CLASSIFICATION BASED ON MODE OF ENTRY: The way in which insecticides penetrate into an insect
From out side vary with the chemical nature of the insecticide. Four major routes of entry in to an insect body have been recognized and accordingly insecticides are grouped under four major categories as follows.
1) CONTACT INSECTICIDES: These are highly toxic insecticides which have the ability to penetrate the body surface of insects on contact with it. After getting into the body of insects they interfere with its nervous system and kill it.
Eg:- DDT, HCH, Aldrin, Parathion, Nicotine.
2)STOMACH POISON: These are chemicals which become toxic and fatal to the insect only when the insect ingests/eat them. From the gut they are absorbed to the tissues, interfere with the normal metabolism and kill the insect. They are basically compounds of Arsenic or fluorine.
3) FUMIGANTS: These are highly volatile insecticides, whose gases can produce a toxic cover around the insect. Fumigants are gases at normal temperature and pressure and hence they are stored in pressurized containers. They get into the insect body through spiracles. Fumigants are usually used to protect stored grains and other materials.
Eg:- Hydrogen cyanide, Methyl bromide, Ethylene dichloride, Ethylene dibromide, Lindane, Dichlorvos.
4) SYSTEMIC INSECTICIDES: Systemic insecticide is a compound which can get absorbed to the sap stream of plants from stem, leaves, fruits and roots, generally it is through roots. They move along the vascular system in an apical direction from the area of application. This may poison the insects that feed on the sap of these plants.
Eg:- Parathion, Malathion, Diazinon, Lindane, Nicotine.
The advantage of systemic insecticides are that (1) They need not be applied all over the plant body, (2)Action persists for long time,(3) No harmful effect on non-sap feeders and beneficial insects (4)They can be applied as direct foliar sprays or can be injected to the shoot system.
CLASSIFICATION BASED ON APPLICATION: Based on the nature of their application, chemical pesticides can be grouped as the following categories.
1)ATTRACTANTS: These are substances which can attract insects without contact. Synthetic chemical attractants are important in pest control. Both male and female insects will respond to them for feeding purpose, while only mature female insect will be attracted for egg-laying purpose.
2) REPELLENTS: These are not successful in controlling plant pests, because a continuous emission is essential for effective protection. But chemical repellents are effective for personal protection from blood- sucking insects.
3)FEEDING DETERRENTS: These are chemicals which suppress the feeding instinct of insect pests. They influence the pests only after contacting them.
4) AUXILIARY SUBSTANCES: These are substances that are mixed with insecticides to boost up its action.
CLASSIFICATION BASED ON CHEMICAL NATURE:
INORGANIC INSECTICIDES: These are mainly made up of sulphur and mineral compounds. The common mineral compounds are the compounds of arsenic, copper, lead, mercury and fluorine. They are broad- spectrum poisons, which are highly toxic and essentially non-degradable. They can remain in the soil for log time and can cause permanent damage to most of the organisms.
Arsenic Compounds:- Lead arsenate, Calcium arsenate, White arsenic, Paris green.
Fluorine compounds:- These are primarily stomach poisons, and is soluble in the digestive juice of insects. Eg:-Sodium fluoride, Sodium floroalumintate, Sodium fluorosilicate.
Sulphur:- Sulphur is mixed with
Monday, October 15, 2018
PESTS: Pests are harmful species, whose population size or population density goes beyond the damage threshold level, either throughout the year or during specific seasons, adversely affecting the availability, quality and value of human resources.
NATURAL PEST CONTROL: This involves the operation of natural factors, without much human influence. Includes Climatic, Topographic and Biological Factors.
a) Temperature: Temperature is the most effective and most important factor in insect control. Each insect requires an optimum range of temperature for each stage of its life cycle. If the temperature goes above or below the optimum range, it will have a damaging effect on insect population and even kill the insects.
b) Rain: Too much or too little rain fall can control the growth of insects. Eg:- Red hairy caterpillar of Cut worms has to burrow in to the soft soil for pupation and moderate rain enables this. Absence of rain makes the soil hard and caterpillar find it difficult to enter in to the soil for pupation.
c) Humidity: High humidity helps the developments of certain fungi which attacks the insects and thereby control insect population. Eg:- In Nilgiri area, during October to January, when humidity goes high, resulting in the growth of a fungi, Cephalosporium lecanii on Green Scale Insect of Coffee and controls it.
