INSECT ENDOCRINE SYSTEM: ENTOMOLOGY (HEXAPODOLOGY)

FIGURE: CEPHALIC ENDOCRINE SYSTEM (diagrammatic)

hypersensetivity

·         It is an exaggerated response of immune system that leads to the damage of the tissue and cells, and is shown by an individual on a second contact with the antigen.

·         Coombs and Gell classified the hypersensitivity reactions in four classes of reactions

Type I hypersensitivity:

·         The type I hypersensitivity is also known as allergic reaction. It is induced by antigens which are referred to as allergens.

·         Allergens are specifically non parasitic antigens capable of stimulating type I hypersensitivity responses.

·         The type I hypersensitivity reactions are IgE mediated reactions.

·         The reaction is stimulated by IgE to high affinity IgE-specific Fc receptors expressed on the mast cells and the basophil cells

·         When activated by the antigens (allergens) the IgE antibodies stimulates the mast cells and basophil cells to release primary mediators: vasoactive amines, stored in the granules (degranulation)

·         The chief mediators are the proteases, heparin and histamines etc..

·         The mediators are responsible for all the normal consequences of an acute inflammatory reaction. I.e. granulocyte chemotaxis, vascular permeability and all sorts of the consequences of inflammations.

·         The type I hypersensitivity is further classified as :

Ø  Anaphylaxis: this type of the type I hypersensitivity is highly rapid, life threatening, severe and are spread to whole body, they are caused due to the re-exposure of the individual to the antigen (allergens)

Ø  Atopy: if the tendency to develop allergic reactions is inherited genetically, they are called the atopic hypersensitivity reactions.

Type II hypersensitivity:

·         The type II hypersensitivity reactions cause the destruction of the host cells and tissues; by lysis or toxic mediators, hence they are also called as cytotoxic or cytolytic reactions.

·         It is an IgM and IgG mediated response.

·         It is caused by the binding of the antibodies to the cell or tissue antigens.

·         They (IgG and IgM) cause cell destruction by Fc-mediated mechanisms, either directly or indirectly activating the complement via the classical pathway.

·         Example of the hypersensitivity class ii reaction is the hypersensitivity shown by an individual who has been transfused blood of blood group other than that of the individual.

·         The antibodies attach to the cell membrane component, leading to complement fixation; this activates the complement chain and leads to either lysis or oposonization of the cell.

·         Lysis of target cell is analogous to that of cytotoxic T cells and involves the release of cytoplasmic granules, containing perforin and granzymes that activates the event leading to the apoptosis.

Type III hypersensitivity:

·         It is mediated by immune complexes of IgG antibodies with soluble antigens.

·         The circulating immunity complexes may accumulate at various tissue sites, where they activate complement and subsequently cause tissue cell lysis.

·         Normally these complements are phagocytized by the monocyte-macrophage system.

Type IV hypersensitivity:

·         Commonly it is known as delayed type of hypersensitivity.

·         Only class of hypersensitivity that is triggered by antigen-specific T cells. (cell mediated immunity reactions)

·         This is mediated by T-cell dependent effector mechanisms involving T_H cells.

·         This reaction has nothing to do with the antibodies.

PCR: polymerase chain reaction.

·         PCR is a very simple process.

·         All that happens in PCR is a short region of DNA molecule, let’s take for example a single gene, and is copied many times by DNA polymerase enzyme.

·         The PCR has a variety of applications in genetics, research and in broader areas of biology.

An outline of polymerase chain reaction:

·         It results in selective amplification of chosen reaction of the DNA molecule.

·         For amplification, a region of DNA is chosen (whose sequences in border regions are known)

·         The border sequences of the DNA fragment to be amplified must be known, because in order to carry PCR, two short oligonucleotides must hybridize to the DNA molecule, one to each strand of double helix.

·         These oligonucleotides are used as DNA primers for DNA synthesis reaction.

·         Amplification is usually carried out by DNA polymerase I enzymes derived from thermus aquaticus (this bacteria inhabits the hot streams)

·         The polymerase is named taq polymerase after the name of bacteria from which it is derived.

·         Taq polymerase is thermostable and can withstand temperature up to 96 ⁰ C.

·         The PCR is a very sensitive technique; it can even start from a single target molecule.

·         The size of DNA that can be amplified by this technique is 10 to 40 Kb.

Components required to carry out polymerase chain reaction (PCR):

·         DNA template (with known end sequence)

·          Primers ( the primers complementary to the known sequence of target DNA molecule,

·          taq DNA polymerase (isolated from bacteria thermus aquaticus) living in hot springs. It can withstand temperature up to 96 ⁰ C),

·          fixed buffer( to maintain favourable environment during the PCR),

·          Divalent cations (Mg²⁺ is used in general. Mn²⁺ can be also used, but at higher concentration it causes mutation),

·          monovalent cations (K⁺ is used in general)

·         Large number of DNA nucleotides

Procedures of PCR:

·         The PCR consists of 20 to 40 thermal cycles.

·         Each cycles has discrete steps

1.       Hold: the cycle starts with a temperature of 96 ⁰ C. the hold lasts for a brief period.

2.       Initializing step: the temperature is raised further to 94 to 96 ⁰ C. (if the DNA polymerase to be used is highly thermostable then the temperature can be raised up to 98 ⁰ C.)

This step lasts up to 1 to 6 minutes.

3.       Denaturation step: at the 94⁰ C to 96 ⁰ C the tubes containing the target DNA is placed in the machine.

At this temperature the DNA melts—the strands get separated by breading of hydrogen bonds. At the end of the denaturation step the result is the 2 separated ssDNA molecules.

4.       Annealing step: in this step the temperature is decreased down to 50 to 60 ⁰ C and primers are added and are carried out for 20 to 40 seconds.

Also the DNA polymerase is added too. The primers pair with the complementary sequences on target DNA molecules.

Note: annealing temperature should always be 2 to 3 ⁰ C less than melting temperature of primers, to prevent the primers from melting down.

At this temperature H-bonds are formed and DNA polymerase binds to end of primers.

5.       Elongation: at this step the temperature is raised to 70 to 75 ⁰ C.

At this temperature taq DNA polymerase acts at its best (best temperature is 72 ⁰ C)

6.       Final elongation: at this step the temperature is maintained from 70 to 74 ⁰ C for 5 to 15 minutes after last cycle of PCR, to ensure that all last DNA are fully extended.

 

Entomology: trap cropping

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• Trap cropping involves planting small areas of crop or other species plants near the protected crop.
• The trap cropping must be done, after closely understanding the seasonal cycle.
• The insects are left to develop in the trap and are killed with pesticides, this process is beneficial, since the pesticides are not spread on the whole of the crop, and thus environment friendly and economically sound too.
• In this practice the trap may be of different species of plant or the same crop but planted in different time.
• For example: an early maturing variety of crop to be protected must be planted on say 8-10 percent of the field. And the main crop is of a late maturing variety. Now the early maturity of the early maturing variety species will attract the pests, they seek food and will lay eggs of the first generation. treatments of insecticides are made in the trap around 7 to 10 days after the emergence of first generation adults, in order to prevent infestations in main planting.

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