (b) Highly expensive

The phenomenon of using a predator for controlling a pest is

[CBSE PMT 1996]

(a) Biological control (b) Genetic engineering

Which is a microbial insecticide [AIIMS 1997]

(a) Bacillus thuringenesis (b) B. subtilis

Which weed has been eradicated by biological control

[DPMT 1997]

(a) Parthenium (b) Cactus

Third generation pesticides are [CBSE PMT 1998]

(a) Insect repellents

(b) Pheromones

(d) Insect hormone analogues

IPM (Integrated Pest Management) involves [CPMT 1998]

(a) Biological control

(b) Pesticides

(d) Biofertilizers

Corpora allata is removed from a nymph. It will

[RPMT 1998]

(a) Remain nymph for life

(b) Become adult

(d) Die after some time

Latest trend in plant disease control is [Pb. PMT 1999]

(a) Chemical control

(b) Biological control

(d) Breeding for disease resistance

A third generation pesticide is [AFMC 2000]

(a) Pheromone

(b) Weedicide

(d) Sterilogastrone

IPM stands for [Wardha 2001]

(a) International Population Management

(b) Integrated Pest Management

(d) Integrated Plant Management

Insecticide obtained from neem plant is [MHCET 2004]

(a) Pyrethrin (b) Pyrethroid

BT cotton is resistant to [Orissa 2005]

(a) Insect (b) Herbicides

By the turn of twentieth century, fertilizer consumption in India is expected to

(a) 9.2 M tonnes (b) 15 M tonnes

Free living nitrogen fixing bacteria can bring about saving of nitrogen fertilizer to the tune of

(a) 10 – 25 kg/ha (b) 30 – 50 kg/ha

Most active nitrogen fixing blue-green alga of rice fields is

(a) Anabaena azollae

(b) Aulosira fertilissima

(d) Nostoc cycadacearum

Nitrogen content of urea is [CPMT 1988]

(a) 26% (b) 56%

Which one is green manure/biofertilizer [Wardha 2002]

(a) Sesbania (b) Maize

A major pest eradicated through release of sterile males is

(a) Screw worm (b) Aphids

Ladybug is a predator of

(a) Moths (b) Beetles

Sporeine was developed in [CBSE PMT 1988]

(a) Germany (b) France

Thurioside is proteinaceous toxin obtained from

[AFMC 1999]

(a) Biofertilizer (b) Green manure

Brown Plant Hopper is [Kerala PMT 2000]

(a) Nilparavata lugens (b) Calliphora erythrophala

(e) Carasius morosus

Read the assertion and reason carefully to mark the correct option out of the options given below :

(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion

(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion

(c) If the assertion is true but the reason is false

(d) If both the assertion and reason are false

(e) If the assertion is false but reason is true

Assertion : Manures improve soil conditions.

Reason : In manures elements are not present in adequate proportions.

Assertion : Farmyard manure is the most commonly used organic manure in India.

Reason : Manure forms colloidal particles and soil crumbs.

Assertion : Compost is formed after decay of vegetable matter and organic refuse

Reason : Green manure is prepared by ploughing back any green plants into soil.

Assertion : Azotobacter fixes nitrogen in symbiotic form.

Reason : They form root nodules in the roots of leguminous plants.

Assertion : Azospirillum lipoferum shows associative mutualism.

Reason : It lives around the roots of higher plants.

Assertion : Rhizobium forms nodules on the roots of legume plants

Reason : In Sesbania rostrata, nodules are present on the stems, not on the roots.

Assertion : Intercropping checks the population of insects.

Reason : Plant pests can be controlled biologically by their natural parasites and pathogens.

Assertion : Pheromones are sex attractants given out by female insects

Reason : Pheromone traps and confusion technique are used to check the population of insects.

Assertion : Juvenile hormone inhibits maturation of insects if given artificially in later stages of growth of insects.

Reason : If forms giant larvae.

Assertion : Pyrethrum is collected from the leaves of Chrysanthemum cinerarifolium.

Reason : Pyrethrin is prepared from pyrethrum.

Assertion : Bacillus thuringenesis is toxic to many insects.

Reason : It inhibits ion transport in the midgut.