Geographical barriers like large mountain ranges, large water bodies, vast deserts, dense forests etc limits or restrict the dispersal of insects. The nature of lakes and rivers like the larva of some insects survive only in stagnant or slow moving waters, while the larva of black flies and caddis flies live only in swift flowing streams.
For any insect there are natural enemies. They may be parasites or predators. Predators include other insects, mites, spiders, birds, reptiles, fishes and mammals. Parasites include insects, mites and disease causing viruses, bacteria and fungi. These keep the insect population in an optimal size. Birds are very effective in controlling insect population as they feed on grass hoppers, caterpillars, wood-boring insects and scale insects. Many larvivorous fishes feed on the larvae of insects.
CULTURAL PEST CONTROL:
Cultural pest control is the deliberate modification of agricultural practices so as to destroy the insect pests or to prevent them from destroying the crop. Pests are either locally eliminated or are reduced to well below the damage threshold level. This method is the cheapest of all control measures, has no toxicity and minimal harm to non targeted organisms. This include
a) Crop Rotation: This is the practice of growing a different crop in a field every year in a 2-6 year cycle. It keeps the pest population from building up. This is most effective to control soil- inhabiting pests. If the same crop is grown continuously for many years, the pest of that crop will get a regular and continuous source of food and breeding sites, which will result in an uncontrolled increase of that pest. Eg:- A soya bean Corn crop rotation is effective and economical against some weevils because the host plant of the insect will be altered and is deprived of food supply.
b) Trap Cropping or Companion Cropping: In this method, small ‘trap plots (Plots where more susceptible or preferred crops are grown) are maintained near the major crop. Trap crop act as a trap’ and attracts the pest. After the pest had established on the host in the trap plot, the plot is either ploughed or treated with pesticide. Eg:- Castor plants are often planted near chilly cultivation and Tomatoes in Citrus orchards.
c) Mixed Cropping: In this method 2 or more crops are grown simultaneously in the same plot. Even if one crop suffers from pest attack, the others grow up well.
d) Tillage Operation:- Thorough ploughing helps to burry and kill soil inhabiting insects and their eggs, larvae and pupae. This is also helpful in exposing hiding and hibernating stages of pests to hot sun, desiccation and bird predation.
MECHANICAL PEST CONTROL:
These are procedures by which pest species are trapped or killed by mechanical means, or are prevented from gaining access to the host plants by making barriers. It is very effective in the initial stages of infestation of some insect pests, such as aphids, jassids, scale insects etc. The commonly used mechanical pest control procedures are the following.
1) Killing of the eggs, Larvae and other inactive stages of pests by hand picking, net collection etc.
2) Collection and destruction of pests using Traps and Trenches like Cricket-traps, Light-traps, Suction- traps, Electric traps etc.
3) Sieving and winnowing for stored products.
4) Mechanical exclusion using barriers, which will prevent the pests from reaching the crop.
5) Destruction of affected plants and plant parts together with the pest.
6) Spiking of stem- borers in their bore holes.
7) Banding of fruit trees with grease or other banding materials to stop or entangle & kill crawling pests.
8) Shaking of trees & shrubs to dislodge and kill pests.
9) Flooding of the infested fields after harvest to kill the soil- inhabiting larvae, pupae, and adult pests.
10) Pest- proof packing of stored products.
11) Covering of fruits and vegetables.
PHYSICAL PEST CONTROL:
This involves the deliberate modification of some physical factors to slow down the growth or minimise or prevent pest infestation. They include,
a) Use of Drie- die: Drie die is a material formed of highly porous silica gel. Its application causes the excessive loss of moisture from the body of insects, result in their death. This method is effectively used against the pests of stored grains in USA.
b) Use of high and low lethal temperatures: High frequency radio waves generate a temperature of about 80*C and is used to kill granary weevils and flour beetles.
c) Use of ionizing radiations to kill insect pests or to induce sterility; male insects can be made sterile by exposing them to gamma radiation.
d) Blowing of refrigerated air through stored grains to maintain a very low temperature and to kill the pests.
e) Use of light traps to attract, catch and kill nocturnal insects.
f) Use of colour traps to attract, catch and kill some diurnal insects.
LEGAL OR REGULATORY PEST CONTROL:
Legal or legislative pest control is the control of pests through the enactment of laws and regulations. This prevents the entry of pest species from one country to another so that living things could not be freely imported or exported between countries. The legal measures, now in force in different countries are
1) Legislation for foreign quarantine to prevent the introduction of new pests, diseases and weeds from foreign countries.
2) Legislation for domestic quarantine to prevent the spread of established pests, diseases and weeds from one part of the country to another.
