Agricultural Entomologys Important Study Point (5)

Agricultural Entomologys Important Study Point

Agricultural Entomologys Important Study Point

Pupa:-Pupa is the resting and inactive stage in all holometabolous insects.

There are three main types of pupae.

1.Obtect:- Example- Moth pupa.

Obtect is also divided into two part-

i.Chrysalis:- It is the naked obtect pupa of Butterfly.

• The pupa is attached to the substratum by hooks present at the terminal end of the abdomen called Cremaster.
• The middle part of the chrysalis is attached to the substratum by two strong silken threads called Gridle.

ii.Tumbler:- Pupa of Mosquito is called tumbler.

• It is comma shaped with rudimentary appendages.
• The pupa is very active.

2.Exarate:- Example- Pupa of Rhinocerous beetle.

3.Coarctate:- The pupal case is barrel shaped.

• The hardened dark brown pupal case is called puparium.
• Example- Fly pupa.

• Foregut is Ectodermal in origin.
• Internal cuticular lining is present.
• Terminal mouth parts leads into a Preoralcavity.
• Preoralcavity between epipharynx and hypopharynx is called as Cibarium.
• Preoralcavity between hypopharynx and salivary duct is called Salivarium.

Foregut include some parts:-

i.Pharynx:-

• Behind the mouth a well musculated organ called Pharynx.
• Pharynx acts as a sucking pump in sap Feeders.

ii.Oesophagous:- It is a narrow tube which conducts food into crop.

iii.Crop:-

• It is acting as food reservoir.
• In Bees crop is called as Honey Stomach where nectar conversion occurs.

iv.Proventriculus or Gizzard:-

• It is the posterior part of foregut and is musculated.
• It is found in Solid feeders and absent in Fluid feeders or Sap feeders.

The internal cuticle of gizzard is variously modified as follows.

Modified Type	Example	Features
Teeth like	Cockroach	To grind and strain food.
Plate like	Honey bee	To separate pollen grains from nectar
Spine like	flea	To break the blood corpuscles

Note:- Food flow from foregut to midgut is regulated through Cardiac valve or Oesophageal valve.

2.Midgut /Stomach /Ventriculus:-

• Midgut is Endodermal in origin.
• It is also called as mesentron.
• This part contains no cuticular lining.

Midgut is made up of three types of epithelial cells-

1. Secretory cells (Columnar cells)
2. Goblet cells (aged secretory cells),
3. Regenerative cells which replaces secretory cells.

Some important features of midgut

i.Peritrophic membrane:-

• It is the internal lining of midgut, secreted by anterior or entire layer of midgut epithelial cells.
• It is present in Solid feeders and absent in Sap feeders.
• This layer is semipermeable in nature to digestive juices and digestion products.

Functions of Peritrophic membrane-

• Lubricate and facilitate food movement
• Envelops the food and protects the Midgut Epithelial Cells against harder food particles.

ii.Gastric caecae:-

• It is also known as Enteric caecae or Hepatic caecae.
• Finger like outgrowths found in anterior or posterior ends of midgut.

iii.Pyloric valve:-

• It is also known as Proctodeal valve
• Midgut opens into hindgut through pyloric valve, which regulate food flow.
• In certain immature stages of insects midgut is not connected to hindgut till pupation. Such as- Honey bee grub

iv.Filter chamber:-

• This is useful to short circuit excess water found in liquid food in homopteran insects.
• This process avoids dilution of digestive enzymes and concentrates food for efficient digestion.
• It is Also helps in osmoregulation by preventing dilution of haemolymph.

3.Hindgut:-

• Hindgut is Ectodermal in origin.
• Internal cuticular lining is present, which is permeable to salts, ions, aminoacids and water.
• The main functions of hindgut are the absorption of water, salt and other useful substances from the faeces and urine.

Hindgut is differentiated into three regions:-

1. Ileum,
2. Colon and
3. Rectum.

In the larva of Scarabids and Termites, illeum is pouch like for housing symbionts and acts as fermentation chamber. Rectum contains rectal pads helping in dehydration of faeces and it opens out through anus.