Biofertilizer

1	b	2	a	3	d	4	b	5	b
6	c	7	d	8	c	9	a	10	d
11	c	12	a	13	c	14	a	15	b
16	a	17	b	18	b	19	c	20	b
21	d	22	c	23	b	24	c	25	c
26	d	27	c	28	b	29	d	30	c
31	b	32	b	33	c	34	a	35	b
36	a	37	c	38	c	39	b	40	d
41	d	42	a	43	a	44	b	45	a
46	b	47	d	48	d	49	b	50	b
51	d

Pest control

1	c	2	c	3	b	4	a	5	d
6	d	7	c	8	d	9	a	10	c
11	c	12	d	13	d	14	a	15	b
16	c	17	d	18	d	19	a	20	d
21	c	22	a	23	a	24	b	25	d
26	a	27	a	28	b	29	c	30	b
31	d	32	a

Critical Thinking Questions

1	c	2	a	3	b	4	c	5	a
6	a	7	d	8	a	9	c	10	a

Assertion and Reason

1	b	2	b	3	c	4	e	5	b
6	c	7	b	8	b	9	b	10	e
11	a

Biofertilizer

(b) Rhizobium leguminosarium bacteria live symbiotically in root nodules of legumes and some non-legumes which fixes atmospheric N₂ and hence increase the fertility of soil.
(d) Green manure ploughed back young leguminous crop like Sesbania aculeata, Crotaloria juncea, Sesbania rostrata, etc.
(b) Azolla pinnata contains symbiont Anabaena in its leaf cavities.
(c) Endomycorrhizal fungal hyphae are present inside or between the cells of cortex. In many grass and some other crops the fungal hyphae penetrate to the cortical cells which swell to form vesicles or arbuscules called vesicular arbuscular mycorrhiza (VAM).
(d) A bacterium Azospirillum lipoferum forms loose association with roots of maize and some Brazilian grasses which increase the crop yield upto a large extent.
(a) Composited mannure is rotten vegetable matter, garbage, sewage sludge and animal refuse often enriched with small amount of chemical fertilizers during decomposition stage.
(d) Biofertilizers are of three types : nitrogen fixing bacteria, nitrogen fixing cyanobacteria and mycorrhiza.
(c) Mycorrhiza is a mutually beneficial relationship between fungus and roots of higher plants.
(c) Green manure not only maintains soil form but also increases in nitrogen content thus increasing crop yield by 30-50%.
(b) Phosphorous is recommended for better nitrogen fixation, so the mixture of phosphate fertilizer and Rhizobium culture is recommended for a better result.
(c) Mycorrhiza refers to symbiotic association between the fungus and roots of higher plants.
(b) Molybdenum (Mo) is responsible for nodulation in legumes. It is part of nitrate reductase enzyme which helps in nitrogen fixation.
(c) A root nodule has a growing point, vascular strand and reddish pigment leghaemoglobin but lacks root cap and root hair. Its central infection zone has large cells with groups of bacteriods covered by membrane lined by leghaemoglobin.
(b) Azotobacter and Bacillus polymyxa are free living or non-symbiotic nitrogen fixing bacteria of soil, which increase fertility of soil and hence yield of crop plants.
(b) They are the free living nitrogen fixing cyanobacteria and increase nitrogen content of moist soil and water bodies, which can be used in increasing paddy yield.
(d) Young leguminous crops are used for green manuring because they increase the nitrogen fertility of soil e.g., Crotalaria juncea, Sesbania aculeata, etc.
(b) Because Rhizobium bacteria live symbiotically in root nodules of legumes and some non-legumes.
(a) Nostoc is a free living nitrogen-fixing blue green algae probably with the help of heterocysts. Photosynthesis provides the energy for nitrogen fixation.
(b) Azolla pinnata (aquatic fern) is a symbiotic nitrogen fixing cyanobacteria which is inoculated in rice fields in south-eastern Asia, and found to increase yield upto 50%.
(c) Biofertilizers provides the essential elements to the soil and hence maintain or increase the soil fertility.
(b) VAM has significant role in phosphate nutrition of plants.
(d) The nodule cells have a pigment called leghaemoglobin. The fixation of nitrogen is brought about by the enzyme nitrogenase are those nodules where leghaemoglobin is not produced cannot fix nitrogen.
(a) Manure is a semi-decayed organic matter which is added to the soil in order to maintain its fertility, crumb structure, aeration and hydration capacities, e.g., dung, farm refuse, rotten vegetable matters etc.
(b) Leguminous plants are having root nodules and nodules contains a red coloured pigment called leghaemoglobin. This pigment is the oxygen carrier. It keeps the level of molecular oxygen low inside the bacteriod.
(b) Mycorrhiza is a mutually beneficial relationship between fungus and roots of higher plants. It helps in absorption of water, minerals from organic matter and protection from soil borne pathogenic fungi.