3) Legislation to ensure the application of effective control measures to prevent the damage by established pests, diseases and weeds.
4) Legislation to fix the permissible level of pesticide residues in food stuffs and also to prevent the adulteration and misbranding of pesticides.
5) Legislation to regulate pest- control activities and operations and also to regulate the applications of hazardous pesticides.
In India presently there are 2 kinds of regulatory measures for pest control. They are
1) Legislative measures through plant quarantine - This deals with the prevention of introduction of exotic pests and diseases in to the country and their spread from one state or union territory to another.
2) Legislative measures through State Agricultural Pests and Diseases Act. This deals with the prevention of spread of pests and diseases in areas within a state or union territory.
other insecticidal dusts, which prevents the balling of the dust. Eg:-Lime sulphur, Borax (Sodium tetraborate).
ORGANIC INSECTICIDES: Organic insecticides are different types and are widely used in modern agricultural practices. The major categories are 1) Hydrocarbon oils, 2) Organic compounds of animal origin, 3) Organic compounds of plant origin, 4) Synthetic organic insecticides.
HYDROCARBON OILS:- These are the insecticides, formed of Hydrogen and Carbon. Mineral (petroleum) oils and coal tar are example. The insecticidal property of these oils is due to the presence of a heterogeneous mixture of cyclic and saturated as well as unsaturated hydrocarbons in them.
Hydrocarbon oils are widely used as insecticides mainly because they are cheap, have good spreading capacity, are less toxic to animals, are easy to mix, and insect develop no resistance against them. The disadvantages of hydrocarbon oils include, they are more toxic to plants and less toxic to insects, and are unstable to store. Often they damage the rubber parts of the spraying instruments.
ORGANIC INSECTICIDES OF ANIMAL ORIGIN:- There are only very few insecticides of animal origin. The most important of this type is the toxic substance extracted from the marine Annelids Lumbrineris heteropoda and Lumbrineris brevicirra. This extract is called Neristoxin (Dimethylamino dithiolane) and is very effective.
ORGANIC INSECTICIDES OF PLANT ORIGIN:- These are generally called botanicals . They are extracted from plants. The following are examples.
Nicotine :- Nicotine is the main alkaloid present in tobacco, is well known for its insecticidal property. It is present in the leaves of Nicotiana tabacum. Nicotine is neurotoxic and it can enter into the body of insect pests through cuticle, spiracles and ingested food. It can be sprayed as a solution with soap, lime or ammonium hydroxide. The solution can be prepared by boiling 1 kg of tobacco waste in 10 litres of water for 30 minutes and then by diluting it into 30 litres and adding 90 gm of soap. This solution is an effective insecticide.
Pyrethroids:- Pyrethroids are extracts of the plant Chrysanthemum coccineum. The insecticidal property of pyrethroids is due to the presence of esters. The flowers of Chrysanthemum are powdered and a mixture of this power and talc or clay is used as an insecticidal dust. This is a contact poison. When this powder is dusted on a pest, it knocks down the pest immediately. Usage of increased concentration of this pesticide ensures the death of the pest and prevents recovery of the pest due to enzymatic degradation of pyrethroids. They have broad insecticidal property and low mammalian toxicity.
Rotenoids:- Rotenone is a compound present in the roots of plants Derris and Lonchocarpus. It was first extracted in 1848, and used against leaf-eating caterpillars. Insects, poisoned with rotenone , show a decline in oxygen consumption, leading paralysis and death. On exposure to light and air, rotenone may get oxidized to a non-insecticidal compound.
Neem products:- The comounds extracted from Neem plant, Azadirachta indica are of high inscecticidal usage. From neem tree compounds such as Nimbecidine and from the kernels of neem tree Azadirachtin is extracted.
SYNTHETIC ORGANIC INSECTICIDES:-
These include organochlorines, organophosphorus compounds, carbamates, synthetic pyrethroids, insect growth regulators, organic thiocyanates and dinitrophenols.
Organochlorines :- They are also called Chlorinated hydrocarbons. They consists of an aliphatic or aromatic hydrocarbon nucleus and varying number of chlorine atoms attached to it. DDT, BHC (more correctly termed HCH- Hexachlorocyclic hexane.), Chlordane, Lindane, Heptachlor, Toxaphene, Aldrin, Dieldrin,Endrin, Endosulfan are some of the examples.
Organochlorines are hard or persistent pesticides, because they are not easily bio-degradable. They persist in the soil up to 15 years, get biologically magnified and are stored in the fatty tissues of a variety of organisms. This causes severe problems with environmental contamination and residues in soil and harvested food products.
