Microbes as Biocontrol Agents Questions in English

(B) $Bacillus$ $thuringiensis$ is a soil-dwelling bacterium that produces insecticidal proteins known as $Cry$ proteins or $\delta$-endotoxins.
These proteins are used as a $Biopesticide$ to control various insect pests.
It is widely used in agriculture,either through the development of transgenic crops (like $Bt$ cotton) or by spraying bacterial spores directly onto crops.

(A) The correct answer is $A$.
Genetically modified strains of $Pseudomonas$ (often referred to as 'superbugs') have been engineered to possess the ability to degrade complex organic pollutants,such as petroleum hydrocarbons and oils,in oil spills.
$Rhizobium$ is involved in nitrogen fixation in legumes.
$Nitrobacter$ and $Nitrosomonas$ are involved in the nitrogen cycle (nitrification).

(D) $Trichoderma$ $viridae$ is a free-living fungus that is very common in the root ecosystem. It is an effective biocontrol agent for several soil-borne plant pathogens. It acts by producing enzymes and antibiotics that inhibit the growth of harmful fungi,thereby protecting crops from diseases.

(A) Malaria is a disease transmitted by the bite of infected female $Anopheles$ mosquitoes.
To control the spread of malaria,biological control methods are used to reduce the mosquito population.
$Gambusia$ is a larvivorous fish that feeds on the larvae of mosquitoes in water bodies,thereby preventing them from reaching the adult stage.
Therefore,$Gambusia$ is used as a biological control agent for malaria.

(A) $Gambusia$ is a type of fish that is widely used as a biological control agent.
It is a predator that feeds on mosquito larvae.
By consuming mosquito larvae in water bodies,it helps in controlling the spread of diseases like malaria and dengue.

(C) Stomach poisons are a type of insecticide that must be ingested by the pest to be effective.
These substances reach the alimentary canal or stomach of the insect along with its food.
Once ingested,they act on the digestive system of the insect,leading to its death.
Therefore,the correct option is $C$.

(A) $IPM$ stands for Integrated Pest Management.
It is an ecological approach to pest control that focuses on long-term prevention of pests or their damage through a combination of techniques such as biological control,habitat manipulation,modification of cultural practices,and use of resistant varieties.
Pesticides are used only after monitoring indicates they are needed according to established guidelines,and treatments are made with the goal of removing only the target organism.

(A) Pyrethroids are synthetic derivatives of pyrethrins, which are natural compounds found in the flowers of chrysanthemum species such as $C. \text{ marshalli}$, $C. \text{ cinerarifolium}$, and $C. \text{ coccineum}$. While pyrethrins are of plant origin, pyrethroids are chemically modified synthetic versions designed to be more stable and effective as insecticides. Therefore, they are considered to be of synthetic origin.

(B) The 'Bordeaux mixture' is a fungicide used to control various fungal diseases in plants.
It is traditionally prepared by mixing copper sulphate $(CuSO_4)$, calcium hydroxide $(Ca(OH)_2)$, and water in a specific ratio.
The standard formulation is $4$ parts of $CuSO_4$, $4$ parts of $Ca(OH)_2$, and $50$ parts of water.
Therefore, the ratio is $4 : 4 : 50$.

(C) Bordeaux mixture is a fungicide used to control various fungal diseases in plants.
It is prepared by mixing copper sulphate $(CuSO_4)$ and calcium hydroxide ($Ca(OH)_2$,also known as slaked lime) in water.
Therefore,both $(a)$ and $(b)$ are required to make the mixture.

(D) $Zinc \ phosphide$ $(Zn_3P_2)$ is a highly toxic inorganic compound used primarily as a rodenticide. When ingested by rodents,it reacts with stomach acid to release $Phosphine$ $(PH_3)$ gas,which is lethal to the animal. Therefore,it is specifically used to control rodent populations.

(C) Paris green is a bright green pigment that was historically used as an insecticide and rodenticide.
Its chemical composition is copper$(II)$ acetoarsenite.
The chemical formula is represented as $Cu(C_2H_3O_2)_2 \cdot 3Cu(AsO_2)_2$.

(B) The 'Bordeaux mixture' is a combination of copper sulfate $(CuSO_4)$,lime $(Ca(OH)_2)$,and water.
It is primarily used in agriculture and horticulture as an inorganic fungicide to control fungal diseases on crops,fruits,and ornamental plants.
Therefore,the correct option is $B$.

(C) Ethylene dichloride $(EDC)$ is a chemical compound commonly used as a fumigant.
It is primarily used to control pests in stored grains and agricultural products by releasing toxic vapors that penetrate the target organisms.
Therefore,it is classified as a fumigant.

(D) Malathion is an organophosphate pesticide that has a strong effect on the nervous system.
It functions by inhibiting the activity of the enzyme acetylcholinesterase.
This inhibition leads to the accumulation of the neurotransmitter acetylcholine at the synaptic cleft, causing continuous nerve stimulation and eventually paralysis or death of the pest.