Pest control

Bioherbicides are involves the biological control of weeds by some living organisms and bioinsecticides are non persistent, non toxic and biodegradable.

(c)Transgenic crops are crops having genes of smoother crops, pest and herbicides resistance. e.g., transgenic tobacco.
(b) Transgenic crops are crops having genes of smoother crops, pest and herbicide resistance e.g., transgenic tomato (against horn worm larvae).
(a) The first bioherbicide was developed in 1981. It is a mycoherbicide, based on the fungus, Phytophthora palmivora. Which controls the growth of milk weed vines in citrus orchards.
(d) Devine and Collego derived from the fungal spores. Devine was first mycoherbicide and another mycoherbicide was Collego. Its controls growth of the milk weed vines in citrus orchards and growth the northern jointvetch growing in rice fields respectively.
(d)The pheromones are those chemical messengers which help in communication between the insects and useful in sending alarm signals, marking traits or attracting male.
(c) The rotenone is a natural powerful insecticide and is obtained from the roots of Derris elliptica.
(d) Azadirachtin, rotenone, nicotine, pyrethrum and cinerin are natural insecticides. Natural insecticides are obtained from living organisms (plants).
(a) In India and Australia, prodigious spread of prickly pear (opuntia) was controlled by introduction of cochineal insects (Cactoblastis cactorum).
(c) Pheromone traps are cylindrical traps coated internally with female pheromones will attract all males.
(c) Confusion pheromone technique are small paper pieces having female pheromones are thrown over the area and males will not be able to located females.
(d) Juvenile hormone at the late stage of larval development. The larva develops into gaint larva (immature adult) which die quickly without attaining maturity.
(d) Pyrethrum are obtained from the dry inflorescence of Chrysanthemum cinerarifolium. Pyrethrin is also used for sprays, mosquito coils mats and aerosols.
(a) Thurioside is toxic to several insects and produced by bacterium Bacillus thuringiensis.
(b) Neem extracts contain an antifeedant compound azadirachtin which keeps way the insects.
(d) Nicotine, pyrethrin and cinerin are natural insecticides and nicotine obtained from tobacco, pyrethrum and cinerin obtained from Chrysanthemum cinerarifolium.
(a) One of the earliest pesticides used by man was Margosa (neem) leaves.
(d) Sporeine was the first bioinsecticide developed on commercial scale in Germany and it kills the insect by inhibiting ion transport in the midgut.
(c) The control organism which parasitises/preys upon/ inhibits the target pest, multiplies itself and is, hence, self-perpetuating.
(a) Predators is example of biological control and lady bug (lady bird beetle) and praying mantis can control scale insect or aphid pests of vegetables.
(b) Biological pest control is one of the suitable methods, i.e., use of other organisms to kill the pests constitutes biological pest control.

Critical Thinking Questions

(b) Aulosira fertilissima is member of cyanophyceae.
(a) It is ploughed back young leguminous crop like Sesbania aculeata, S. rostrata, Crotalaria juncea etc.
(a) A large number of sterile males are released which mate without producing offspring e.g., screw worm (Kiplings 1955).
(a) Sporeine developed in Germany is the first commercial bioinsecticide obtained from Bacillus thuringiensis.
(c) Thurioside from Bacillus thuringiensis, is toxic to several insects.