Chlorinated hydrocarbons are quick acting and highly toxic to most of the organisms. They are neurotoxins, which inhibit iron transport across nerve membrane and interfere with the transmission of nerve impulses. Some of them have hormone-like growth regulating properties. Most organochlorines act by contact, some by ingestion and others by vapour action. The toxicity to human beings varies with their kind and there is no effective remedy for mammalian poisoning.
DDT (dichloro diphenyl trichloro ethane) is the most important organochlorine compound. In India, the use of DDT in agriculture is banned. It was first synthesized by Othnar Zeidlar in 1874 and insecticidal properties were discovered by Paul Muller in 1934. DDT is a stomach poison and a contact insecticide of high persistence. It affects sense organs and nervous system. Many insects developed resistance to DDT due to irrational use.
Endosulfan is a chlorinated hydrocarbon and an organic sulphate. It was using since 1956 as an insecticide. It acts as a contact poison and also a stomach poison. It is effective against insects which sucks plant juice. Endosulfan is discussed widely now a days because of the toxicity caused to human beings and other organisms due to the over and irrational usage in the cashew plantations of Kasaragod District. Thousands of people are affected due to environmental contamination in soil, water and air and residues in soil and harvested food.
ORGANOPHOSPHORUS COMPOUNDS:- These are organic pesticides, with a invariable phosphorus- containing central core and variable remaining part. This group includes some of the most toxic insecticides such as parathion, malathion, diacinon, trithion, ethion, fenthion, dichlorvos, etc.
These are nerve poisons, extremely toxic to not only insects, but also to fishes, birds and mammals including human beings. They inhibit the action of choline esterase enzyme, which degrades the excess of the neurotransmitter and thereby prevents persistent post-synaptic depolarization. They are bio-degradable and hence are not persistent, which remain in the atmosphere only for few hours or days. Most of them are contact poisons, while demeton-S-methyl is systemic poison and dichlorvos is a fumigant.
CARBAMATES or URETHANES:- They are derivatives of carbamic acid and have a carbamic acid nucleus. They are inhibitors of choline esterase. Carbaryl (sevin), isolan, pyrolan, aldicarb (temik), aminocab (zeneb), carbosulfan, carbofuran (baygon), etc are examples. Carbaates like carbaryl are less toxic , mostly used for horticultural purposes, while others are highly poisonous.
SYNTHETIC PYRETHROIDS:- Synthetic pyrethriods can over come the draw backs of natural pyrethrum since they are more stable and more toxic and are effective against a wide range of insect pests. Eg:- Permethrin, Cypermethrin, Allethrin, Cyfluthrin, Fenvalerate.
INSECT GROWTH REGULATORS (IGRs) :- These are chemicals with the properties of moulting and growth hormones of insects, and also with the potentiality to kill insects. They interfere with the action of insect growth hormone systems and thereby inhibit moulting and growth , eventually killing the insects. Eg:- Dimilin, Penfluron, Juvabione, Methoprene, Ecdysoid etc.
Wednesday, November 8, 2017
Genetic material is the substance that carries the biological information regarding the structural, functional, developmental and behavioural properties of organisms. It also serves as the agent that transfers or transmits biological information from parent to progeny. In most organisms, DNA is the genetic material. But, in some viruses, RNA serves as the genetic material.
Properties of the genetic material
Some of properties are the following:
(i)Genetic material should be present in every cell.
(ii) Ability to store and transmit biological information in a stable form.
(iii) Ability to replicate with high fidelity to produce identical functional copies.
(iv) Ability to distribute its copies equally from parent cells to daughter cells with extreme accuracy and minimal error.
(v) High physical and chemical stability to prevent the loss of information and also to ensure genetic constancy in organisms.
(vi) Potentiality to generate variations (through mutation, recombination and minor errors in replication and distribution) in order to promote genetic diversity.
(vii) Ability to act and express itself for controlling the inheritance of characters specified by it.