(A) 'Flit' is a well-known insecticide spray.
Its two primary active ingredients are $Malathion$ and $Pyrethrin$.
$Malathion$ is an organophosphate insecticide,while $Pyrethrin$ is a natural insecticide derived from chrysanthemum flowers.

(B) The correct answer is $B$.
$Dithiocarbamates$ are a class of chemical compounds derived from $dithiocarbamic$ acid.
Many $dithiocarbamates$ are widely used in agriculture as fungicides to protect crops from various fungal infections.
Examples include $Mancozeb$ and $Zineb$.

(A) Pyrethrins are natural insecticides obtained from the flowers of the plant $Chrysanthemum$ $cinerarifolium$. These compounds act as potent neurotoxins to insects and are widely used in organic farming and household pest control. Pyrethroids are synthetic chemical derivatives that mimic the structure and action of natural pyrethrins.

(B) Bordeaux mixture is a fungicide used to control various fungal diseases in plants. It is prepared by mixing copper sulphate $(CuSO_4)$ with lime (calcium hydroxide,$Ca(OH)_2$) in water. The term 'Milk of lime' refers to a suspension of calcium hydroxide in water,which is the correct ingredient used in this preparation.

(C) Endosulphan is an organochlorine insecticide and acaricide that is used to control a wide range of pests,including aphids,caterpillars,plant bugs,and borers on various crops.
It acts as a contact and stomach poison,effectively managing insect populations in agricultural settings.

(A) Biological control refers to the use of biological methods for controlling plant diseases and pests. This method relies on natural predation,parasitism,or other natural mechanisms rather than the introduction of chemicals. Examples include using ladybird beetles to control aphids or Bacillus thuringiensis to control butterfly caterpillars.

(B) The correct answer is $B$.
In Australia and other regions,the invasive spread of the prickly pear cactus $(Opuntia)$ caused significant ecological damage.
To control this,the moth $Cactoblastis$ $cactorum$ (a cochineal insect) was introduced as a biological control agent.
This insect feeds on the cactus,effectively checking its rapid growth and spread.

(C) $Gambusia$ is a carnivorous fish. It feeds on the larvae of $Anopheles$ mosquitoes. This fish is widely used in the biological control of mosquitoes to prevent the spread of diseases like malaria.

(D) In $1920s$,the prickly pear cactus $(Opuntia)$ was introduced into Australia,where it spread rapidly into millions of hectares of rangeland.
It became a major menace to the local ecosystem and agriculture.
It was successfully controlled by the introduction of the cochineal insect $(Cactoblastis cactorum)$,which is a biological control agent that feeds specifically on the $Opuntia$ cactus.
This is a classic example of biological control of weeds.

(D) The most popular bioinsecticide in India is derived from the neem tree, $Azadirachta$ $indica$.
It contains active compounds like azadirachtin, which act as effective natural pesticides and insect repellents.
Therefore, the correct option is $D$.

(B) Biological control is a method of controlling pests using other living organisms (predators or parasites).
One of the major challenges in this method is that the predator or parasite introduced to control a specific pest may not always survive or adapt well when transferred to a new environment,as it may be sensitive to the local climate,lack of alternative food sources,or other ecological factors.
Therefore,option $B$ is the most significant practical difficulty among the choices provided.

(A) Before the widespread use of synthetic chemical insecticides like $DDT$ in the $1940s$,humans relied on natural substances for pest control.
Pyrethrum (extracted from Chrysanthemum flowers) and rotenone (extracted from the roots of certain tropical legumes) were the two primary natural insecticides used extensively before $1940$.

(D) Insecticides are chemical substances used to kill insects.
They are generally non-selective in their action,meaning they do not distinguish between harmful pests and beneficial insects (such as pollinators like bees or natural predators).
Therefore,the indiscriminate use of insecticides leads to the destruction of both harmful and useful insects.

(D) Bio-insecticides are biological agents used to control insect pests. They include:
$1$. Pathogens: Such as bacteria $(Bacillus thuringiensis)$,viruses $(Baculoviruses)$,and fungi.
$2$. Parasites: Organisms that live on or inside the host to derive nutrition,often killing the host.
$3$. Predators: Organisms that hunt and consume insect pests (e.g.,ladybird beetles,dragonflies).
$4$. Other methods: Including insect hormones and natural insecticides.
Therefore,all the listed options are components of bio-insecticides.

(A) The first natural insecticide used by the Chinese was $Chrysanthemum$ flowers,which contain the active compound $Pyrethrum$. It has been used for centuries as a natural insect repellent and insecticide.

(A) The biological control of insects involves the use of natural predators, parasites, or pathogens to manage pest populations. Extensive research and practical applications of these methods have been primarily conducted in $North \text{ } America$ to reduce reliance on chemical pesticides.

(B) Cochineal insects,specifically $Dactylopius$ $ceylonicus$,are biological control agents used to manage the growth of invasive $Opuntia$ (prickly pear) $Cactus$ species. These insects feed on the $Cactus$ tissues,effectively reducing their population in areas where they have become invasive weeds.

