HOST PLANT SELECTION BY PHYTOPHAGOUS INSECT 🐝🦋
Host plant selection by insect is often divided into host plant finding & host plant acceptance. The central link of host plant finding thought previously to be govern by volatile chemical. It has been suggested that when the background of crop plant or host plant growing in bare soil is made more diverse when non host plant around it. It caused distruption to insect for selecting host plant. Such distruption is considered to be mediated through the non host plant providing.
Theories on the host plant selection by phytophagous insects:
A)The physical opstouption : the physical opstouption ie. Provided by non host plant to host plant on insects is providing then safe gurde to the host plant. For eg. Tall maize plant are used to protect bean plant from paste infestation . Tall plants were considerate to be effective because they obstrupted them )
B) Visual chemoflage : this hypothesis was based on two types of visual stimuli that include low flying insects to land on plants. The 1st is directed response to the colour of the plants which in most cases is green. The second is an optomotor response in which landing provided by plants looping up along the path of the flying insect. Anything that compits with such stimulli such as other green plants or raising the hight of the overol background with weeds so that the distance over which the host plant can be separated from the background & its gives them a visual chemouflage.
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C) Masking of host plantorphi: The release of odor masking substances into the air by non -host plant species is considerate & confer some protection to the associated host plant. For eg. Host plant selection by cabbage root flower was distupted when its host plant are surrounded by a range of different plant including the weeds, fat- he, fumuturi & spurrey& cultivated plants like pea, onion ,carrot etc.
D) Repellont chemical : the odors given up by the non host plant are sufficiently strong to actually repeat the searching insects,Eg. Diamond black moth would be repeated from cabbage intercropping the cabbage
with tomatoes. Plant choose for their odorous nature such as French marigold fail to deter the carrot fly when used as the inter crop in carrots.
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Excretory System of insect 🐝
Excretion is the process whereby an organism eliminates metabolic wastes and unwanted chemicals from its system. Metabolism is the sum total of all the chemical reactions occurring in the cells and body. Some products of these metabolic reactions are toxic and so must be processed or eliminated from the body.
Others are simply materials that are present in excess and so must be eliminated as waste. The process of excretion is quite different to defecation, which is the removal of undigested food wastes from the gut.
However, the gut of many animals also has a role in excretion as some materials may be excreted into the gut and eliminated with the faeces. In insects most excretory products are excreted into the gut lumen and eliminated along with faecal matter. Excretion is also important in eliminating excess water and other unwanted chemicals that may be ingested and enter the body fluids, such as plant poisons and excess
salts.One of the main functions of excretion is to remove excess nitrogen. Nitrogen enters the diet in the form of amino acids, nucleic acids and certain salts. One of the main products of excretion in aquatic organisms is ammonia. Ammonia contains nitrogen and is a small molecule which dissolves readily in water. This allows it to be easily excreted into the surrounding water. However, this becomes a problem for terrestrial organisms. Ammonia is toxic to cells and so must be quickly ejected from the body, however, being water-soluble it is typically ejected in solution, which requires water. The mammalian solution is to convert the ammonia into a less toxic substance called urea. This conversion takes place in the liver: the ammonia produced by cells enters the bloodstream where the liver removes it, converts it into urea which again enters the bloodstream to be excreted by the kidneys. Being less toxic, the urea can be temporarily
stored and excreted in a concentrated solution, requiring less water.Birds and reptiles have a better water conserving system; they excrete uric acid (or urate salts).
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Uric acid is not readily soluble in water and is of low toxicity and so can be excreted with very little water. The dry excreta of birds is a mixture of faecalmatter and uric acid crystals and when water is scarce birds can produce very dry excreta.Arthropods,
including insects, have adopted similar solutions. Woodlice, which are not insects but crustaceans, are only partially adapted to terrestrial conditions, preferring moist habitats, but they do excrete ammonia.
Interestingly they can vent off ammonia gas, rather than relying on the wastage of water to remove the ammonia in solution. Insects are better adapted to dry conditions, although aquatic insects and some insect
larvae excrete ammonia, most terrestrial forms excrete uric acid (or salts of uric acid
called urates, such as ammonium urate).If one considers how small an insect is and how rapidly a small drop of water may evaporate, then one realises that insects have outstanding water-conserving systems.
Bedbugs ( Rhodnius ) can survive for weeks without ingesting any water! Some insects can tolerate extremely dry conditions and may excrete uric acid as a dry crystalline powder, along with bone-dry faeces! Insects generally produce only trace amounts of urea.