Sunday, November 5, 2017
bacterium, the ability of purified polysaccharide to transform was also tested, but no transformation
Avery, MacLeod and McCarthy repeated Griffith's expts in vitro in a much refined way. Culture of live IIR cells produced typical IIR cell colonies, while a culture of heat-killed III s cell or a a culture of the DNA isolated from IIIS cells produced no colony. At the same time. of IIR cells, mixed either with heat-killed IIIS cells or with the DNA isolated from lllS on a medium containing antibodies for IIR cells (Ab IIR), produced some colonies of III s cells. AbIlR was used for inactivating some llR cells so that the number of IIR cells may not exceed the number of IIIS cells. These findings reveal that DNA can be the transforming Since DNA preparations often contain traces of RNA and proteins. this conclusion is not beyond doubt. In order to establish beyond doubt that DNA alone is the transforming principle, Avery and associates conducted two separate experiments, using the DNA isolated from lllS cells.In one of them, the DNA isolated from lllS cells was treated with the enzyme RNAse (to digest RNA if any), and in the other with the enzyme protease (to digest protein), before it was mixed with live llR cells. ln both these expts, some IllS cell colonies were fomied. This clearly shows that RNA and Proteins are not responsible for the transformation of III R cells to lllS cells.In another expt DNA was treated with the enzyme DNAase before it was mixed with live IIR cells.This did not yield a III S colony.This confirms that DNA is the transforming principle.
Sunday, September 17, 2017
Hemoglobin is a globular heme protein in vertebrate red blood cells and in the plasma of many invertebrates that carries oxygen and carbon dioxide; heme group binds oxygen and carbon dioxide and as well as imparts red color to the blood; also spelt as hemoglobin.Red colored conjugated protein (made up of heme and Globin) present inside the RBCNormal Hb% in adult male is 14 to 16 gm.Approximately 6.25 gm of Hb are synthesized and destroyed every day.Heme structure does not vary from species to species.It is the basic protein globin that varies in amino acid composition and sequence in different species.Globin is rich in Histidine and lysine.
Structure of Hemoglobin: Hemoglobin is a conjugated protein. It consists of a
protein combined with an ironcontaining pigment. The protein part is globin and the iron containing pigment is heme. Heme also present in the structure of myoglobin ie oxygenbinding pigment in muscles and neuroglobin ie oxygenbinding pigment in brain. Heme is iron porphyrin compound.Iron is present in ferrous (Fe2+) form. It is in unstable or loose form. In some abnormal conditions,the iron is converted into ferric (Fe3+) state, which is a stable form.The pigment part of heme is called porphyrin. It is formed by four pyrrole rings (tetrapyrrole) called, I, II, III and IV. The pyrrole rings are attached to one another by methane (CH4) bridges.The iron is attached to ‘N’ of each pyrrole ring and ‘N’ of globin molecule.Globin contains four polypeptide chains. Among the four polypeptide chains, two are βchains and two are α-chain /α-chain is made up of 141 aminoacids β-chain is made up of 146 aminoacids.
Varieties of normal human Hb are
HemoglobinA1 (two α-chains and β-chains)
HemoglobinF (two α-chains and ¥-chains)
HemoglobinA2 (two α-chains and delta-chains)
Embyonic Hemoglobin (two α-chains and €-chains)
Hemoglobin-A3 (Altered from Hb-A found in old red cells)
HemoglobinA1C (Glycosylated Hb, present in concentration of 3-5% of total Hb). In diabetes mellitus it is increased to 6 to 15%.
1 Hemoglobin as oxygen carrier:The main function of hemoglobin is to carry oxygen from the lungs to all the tissues of the body. This is due to the affinity of hemoglobin for oxygen. When hemoglobin comes in contact with oxygen, it combines with it and form oxy-hemoglobin. This is a week bond. When blood reaches to tissues, where oxygen is deficient, the bond is broken and oxygen diffuses out to tissues.
2.Hemoglobin as carbon dioxide carrier:Some of carbon dioxide is transported from tissues to lungs through hemoglobin. Although the majority of it is transported via plasma but still it carries some of CO2 to lungs.
3.Give color of blood:The red color of blood is due to hemoglobin. When red blood cells are separated from the blood, the red color disappears. This means that the red color of blood is due to red blood cells. Hence the name red blood cells is given to it. And as we know that hemoglobin is present inside red blood cells, therefore it gives red coloration to RBCs
4.Buffering action:Hemoglobin also acts as a buffer.Buffer means to resist change in pH.Blood has 7.4 pH and it remains in the narrow range.Because, if it changes the life of the person may be endangered.Therefore, hemoglobin plays very important role in keeping the pH of blood constant.
5.Erythrocyte metabolism:Hemoglobin plays an important role in the modulation of erythrocyte metabolism.
6.Interaction with drugs:Not only for oxygen, but hemoglobin act a very important role the transport of various drugs to their site of action.
7. Physiological active catabolites:Hemoglobin is a source of various physiological active catabolites.