(C) Biopesticides,or pesticides of biological origin,are primarily categorized into two types: bioherbicides and bioinsecticides.
Bioherbicides involve the biological control of weeds using specific living organisms.
Bioinsecticides are agents that are non-persistent,non-toxic,and biodegradable,used to control insect populations.

(A) The first bioherbicide was developed in $1981$.
It is a mycoherbicide based on the fungus $Phytophthora$ $palmivora$.
This bioherbicide is used to control the growth of milkweed vines in citrus orchards.

(D) 'Devine' and 'Collego' are examples of mycoherbicides, which are biological agents used to control weeds.
'Devine' is a mycoherbicide derived from the fungus $Phytophthora$ $\text{palmivora}$, used to control milkweed vines in citrus orchards.
'Collego' is a mycoherbicide derived from the fungus $Colletotrichum$ $\text{gloeosporioides}$, used to control the northern jointvetch in rice and soybean fields.
Therefore, both are classified as bioherbicides.

(C) Rotenone is a natural,powerful insecticide that is extracted from the roots of the plant $Derris$ $elliptica$.

(D) The correct answer is $D$.
$Azadirachtin$ is extracted from the neem tree $(Azadirachta \, indica)$.
$Rotenone$ is a natural pesticide obtained from the roots of several tropical plants.
$Nicotine$ is obtained from tobacco plants, while $Pyrethrum$ and $cinerin$ are extracted from the flowers of $Chrysanthemum$ species.
Since all these substances are natural insecticides derived from plants, the correct option is $D$.

(A) The cochineal insect,specifically $Cactoblastis cactorum$,is a biological control agent.
In countries like India and Australia,the rapid and invasive spread of the prickly pear cactus,known as $Opuntia$,caused significant ecological damage.
To control this,the cochineal insect was introduced as a biological control method,which successfully fed on the $Opuntia$ plants and checked their wild growth.

(C) Pheromone traps are specialized devices used in integrated pest management.
These traps are coated internally with synthetic female sex pheromones.
Since male insects are highly sensitive to these chemical signals,they are attracted to the trap in search of a mate.
Once they enter the trap,they get stuck,which helps in monitoring or reducing the population of the pest species.

(C) The confusion technique involves using small paper strips coated with synthetic female pheromones. These are scattered over an area to create a high concentration of pheromones in the environment. This masks the natural pheromone trails released by females,making it impossible for males to locate and mate with them,thereby disrupting the reproductive cycle.

(D) Pyrethrin is a natural insecticide obtained from the dried inflorescence of $Chrysanthemum$ $cinerarifolium$. It is widely used in various household insect control products, including mosquito coils, fly sprays, and mosquito mats, due to its effective knockdown properties against insects.

(B) The correct answer is $B$.
$Azadirachtin$ is a chemical compound extracted from the neem tree $(Azadirachta \text{ indica})$.
It acts as a potent antifeedant, meaning it inhibits insects from feeding on the plant.
It disrupts the growth and development of insects, making it an effective natural biopesticide.

(C) The confusion technique,also known as mating disruption,is a pest management strategy that uses synthetic pheromones to interfere with the mating process of insects.
By releasing high concentrations of female sex pheromones into the environment,males are unable to locate females,which prevents successful mating and reduces the population of the next generation of pests.

(D) Pyrethrin is a natural insecticide obtained from the dried flower heads of the plant $Chrysanthemum$ $cinerarifolium$. It is widely used as a botanical pesticide due to its rapid knockdown effect on insects.

(A) The earliest pesticide used by humans was Margosa,commonly known as $neem$ leaves. It has been used for centuries in traditional practices to protect stored grains and crops from pests.

(D) The correct answer is $D$.
$Sporeine$ was the first bioinsecticide developed on a commercial scale in Germany.
It is derived from the bacterium $Bacillus$ $thuringiensis$ $(Bt)$.
It functions by producing crystalline protein toxins that,when ingested by the insect,inhibit ion transport in the midgut,leading to the death of the insect.

(C) Biological control refers to the use of biological methods for controlling plant diseases and pests.
$(c)$ The control organism,which parasitizes,preys upon,or inhibits the target pest,multiplies itself in the environment and is,therefore,self-perpetuating.

(A) The use of natural predators or parasites to control pest populations is known as $Biological \ control$.
This method relies on natural predation rather than chemical pesticides.
For example, the $Ladybird$ beetle is used to control aphids, and the $Dragonfly$ is used to control mosquitoes.
These organisms act as biocontrol agents to maintain ecological balance.

(A) $Bacillus$ $thuringiensis$ (often abbreviated as $Bt$) is a soil-dwelling bacterium that produces insecticidal crystal proteins ($Cry$ proteins).
These proteins are toxic to specific insect larvae, such as those of lepidopterans, coleopterans, and dipterans, making it a widely used microbial biocontrol agent in agriculture.

(B) Biological control refers to the use of biological methods for controlling plant diseases and pests. In the case of the prickly pear cactus $(Opuntia)$,it was successfully controlled in Australia using the moth $Cactoblastis$ $cactorum$. This is a classic example of biological control where a specific insect predator was introduced to manage an invasive weed species.