Question

Entomology: Please help me answer in essay format!/answer in paragraphs (1-3 paragraphs). If you can answer in a shorter amount of sentences, great! Also, only answer if your very knowledgeable of entomological science. Thanks!

1. Define the following: . {hemimetabolous, holometabolous, ametabolous, metamorphosis, molting, instar, imaginal discs, subimago, ecdysis, apolysis, teneral, pharate, eclosion, tanning, melanization, sclerotization, chitin, exoskeleton, PTTH (brain hormone), juvenile hormone, ecdysteroids(s), sequester etc.}

2. Using the terms above, please show and give an example of how sequential pathways of stages of growht and development in an insect occur. (Use any insect as an example). OF what significance is the insect "integument" to the success of the insect? (Be able to answer this question using anatomical and physiological processes of the integument associated with molting and metamorphosis.

Answer 1

First I am defining metamorphosis - It is the change in the form and often habitat that an animal undergoes after birth or hatching to become adult.

Animals are divided into different groups depending upon whether they undergo complete metamorphosis, incomplete metamorphosis or no metamorphosis. All these types are found in insects.

Hemimetabolous - In this type the animal undergoes incomplete metamorphosis. The young ones are called nymph which resemble adults in habits and habitats. But they do not possess wings and reproductive organs. They are smaller in size. The three stages in the life of these insects are - egg, nymph, adult, ex. Grasshopper, Dragonfly.

Holometabolous - These insects undergo complete metamorphosis. The young one is called larva which differs from the adult in form, structure and mode of life. The life-history stages are egg, larva, pupa and adult, ex, butterfly. housefly.

Ametabolous - These groups lack metamorphosis in their life. Young ones are similar to the adults, ex. silver fish.

Moulting - Arthropods possess a hard chitinous exoskeleton as covering of their body. In order to grow, this chitinous exoskeleton has to be shed. After growth again a new skeleton is made. This process of periodic shedding of exoskeleton for growth is called moulting.

An arthropod may moult several times. The developmental stage between each moult is called instar.A caterpillar moults 5 times before it becomes pupa. The 5 instars are the 1st, 2nd, 3rd, 4th and 5th instars.

Imaginal disc - In holometabolous insects, the distinct clusters of cells in larval epidermis, which give rise to adult structures are called imaginal discs.

Imago - Certain insects like Mayflies are hemimetabolus. There is a stage in their life cycle between nymph and adult ( imago) called subimago which is able to fly but require another moult to become adult.

Though the two terms, moulting and ecdysis are used synonymously but there is a subtle difference. Moulting is shedding of skin, hair, feathers or other structure in insects, other arthropods , snakes etc. while ecdysis is the shedding of cuticle, the outer layer of skin in insects, other arthropods and snakes.

Apolysis - It occurs before ecdysis. Apolysis is the process of separation of cuticle from the epidermis assisted by a number of enzymes which digest the old cuticle. It occurs before ecdysis.

Teneral - This is a condition of an insect which has just undergone moulting and having an exoskeleton which is not hardened and darkened yet.

Pharate - It is the stage in an insect which has completed metamorphosis but still at the pupal stage i.e. still inside the cocoon.

Eclosion - The emergence of insect larva from egg or adult from pupal case.

Tanning - It is the process in which colour of the cuticle changes to brown.

Sclerotization - It is the process in which the newly formed cuticle is stabilized by formation of cross-links between protein and chitin. Sclerotization is often accompanied with tanning.

Melanization - It is the formation of melanin pigment in the body of insects under the influence of phenol oxidase enzyme cascade system. Melanization occurs in response to pathogens. Blood darkens, melanin surrounds the infecting pathogen and kill it.

Exoskeleton - Exoskeleton means outside skeleton. It is the hard outer covering which protects the bodies of some animals like insects, which do not have a backbone.

Chitin - Chitin is a nitrogen containing polysaccharide It is a derivative of glucose which is the main component of the cell wall of fungus and exoskeleton of insects. It is chemically N- acetyl glucosamine.