Assertion and Reason

(b) Manures are organic wastes which are made to decay partially and added to the soil in order to increase its fertility, aeration and water holding capacity. They are relatively bulky materials such as animal and green manures, which are added mainly to improve the physical condition of the soil, to replenish and keep up its humus status, to maintain the optimum conditions for the activities of soil micro – organisms and make a small part of the plant nutrients removed by crops or otherwise lost through leaching and soil erosion. They, thus, supply practically all the elements of fertility which crops require, though not in adequate proportions.
(b) Good – quality farmyard manure is perhaps the most valuable organic matter applied to a soil. It is obtained by the partial decay of dung of farm animals, farm refuse, dead leaves and twigs. The various materials are placed in heaps and allowed to decompose till they form a dark amorphous substance. Manure contains humus or degradation product of cellulose and lignin. It forms colloidal particles in the soil which can imbibe water and cement soil particles. It also forms soil crumbs. It loosens the soil, increases soil aeration and allow easy penetration of roots.
(c) Compost is a prepared mixture made of rotted vegetable matter and manure. An enriched composited manure is made by dumping all kinds of plant matter including garbage of vegetable markets and other organic refuse in heaps interspersed by the thin sprinkling of chemical fertilizers like ammonium sulphate, superphosphate, sodium nitrate, lime etc. it requires – 6 months for preparation of manure. Green manure is prepared from young, green crop plants by ploughing them beck into soil. Usually young leguminous crops are used for green manuring because they also increase the nitrogen fertility of the soil. The plants are slowly converted into manure through the activity of micro organisms.
(e) Azotobacter is a non symbiotic nitrogen fixing bacteria that is it lives freely in the soil and perform nitrogen fixation. It is saprotrophic living on organic remains. Root nodules are formed by bacteria. Rhizobium is a symbiotic nitrogen fixing bacteria.
(b) Certain nitrogen fixing bacteria live around the roots of higher plants without developing any intimate relationship. It is often called rhizosphere association. The bacteria obtain some plant exudate and use the same as part of their food requirement. The bacteria fix nitrogen and exude a part of the fixed nitrogen for use by the plant. The phenomenon is termed as associative mutualism. Azospirillum also shows such association.
(c) Rhizobium forms nodules on the roots of legume plants, there are about a dozen species of Rhizobium which form association with different legume roots, g., R. leguminosarum, R.lupini, R.trifolli, R.meliloti, R.phaseoli. They develop the ability to fix nitrogen only when they are present inside the root nodules. One legume plant, Sesbania rostrata, has double symbiotic relationship with nitrogen fixing bacteria – Rhizobium in the root nodules, Aerorhizobium caulinodans in the stem nodules.
(b) Intercropping keeps the population of insects at low level. In intercropping, the pest-susceptible crop is grown alongwith other crops which are repellent to pests. Plant pests are controlled biologically through the means of their natural parasites and pathogens. For example, Baculovirus heliothis can control cotton ballworm, Bacillus thuringenesis can control the cabbage hooper and Entomophthora ignobilis can control the green peach aphid of potato.
(b) Pheromones are chemical substances which when released into an animals surroundings, influence the behaviour of development of other individual of same species. These also include sexual attractants in many insect species. Pheromones useful in controlling insect pests are sex attractants given out by female insects for attracting males during mating season. The males are able to detect the sex pheromones with the help of their antennae. In pheromone traps, traps controlling hollow cylinders coated from inside with a sticky substance and sex pheromones are kept at different places in the fields. The male insects fly into the traps and get immobilised. In confusion technique small pieces of wettable paper containing sex pheromone of a particular insect are dropped over the fields. The males will not be able to locate the females because the pheromone is spread everywhere.
(b) Juvenile hormone prevents maturation and induces growth. If juvenile hormone is given artificially in later stages of growth of insect, the latter does not undergo maturation but instead forms giant larva which die quickly.
(e) Pyrethrum is an insecticide which is obtained from the inflorescence of Chrysanthemum cinerarifolium, C. coccineum and marshallii. The active compounds are pyrethrin and cinerin. Pyrethrin is also used in fly sprays, aerosols, mosquito coils etc.
(a) Thurioside is a toxin produced by bacterium Bacillus thuringenesis. The toxin is highly effective against different groups of insects like moths, flies, mosquitoes and beetles. It kills the susceptible insects through inhibiting ion transport in the mid gut.