Digestive glands

(a)Salivary glands:-

• In Cockroach a pair of labial glands acts as salivary gland.
• In Caterpillars mandibular glands are modified to secrete saliva, where the salivary glands are modified for Silk production.

Digestive enzymes

Insect group	Enzyme	Substrate
Phytophagous larvae	Amylase	Starch
	Maltase	Maltose
	Invertase	Sucrose
Omnivorous insects	Protease	Protein
	Lipase	Lipid
Nectar feeders	Invertase	Sucrose
Wood boring Cerambycid grub and Termites	Cellulase	Cellulose
Meat eating maggots:-	Collagenase	Collagen & Elastin
Bird lice	Keratinase	Keratin

Structure & Functions of Circulatory System

• Open circulatory system is found in Insect.
• The main pump is the pulsatile dorsal vessel.
• The anterior part of pulsatile dorsal vessel may be called Aorta
• The posterior part of pulsatile dorsal vessel may be called the Heart.

• It is often clear and Colourless but may be variously pigmented or rarely red due to haemoglobin in the immature stages of few aquatic and endoparasitic flies (e.g., Chironomid larva).
• Haemolymph performs the function of both Blood and lymph.
• It is not involved in Gas transporting function (respiration).
• Haemolymph contains a fluid portion called plasma and cellular fractions called Haemocytes.
• pH is usually acidic (6.7) of plasma.

• The removal of waste products of metabolism, especially nitrogenous compounds from the body of insects is known as Excretion.
• The excretion process helps the insect to maintain salt water balance and thereby physiological homeostasis.

 Some Important Excretory organs-

• Malpighian tubules are the major organ of excretion.
• Predominantly involved in regulation of salt, water and nitrogenous waste excretion.
• Malpighian tubules was discovered by Marcello Malpighi.
• Malpighian tubules are outgrowths of the alimentary canal

Insect Example	Number of MT
Aphids	Absent
Scale insects	2
Bugs	4
Mosquitoes	5
Moths and Butterflies	6
Cockroach	60
Locusts	>200

Note:- Primitive number of Malpighian tubules (MT) is generally six.

2. Nephrocytes

3. Fat bodies

4. Oenocytes

5. Integument

6.Tracheal system

7. Rectum

• Terrestrial insects excrete waste products as Uric acid or certain of its salts called Urates.
• This type of excretion is known as Uricotelism.
• In aquatic insects Ammonia is the excretory product.
• This type of excretion is known as Ammonotelism.

• The distal ends of the Malpighian tubules are held in contact with the rectal wall by the Perinephric membrane
• Example- Adult Coleptera, larval Lepidoptera and larval symphyta.

• The excretory waste materials are retained within the body in different sites.
• Uric acid is stored as urates in the cells of fat body. Example- American cockroach.
• Uric acid is stored in the body wall, giving white colour, Example- Red cotton bug.
• Uric acid is stored in the wing scales giving white colour. Example- Pierid butterflies.

• Similar to aerobic animals, insects must obtain oxygen from their environment and eliminate carbon dioxide respired by their cells.
• Gas exchange occurs by means of internal air-filled Tracheae.
• The finest branches called Tracheloe.
• Air usually enters into the tracheae by Spiracle openings positioned laterally on the body.
• Each spiracle is set in a sclerotized cuticular plate called a Peritreme.
• The ringed appearance of the tracheae is due to the spiral ridges called Taenidia.
• Tracheoles are less than 1 cm in diamete

• The basic component in the nervous system is the Nerve cell or Neuron.

Neurones are of following types based on structure and function:-

Structural basis
Monopolar	Neurone with a single axon
Bipolar	Neurone with a proximal axon and a long distal dendrite
Multipolar	Neurone with a proximal axon and many distal dendrites.
Functional basis
Sensory neurone	It conducts impulse from sense organs to cennervoussystem(CNS).
Motor neurones	It conducts impulse from CNS to effector organs
Inter neurones (association neurone)	It interlinks sensory and motor neurones.